Technical Turning on A/C cuts engine at idle

[tonyb0902]

Thinking this though as logically as I can.

So everything presumably worked ok before the thermostat was changed. AC system wasn't touched and I imagine it would be a really unlucky coincidence that the compressor or AC system developed a fault as a result of the thermostat being changed, given there isn't any interaction between these two systems.

So the car was previously operating with very high fuel consumption, it would be reasonable to conclude then that the car was over fueling and running very inefficiently.

Now there are two ways to regulate the idle on modern cars, an electronic air idle control valve, or more recently an electronic throttle butterfly that is opened and closed to regulate the idle.

As stated, previously everything was working, the car, aircon etc was functioning just with high consumption so it maybe the car was operating with the butterfly open more than is would be normally trying to control fueling with a cold engine.

Weird question perhaps but is the cutting out issue better or worse when the engine is hot/cold. Ie when its cold is it more likely to cut out, when its warm or is it about the same? Just something to think about.

When the car engine is cold, it operates in "open loop" the oxygen sensor needs to be warm to function therefore until it has warmed up idle is usually maintained higher until the oxygen sensor is warm and it can switch to operating in "closed loop" when the oxygen readings dictate the fueling. If the car is running in open loop with a cold engine then I might expect it to work much like before the thermostat was changed and be less likely to stall at idle.
So that might point towards the issue.


I would be inclined to take a Neanderthalic approach to this and rather than thinking that the scanner is going to give you all the answers (if its a cheap one from HongKong the information it gives is going to be limited to just reading out codes)

Instead I would take the air box off, run it on the drive without the airbox, to answer the question 'is the engine getting enough air' if there is a restriction in the air box or filter this might affect idle.

The engine and valves might be badly coked up if its been running badly for some time, so I would then spray a can of carb cleaner into the throttle body while the engine is running (not all in one go, short little bursts) if there is a lot of build up on the valves then they might be restricting airflow.

So once you have sprayed a can of carb cleaner into and left it running for a bit to burn off any residual cleaner turn the car off.
Locate the fuse for the ECU and pull it.
Walk a way and have a cup of tea for an hour.

This should reset the parameters of the ecu to a default setting. no different to turning your computer off and on again when it stops working or crashing.

This will set the cars ECU to a sort of safe mode that will operate the engine, slightly less efficiently but without issue. It then needs time in closed loop, to learn the best way to handle the fueling and idle of the engine, so taking for a long run. (probably put the air box and filter back on)

Other things to check (panda people will have to help me here) is the mass airflow sensor in the airfilter box, is there an intake air temperature sensor on these? are these sensors plugging in and working if the mechanic took the airbox off he might have damaged one of these or not plugged them back in correctly.

I think if you can do these things over the weekend you probably wont need to worry about the code reader and you might well solve your problem. If not you have the added back up of the code reader coming and you can then see if it is throwing up any errors.

I think its unlikely the button or the compressor is causing the issue. and I think 800rpm might be fine as idle with the AC off and ie no load on the engine and a nice warm engine running closed loop but I's expect it to be higher when the engine is cold and operating in open loop.

Hi
You are correct. At start up, with cold engine, the A/C does not stall the engine (all is fine). After around 5 minutes the rpm drop at idle and the A/C cuts the engine out. Without A/C at this point the idle is stable at 800rpm.
This was the only applicability that I could relate the change of thermostat to.
As we might understand the causal factor viz open loop control, any ideas as to how to fix it? Is one of the HEGO’s defective and was previously hidden by the defective thermostat?
The Scanner might indicate this?

 

[koalar]

Cool we are moving forwards

We now know the compressor is fine, A/C works, doesn't stall if the revs are raised

And only fails when the engine is warmed up

We now know it's has coils In front next to the thermostat

So were probably removed to change the thermostat, I done them both ways its quicker and easier to move them out of the way

These engines will idle and run fine on 3 cylinders

Checking for 4 good sparks would be one direction to go next

 

[Mike1alike]

The idle RPM for worm engine and AC off is 750. AC on is 850.
The oxygen sensors have the heating element included in order to be functional as soon as you turn the key on. So it's not coming from them.
ECU keeps the RPMs up on cold engine due to temperature, cold combustion chambers need RPM a little up for the engine to run smooth, but it drops on idle mode relatively quickly.

But... there is a correlation between cooling system and AC system actually. The pressure! If the pressure is high inside cooling system, the one in AC system is too high as well. And high pressure in cooling system can be caused by fan not coming on when it should. And that can happen if the thermic fuse on the fan is burned. Then the fan won't operate on 1st speed, only on 2nd speed, but fan kicks in on second speed when the temperature and pressure are higher than normal inside cooling system. I don't know if that can cause the engine to cut out but it is possible. And that is definitely the correlation between the two systems.
So check the thermic fuse. It is located on the radiator fan, has the 2 wires connected to it.

 

[PuntoHowTo]

Hi
You are correct. At start up, with cold engine, the A/C does not stall the engine (all is fine). After around 5 minutes the rpm drop at idle and the A/C cuts the engine out. Without A/C at this point the idle is stable at 800rpm.
This was the only applicability that I could relate the change of thermostat to.
As we might understand the causal factor viz open loop control, any ideas as to how to fix it? Is one of the HEGO’s defective and was previously hidden by the defective thermostat?
The Scanner might indicate this?

I think it will very much come down to what scanner you have bought. Some of them literally only give a list of codes that you then have to look up in a code book to see what they mean.

it seems the issue can be pinned down to the engine operating in closed loop. The engine is maybe no compensating properly for the additional load of the AC.

I would try, and it is only a try I can't say it will definitely work but it may be the valves are coked up the throttle body etc., so a can of carb cleaning down the throttle body might help. Check any sensors in or around the air box to make sure they are connected properly.

Obviously if something isn't connected properly or the readings are wrong from a sensor this could bring up an error code, but as I say depending on the code reader you have ordered, it might not give detailed information such as the readings from the various sensors, so what the engine thinks is "normal" might not be.

If the ECU was disconnected by the garage or if the ECU is running on parameters that it calculated from the faulty thermostat then it might take driving a good few miles for the ecu to relearn its parameters now the thermostat is fixed.

Have a tinker over the weekend, clean up the throttle body and spay some carb cleaner into the intake with the engine running (a little at a time) and it might help the situation.

I know people like to say "the problem with cars these days is everything is electronic" and "you can't fix them without plugging them into a computer" but actually if you understand how an old mechanical engine works (spark, fuel air + the right quantities of each) then really all the computer does is regulate the amounts and if you can understand that, you can find work arounds to work out what's going on quite often without reading the error codes.

if you have a link or model number of what you have orders, I could take a look and see what sort of information you might be able to get from it.

 

[Mike1alike]

In regard to reset the self-adaptation parameters I've seen a lot this recommendation to disconnect the battery. But I don't think that does anything. I've had the battery disconnected from the car and there was no signs a reset took place. On the other hand, when I performed a reset using MultiEcuScan first thing after the reset when turning the engine on the MIL light is flashing. And it flashes continously until you set the new parameters by revving 3x ~5500 RPM on wormed engine, as described.

 

[PuntoHowTo]

The oxygen sensors have the heating element included in order to be functional as soon as you turn the key on. So it's not coming from them.

True they do have a heating element to help them reach temp quicker, but this is still not instant. They need to reach a toasty 300+ Celsius so they do operate for a period in open loop before the O2 sensor comes online. These little engines do heat up quite quick.

With the next bit you have totally lost me.

But... there is a correlation between cooling system and AC system actually. The pressure! If the pressure is high inside cooling system, the one in AC system is too high as well. And high pressure in cooling system can be caused by fan not coming on when it should.

The pressure in the coolant is either zero when cold up to around 1bar at normal operating temperature and this mechanism helps keep the coolant under pressure below the vapour pressure of the coolant and therefore prevents the coolant from boiling. The pressure is maintained by the heat in the system regulated by the thermostat and the cap on the coolant tank which has a bypass should the pressure get to high. So really in a healthy system there is never a situation where the pressure should be "high" in the coolant system, and it is an electronic sensor that measures temperature that decides if the engine cooling fan comes on or not.

The AC works in a completely different way the AC gas is compressed fed into an expansion valve and then filters back to the compressor. you have the high and low side, the pipe coming away from the compressor is the high side, arround 200PSI and between the expansion valve and the pipe going into the compressor the gas is at low pressure (low side) the gas is arround 50PSI (this might differ a bit on new systems.

The pressure sensor in the system does a number of things. if there is insufficent pressure in the system (i'e not high enough PSI when the compressor is not running) then a fail safe prevents the system from turning on the compressor.

Now if you have the system filled with the correct weight of coolant then technically speaking there should never be an eventuality where there is too much pressure in the system. The pressure system monitors for high pressure and on older systems like you would find in the panda the compressor is immediately switched off to reduce pressure in the system, then once back to normal the compressor cycles on again. the cycling on and off of the compressor maintains the high and low side of the system to ensure efficient cooling in the cabin. (if you want to really deep dive in this you can go down a whole rabbit hole on how the external air pressure also affects the efficiency of the system.

So there is never an issue with the pressure going too high.
In AC equipped cars they either have a multi speed single fan or multi fan unit (sometimes that also does multiple speeds) where low speed or a single fan is used to manage the temperature of the coolant, say sitting in traffic with no AC on, the coolant starts to creep up in temperature and the fan comes on.

On AC systems as long as the car is moving above a certain speed the airflow through the condenser is sufficient to cool the gas so the fan will not operate while the car is moving. If the gas pressure in the system goes too high because it is getting too hot the car will simply turn off and cycle the compressor.

When stopped to ensure the the gas is cooled, if you sit idle in the car on a hot day with the AC on. you need double the cooling to cool the engine and to cool the gas in the condenser. if you didn't heat from the condenser can creep across into the radiator and cause the engine to heat up quicker. so you use a much more powerful fan which the engine will switch on whenever the compressor is active and the car not moving at idle.

If you park up, turn on the engine, run the AC and then listen to the fan turning on and off you will find this corresponds with the compressor cycling on and off.

So there should be no situation where an over pressure in either the coolant or the AC would prevent the fan from coming on. There should be no situation in a healthy system where the fan should not come on when it is intended.

So to clarify my statement in my previous post, there is nothing that you can do to the thermostat, which will have any impact on how the AC system works.

And that can happen if the thermic fuse on the fan is burned. Then the fan won't operate on 1st speed, only on 2nd speed, but fan kicks in on second speed when the temperature and pressure are higher than normal inside cooling system. I don't know if that can cause the engine to cut out but it is possible. And that is definitely the correlation between the two systems.
So check the thermic fuse. It is located on the radiator fan, has the 2 wires connected to it.

If there is no power getting to the fan for any reason, the pressure in the AC system will rise and very quickly the compressor will switch off. wait for the pressure to decrease and then it might cycle the compressor back on again if it is a pretty dumb system with no way to monitor if the fan is working or not.
If the fan function is electronically monitored as it is on more advanced cars, then it will not try to run the AC compressor until the fault is fixed.

As far as I am aware there is nothing monitoring the pressure inside the engine coolant system. The cap on the expansion bottle should release any over pressure and once the coolant has boiled off the engine will over heat.

I have no idea what you are saying about Thermic fuses but the fan on any car with a two speed fan will only operate at high speed while the AC is running, it will not run at low speed as this does not provide sufficient cooling for the engine and the AC condenser


So to clarify again. There is no part of the engine cooling system that has any impact on weather or not the AC compressor will function. Now that being said we know that the compressor is functioning in this case because it stalls the car when it does. The AC compressor stalling the engine, has nothing to do with the radiator, thermostat. The only caveat to this is when the engine is over heating the ECU will try to manage this by turning off the AC to reduce heat soak into the radiator, and while I have spent far to long explaining all of this, non of it has anything to do with the problem that tony is having.

 

[koalar]

Not sure where we are going but let's stay on track

The car has been running correctly just at the wrong temperature, faulty thermostat, fueling will still be correct just the engine running colder than normal

The new adaptive memory is learnt in the first 20 miles,, adaptive memory is none volatile, can only be cleared via software, most free software will do it, shouldn't need doing though

Engine switches from open loop to close loop within a few seconds

With the Aircon on the fan still works at two speeds unless part 71740060 is faulty

they will idle well below 600 so shouldn't even be close to stalling

There's no MAF sensor

As far as I remember 90% sure the revs don't increase when the compressor engages, but fall slightly then immediately return to normal, I don't remember sitting in traffic hearing the revs raise as the compressor engages and disengages

The Aircon is tested and functioning correctly the car does not stall if the revs are manually raise first

The fault manifest itself during a routine thermostat change

Battery and tray will have been out, coils probably moved out of the way

The obvious course of action is to get the person that broke it to fix it, the fact it now on here probably means that not an option

Do you have jump leads, and access to another vehicle

Do you have a volt meter and or test lamp

 

[Mike1alike]

With the next bit you have totally lost me.

It's true, the cooling system doesn't have a pressure monitoring sensor. It does have the valve in the cap that opens up and releases pressure when it goes above 1.2 bar. And pressure goes hand in hand with temperature, when cooling liquid temperature rises, the pressure rises, too.

Tony says the thermostat was broken long time before replacing it, stuck open and the engine never reached the working temperature in that period.

What you've described is technically correct, but there are limits within functioning conditions, it's not all set to just a specific number, but within range (AC pressure and temperatures and all that).

This is what happened to my car once. I went to an AC specialist and he did a gas refill. After performing it and watching how it works he said "the AC pressure is on the higher side, shouldn't be that high, there's something wrong with the radiator fan, have it checked". Obviously, the guy was paying attention to what he was doing and new what he was doing, not like other AC specialists we hear stories about. Turned out the fan had problems indeed and it would work only on 2nd speed.
The thermic fuse I'm talking about is on the resistor @koalar mentioned, part number 71740060. Inside of it, on the 1st speed circuit there is this safety thing, thermic fuse, it blows if temperature on it goes above 125⁰C. It's this one in the picture.

When that fuse is ok it has continuity through it, so is easy to test.
The fan's 2nd speed circuit has no fuse on it and it kicks in when the coolant temperature is on the higher side. Not overheated, because that's the role of the fan, to prevent overheating, but on the high side. ECU doesn't know if the thermic fuse is blown, it feeds voltage to 1st speed circuit and then, considering rising temperature feeds the 2nd speed.

I thought this is worth mentioning and Tony should check that circuit, to be on the safe side. If you have MultiEcuScan is easy to check, you can start the fan by it, with engine off, speed 1 or 2 and see if it runs. There is another detail that I've noticed, if you are aware of it you'll know if the thermic fuse is blown or working. On hot summer days when you run the car with AC on, after you stop the engine you will hear the fan is still running, it runs on 1st speed for about 20~30 seconds. If when turning the engine off fan is not running, total silence, means the thermic fuse is blown.

You guys keep mentioning the coils and how they were needed to be taken down and they are causing the problem. My feeling is that if there were something wrong with the coils/leads, the problem would not manifest just in the specific moment the AC is turned on, but it would be more often, with AC on or not. There is no mention of engine running bad. I think the coils are alright but checks can be performed, of course.

I'm coming back on the cooling system pressure, this idea came to me now. The pressure is 'monitored' by the valve on the radiator's cap. But... engine running 2-3 years under-heated means that valve didn't open a long time and could be stuck, not opening now even if pressure inside cooling system goes above 1.2 bar. Tony, very careful, because hot coolant could spray out, take a look on the cap. After running the engine and it is hot, with engine off take down the radiator's cap. With care, as mentioned. If it's ok, you should hear a pressure realese sond, a 'psss' and be able to take the cap off without coolant coming out. If coolant starts coming out as you unscrew the cap (again, carful cause it will be hot, but going downwards, just don't take the cap off completely in that situation), means the valve is not opening anymore and there is buildup pressure inside the cooling system. You'll need a new cap, they are not expensive. High pressure in the cooling system is not good for the engine and could cause the problem. Also, when the engine is cold there is no pressure inside cooling system and would explain the AC working without any problem.

 

[tonyb0902]

It's true, the cooling system doesn't have a pressure monitoring sensor. It does have the valve in the cap that opens up and releases pressure when it goes above 1.2 bar. And pressure goes hand in hand with temperature, when cooling liquid temperature rises, the pressure rises, too.

Tony says the thermostat was broken long time before replacing it, stuck open and the engine never reached the working temperature in that period.

What you've described is technically correct, but there are limits within functioning conditions, it's not all set to just a specific number, but within range (AC pressure and temperatures and all that).

This is what happened to my car once. I went to an AC specialist and he did a gas refill. After performing it and watching how it works he said "the AC pressure is on the higher side, shouldn't be that high, there's something wrong with the radiator fan, have it checked". Obviously, the guy was paying attention to what he was doing and new what he was doing, not like other AC specialists we hear stories about. Turned out the fan had problems indeed and it would work only on 2nd speed.
The thermic fuse I'm talking about is on the resistor @koalar mentioned, part number 71740060. Inside of it, on the 1st speed circuit there is this safety thing, thermic fuse, it blows if temperature on it goes above 125⁰C. It's this one in the picture.
View attachment 474351
When that fuse is ok it has continuity through it, so is easy to test.
The fan's 2nd speed circuit has no fuse on it and it kicks in when the coolant temperature is on the higher side. Not overheated, because that's the role of the fan, to prevent overheating, but on the high side. ECU doesn't know if the thermic fuse is blown, it feeds voltage to 1st speed circuit and then, considering rising temperature feeds the 2nd speed.

I thought this is worth mentioning and Tony should check that circuit, to be on the safe side. If you have MultiEcuScan is easy to check, you can start the fan by it, with engine off, speed 1 or 2 and see if it runs. There is another detail that I've noticed, if you are aware of it you'll know if the thermic fuse is blown or working. On hot summer days when you run the car with AC on, after you stop the engine you will hear the fan is still running, it runs on 1st speed for about 20~30 seconds. If when turning the engine off fan is not running, total silence, means the thermic fuse is blown.

You guys keep mentioning the coils and how they were needed to be taken down and they are causing the problem. My feeling is that if there were something wrong with the coils/leads, the problem would not manifest just in the specific moment the AC is turned on, but it would be more often, with AC on or not. There is no mention of engine running bad. I think the coils are alright but checks can be performed, of course.

I'm coming back on the cooling system pressure, this idea came to me now. The pressure is 'monitored' by the valve on the radiator's cap. But... engine running 2-3 years under-heated means that valve didn't open a long time and could be stuck, not opening now even if pressure inside cooling system goes above 1.2 bar. Tony, very careful, because hot coolant could spray out, take a look on the cap. After running the engine and it is hot, with engine off take down the radiator's cap. With care, as mentioned. If it's ok, you should hear a pressure realese sond, a 'psss' and be able to take the cap off without coolant coming out. If coolant starts coming out as you unscrew the cap (again, carful cause it will be hot, but going downwards, just don't take the cap off completely in that situation), means the valve is not opening anymore and there is buildup pressure inside the cooling system. You'll need a new cap, they are not expensive. High pressure in the cooling system is not good for the engine and could cause the problem. Also, when the engine is cold there is no pressure inside cooling system and would explain the AC working without any problem.

I am very appreciative for your help. Reading thro’ the dialogue I can confirm that Battery was not removed nor were the Coil Packs. The related fasteners have not been touched and this confirms what the Technician told me (he lives just 4 houses away from me). He was stumped and was why he rang me.
I think that access to a Scanner might help us by checking out some of our theories. Understand that it is on a flight out of Hong Kong at 12.13 (!) - sort of surreal.
Also, reading another thread where an owner swapped his pre and post Cat connections and solved his (very similar) issue I am still thinking about earlier discussion upon open and closed loop fuel control during warm up. I would expect the MIL light to have signalled a Lambda Sensor failure but?
Hong Kong is in the grip of a nasty storm but I am hoping that will clear allowing the aircraft to leave
This is such an odd ball issue under unusual circumstances.
Please keep interested

 

[jrkitching]

It does have the valve in the cap that opens up and releases pressure when it goes above 1.2 bar

The release valve in the radiator cap should never open in normal service. It's only there to stop a dangerous overpressure in the cooling system in the event of a fault.

At 1.2 bar cooling system pressure, the coolant temperature would be around 119C. There's no way it should ever get anywhere near that unless there's a serious fault, and by then all the overheat warnings should be screaming at you. From memory, the thermostat should start opening at 88C.

The cooling system is designed so that the coolant temperature should never rise anywhere near the point where the safety valve in the rad cap will open.

Again from memory, some Panda thermostats are set to open at different temperatures. It's possible that the one you had replaced was the wrong type, though I still don't see how that could be related to the current issue.

I agree it's a curious fault; I'm following this thread with interest.

Now this is mere speculation, and I've no idea if there's any truth in this, but if the coolant temperature were to rise above the point where the cooling system couldn't contain it even with the 'stat fully open, it would make sense for the ecu to automatically shut down the A/C to reduce the power demand on the engine. I've no idea if it actually does this on a Panda, but if it did, and if the ecu thought the car was dangerously overheating, it would explain your issue.

Switching the A/C on when the car is idling in closed loop at 800rpm often puts on the radiator fan shortly afterwards, and may put it into second speed if it's already running, because there's otherwise no airflow through the radiator. I hesitate to suggest this, because it requires the car to be put into neutral for a while at speed, but I'm wondering what would happen if you were running at speed (so airflow through the rad), A/C off, in neutral with the engine at idle, and then turned the A/C on. Does this still stop the engine? Something that should only really be tried on a track; we're into test pilot territory now. Not something that should be done on a public road.

I'm trying to work out what has to be there before switching on the A/C stops the engine, and if that's in any way related to coolant temperature.

The one thing we know for reasonably sure is that replacing a failing thermostat will have changed the coolant temperature for any given operating condition.

 

[tonyb0902]

The release valve in the radiator cap should never open in normal service. It's only there to stop a dangerous overpressure in the cooling system in the event of a fault.

At 1.2 bar cooling system pressure, the coolant temperature would be around 119C. There's no way it should ever get anywhere near that unless there's a serious fault, and by then all the overheat warnings should be screaming at you. From memory, the thermostat should start opening at 88C.

The cooling system is designed so that the coolant temperature should never rise anywhere near the point where the safety valve in the rad cap will open.

Again from memory, some Panda thermostats are set to open at different temperatures. It's possible that the one you had replaced was the wrong type, though I still don't see how that could be related to the current issue.

I agree it's a curious fault; I'm following this thread with interest.

Now this is mere speculation, and I've no idea if there's any truth in this, but if the coolant temperature were to rise above the point where the cooling system couldn't contain it even with the 'stat fully open, it would make sense for the ecu to automatically shut down the A/C to reduce the power demand on the engine. I've no idea if it actually does this on a Panda, but if it did, and if the ecu thought the car was dangerously overheating, it would explain your issue.

Switching the A/C on when the car is idling in closed loop at 800rpm often puts on the radiator fan, and may put it into second speed if it's already running, because there's otherwise no airflow through the radiator. I hesitate to suggest this, because it requires the car to be put into neutral for a while at speed, but I'm wondering what would happen if you were running at speed (so airflow through the rad), A/C off, in neutral with the engine at idle, and then turned the A/C on. Does this still stop the engine? Something that should only really be tried on a track; we're into test pilot territory now. Not something that should be done on a public road.

I'm trying to work out what has to be there before switching on the A/C stops the engine, and if that's in any way related to coolant temperature.

Hi

 

[koalar]

The compressor cuts off if the engine is to hot

Coolant temperature or pressure does not come into the equation

Open and closed does not come into the equation

The car is in closed loop in less than 10 seconds

How a mechanic cleaned up the matting faces properly without removing the battery tray is beyond me

 

[tonyb0902]

Hi

Tried the coasting and A/C still cuts off engine.
Started engine from cold this morning.
Key on, crank, start all good with idle at 1400rpm.
Turned on A/C immediately (within 2 secs of starting) and all good - 1000rpm dipping to 800 rpm as A/C kicks in. After 23 secs A/C drops out and rpm blips momentary to 1100rpm before returning to 800rpm. This in/ out cycle continues (normal behaviour in our experience).
All good for 211 secs (3 min 31 secs) from initial start but then Idle starts to dip to 600 rpm when A/C kicks in and then next time engine stalls as A/C kicks in.
Must be fueling as engine goes through Open Loop to Closed Loop.
Thoughts?

 

[tonyb0902]

Tried the coasting and A/C still cuts off engine.
Started engine from cold this morning.
Key on, crank, start all good with idle at 1400rpm.
Turned on A/C immediately (within 2 secs of starting) and all good - 1000rpm dipping to 800 rpm as A/C kicks in. After 23 secs A/C drops out and rpm blips momentary to 1100rpm before returning to 800rpm. This in/ out cycle continues (normal behaviour in our experience).
All good for 211 secs (3 min 31 secs) from initial start but then Idle starts to dip to 600 rpm when A/C kicks in and then next time engine stalls as A/C kicks in.
Must be fueling as engine goes through Open Loop to Closed Loop.
Thoughts?

Apologies, one observation.
The two Lambda Sensor wiring harnesses pass thro’ the gap just above thermostat housing.
There is next to no space in that location as Kaolar just commented (I agree your comments). I had purchased the thermostat Housing and thermostat to do the job myself (would have removed modules and Coils to get reasonable access) before I had a small medical issue.
I wonder if the technician either tried to force harnesses out of the way or disconnected them? Perhaps damaging harness internally (old car) or not correctly reconnecting connectors.
Can you mis connect (by 180 degrees)?
Your thoughts would be appreciated.

 

[jrkitching]

From the reading I have been doing recently I understand that this was a period of real changes in short periods of time.

I think you've got a 60HP Euro 4 1.2 (the £35 RFL one), in which case it's exactly the same as my own Panda. And I've changed the 'stat on that, fortunately without any of this shenanigans.

You do need to remove the battery and battery tray, but everything else can be unbolted or unclipped and swung out of the way - there's no need to disturb any electrical connections except those on the battery itself. But it is a confined space and there's always the possibility of knocking something.

The thermostat and housing don't have any built in temperature sensor (unlike the later cars), so that's not been disturbed either.

So the only thing that should be different now is that the coolant temperature will be different (higher) in any given operating condition. Why this might be causing an issue, we don't know yet.

Are we sure it's the correct thermostat for the car?

 

[tonyb0902]

I think you've got a 60HP Euro 4 1.2 (the £35 RFL one), in which case it's exactly the same as my own Panda. And I've changed the 'stat on that, fortunately without any of this shenanigans.

You do need to remove the battery and battery tray, but everything else can be unbolted or unclipped and swung out of the way - there's no need to disturb any electrical connections except those on the battery itself. But it is a confined space and there's always the possibility of knocking something.

The thermostat and housing don't have any built in temperature sensor (unlike the later cars), so that's not been disturbed either.

So the only thing that should be different now is that the coolant temperature will be different (higher) in any given operating condition. Why this might be causing an issue, we don't know yet.

Are we sure it's the correct thermostat for the car?

Correct thermostat all OK. Temperature Gauge now operating fine (after 2 - 3 years!).

 

[Mike1alike]

Tried the coasting and A/C still cuts off engine.
Started engine from cold this morning.
Key on, crank, start all good with idle at 1400rpm.
Turned on A/C immediately (within 2 secs of starting) and all good - 1000rpm dipping to 800 rpm as A/C kicks in. After 23 secs A/C drops out and rpm blips momentary to 1100rpm before returning to 800rpm. This in/ out cycle continues (normal behaviour in our experience).
All good for 211 secs (3 min 31 secs) from initial start but then Idle starts to dip to 600 rpm when A/C kicks in and then next time engine stalls as A/C kicks in.
Must be fueling as engine goes through Open Loop to Closed Loop.
Thoughts?

600 RPM is too low. Normal idle is ~750RPM. I think the gauge is more 'orientative', it does not reflect the exact RPM engine is running. You can see the exact RPM using a tester, hope yours will help you in that regard and wish you to get it as soon as possible. If the RPM is really 600 it is too low and that can be the cause engine cuts off when you add extra load by turning AC on. Then you should find out what's causing that low RPM. Resetting parameters could be helpful, again, hope your scanner to help you there once you get it. One thing you can do, but it will take a bit of time until effective, you'll need to run the car a bit, is to add fuel injector cleaner. Carbon deposits on injectors can affect the amount of fuel passing through and there are cleaners that do the job. I recommend STP, it's not expensive and it made a difference when I used it. You can pick anything you like, of course.

The release valve in the radiator cap should never open in normal service. It's only there to stop a dangerous overpressure in the cooling system in the event of a fault.

We don't know if the engine runs in normal service, it ran 2-3 years under-heated. I say my questions about the cooling system are valid. (The questions are: is the pressure inside the system normal and is the fan working on 1st speed?)
Tony, do you want to check the pressure in the cooling system? As I've mentioned, careful, after engine is wormed up, turn off the engine and see if you can take off the radiator's cap without coolant spilling out. I'm really curious about that and it is a normal check to make sure cooling system performs normally.

 

[PuntoHowTo]

Tried the coasting and A/C still cuts off engine.
Started engine from cold this morning.
Key on, crank, start all good with idle at 1400rpm.
Turned on A/C immediately (within 2 secs of starting) and all good - 1000rpm dipping to 800 rpm as A/C kicks in. After 23 secs A/C drops out and rpm blips momentary to 1100rpm before returning to 800rpm. This in/ out cycle continues (normal behaviour in our experience).
All good for 211 secs (3 min 31 secs) from initial start but then Idle starts to dip to 600 rpm when A/C kicks in and then next time engine stalls as A/C kicks in.
Must be fueling as engine goes through Open Loop to Closed Loop.
Thoughts?

There are lots of words above, there are some good points from @jrkitching

Going back to my initial post and your results here. To me it seems the fault becomes more of an issue as the engine warms and the idle drops with the car moving to closed loop function

The O2 is not fully functional at 10 seconds as some have claimed. It can take anything up to a minute to reach operating temperature and even then the sensor has to pass “drive cycle” for the ECU to fully accept the readings from the O2 sensor.

It could be if the car had been over fueling for a long time with the faulty thermostat this has damaged the o2 sensor which is sensitive to unburnt fuel in the exhaust.

Maybe not enough to flag an engine warning light, the figures might look in spec to the ECU but is giving a wild enough error to under fuel or under cut the idle too much once operating in closed loop.

I’ve driven diesels for the last 18 years so I don’t really know what the actual idle should be on this car but 800grams a little too low. Not massively low but a little low, and it under fueling the the load of the ac kicking in might be enough to cause the stall as the power isn’t there at idle.

No a nice long drive. 20-30 mins, then when you get back don’t turn the car off and leave to idle and then turn on the AC.

The long drive should be more than enough for the ECU to accept the readings from the o2 sensor. The engine will have had plenty of opportunity to find the best oppressing parameters. The car will be nice and warm. If the issue persists then the problem might just be the o2 sensor which while seemingly odd, that’s where I think the issue is pointing.

Scanner might give you a fault code if something has been picked up but might not be problematic enough to flag the EML

 

[jrkitching]

OK, so the A/C was working properly before the thermostat was changed, and after changing the thermostat, it isn't.

Basically there are two possibilities:

a) there was a preexisting fault, but the fault was masked because the faulty thermostat didn't allow the engine to reach normal operating temperature.

There are plenty of ways to drive yourself mental searching for a preexisting fault which may never even have existed.

or

b) the fault is the result of something that happened during the repair.

This is always my go-to position whenever I experience a new fault condition shortly after working on a car.

Disturbing electrical connections on an older car does carry some risk. Unfortunately we don't know exactly what was, or wasn't, dismantled during that repair.

If it's reaching the midpoint on the gauge and holding steady at that, I don't think there's anything wrong with the cooling system now.

Most of the A/C parts are on the opposite side of the engine, I don't see how any of that would have been disturbed either. If there were a significant compressor fault, you'd know about it by now.

I'd double check all the relevant wiring and connectors, especially if there are any tell tale signs of a connection having been touched during the repair, though I'd expect you've done this already.

It could be if the car had been over fueling for a long time with the faulty thermostat this has damaged the o2 sensor which is sensitive to unburnt fuel in the exhaust.

That's a well thought out suggestion, though I'm not sure how this would cause the exact sequence of the fault as it's being described here.

When I changed mine in basically the same scenario, everything functioned normally once the new 'stat was in. It had run for at least a month with a failing stat, and quite probably longer, but there was no apparent damage to any of the sensors. Fuel economy also quickly returned to what it was before the 'stat started to fail. I didn't break any electrical connections save for those on the battery itself.

Could be tested by swapping the upstream and downstream lambda sensors (they're the same part), but I'd not want to risk trying to get them out on a 16 yr old Panda.

I'm thinking some real live running scan data whilst the fault is being replicated might be useful.

 

[koalar]

Do you have jump leads
Do you have a multimeter and or test light
Does the clock ever reset during cranking
Does the power steering ever fail

Is it sparking correctly at all four plugs

Does it feel down on power