Following on from my recent posts about thermostat problems on my son's Mk1 Punto, he now has quite separate troubles with the damn thing.

He bought this car two months ago (regretfully!) and, in addition to various other things, cold starting has never been easy. Generally, though, it has usually started after several attempts. The other day it wouldn't have it at all, so he called out the RAC. Their chap said that there was a 'healthy' spark, and that it must be a fuel problem, so he sprayed something into what passes for a carburettor these days and away it went.

Since then it just doesn't seem to want to know. His first thought was that the coolant sensor could be responsible, so he decided to investigate around this area. Measuring the resistance of the sensor when cold produced a reading of around 7k Ohms - which we thought about right - and there was +5Volts on its input, so (we think?) that everything around there is in order.

When the ignition is turned on, fuel pump operation can be heard - so, again, that seems to be ok.

Does anyone have any further ideas about what might be causing this problem?
:bang:

I'm presuming it's running fine once it's started, no warning lights, lumpy idling, misfires etc.

If it's fueling then it could be an injector fault, which cures once it's warm, have you tried using an injector cleaner when you (he) fills up? I recommend Redex, seems to be better value than most. Make sure you get injector cleaner and not carb cleaner, though I don't think it makes much difference, better safe than sorry.

Another thing you can do is just check that all the connections on the injectors are secure and nothing's worked loose, and give each connection a squirt of WD40 to keep out moisture.

As and alternative, or you can't source the problem you can take it to a Lucas garage, who can do a health check on the injection system, though it won't be particularly cheap; individual injector checks cost £22, so £88 for all four, and extra for checking the fuel rail and pump etc., but they may do a special price for a whole system, and they seem to be pretty thorough.

Good luck.

Is the 7k ohms correct for the coolant temp sensor? It sounds high to me - but then I am thinking of other models where 500ohms might be expected. Perhaps a Haynes manual would be a good investment - for other FIATs I've owned they covered that sort of thing (expected component test values).

Fuel pressure? Perhaps the fuel pump is not running properly?

Is it a single injector (you mentioned something that appears like a carburettor, so I'm guessing that it is just the single injector.) The idea of a Lucas specialist sounds a good one to me - perhaps they can clean and flow-test the injector and check the fuel pressure.

Cheers,
-Alex

Thanks for the replies. Yes, it is running ok when he does get it started. He does have a Haynes manual, Alex, but I didn't get the value of around 7k Ohms from that. I have a workshop cd for the Punto, and that lists the resistance of the coolant sensor as around 10k Ohms at a temperature of 0C - reducing to around 300 Ohms at 80C. I must admit that (as yet) we are reluctant to try the Lucas route - he has already spent more than he can afford on the car (which he, obviously mistakenly, hoped would be a cheap runaround until he could afford something better.

I'll get him to check around the injectors - and try the injector cleaner - and see if that helps.

Thanks again.

why trust the rac when did it last have a set of plugs

that's what i would try first

make sure you get the right ones for the car they wont be very expensive from fiat atall

they should be changed every year

remember just cos you can see a spark when the plugs are out the car does not mean they are sparking under compression

compressed air is harder for a spark to jump across

Yes, plugs were my first thought - I should have mentioned that they were replaced a few weeks back when this starting problem first occurred. We got the same type as were already fitted in the car - can't remember what type that was (this is my son's car and he is 200 miles away).
We got them from a local motor parts shop - not from Fiat - is there a possibility that they are not exactly right and therefore causing the problem? ( I'll get the type fitted later and post it here).

newbieboy said:

Yes, plugs were my first thought - I should have mentioned that they were replaced a few weeks back when this starting problem first occurred. We got the same type as were already fitted in the car - can't remember what type that was (this is my son's car and he is 200 miles away).
We got them from a local motor parts shop - not from Fiat - is there a possibility that they are not exactly right and therefore causing the problem? ( I'll get the type fitted later and post it here).

Click to expand...

well even the wrong plug would work for a wile before it failed so i wouldn't have thought so, so i would discount that

a few things for your son to keep in mind are these cars must be started with your feet off the throttle dont try and use it to aid starting it actually hinders it

the cars idle control valve can rev the car to 5000 rpm so i'm sure it can handle cold starting on it's own using the throttle on these tends to confuse the idle learn procedures

also after one failed attempt to start they become much harder to start as the unburned fuel becomes to much for it so tell him not to be afraid to hold the key until he's sure it's started the starter has a one way ratchet so it wont damage it or spin it up or anything

the coolant sensor is a possibility as it's a cold starting issue not a hot one also

if it's running ok i wouldn't suspect any fuelling issues


other things that could affect cold starting are corroded engine earth meaning a weak spark

or a starter motor drawing too much current on start-up meaning again a week spark

you could check the voltage of the battery during start-up i would expect it to drop to 10 or 9 volts but less is a problem

Thanks for the very helpful reply. We were aware of not pressing the throttle when starting - I think that I read it one of your posts elsewhere - so he is careful not to do that. One of our first thoughts was the coolant sensor, but this appears to be ok, reading quite a high resistance when cold - which it should, being an NTC thermistor (I know very little about these cars, but I am an electronics engineer).

Someone suggested putting some injector cleaner in the fuel tank, so I passed this information on. Yesterday he got the car started using some 'easy start spray', filled up with petrol and put a can of injector cleaner in the tank - after that he took the car for a 70 mile drive.

He left it for a few hours afterwards, and it started first time when he tried. This morning it also started first time, and again this afternoon after standing outside for a few hours. I would say it's a bit too early to get too excited, but it's looking quite promising.

Thanks for all the help, if it plays up again we'll try the other things you suggested.

Try taking the injector to be cleaned on an ultrasound rig will clean all the deposits off it. Maybe change fuel filter too

Yes, we had thought about changing the fuel filter. How is this 'ultrasound' cleaning done (does the injector have to be removed?) - and how much does it normally cost?

newbieboy said:

Yes, we had thought about changing the fuel filter. How is this 'ultrasound' cleaning done (does the injector have to be removed?) - and how much does it normally cost?

Click to expand...

Yes you have to remove the injector, the basic principle is ultrasound is used to make a cleaning solution vibrate through the injector blasting all the crud off it.

Don't think it costs too much, trying to find a place locally to have it done to mine.

Makes a difference when you only have 1 injector!!

This is the best method's web site with a service centre locator

http://www.asnu.com/

Thomas_Si said:

Yes you have to remove the injector, the basic principle is ultrasound is used to make a cleaning solution vibrate through the injector blasting all the crud off it.

Don't think it costs too much, trying to find a place locally to have it done to mine.

Makes a difference when you only have 1 injector!!

This is the best method's web site with a service centre locator

http://www.asnu.com/

Click to expand...

i would have thought this cleaning process would be more suited to direct injection engines like diesel and alfa jts

as these injectors are in the combustion chainbur

redex and other such products are more suited to cleaning regular manifold or throttle body mounted injectors

many people sware by fuel additives and they do get results

they don't just clean your fuel system also they loosen carbon deposits on the pistons and head

this means if your car is over fuelling and carboning the plugs this will have a temporary effect on the problem

so if it does come back it may just be that

what colour were the plugs you removes

Redex Advanced did make a difference to mine. £14 a tin is a bit much though

Anyone recommend anything specifically as being quite good.?

forte system cleaner

littlepip17 said:

what colour were the plugs you removes

Click to expand...

They were quite carbonised - we put this down to the thermostat problem (it was actually missing), obviously with the engine not getting properly warm the mixture would have been fairly rich - but this has now been rectified.

BTW, the spark plugs we fitted were NGK - BCP 6ES types - do you think that these are correct?

newbieboy said:

They were quite carbonised - we put this down to the thermostat problem (it was actually missing), obviously with the engine not getting properly warm the mixture would have been fairly rich - but this has now been rectified.

BTW, the spark plugs we fitted were NGK - BCP 6ES types - do you think that these are correct?

Click to expand...

yes they are right

but i do refer the champion plugs but now i'm being piky there are a few variants available from fiat

well if they are still black then it's running rich for sure

still thinking lambda here

did you check the plug gaps before you put them in

should be 35 thousandths of an inch

not that it's related to the fault as it was there before anyway but just something to take note of

littlepip17 said:

yes they are right

but i do refer the champion plugs but now i'm being piky there are a few variants available from fiat

well if they are still black then it's running rich for sure

still thinking lambda here

did you check the plug gaps before you put them in

should be 35 thousandths of an inch

not that it's related to the fault as it was there before anyway but just something to take note of

Click to expand...

Thanks. I did check and adjust the plug gaps before fitting them.

He has since told me that it still does not always start straight away, so I will continue to check things, as advised. When he comes home at the weekend I will take the spark plugs out again (he doesn't have the correct size socket, he tells me) and check their condition, and re-check the gap.

Why do you think the lambda sensor could be faulty?

newbieboy said:

Thanks. I did check and adjust the plug gaps before fitting them.

He has since told me that it still does not always start straight away, so I will continue to check things, as advised. When he comes home at the weekend I will take the spark plugs out again (he doesn't have the correct size socket, he tells me) and check their condition, and re-check the gap.

Why do you think the lambda sensor could be faulty?

Click to expand...

well if other sensors fail they will alter the mixture but the lambda sensor will adjust them back again as it measures the final burnt gasses

so it's quite likely others that will affect cold starting are water temperature also

if you have a test meter and a haynes manual you can test various sensors and compare them with the manufacturers specifications

lambdas are a little harder to test

you need to form some sort of break out to keep them plugged in and watch the voltage from the sensor go up and down normally between 200 and 400 mv it does it quite quickly

or a scope would be good to have

Have just solved exact same problem with 2004 Punto 1.2 Active Sport. Was an incorrectly functioning air bypass valve (driven by the idle control stepper motor) supplying less air than required for cold starting. You can tell this is the problem if you run the engine from cold with the air filter housing removed. If the air bypass valve is working correctly, you will hear a hiss of air being sucked into the small chamber at the front of the air intake opening. The sound reduces in magnitude as the engine warms up and the valve progressively closes. If you don't hear this then the valve is stuck closed or the valve port is blocked with debris.

Firstly, ensure there is a very good earth connection to the front of the throttle body. Clean off any corrosion and dirt from the mating faces of the connector and throttle body and ensure it is bolted down correctly. I also coated the surfaces with petroleum jelly.

If this doesn't solve the problem, remove the throttle body and spray WD40 onto the air bypass valve, clean it's surfaces and the airflow port, then refit it ensuring all the electrical connectors and the earth are properly refitted.

If this doesn't work then you'll need a replacement throttle body.