Help with a miss

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.

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

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.

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.

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.

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?

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).

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?

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.

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.

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?

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

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.

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.

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?

Here's the update. The car has been fixed. yay. So here's the scoop. The #3 injector did in fact end up being bad. First, he found there was a leak at the o-ring and replaced them but the miss remained. He then found out there was a air leak in the upper intake manifold, so he replaced that gasket. The miss remained. Then he finally found that the injector was bad. The order that he really found all the problems may have been different but I do know that he had to tear everything back down at least twice to finally find all the errors. I will be getting the car back tomorrow finally. I think it will be a great car after fixing everything that was needed. I paid $900 for the car originally. It is a 98 Malibu with 104,000 miles. The heads were redone at a cost of $300. New plugs and wires were put on the car at around $40. This last go around cost $393. So all in all, I have a car that ended up costing $1637. That a pretty good deal if you ask me. :smokin:

Yes, good price on a car with only 100,000 miles expecially if the body is in good shape.

Glad to hear everything is back to normal!

thanks for the feedback, we're glad to hear she's running right again and it didn't cost you an arm and a leg.

The body is in excellent shape for a 98. I think after the engine had some problems, the person just wanted to get rid of it. Dad got it at an auto auction. Here's another question though. I had a 02 Grand Prix GT so I got used to more hp and torque. This car has a lot softer transmission that what I got used to. Is this normal? The malibu is rated at 155 hp I believe so I know it won't have the torque to make the car surge like a GP. Dad said he thought maybe the trans fluid is low. The cars have a sealed transmission with no dip stick. I've changed the trans fluid in a GP, but this is a different setup. Would you recommend getting this done at a shop?

If you want to change the filter, that's fine, then just replace what fluid comes out when you drop the pan. It is not advisable to do a fluid exchange on a transmission with over 75k miles on it. The reason is that new fluid is grippier than old fluid, and the shock of the grippier new fluid will shear the clutch fibers from their backing plates ruining the transmission. The 4T40E transmission in your car have a special refill/level check proceedure that would be best left to a shop unless you have a good service manual and know what you are doing.

So you are saying that if I want to put a new filter in the transmission, I should put the fluid that comes out of it back into the transmission and then top it off with new fluid if necessary? How much do you think it should cost to have someone do that procedure in a shop? I know how to do it, but I don't have a lift handy to keep the car level.