This is someone elses car Im working on with tuned port injection.

The symptoms:

At idle, basically one cylinder seems to have a lean misfire in open loop. Once the car is in closed loop, it evens out, but runs very rich. Under high load, the engine runs well. All the spark plugs are a dark tan (should be white with EFI) except for one, which is white. When the O2 is unplugged, the lean misfire returns. The one plug on the misfiring cylinder turns a grey/black color from deposits. I replaced the O2 with a wideband O2 and found out the following on that bank of cylinders.

With the faulty cylinder's injector unplugged, the wideband reads 23-26:1 AFR, which indicates a higher oxygen content. With any one of the other functional cylinder's injectors unplugged, the AFR reads 20:1, which indicates less oxygen content. The engine also seems more heavily loaded with that one faulty cylinder's injector unplugged. The others it just runs rough. On this cylinder, its noticably more loaded, and seems like it wants to stall. To me, it would indicate there is more air in that one cylinder then there should be. I performed a compression check, and although it could be better, the static compression was similar to the other cylinders on that side of the motor.

So far, I havnt found any external vacuum leaks on the parts of the intake manifold I have access to. All the hoses appear to be ok as well. Before I go tearing into it, is this an acceptable assumption that it has a vacuum leak? Is it possible for the vacuum leak to be internal to the motor? Is there any way it could be an injector? They where replaced recently, but its still no proof that theyre working properly. I dont want to go through a bunch of work only to have the misfire migrate to another cylinder when Im done. Or even worse, still persist on that one cylinder.

 

try pulling the manifolds and the fuel rails but leave the fuel lines connected and see if any of the injectors are leaking then test to see if the 1 injector is getting any fuel . i had the same problem with my 87 tpi and the 1 injector had a plugged filter in the injector might be woth a shot.

 

That sounds exactly like a vacuum like a vacuum leak. I'm not wise enough with EFI to say where it could be from though....