gclay

Help,

I am trying to diagnose and repair a rough running engine code for a 3100 engine. It was just swapped and a mistake in installing the engine could be the problem.

I have an Actron reader (the better one) and it reports the following two cedes consistently

P0303 Mod$10 1/2 Cylinder 3 Misfire detected
P0303 Mod$10 2/2 Cylinder 3 Misfire detected

I checked the shop manual and it indicates that even though the codes specify a specific cylinder, that the problem may not be for that specific cylinder. The diagnostic procedure indicates that one should use the computer interface to sequentially shut down each injector (and measure the rpm change). While my meter is pretty good, and I have a lot more functionality than simply code reading, I do not have the capability of shutting down the injectors from the Actron. Can I accomplish the same test by sequentially pulling each spark plug wire?

Also, in the shop manual it indicates that checking the electrical circuit for an injector requires a special tool. Can the circuit be checked with a multimeter?

I guess I am looking for a strategy for debugging an injector/injector wiring problem using pretty darn good tools, but not super exotic tools.

Any suggestions?

Thank you for Help.

George

Vader

GClay,

No, you cannot necessarily just pull the spark plug wires and expect to perform a successful power balance test. Many 3.1L and other V-6s use coil packs and a wasted spark system, whereby each coil operates two plugs simultaneously. You may in fact need to ground the plug wire you remove to complete the circuit for the opposite plug, depending on the year and system you have.

Your other option would be to remove the electrical connector from the injector in question, but that won't necessarily be accurate if the injector happens to be leaking.

This isn't on a ThirdGen, is it?

gclay

Vader,

You got me. I was swapping a 1998 Monte Carlo Engine into a 1996 Buick Century, but I figured the priciple was universal and could happen with a 3rd Gen computer controlled Fuel injected car.

If I ground the Spark plug will that allow me to simulate the test of shutting down a specific injector to check for rpm drop?

The next step depending upon the results of the above test is to remove the electrical connection and attach some special tool to the connection. I was wondering if I could test the voltage, or continuity to the connector utilizing a regular multimeter?

Vader

You can adapt to or back-probe a GM injector connector, but a standard SVM or analog meter probably won't be fast enough to catch the very short injector pulse at idle RPM. A cheap-and-dirty method is a 'noid light. Usually a bulb will get enough energy to at least flicker. A more sophisticated method is to record and measure actual pulse width duration and peak voltage with an oscilloscope.

You have verified that the coil packs, plugs, and ignition wires are intact, right?

Yes, this can apply to a ThirdGen V-6 as well, but most of them are not SFI. Turbo Buick 231s are the most notable exception.

gclay

THank you Vader for your help on this slightly off topic question. My son checked the wires and the plugs, but I haven't yet checked the coil packs. What I am doing is trying to establish a "plan of attack" for this. Your response has been most helpful. I will most definately recheck the wires and plugs before continuing.

We have put an induction timing light on the wires and they are all flashing.

I don't know off the top of my head "How do you check the coil pack?

If you don't know maybe I can find it in the shop manual?

again thank you for your help.

George