This tutorial will help you to do a cylinder balance test on your 3.8L equipped Buick (Chevy, Olds, or Pontiac) car or mini-van.
Why a cylinder balance test? Because it's the best way to find a ‘dead’ cylinder on your 3.8L V6 engine if:
This is where knowing how to do a cylinder balance test can cut down your troubleshooting time.
You can find this tutorial in Spanish here: Cómo Hacer la Prueba Balance de Cilindros (GM 3.8L) (at: autotecnico-online.com).
What the 3.8L cylinder balance test involves is disconnecting and reconnecting one fuel injector at a time while the engine is running in your car or min-van.
If the engine cylinder (who's fuel injector you just disconnected) is working a 100%... then unplugging the injector will cause the RPM's to drop and you will hear it and feel it.
If the cylinder is ‘dead’, unplugging the fuel injector will not cause any change whatsoever in the RPMs and you won't notice any change in the hum of the engine's idle.
To get a more accurate test result, what I do is connect a vacuum gauge to a Vacuum Hose (on the engine) that has vacuum (when the engine is running) with a plastic T. As I disconnect and reconnect each fuel injector, I can see if the vacuum gauge's needle reacts or not. Now, this step is not necessary/critical, so if you don't have a vacuum gauge or can't get a hold of one, you don't need to worry about it.
OK, this is what you need to do:
Connect your vacuum gauge.
Crank and start the engine..
Disconnect and reconnect one fuel injector at a time.
Repeat the test on the same cylinder.
Reconnect the fuel injector and test the next one.
Interpret the results. After testing all cylinders, now you need to interpret the results...
CASE 1: Unplugging the fuel injector caused a drop in the RPMs. This tells you that the specific cylinder you tested is OK and not the cause of the misfire (miss or ‘dead’ condition).
More specifically, this test result lets you know that the fuel injector, spark plug, spark plug wire, Coil Pack is OK for that specific cylinder.
CASE 2: Unplugging the fuel injector DID NOT cause a drop in the RPMs this tells you that the specific cylinder you tested is ‘dead’.
The cylinder could be ‘dead’ for a number of reasons. For example:
Don't let this big list of ‘possibles’ worry you... because one of the most important things you've accomplished with the cylinder balance test, is to find out which cylinder is the ‘dead’ one and this narrows down and focuses your troubleshooting efforts.
You'll find a list of articles that will further help you track down the problem that's causing that specific cylinder to misfire here: Misfire Troubleshooting: The Tutorials.
NOTE: Every now and then, I've seen cases where the engine has a rough idle condition and I mean it's shaking all over the place... When I've done the cylinder balance test, unplugging each fuel injector did not cause any change/drop in the RPMs. Why? This is because whatever is causing the rough idle or miss is affecting all cylinders evenly.
Although it's beyond the scope of this article to test such a condition, I can tell you that the most likely culprit behind this type of problem is a leaking intake manifold causing the air/fuel mixture to lean out. Among other things:
“I bought a perfect second car... a tow truck.”