Help with a miss

accuab · #1 08-04-2009, 10:59 AM

I have a 98 malibu which has the 3.1L engine that I'm sure a lot of ya'll grand prix guys are used to. The malibu forum isn't very useful so I figured I would ask ya'll. The car has 104k miles on it. Head gasket was just replaced. The car has new plugs and wires on it. The coils are sending spark and the injectors are spraying well. The plenum was checked on the car as well. What am I missing that would still be causing a miss in the engine.

BNaylor · #2 08-04-2009, 08:28 PM

Is it a random misfire P0300 DTC or specific cylinder misfire like P030X.

tblake · #3 08-04-2009, 09:52 PM

Was the car running fine after the LIM job, or did the miss start after you got done replacing the lower intake gaskets?

I would check and make sure all the pushrods are in the correct spots.

accuab · #4 08-05-2009, 02:03 AM

The miss was there before the head gaskets were changed. We thought that may have been the source of the miss. But it stayed the same afterward. The misfire is on the number 3 cylinder. I believe the code is P0303. Dad took it to a Goodyear place today and they put it on their computer and said that it either had to be the plug, wire, or the injector for that cylinder. Another mechanic dad trusts checked all the internals and said that everything was moving like it was supposed to. Also, dad had checked all the valves to verify they opened and closed correctly before sending it to have the heads redone. I appreciate ya'll trying to help on this. I always put my questions for my gp on here and always got a good response. I'm not sure why I don't get very many on the malibu forum.

BNaylor · #5 08-05-2009, 07:03 AM

Have you checked or swapped the ignition coil packs? What brand/heat range spark plugs and wires?

Also, a fuel injector issue will cause a fixed cylinder misfire.

accuab · #6 08-05-2009, 09:16 AM

As far as the coil packs, I swapped them around myself yesterday to no avail. The miss remains on the #3. The wires are Autolite and the plugs are Autolite Double Platinum. I'm not sure what the heat range of those two items are. Dad's mechanic said the car had plenty of spark and plenty of gas, but it has to be one of those items since the miss is located on only one cylinder. Right?

tblake · #7 08-05-2009, 04:38 PM

Ohm check the injector and get back to us. You may be able to do it without removing the UIM through a single plug near the alternator.

Could also ohm check the wire. no more than 10k ohms (if my memory serves me correctly).

accuab · #8 08-06-2009, 11:52 AM

I don't have a multimeter handy to be able to check the resistances. Another question for you though. Dad pulled an injector from a donor 95 Grand Prix with the 3.1L. He brought the malibu to a mechanic, but the mechanic stated that all the injectors should be replaced- not just one. He also said that even though the computer said the miss was on cylinder 3 that it could be a different cylinder that could be causing #3 to misfire. Does this sound correct?

BNaylor · #9 08-06-2009, 07:55 PM

Quote:

Originally Posted by accuab

He also said that even though the computer said the miss was on cylinder 3 that it could be a different cylinder that could be causing #3 to misfire. Does this sound correct?

It is possible but the only way to prove it is with a scan tool like a GM Tech 2 that has a provision for monitoring cylinder misfire counters.

richtazz · #10 08-07-2009, 01:20 PM

the mechanic that told you that you should change all the injectors instead of 1 must have a boat payment to make or something. It is important for all the injectors to be balanced (meaning that the injector resistance should be very close to the same on all 6), but there is no reason to change all 6 if only one is bad.

I was suprised to see that the 95 GP and your Malibu use the same injectors Delco # 217-1388 (GM 17113572). If teh resistance in that injector is within .5 ohms of your other 5, then there is no reason not to use it. Just be sure to buy new o-rings for all of them to avoid the chance of a fuel leak.

On plug wires, 500-600 ohms per inch of length is acceptable.

accuab · #11 08-07-2009, 07:15 PM

So does it sound like to ya'll that it is the injector? I know you can't tell for sure without having the car in front of you, but what do you think? Also, in saying replace the o-rings on the injectors, are you saying I should go ahead and redo all the o-rings on all the injectors?

tblake · #12 08-07-2009, 08:37 PM

Yes, re-do all them. Uppers and lowers.

richtazz · #13 08-10-2009, 09:08 AM

If you can get your hands on a DMM, check the resistance on the injectors (you'll need to remove the upper plenum to reach most of them). If the #3 injector is way off from the other 3, then it's the issue. Since you swapped coils and the miss remained, you're down to plug, wire, or injector on cylinder #3, or a bad circuit in the ignition module.

accuab · #14 08-12-2009, 10:25 AM

Here's the newest piece of information. Dad had someone checking the injector and he said the injector was fine so he just put new o-rings on it. Dad told him to just fix the car. He is one of those few older mechanics still around that will fix your car without breaking your wallet in the process. What else could the problem be? I'm running out of time and answers trying to get this fixed.

richtazz · #15 08-12-2009, 10:57 AM

3 questions:

1. Has anyone checked misfire data on other cylinders to see if the counts are just below the threshhold to trip a random misfire code (P0300).

2. Did he check the injector when it was cold, or after the car had warmed up? Injector windings can fail due to heat, and check fine when cold.

3. Has anyone ohm checked the wire and checked the plug itself for cracks in the ceramic insulator? Have we tried swapping the #3 and say #1 or #5 plugs and wires (as the wires should be close enough in length to reach for testing purposes) to see if the miss moves then?

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