Misfire driving me nuts

[chadicenhour]

Hello, I have a 99 Grand Am Gt with a 3400. I have a cylinder number 3 missfire that is driving me nuts. I have new plugs and wires on it. I swapped the coils and it made no difference so I know its not a coil. Here is the odd part. When the engine hits about 2000 RPMs, the miss goes away. I watched the misfire data on my Solus and it shows it to be worse while idling. Although it did throw a p0300, as bad as it is, it never offered a p303. The others cylinders very seldomly missed and didn't seem to make a difference. I'm thinking it could be the ICM, but I'm not gonna rule out the injector. It just seems odd to me that the miss goes away at 2000 RPMs. I don't want to just throw expensive parts at this thing as I've just got done replacing many parts the previous owner had rigged as well as replacing the headgaskets and such. Anyone have any ideas? Does this sound more like an ICM or injector? Thanks in advance!

[SappySE107]

I would guess injector related. 6 and 3 are linked in the igntion system, so I would doubt that it is the ICM or Coils. The spray pattern might be messed up, or it could be stuck open to some degree, making it extra rich below 2k that it knocks but isn't as rich once there is need for more fuel.

[Superdave]

I would guess injector related. 6 and 3 are linked in the igntion system, so I would doubt that it is the ICM or Coils. The spray pattern might be messed up, or it could be stuck open to some degree, making it extra rich below 2k that it knocks but isn't as rich once there is need for more fuel.

x2

there is a GM bulletin out about this.


smack the injectors around with a screwdriver and see what happens...

[60dgrzbelow0]

On a non-moonlit night and without any ambient street lighting, you might try using a couple of blankets to cover the side areas of the front of the engine compartment with the hood wide open and up, and while keeping your hands and clothing completely away from the pulleys and belts while leaning inside, have someone raise and lower the RPMS of the engine and see if there are any Tell-Tale Blue sparks that will reveal failing igntion wires or electrical leaks that might explain the misfire. This is a very simple test and a reliable way to quickly pin-point or eliminate the possibility of such problems, too.

[Weatheralls Auto]

Though 3/6 tied together, I have seen ICM cause a single cylinder misfire (don't ask how, I don't know lol)
Your system, though, sounds like an injector.
You can try a cleaning or even swap 2 to verify.

[Weatheralls Auto]

To add, I find injector misfires to be the worst just Off Idle and low range.

[60dgrzbelow0]

http://www.fixya.com/cars/t3412483-motor_misfire_problem_code

[chadicenhour]

Thanks so much guys, you've been a big help. I'm gonna get some Techron to run through it. If that doesn't take care of it, when I get time I'll swap the injectors between cylinders to verify the problem. Once I verify it, I'll buy some rebuilt injectors. If anyone else has any ideas, please chime in. Thanks again!

[chadicenhour]

UPDATE!!

Alright guys, I just wanted to give you an update. The problem is solved. Today I tagged the car. I went to the junkyard and took a set of injectors off a van which was a PITA since I didn't have the correct tools with me. I got the injectors home and installed them with no change in the miss. After that, I went and bought a brand new ignition module as well as 3 brand new coils and installed them with no change in the miss. Since I only had a miss in cyl 3, I swapped the wires from cyl 3 to cyl 5 just in case I got a bad set of new wires.....well that didn't make a difference. Finally I swapped cyl 3 spark plug with cyl 4 and the Solus showed the miss went to cylinder 4. So after spending almost $300 today trying to fix this miss, it was all because of one new sparkplug from a set that was given to me by the previous owner when I bought the car. The junky spark plug with zero miles on it was a Bosch platinum plug. I swapped in one AC Delco from a 3100 thats in my step dad's grand prix to drive the car and make sure the miss is definately gone and it was. Tomorrow morning when I get the Grand Am back from having the rigged exhaust fixed I'm gonna get a set of AC Delcos or is there a better plug for this engine? Anyway, Thanks alot guys for the help.

[bszopi]

AC Delco all the way. These engines and Bosch plugs don't get along very well...

[Superdave]

AC Delco all the way. These engines and Bosch plugs don't get along very well...

pretty much anything Bosch seems to disagree with our engines...


Glad it's fixed!