Misfiring on #3 with P0303, flashing SES

[poncho]

My son's 2000 Bonnie with 3800 N/A has a misfire on #3 and here's what I did and still no fix. I used a new spark plug and a new wire to check the spark from each terminal on the coil packs by grounding the spark plug to the engine. I got a spark on all except #3. I switched coil packs, but the misfire did not move with the coil. I had the ignition control module (under the coils) checked out at two different parts suppliers, both said it passed after three checks each. So, what can I check? I only have a code reader, no scanner. I think I read every thread posted related to "misfire" and have not really found the answer.

[bszopi]

First off, welcome. Second, this isn't a site for the 3800 engine, but its a simple misfire issue, so I'll let it slide.

Just to clarify, you said that you switch coil packs, but the misfire DID move with the coil. Was that supposed to be DIDN'T?

[poncho]

OOPS my bad.

bszopi - thanks for the reply, I did not realize the 3800 is not 60* and in fact is a 90*. Is it advisable to post on another forum? But as you suspected I edited my post to read "did not". Hope I see some responses, because this issue effects other GM platforms with coil packs and ICMs. Thank you in advance.

[bszopi]

Ok, so we know the issue is not with the coil, and the issue should not be with the ICM since it was tested multiple times by 2 different places. You also said that the wire and plug are new. Have you tried moving the wire and/or plug around to see if the misfire follows either of them? Just because they are new doesn't always mean they are good.

[poncho]

Common wire and plug

I used the same new spark plug wire and a new spark plug, then I moved the wire to each coil terminal and grounding the spark plug body to the engine and started the car. Each time a different spark plug is disconnected from the coil and the new wire/plug connected in it's place. I repeated this process for six plugs, twice to duplicate the results. The result was the same, with #3 not firing. Remember I also moved the coils around,repeated the process and the misfire stayed relative to the ICM NOT the coil. I even had a brand new coil which performed the same way the others did. My thinking is the fault is between the ICM connector (no bent pins) to the PCM. How can I check this or are there other checks to address? Thanks again.

[bszopi]

There aren't individual wires for each cylinder going from the PCM to the ICM. Therefore any wiring there should be ignored. It sounds like its an issue with the ICM, regardless of what other tests said. I'm not sure how those are tested, so I can't say if there is a chance that a fault wasn't detected. I would probably buy a new ICM and go from there.

[poncho]

I'm not surprised to hear that the tests may not be accurate. Twice before I took an alternator to have them checked and both times I replaced the units after they were rendered good. One cost me a fried battery. It overcharged at about 18v, yet the part supplier said it passed the test. Checked it myself with a multimeter to find it was too late to save the battery. Anyway, I gather from your suggestion that it's useless to attempt tracing the wires from the connector and buy a new ICM. Man these things are not cheap and non-returnable. I watched the guys at two separate places hook up the unit to the tester by hooking four alligator clips to the ICM. A purple wire went to the terminal furthest away from the connector end and the other three red wire clips went to one of the paired terminals on the ICM closest to the connector end. So starting with the opposite end of the connector, there are three pairs of terminal, they were hooked up this way. Purple, red, blank, red, blank and red. Yet as the tset progressed, it lit up a pass green light to indicate a PASS status. Why is one terminal left untested? Are they connected to the other terminal. Maybe I'm going too deep here, just frustrated how two different places can check the ICM to be OK and yet still have a problem. So I'll wait a little longer hoping someone comes up with something else before I open the vault for a new one.

[95Grand-Am]

Try pulling the # 3 plug wire off the spark plug hook it to a grounded spark plug and watch to see if it has a good spark. If it does I would check the resitance in the fuel injector on that cylinder I belive its supposed to be around 13 or 14 ohms. I have seen feul injectors cause misfires also.

[bszopi]

Try pulling the # 3 plug wire off the spark plug hook it to a grounded spark plug and watch to see if it has a good spark. If it does I would check the resitance in the fuel injector on that cylinder I belive its supposed to be around 13 or 14 ohms. I have seen feul injectors cause misfires also.

If you reread the first post, I'm pretty sure that is what he already did.

[95SleeperAcheiva]

um guys.... misfire doesn't always mean spark.

Ohm the injectors.
possible options are:

1.you got a bad injector,
2. worn flat cam that ain't opening the valve and choking the cylinder for air.
or
3. loss of compression. No compression, no boom.

And don't feel bad, I ask questions about my 2.2L S-10.

and I didn't mean to step on any toes there BZ, I respect you guys big time, you've all helped me out tons, and I'm a certified Master tech.

EDIT: Oh hell, I missed the part about the injectors too. My apologies.

I also read about a TSB on the ring for the crank trigger getting cracked. The ring behind the dampner. I don't know if that will cause one cylinder to die though, I doubt it.

[poncho]

problem solved

Once again, I have very little faith in these FREE checks. I replaced the ICM and no more misfire. Maybe it was the connection at the connector, so someone might say. Sometimes removing and reconnecting wires cures some problems. So I switched the ICM to the old one and the misfire was back at #3. Enough of this $#!t. The new went back on and the car is running fine. Thanks for all the input, even if this is not a 90*V6 forum.

[bszopi]

Glad to hear its fixed. And yeah, the checks can not always be trusted. But they are sometimes a good place to start. But the other troubleshooting you did brought you right back to the issue.