Technical Bad idle and sputtering only at idle after installing a new Magneti Marelli throttle body!!

[Alfa33boxer81]

Fingers crossed Oxygen Sensor should survive

Thank mate, I hope it's like what you sayand thank you for your support

I will post the updates whenever I'm able to install the new staff

 

[Alfa33boxer81]

Hi everyone again, just a little update here

I changed yesterday:

Spark plugs (the once that were in NGK BKR6E were kinda ok, no soat, no sign of collant burning). I put the new once NGK BCPR6ES

Changed the still original cables to some silicone new once

Put new ignition coils

Changed the Lambda pre cat and put new NGK one

Changed the crankshaft sensor and put a new Bosch one


Rechecked every thing and started the engine...but still doing the same thing... idling unstable and sputtering now and than, otherwise in gear driving perfect.

At this point i think the problem might be a mechanical issue because I don't have any other explanation

 

[bugsymike]

I keep thinking weak mixture.
Another thought was in the direction of throttle pedal position sensor, like a dead spot.

I found this about going from closed loop to open loop etc. It may be totally unrelated, there was a lot more, but this point seemed worth checking. https://www.ericthecarguy.com/forums/topic/car-going-in-an-out-of-closed-loop/
"
It’s very possible. Ideally the front sensor should switch between .2v to .8v and the post cat sensor should float around .5v . If the ECM cannot correct a lean or rich condition it will go into open loop. It looks lean to me.
I would be looking for a vacuum leak or insufficient fuel pressure or flow."

 

[Alfa33boxer81]

I keep thinking weak mixture.
Another thought was in the direction of throttle pedal position sensor, like a dead spot.

I found this about going from closed loop to open loop etc. It may be totally unrelated, there was a lot more, but this point seemed worth checking. https://www.ericthecarguy.com/forums/topic/car-going-in-an-out-of-closed-loop/
"
It’s very possible. Ideally the front sensor should switch between .2v to .8v and the post cat sensor should float around .5v . If the ECM cannot correct a lean or rich condition it will go into open loop. It looks lean to me.
I would be looking for a vacuum leak or insufficient fuel pressure or flow."

Very interesting article indeed...I went through the whole thread.

Anyway I have someone, in another Centos group, that is insisting that it might be a compromised head gasket between two cylinders and it is possible it affects the engine operating only at idle and not under load... For me would make sense but it should be affecting the engine under load because it looses compression in the 2 cylinders next to each other also and the misfire would appear as 2 cylinder misfire. As I have already stated in gear the car runs flawless through the whole rev range

 

[bugsymike]

Very interesting article indeed...I went through the whole thread.

Anyway I have someone, in another Centos group, that is insisting that it might be a compromised head gasket between two cylinders and it is possible it affects the engine operating only at idle and not under load... For me would make sense but it should be affecting the engine under load because it looses compression in the 2 cylinders next to each other also and the misfire would appear as 2 cylinder misfire. As I have already stated in gear the car runs flawless through the whole rev range

I have had customers cars with a slight head gasket weep , leaking water into the combustion chamber giving a misfire on startup that quickly clears.
However I would expect at least a small amount of coolant loss.
When testing for that I was able to do a "leak test" involving pressurising each individual cylinder and in this case with the coolant cap off and filled to the brim, it results in the coolant starting to overflow pointing to that cylinder.

 

[Alfa33boxer81]

I have had customers cars with a slight head gasket weep , leaking water into the combustion chamber giving a misfire on startup that quickly clears.
However I would expect at least a small amount of coolant loss.
When testing for that I was able to do a "leak test" involving pressurising each individual cylinder and in this case with the coolant cap off and filled to the brim, it results in the coolant starting to overflow pointing to that cylinder.

No misfire at start up that's what confuses me. It starts spot on and fires perfect in all 4 cylinder. Yeah a leack down test or compression test would be a starting point. I don't know anyone who does a lack down test but I can buy a kit for doing a compression test at home. When I took the plugs out they were all same colour about the right colour...
Anyway with engine on and coolant cap off I don't se any bubbles or rise in the expansion tank level. Even from the bleeding screw coming no bubbles no coolant lose and I check every day


Im thinking it could be also a faulty ECU (micro) but I'm not familiar with the symptoms it causes...and they're not cheap

 

[bugsymike]

No misfire at start up that's what confuses me. It starts spot on and fires perfect in all 4 cylinder. Yeah a leack down test or compression test would be a starting point. I don't know anyone who does a lack down test but I can buy a kit for doing a compression test at home. When I took the plugs out they were all same colour about the right colour...
Anyway with engine on and coolant cap off I don't se any bubbles or rise in the expansion tank level. Even from the bleeding screw coming no bubbles no coolant lose and I check every day


Im thinking it could be also a faulty ECU (micro) but I'm not familiar with the symptoms it causes...and they're not cheap

Also you saw no indication when looking at spark plug colour so probably not that.
Re the "Leak Test", as Foreman of a mixed Dealership in the 1970s, we were awarded in a customer workshop satisfaction competition a set of Sun Tune Diagnostic tools. Amongst them was a petrol leak tester, it came with adaptors and could measure % loss etc. I was impressed with it's use and made a basic version using a spark plug adaptor and high pressure airline. So locking engine up on firing stroke on TDC each cylinder at a time, I then introduced 150 PSI down the plug holes and was able to test each individual cylinder for head gasket seepage, valves sealing, piston/rings sealing etc. I still use that one and I also now have a Bosch version for diesels. So as long as you have a good supply of compressed air, you can cheaply make up this useful tool,

 

[Alfa33boxer81]

I mean you would expect at least a little bit of soat on 2 spark plugs in the 2 cylinders affected... I didn't see anything even though the plugs were not quite the right ones (they were clean)

I don't actually have compressed air at my garage as I'm not a mechanic, am just a hobby screwer that loves cars.

I just didn't needed any troubles with the little fiat right now in the middle of rebuild process of my Giulietta Cloverleaf. Sadly few days ago I got the news that the turbocharger has also been destroyed when the engine went . Now buying also a new turbocharger wich adds few thousands to the total bill. Otherwise I would have already opened the Seicento engine and redone a couple of things including the head gasket just to have some peace of mind.

 

[bugsymike]

I mean you would expect at least a little bit of soat on 2 spark plugs in the 2 cylinders affected... I didn't see anything even though the plugs were not quite the right ones (they were clean)

I don't actually have compressed air at my garage as I'm not a mechanic, am just a hobby screwer that loves cars.

I just didn't needed any troubles with the little fiat right now in the middle of rebuild process of my Giulietta Cloverleaf. Sadly few days ago I got the news that the turbocharger has also been destroyed when the engine went . Now buying also a new turbocharger wich adds few thousands to the total bill. Otherwise I would have already opened the Seicento engine and redone a couple of things including the head gasket just to have some peace of mind.

Also, if no coolant lose then not a likely cause. Where coolant has got on plugs , you may see a different colouration from the coolant/antifreeze so not soot, sometimes a green or yellowish tinge.
Even a small hobby type compressor is handy at home for other jobs like checking your tyre pressures etc.
Giulietta sounds expensive

 

[Alfa33boxer81]

Also, if no coolant lose then not a likely cause. Where coolant has got on plugs , you may see a different colouration from the coolant/antifreeze so not soot, sometimes a green or yellowish tinge.
Even a small hobby type compressor is handy at home for other jobs like checking your tyre pressures etc.
Giulietta sounds expensive

Yes tru if coolant gets inside the combustion chamber the spark would have a strange coating not of a normal colour. So the issue might be of another nature rather than a blown head gasket (either mechanical or electrical) like injectors, valve clearance ect.
It is only strange to me the fact that when it's idling like that and the electric fan kicks in the idle catches it self and the car idles normally as long as the fan stays on. Then the fan cuts out and it starts doing the same thing ...it is very confusing.

Yeah I actually have a tiny compressor for the wheels that works with 12v , it migh be good enough if I find a leak down test kit.



Yeah, Giuliettas especially the QV () 235 hp 1.8 Tbi engine are very expensive to service and especially the spear parts are getting crazy expensive to buy and also to find. It has also elevated running costs but I'm an alfista and i love that car, it's really a wonderful piece of Italian art


I would like to thank you for the support you are giving me all the time, I really appreciate that

 

[bugsymike]

Yes tru if coolant gets inside the combustion chamber the spark would have a strange coating not of a normal colour. So the issue might be of another nature rather than a blown head gasket (either mechanical or electrical) like injectors, valve clearance ect.
It is only strange to me the fact that when it's idling like that and the electric fan kicks in the idle catches it self and the car idles normally as long as the fan stays on. Then the fan cuts out and it starts doing the same thing ...it is very confusing.

Yeah I actually have a tiny compressor for the wheels that works with 12v , it migh be good enough if I find a leak down test kit.



Yeah, Giuliettas especially the QV () 235 hp 1.8 Tbi engine are very expensive to service and especially the spear parts are getting crazy expensive to buy and also to find. It has also elevated running costs but I'm an alfista and i love that car, it's really a wonderful piece of Italian art


I would like to thank you for the support you are giving me all the time, I really appreciate that

Is the spluttering across the engine or one cylinder down?
When it is spluttering is it possible to see the cylinders/spark plugs/injectors on your diagnostics to maybe point to one.
Sometimes injectors and coil packs use separate earthing points.
If it changes when fan on is it possible an earthing point is feeding back through fan circuit at that time effecting the engine?
Sorry 12volt compressor no good, it needs either a full size one or a mains 240 volt one with a reasonable reservoir/tank as the loss past even good pistons will soon drain the tank.
I had an 1971 Alfa 1750 GTV Bertone when they could be bought cheap, ex wife got that and part exchanged it for a Morris Marina, I bet she wished she had kept it.
Sometimes just talking through the problem can help you find the fault. I had an Iveco Daily Van with an electrical issue and someone mentioned the brake pedal wires, I looked at them and a previous owner had fitted some kind of alarm or tracking device which was causing the ignition light to come back on when you walked away after locking the vehicle, disconnected that and problem solved

 

[Alfa33boxer81]

Is the spluttering across the engine or one cylinder down?
When it is spluttering is it possible to see the cylinders/spark plugs/injectors on your diagnostics to maybe point to one.
Sometimes injectors and coil packs use separate earthing points.
If it changes when fan on is it possible an earthing point is feeding back through fan circuit at that time effecting the engine?
Sorry 12volt compressor no good, it needs either a full size one or a mains 240 volt one with a reasonable reservoir/tank as the loss past even good pistons will soon drain the tank.
I had an 1971 Alfa 1750 GTV Bertone when they could be bought cheap, ex wife got that and part exchanged it for a Morris Marina, I bet she wished she had kept it.
Sometimes just talking through the problem can help you find the fault. I had an Iveco Daily Van with an electrical issue and someone mentioned the brake pedal wires, I looked at them and a previous owner had fitted some kind of alarm or tracking device which was causing the ignition light to come back on when you walked away after locking the vehicle, disconnected that and problem solved

Gtv Bertone ...but every Alfa Romeo is special. My Giulietta QV has also the numbers of the leggendari engine 1750 Tbi


I can't actually pinpoint if the sputtering (the cutting) happens only in one cylinder or crossing the engine I really can't tell even through the Multiecuscan I don't see anything to pinpoint the problem or where does it happened. I can try disconnecting the cables one by one and se which cylinder affects the less the engine but it won't help much as the problem is not severe.

I did a video this afternoon, so if you can have a look at it whenever you find some time I would appreciate it

0 new items by elvisgjergji

photos.app.goo.gl

 

[bugsymike]

I did listen to it and heard it "hunting" although when the fan cuts in due to the noise I couldn't see the improvement in running.
Is it possible that the MPI injectors are worth looking at.
Not so much the normal running as you say it is quite good , more the electrical activating side, especially earth wiring, is it possible to measure voltages at the injectors etc. to see if there is a drop.
It is as though it gets poor fuel delivery at idle when it only needs a little fuel, so if anything reduces that like maybe the wiring connection it becomes noticeable.

 

[Alfa33boxer81]

I did listen to it and heard it "hunting" although when the fan cuts in due to the noise I couldn't see the improvement in running.
Is it possible that the MPI injectors are worth looking at.
Not so much the normal running as you say it is quite good , more the electrical activating side, especially earth wiring, is it possible to measure voltages at the injectors etc. to see if there is a drop.
It is as though it gets poor fuel delivery at idle when it only needs a little fuel, so if anything reduces that like maybe the wiring connection it becomes noticeable.

A stupid question here...
Could a leak in the exhaust flex pipe section after the cat cause this thing, or it's not the case in naturally aspirated engines

Yes it's like you say, it sounds like only at idle it doesn't deliver the right amount of fuel or the electrical system doesn't provide the the right voltage to the injectors at tick over. I would be more tempted to think about the fuel pressure my self. Is there a fuel pressure regulator that can be checked or replaced in the fire engine. Maybe it will be a good idea checking the fuel pump in the tank also, I have heard that the filter is incorporated in the pump and can get clogged, even though I run a full tank with an injection cleaner in it and didn't help.

I'm not really good with electrics but I have a multimeter at home, how can I check for bad earthing at the injector plugs? Also I have cleaned the earthing points in the engine bay. It would be also good to take the injectors out and sends them for a good clean but this is complicated here where I leave because it needs time and this is exactly what I miss because I work every with shifts.

 

[bugsymike]

A stupid question here...
Could a leak in the exhaust flex pipe section after the cat cause this thing, or it's not the case in naturally aspirated engines

Yes it's like you say, it sounds like only at idle it doesn't deliver the right amount of fuel or the electrical system doesn't provide the the right voltage to the injectors at tick over. I would be more tempted to think about the fuel pressure my self. Is there a fuel pressure regulator that can be checked or replaced in the fire engine. Maybe it will be a good idea checking the fuel pump in the tank also, I have heard that the filter is incorporated in the pump and can get clogged, even though I run a full tank with an injection cleaner in it and didn't help.

I'm not really good with electrics but I have a multimeter at home, how can I check for bad earthing at the injector plugs? Also I have cleaned the earthing points in the engine bay. It would be also good to take the injectors out and sends them for a good clean but this is complicated here where I leave because it needs time and this is exactly what I miss because I work every with shifts.

Exhaust leaks don't help , but generally if after all the sensors it is less relevant.
Assuming you have a common rail with a fuel pressure regulator on it, you may have a valve that looks a little like a tyre valve on the rail that pressure could be mechanically tested at, but again as you have no problem at speed or when fan cuts in , then less likely a pressure issue.
However do be careful as fuel may spray out at around 40 psi, so any sparks may result in the problem going away permanently in a ball of flame
Re testing the earthing at injectors, if you are a 100% sure you have the correct earth connection at the injector plug with it unplugged you can use the Ohm setting on a multimeter between that earth wire and your cars battery earth wire and should get the same reading as if you hold the two probes together, as in no resistance from a poor connection. If you get any resistance reading in Ohms it indicates a poor earth connection.
Do not accidentally touch a live wire on this multimeter Ohm setting as it will destroy the multimeter.
Fuel filter blockage is not likely to be an issue as fault changes electrically with the fan and also you have no problem with full throttle when most fuel would need to pass through the filter.

 

[Alfa33boxer81]

Exhaust leaks don't help , but generally if after all the sensors it is less relevant.
Assuming you have a common rail with a fuel pressure regulator on it, you may have a valve that looks a little like a tyre valve on the rail that pressure could be mechanically tested at, but again as you have no problem at speed or when fan cuts in , then less likely a pressure issue.
However do be careful as fuel may spray out at around 40 psi, so any sparks may result in the problem going away permanently in a ball of flame
Re testing the earthing at injectors, if you are a 100% sure you have the correct earth connection at the injector plug with it unplugged you can use the Ohm setting on a multimeter between that earth wire and your cars battery earth wire and should get the same reading as if you hold the two probes together, as in no resistance from a poor connection. If you get any resistance reading in Ohms it indicates a poor earth connection.
Do not accidentally touch a live wire on this multimeter Ohm setting as it will destroy the multimeter.
Fuel filter blockage is not likely to be an issue as fault changes electrically with the fan and also you have no problem with full throttle when most fuel would need to pass through the filter.

I think I understood what you mean. I'll try doing further tests.

One question though, could a tired battery affect the way the car idles. I always thought the battery is irrelevant to engine operation but reading a few posts where people saying the opposite. Of course a tired battery would affect the electronics but not much there in the seicento. One thing though, the alternator had problems when I bought the car (it was noisy) and I bought and installed a new Magneti Marelli one. Anyway if I check the voltage with Multiecuscan with the engine on it stays @ 13.7V which looks a bit low for me (my Giulietta charges 14.3 V). Whith engine off the voltage of the battery seems also a bit low (if I remember right about 12.2v)

Is there any chance it might be causing all the trouble?

 

[bugsymike]

I think I understood what you mean. I'll try doing further tests.

One question though, could a tired battery affect the way the car idles. I always thought the battery is irrelevant to engine operation but reading a few posts where people saying the opposite. Of course a tired battery would affect the electronics but not much there in the seicento. One thing though, the alternator had problems when I bought the car (it was noisy) and I bought and installed a new Magneti Marelli one. Anyway if I check the voltage with Multiecuscan with the engine on it stays @ 13.7V which looks a bit low for me (my Giulietta charges 14.3 V). Whith engine off the voltage of the battery seems also a bit low (if I remember right about 12.2v)

Is there any chance it might be causing all the trouble?

Re the multimeter tests if not sure let me know and I will try to show what I mean.
Re the battery/alternator side, two things one you could connect another car safely with jump leads and their engine running to see if it makes a difference.
The other thing is if it was as voltage drop causing the issue then why, when the fan cuts in which is an even bigger voltage drain does the engine then run smooth?
If your car is running slow at idle that may account for low charging voltage, normally I would expect most cars to charge with headlights on at around 14volts with engine revs at say 2000rpm. It isn't that far out, but just check that it will still charge with a load like headlights and heater fan etc.
A weak battery could affect what the charging voltage is.

 

[Alfa33boxer81]

Re the multimeter tests if not sure let me know and I will try to show what I mean.
Re the battery/alternator side, two things one you could connect another car safely with jump leads and their engine running to see if it makes a difference.
The other thing is if it was as voltage drop causing the issue then why, when the fan cuts in which is an even bigger voltage drain does the engine then run smooth?
If your car is running slow at idle that may account for low charging voltage, normally I would expect most cars to charge with headlights on at around 14volts with engine revs at say 2000rpm. It isn't that far out, but just check that it will still charge with a load like headlights and heater fan etc.
A weak battery could affect what the charging voltage is.

In poor words, it means, the idle speed could be affected from a low charging voltage which itself could be caused from a not top fitt or tired/to old battery... which can still operate the starter motor but oblige the alternator to work harder and the whole system won't reach the maximal charging voltage and as a side effect you have a poor idle .


The fact that the idle stabilizes, I have heard that if the fan kicks = greater load , the ECU has this already in its map and triggers the engine to idle higher for compensation and this would explain it. I can do this manually with the accelerator if I slightly keep it pressed at idle (just slightly to overcome this resting position of the pedal) it doesn't sputter and it's a perfect rhythmus.

As I said the alternator is new but it's charging the same voltage as the old one that was scrapped and was doing a tremendous noise/whining under accelerations.

I also had the same idea of connecting/bridging the car to another car or charging equipment to see if this makes any change...


If I could find the earthing point of the injectors, I could add another one/wire directly from the negative pole of the battery.

 

[bugsymike]

I can do this manually with the accelerator if I slightly keep it pressed at idle (just slightly to overcome this resting position of the pedal) it doesn't sputter and it's a perfect rhythmus.

As I said the alternator is new but it's charging the same voltage as the old one that was scrapped and was doing a tremendous noise/whining under accelerations.

I also had the same idea of connecting/bridging the car to another car or charging equipment to see if this makes any change...


If I could find the earthing point of the injectors, I could add another one/wire directly from the negative pole of the battery.

Re the engine speed , this may be to do with the basic adjustment at the throttle body, I believe there is some advice re this online. I know there was need for you to alter some of that earlier in your post, I don't honestly know if this will help or not though.
Re the earthing points, I would familairise yourself with the Ohm section of your multimeter and test the injector earthing points first to see if there is a fault before fixing a fault that may not be there.

 

[Alfa33boxer81]

Re the engine speed , this may be to do with the basic adjustment at the throttle body, I believe there is some advice re this online. I know there was need for you to alter some of that earlier in your post, I don't honestly know if this will help or not though.
Re the earthing points, I would familairise yourself with the Ohm section of your multimeter and test the injector earthing points first to see if there is a fault before fixing a fault that may not be there.

Good morning,

From what I have been reading in the forum in the MPI's THB you can't make any adjustments, they come already calibrated from factory. Even the TPS is just pressed in and no way to regulate the signal/voltage it sends to the ECU. The only thing that could be altered is that screw on the right (THB linkage) which must not be touched. Once touched it compromised the resting point of the butterfly and therefore altering the voltage the ECU receives from the TPS at closed position. It can idle better of course but it will be way off from the factory values and this will give you troubles at MOT where they do measure the pollution at idle speed. This was also the reason why I put a new throttle body, because I saw that screw was compromised from someone before...

Yes you are totally right, I will test the injector's electrical plugs firs, when I come back Wednesday. I have a 200 km trip to do today and hopefully without any surprises...