I'm having some serious idle issues lately, which seem to smooth out around 3000 rpm, but runs poorly once I'm into boost again. I'm running AEM engine management which fried one of the stock coils, so I just installed the CD2I and MSD twin tower coils. Still doesn't like to idle smoothly.

If I pull the plug wires one-by-one, all of them will cause the enigne to fall on its face, except the farthest left (#4?) and pulling that has NO effect. So that cylinder's pretty obviously not doing anything. I can listen to the injector and hear that it's firing (also put it on a scope and can see the PWM signal coming through), and the plugs are brand new, so I'm pretty sure I've got spark as well (it's running wasted spark and its "companion" cylinder is firing just fine). When I pull the #4 plug wire, I can hear the coil "clicking" louder, which further makes me believe that when connected, the plug is firing as it should.

Which leaves me to think that either this injector is clogged royally, or possibly the piston's got a hole in it and it's not getting any compression. This I find hard to believe... though the car was up to 398 whp, it was running C16 and was professionally tuned by a conservative tuner, so I can't imagine it burning a hole in a cylinder.

 

Nobody, eh? I'm trying to figure out if the injector's working still... it's definitely firing, but possibly blocked I guess. When I pulled out the #4 injector, i couldn't find the o-ring for the life of me, but it probably just fell off and into the engine bay. If it was missing all this time, I imagine we would have noticed the fuel pouring out all over the place. And I think that would have caused wider-ranging problems than just one cylinder running poorly.

 

Do a leak down or compression test, it is the only way to see if you have a problem with the piston. Does it backfire? You could have a bent valve, but the leak down and compression check will point to that. If nothing else swap plugs and see what happens, then switch the coils, you just have to do some trouble shooting....

 

if you have a hole in the piston youll see alot of smoke out the exhaust.. pull the inj. and see if its firing..

 

what seems odd to me is that if #4 isn't sparking, I would think I'd be smelling a LOT of unburned fuel out the tailpipe... running it with the injector disconnected didn't make any apparent difference in smell, although either way it smells pretty rich at idle (no cats of course)

 

It's definitely "clicking" I think i'll swap it with #3 and see if there's any difference. I've also got some extra 450s that I know are working so I could toss one of those in just to see if it gets it idling. Then I'd KNOW it's a problem with the injector.

I'm not getting any noticeable smoke, which is one reason I wasn't suspecting any major piston damage. if it was just a blown ring land or something it would still get plenty of compression to idle ok.

 

pull the inj out and crank the motor and see if it sprays... pull the plug ground it out, and see if it sparks.. these are the only two ways to tell for sure..

 

Maybe I'm being stupid here, but how can you pull the injector out and keep it connected to the fuel rail when it's pressurized? Rail pressure is plenty to blow the injector clean out of there.

 

Farthest left when looking from in front of car is #1.
Which O-ring? Where it goes into the manifold? That would kill the cylinder at idle and it's unmetered air. The injector fires into the head from the topside of the port, you probably wouldn't see it leaking. What size injectors are they?

 

I feel like a bit of an ***. Apparently SOMETHING got messed up in the AEM tune. It had spark and fuel, they just must have been timed wrong somehow. I uploaded a base map and pasted my fuel and ignition maps into it and it runs just fine now. Considering the car's been doing this since a week after we had it tuned professionally, and started BEFORE I ever messed with the AEM, I have no idea how or what went wrong, but it's all better now.