Last week I went for an emisiions test and failed pretty bad. I went back today for a diagnostic check and aside from them telling me that I have a gutted cat (this is good for airflow but not for emissions) they said I have a dead cylinder.
To be more specific it has good compression and good spark but apparently the injector must not be firing. This caused the O2 sensor to read a lean mixture and now it runs so rich that it fails really bad.
These injectors are brand new 2 months ago (Accel 23#). Everything must have been alright during the first test because the readings weren't nearly as bad as they are now.
What can I check for as far as the "dead" cylinder?

Bob

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350 TPI, 700R4(rebuilt), K&N's, MSD 6AL, Headers, Flowmaster, 160* stat, airfoil, MAF screens cut out. 13.88 @ 101.18 mph

 

check each injector with an ohm meter

 

Do a dead-cylinder test. The easiest way to do this is cut 8 one inch sections of 1/8 vacuum hose and attach each one to the dist cap, and put the wires on top of them. Then start the car and touch a grounded test light to the pieces of vacuum hose one at a time. This way you can kill each cylinder one at a time. While you do this watch the rpm. If killing a certain cylinder does not result in a rpm drop, then you know which cylinder is your culprit. When you do this you should set the rpm to 1200-1400 by blocking the throttle open. Also unplug both the IAC and the O2 sensor so the computer can't correct for the rpm drop by changing the idle.

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91 Z28
Come see The Vicious...

 

You can also check for injector pulse at the harnesses for the injectors with something called a 'noid light'. These are little light bulbs that plug in to the harness in place of the injector that are made to flash when injector pulse is sent through the harness for that particular injector. You can use these to verify that the computer's injector quad drivers are in working order and that the actual wiring is still in one piece. Keep in mind that our cars are batch fire systems and fire each bank of four injectors at one time and alternate sides of the engine.

The noid lights can help narrow down which cylinder is the problem and also can eliminate componants from the possible culprit list for the misfire..... You should be able to purchase them from some auto parts stores and from tool distributers like Snap On or Mac.....

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1987 GTA L98 MD8
355, TFS Heads, LT4 Hot Cam
My GTA

The Minnesota F-body Club

 

Will a test light work the same as a noid light? I've always heard to use a test light.

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91 Z28
Come see The Vicious...

 

Well, I have never used a regular 12 volt test light for this operation... I have always used noid lights...... But I checked the resistance of the two lights and my Blue Point noid light (for Bosch style PFI) is around 3.8 ohms and my Snap On test light read 38.5 ohms.... So I would say use a noid light to be safe.... Don't want to over stress those quad-drivers........

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1987 GTA L98 MD8
355, TFS Heads, LT4 Hot Cam
My GTA

The Minnesota F-body Club

[This message has been edited by Matt87GTA (edited October 24, 2001).]

 

Well, it turns out that 1 injector is bad. When it was swapped to a different cylinder that one was bad. I will be getting a replacement this week and swapping it out. No wonder it wouldn't pass emissions. Funny thing is it still feels like I could beat up on most cars on the road.

Bob

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350 TPI, 700R4(rebuilt), K&N's, MSD 6AL, Headers, Flowmaster, 160* stat, airfoil, MAF screens cut out. 13.88 @ 101.18 mph