Strange Misfire

[razza]

Has anyone come across something like this? Any help would be appreciated.

1991 Galant VR4

When the car is started it idles good, until you touch the accelerator then the idle gets rough. When logging the o2's at idle they are extremely rich. The only way to keep the car from dieing is to keep your foot on the gas. So far we have logged all sensors and found nothing wrong. There are no ECU errors. Fuel pressure is set correctly. We have done a boost leak test and found a small leak at the back of the throttle body but I dont believe it would be enough to cause these problems. The car has recently been chipped to compensate for the 800cc injectors. We have tried a different ECU and a different chip from a running car but problem doesnt go away. When driving under full throttle there isnt any problems, the misfire goes away, however under cruise the car does misfire.

Modifications:

Bosch fuel pump (flows similar to the Walbro 255lph)
800cc Sard/ND Injectors
SX Fuel Regulator
SX Fuel Filter
GT35/40 Turbo
2G MAF
4" Intake Pipe
Large intercooler & 2.5" piping
Tial BOV
Tubular Manifold
Turbosmart External Wastegate
Internally stock engine

Many thanks in advance!!

Regards,

Ryan
Christchurch, New Zealand

 

[TRYMY4]

Did you try another coil pack?

 

[razza]

No we dont have a spare. You think this could be worth trying?

 

[talon96tsi]

Are any of your injectors leaking? Do you have access to a efi fuel system tester? Also check your plugs and make sure your wires are all good. I would try another coilpack if you have access to one as well.

 

[oVaBoost]

try coil pack or check wires diff spark plugs colder ones.

 

[aaronspeed]

I had the same problem and it was a vacuum leak. The clue on a vacuum leak is usually the Rich condition on a Fuel Injected car because the car is trying to correct the lean that a vacuum leak causes. Hunting idle usually happens also since the computer is trying to correct the fuel condition and the throttle motor is not fast enough to keep the idle steady.

 

[GsxEcutioner]

plugs and wires? My galant right now is having problems like hesitation for a couple seconds in low rev 3rd gear =/.

 

[jrohner]

Maybe your injectors actually flow more than they are rated for or your deadtime is set way too high. Are your fuel trims really low and it just can't pull out enough fuel to not be rich?