Why bother with 3
cylinders when 6
AO Silver Member
Join Date: Sep 2012
Location: United Kingdom
V6 misfire at idle.
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.
Unimpressed by cars with less than 4 cylinders or below 1600cc.....and don't get me started on hybrids