Cannot solve code 41 issue

[RibHouse]

The only code my 91 car is putting out on the KOER test is 41 which indicates system lean on the back HEGO sensor. I have replaced the Y pipe and cats, the O2 sensors, the fuel filter, cleaned the MAF and did a 60M mile maintenance. I tried swapping the O2 sensors and got the same trouble code. I pulled a back plug and it was ashen color, confirming it was running lean. The front plugs were slightly carbon fouled. I have checked and double checked for a vacuum leak, but none were found. The cylinder test also came back negative for problems. I have read every tread I could find on the subject and am still at a loss as to what is wrong. It is probably something simple, but I am too close to it to see it. Please tell me what I am missing.

 

[jimtash]

Did you only see the color on one plug or all 3? If it's only affects one then you need to look at the intake coupler for that cylinder. If it affects all 3, suspect the intake gasket.

 

[RibHouse]

I only pulled the back middle plug due to the difficulty of getting to the others, but I have sprayed ether around the intake gasket and rubber couplings with no change in engine idle speed. The intake gasket is new and the couplings do not appear cracked. Could it be a PCM failure? I know it does't seem likely, but I am stumped!

 

[jimtash]

Pull the other 2 out and see what they look like. It'll help narrow down what's wrong with it. You're only having problems with that side of the engine so you need to know if it's just one cylinder or all three.

 

[RibHouse]

I will have to tear back into the engine to check the other back plugs. Assuming they all indicate a lean burning condition, what could cause this other than the intake gasket which I know is good and properly torqued?

 

[jimtash]

No need to tear down the engine to get to the rear plugs. It's easy with an extension bar. This is what I use:

http://www.autozone.com/autozone/ac...extension/_/N-26lo?itemIdentifier=914154_0_0_

Intake runner couplers, clamps not tight, intake gaskets around the runners and couplers, intake not fully seated. If it's just affecting one cylinder, could be that above plus toss in a clogged fuel injector. Search around here to come up with more ideas when you get time.

 

[zak]

You could also have a partially clogged injector or two.

 

[RibHouse]

You could be right. I pulled a second plug in the rear that looked fine. When I did the 60K maintenance I replaced the injectors with a refurbished set, so I had dismissed that possibility before now. Any thoughts on how to confirm the diagnosis?

 

[jimtash]

Here are some tips off another board.

http://clubsearay.com/archive/index.php/t-31189.html

One involves using a fuel pressure gauge and another suggestion is to disconnect the connector and observe the RPMs. Running the cylinder balance test might also confirm it.

 

[zak]

. Running the cylinder balance test might also confirm it.

I know the OP had run the cylinder balance test before, but on the later SHOs there are three levels of sensitivity - the first round of balace testing is looking for coarse changes, the next one finer and the third is the most sensitive. Its been a while, but you might have to do something to activate these finer rounds of testing.

 

[jimtash]

Just press the gas after the repeat of the codes to restart it.

 

[RibHouse]

Code 41 solved. Like those that responded predicted, it was a fuel injector that was not firing. Thanks, guys!