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Discussion Starter #1
I'm putting this thread in here as well as the GTA 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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I'm putting this thread in here as well as the GTA 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.
Have you done a compression test on it again?

Ned
 

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Discussion Starter #3
Have you done a compression test on it again?

Ned
I haven't done yet. Do you think the lack of compression could have reoccurred then?
I'll try that if you reckon it's a possibility. There's no difference in the idle now to when I picked it up the other week. Thinking back to the use it's had since I brought it back I've not been in a situation where it's been left to idle and come up to temperature (the point at which the misfire occurs), it was only when I replicated the scenario yesterday that the fault reared it's head again, so maybe it was still there all along and the compression was a separate issue??...feasible??
 

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I haven't done yet. Do you think the lack of compression could have reoccurred then?
I'll try that if you reckon it's a possibility. There's no difference in the idle now to when I picked it up the other week. Thinking back to the use it's had since I brought it back I've not been in a situation where it's been left to idle and come up to temperature (the point at which the misfire occurs), it was only when I replicated the scenario yesterday that the fault reared it's head again, so maybe it was still there all along and the compression was a separate issue??...feasible??
I don't know with out doing a compression test and leak back test

Ned
 

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Discussion Starter #5
I don't know with out doing a compression test and leak back test

Ned
I've borrowed a compression test gauge, I'll check the rear bank out over the weekend and report back....is it worth doing the front bank too Ned?....no codes stored for the front bank but would it be of use for comparisons sake?
 

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I've borrowed a compression test gauge, I'll check the rear bank out over the weekend and report back....is it worth doing the front bank too Ned?....no codes stored for the front bank but would it be of use for comparisons sake?
Do all 6, don't mix the plugs up so we can compare the condition of the plugs to the results of the compression test

Ned
 

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Discussion Starter #7
Do all 6, don't mix the plugs up so we can compare the condition of the plugs to the results of the compression test

Ned
Okay. The relays I need to pull (fuel pump and fuel injection) are on the front of the battery aren't they?
 

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Very long shot but voltage issue? Maybe lov voltage somewhere in ignition circuit,might explain why it only occurs when the fans start demanding current causing misfire due to insufficient charge to coils/plugs?
 

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How do you "fettle" a ring that hasn't bedded in properly? My only experience of this is on very old diesels (lister-petters) when run with modern oil, the bores glaze and compression falls. Only solution then is to re hone the bore.

Have a look at my GTA thread in the image lounge - I had exactly the same errors and it turned out to be cam timing. However, mine was constant - it didn't miss when stone cold, but started to miss when it got hot, and carried on missing. If the lambda graphs look like mine did, then it is the ECU trying to compensate that causes the miss.

My idle was rough, and after retiming the rear exhaust cam, is as smooth as anything. My engine also pulled like a train - if you just got in and drove it, there was no problem. The problem only showed up when the car was idling (in traffic etc).
 

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Discussion Starter #10
How do you "fettle" a ring that hasn't bedded in properly? My only experience of this is on very old diesels (lister-petters) when run with modern oil, the bores glaze and compression falls. Only solution then is to re hone the bore.

Have a look at my GTA thread in the image lounge - I had exactly the same errors and it turned out to be cam timing. However, mine was constant - it didn't miss when stone cold, but started to miss when it got hot, and carried on missing. If the lambda graphs look like mine did, then it is the ECU trying to compensate that causes the miss.

My idle was rough, and after retiming the rear exhaust cam, is as smooth as anything. My engine also pulled like a train - if you just got in and drove it, there was no problem. The problem only showed up when the car was idling (in traffic etc).
Thanks for the input. You've come a long way in a short time with your GTA. I'll check the compression so that at least it can be ruled in or out. Also it's nice and easy to do, despite being a faff taking the plenum off again. Getting into anything like retiming cams puts me well out of my comfort zone, so I'll start with what Ned has suggested and see what results I get and move on from there.
 

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If you do a compression test, you are 90% of the way there in terms of checking cam timing. See if you can borrow a set of locks and a dial gauge. You may not want to retime yourself, but you can check without disturbing anything.
 

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Discussion Starter #12
Just out of interest (and an excuse to play before work) I set Multiscan up and ran the car. It felt like it had the occasional slight misfire but no MCSF light today. I ran the lambda sensor graph and they were switching between (approximately) .05 and .8 volts, with a nice steady graph display, no blips or big jumps. So the fault seems to be of the intermittent type. However multiscan did timeout just before the car got fully up to temperature so the test maybe wasn't fully conclusive....but equally the fault has occured before at around 70 degrees or so and we were nearly at 90 today before the software timed out. I'll do the compression test over the weekend weather permitting.....I don't do working on cars in the rain.
 

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Discussion Starter #13
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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