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Discussion Starter #1
I'm putting this thread in here as well as the 147/156/GT section as I want to try and get as much coverage as I can in the hope of finding a solution.
My GTA has always run super smoothly, always pulled strongly with no hesitation whatsoever.
Nearly two years ago it started to use coolant (but didn't overheat) and head gasket failure was the problem. The engine was rebuilt (a full rebuild) by Ned and his guys at Autolusso. As a result the engine has once more proved strong, pulls perfectly well with no hesitation or flat spots. However since the rebuild the idle has always been a 'little' lumpy, fluctuating up to around 40 rpm according to Multiscan. Now this isn't the end of the world, and I was/am overall happy to accept this. The main issue is a misfire that occurs as the engine is coming up to temperature. If the car is left to idle, as the temperature rises, and just before or at the time that the cooling fan kicks in, the MCSF light comes on and a multiple misfire code on cylinders 1,2 and 3 is logged. The car only displays the problem whilst idling. If the car is turned off after a drive, and is left just long enough to cool down, then the problem occurs again. It never happens when the engine is cold, or hot, only at this 'switching state' as the thermostat opens and the fans cut in. Sometime it runs really quite rough for a few seconds, then clears, then rough for a few seconds, then it's fine. At other times (like yesterday) it runs rough for up to 30 seconds or so, then clears.
The car went up to Autolusso a few weeks ago to investigate this and to have some other jobs done. Low compression was found in cylinders 2 and 3. After some fettling the issue of low compression was resolved, it seemed that the piston rings hadn't fully bedding in during the running in of the rebuilt engine. Both Ned and I expected this to be the end of the problem, however the idle misfire remains.
I've swapped the spark plugs and coil packs around front to rear with no difference, I've checked for leaks in the induction system after the MAF and found a slight split in the concertina pipe to the throttle body which I repaired but still no change. I've run fuel cleaner through the system, I've cleaned the MAF. I've checked the 'visual' state of relevant electrical connections and all seem fine.
The timing belt was of course changed at the time of the engine rebuild.
Is there anything in the system that I can check that has a very specific state of change as the thermostat opens and the cooling fans cut in??
I've done search after search on here and found quite a few threads where people have had a similar issue, but none mention the specific conditions that my misfire happens in.
Any help would be appreciated as I really want to get to the bottom of this and taking the car on a three and a half hour drive to Autolusso Bedfordshire each time simply isn't realistic.

Thanks in advance for any pointers on this.
 

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Some sort of crank sensor or cam sensor? Tried a different ECU? Got any squashed or perished vacum pipes off the intake manifold?

Also Loz is a lot closer than Dunstable to you...
 

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Discussion Starter #3
The vacuum pipes that I've checked around the plenum all look good.
That's an interesting point about the crank sensor.....sometimes when hot the car doesn't 'catch' as effectively as it might normally do. There have been no error codes relating to this, and the car always starts when hot....I'm not sure if a crank sensor can gradually fail leading to lazy starting?
It may be completely unrelated, but having seen a picture posted by Chris155 it's very easy to get to if it is indeed a possible culprit. I'm happy to try anything within my capabilities to be honest.
I think I'll be using Autolusso Bournemouth for future jobs because they are much closer to me.
 

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I'm putting this thread in here as well as the 147/156/GT section as I want to try and get as much coverage as I can in the hope of finding a solution.
My GTA has always run super smoothly, always pulled strongly with no hesitation whatsoever.
Nearly two years ago it started to use coolant (but didn't overheat) and head gasket failure was the problem. The engine was rebuilt (a full rebuild) by Ned and his guys at Autolusso. As a result the engine has once more proved strong, pulls perfectly well with no hesitation or flat spots. However since the rebuild the idle has always been a 'little' lumpy, fluctuating up to around 40 rpm according to Multiscan. Now this isn't the end of the world, and I was/am overall happy to accept this. The main issue is a misfire that occurs as the engine is coming up to temperature. If the car is left to idle, as the temperature rises, and just before or at the time that the cooling fan kicks in, the MCSF light comes on and a multiple misfire code on cylinders 1,2 and 3 is logged. The car only displays the problem whilst idling. If the car is turned off after a drive, and is left just long enough to cool down, then the problem occurs again. It never happens when the engine is cold, or hot, only at this 'switching state' as the thermostat opens and the fans cut in. Sometime it runs really quite rough for a few seconds, then clears, then rough for a few seconds, then it's fine. At other times (like yesterday) it runs rough for up to 30 seconds or so, then clears.
The car went up to Autolusso a few weeks ago to investigate this and to have some other jobs done. Low compression was found in cylinders 2 and 3. After some fettling the issue of low compression was resolved, it seemed that the piston rings hadn't fully bedding in during the running in of the rebuilt engine. Both Ned and I expected this to be the end of the problem, however the idle misfire remains.
I've swapped the spark plugs and coil packs around front to rear with no difference, I've checked for leaks in the induction system after the MAF and found a slight split in the concertina pipe to the throttle body which I repaired but still no change. I've run fuel cleaner through the system, I've cleaned the MAF. I've checked the 'visual' state of relevant electrical connections and all seem fine.
The timing belt was of course changed at the time of the engine rebuild.
Is there anything in the system that I can check that has a very specific state of change as the thermostat opens and the cooling fans cut in??
I've done search after search on here and found quite a few threads where people have had a similar issue, but none mention the specific conditions that my misfire happens in.
Any help would be appreciated as I really want to get to the bottom of this and taking the car on a three and a half hour drive to Autolusso Bedfordshire each time simply isn't realistic.

Thanks in advance for any pointers on this.
I'm very curious to know how did Autolusso corrected the missing compression from the two cylinders..

If the car was running faultlessly before the rebuilt and now it has issues It would indicate to me that something is amiss with the engine build.
 

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Discussion Starter #5
I'm very curious to know how did Autolusso corrected the missing compression from the two cylinders..

If the car was running faultlessly before the rebuilt and now it has issues It would indicate to me that something is amiss with the engine build.
I'm going to do a compression test over the weekend and see what that shows, then move forwards from there. Ned wants to get to the bottom of this as much as I do.
 

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Does sound a bit like coil pack. Have known this issue before as coil pack warms up if the insulation is poor they will start to fault when warm but not when cold. Have you tried different coil pack or just swapped around.
 

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Discussion Starter #7
Does sound a bit like coil pack. Have known this issue before as coil pack warms up if the insulation is poor they will start to fault when warm but not when cold. Have you tried different coil pack or just swapped around.
I've swapped the rear bank coil packs and plugs to the front and the fault stayed at the rear so coil packs and plugs have been ruled out.
 

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I've had very similar issues with my 147 and until recently I was convinced it was the rear bank pre cat lambda sensor. I changed it when I had the engine out to change the clutch and cambelt and for a general clean and the issue has gone away where-as before it would flag up 15% of the times I stopped at traffic lights with a hot engine.

However, it has recently flagged up another set of misfire codes. This time for 2,3, 5 & 6 whereas before it was consistently for 1,2 & 3.

I'm hoping this is a one off, maybe through a lack of use. Or it may be an issue with the replacement lambdas I've fitted.

Ultimately, changing the rear bank lambda seems to have fixed / nearly fixed it. Perhaps you should consider it?
 

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Discussion Starter #9
I've had very similar issues with my 147 and until recently I was convinced it was the rear bank pre cat lambda sensor. I changed it when I had the engine out to change the clutch and cambelt and for a general clean and the issue has gone away where-as before it would flag up 15% of the times I stopped at traffic lights with a hot engine.

However, it has recently flagged up another set of misfire codes. This time for 2,3, 5 & 6 whereas before it was consistently for 1,2 & 3.

I'm hoping this is a one off, maybe through a lack of use. Or it may be an issue with the replacement lambdas I've fitted.

Ultimately, changing the rear bank lambda seems to have fixed / nearly fixed it. Perhaps you should consider it?
Cheers for the input Chris, all replies are appreciated. As said I'm going to check the compression as advised by Ned and that way at least one potential culprit can be ruled out. Once that is done we can move forwards.
 

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Interesting.
My GT has a similar MCSF issue following a major engine out session. When hot it will throw a temporary MCSF light, recording a misfire on 1, 2 & 3.
Laurence and I have tried lots of tweeks to resolve but no joy so far: new earth strap, compression test, lambda swap, fuel cleaner etc.
Since swapping the lambda leads it has thrown up p1133 & p1153 faults but I've now switch back and it's ok other than the issue on 1, 2 & 3.
The car runs really well and has been remapped with the issue present, pulling 240 before and 265bhp after.
Any thoughts?
 

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Discussion Starter #11
I carried out a compression test this morning on the car...the engine was warm but not hot. Anyway the end result was (from 1-6) 215 psi/215/220/200/216/207. I heard air screeching past the seal on cylinder 4 so in real terms that would be a little higher. On each cylinder the compression built up quickly as you'd expect on a good engine. So there's a 10% difference between the highest and lowest reading which I'm happy with.
The readings were slightly higher when tested at Autolusso, but differences in engine temperature etc explain this, and it's the average of any given test that I'm interested in.
Therefore the search for the intermittent misfire at idle continues, but it's good to know that the engine is strong.
 

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you tried swapping the coil packs over but maybe you have an issue with wiring to the coil packs or injectors on the rear bank.. I know i did a lot of work on mine..
 

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Discussion Starter #13
I've checked over the wiring (as much as can reasonably be reached). It all looks good. It's the fact that the misfire only occurs at around 70-90 degrees (approximately) which baffles me. I'd expect a wiring issue to display the symptoms more of the time.
I'm very happy that the compression test results are strong though.

The injectors are still a possibility....the furthest I've gone with them so far is to run fuel cleaner through them....but I'd expect an issue under load if the problem is fuel??
 

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Did you check/replace the coolant temperature sensor? Check with Multiecuscan and see if the engine temp matches the temp gauge in the car.
 

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Discussion Starter #15
Did you check/replace the coolant temperature sensor? Check with Multiecuscan and see if the engine temp matches the temp gauge in the car.
Funnily enough I thought it might be an issue with the temperature allowing for the fact that the misfire occurs as the engine warms up, but the gauge reads true with the temperature on Multiscan, and the fan kicks in as expected....something relating to temperature and something switching at temperature seems a possible culprit though.
 

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Not sure if you've changed out the fuel pump?

you could measure the fuel pressure for the front vs rear banks to see if there is a pressure drop on the rear.
 

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Discussion Starter #17
Not sure if you've changed out the fuel pump?

you could measure the fuel pressure for the front vs rear banks to see if there is a pressure drop on the rear.
I've not looked at that yet....I'm still working my way around Multiscan, I'll have a look into it though. Hopefully the free version supports fuel pressure values/trims.
 

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If there was a fuel pressure problem, you'd expect it to be most severe under load, which is when the engine is demanding most fuel.
 

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Discussion Starter #20
If there was a fuel pressure problem, you'd expect it to be most severe under load, which is when the engine is demanding most fuel.
This is my reckoning also. I'll have a look into it though as it helps me to learn my way around Multiscan whilst trouble shooting.
 
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