missfire

[fhornerguy]

i was in mammoth a couple of days ago, and when i got back from an all day hike, the car wouldnt start. so i kind of tricked it into starting by pulling the efi fuse on a whim and it worked.

about 20 minutes later it started running really rough and the check engine light came on. my friend and i immediately thought that it was a missfire just because of the way it felt.

so i took it to the mechanic the next day and he ran a diagnostic. the code was cylinder two was missfiring. so they took it in and did a compression check which came back good, which means the vavles arent the problem...hopefully. he then deduced that since only the one cylinder was missfiring, it couldnt be the coil pack since that would affect both of them. after all this he decided that it was the wires running between the cylinder and the coil pack.

after replacing two, it did nothing (i couldnt get to the other one without tools). so another guy just said drive home on it, it wont do any damage, just give you awful gas milage.

i took it to the dealer in san diego, and the code came up with something like four missfires (great). and they replaced the last wire and that fixed it....supposedly. after driving it for 10 minutes the roughness came back and the light came back on.

im at a loss. any ideas? (sorry that was so long-winded, but backstory usually helps)

Greg

 

[greasefingers]

I always suspect the coil pack or spark plugs, when there is a misfire involved.

 

[fhornerguy]

well the plugs are brand new so maybe the packs? ill get them replaced i guess, as the next step

 

[greasefingers]

I have not seen your type of engine before, but usually there is one coil pack for each cyl. In this case, if one suspects a bad coil pack then you swap two packs around and see if the problem follows the pack by now having a misfire in the different cyl.

 

[fhornerguy]

on the 3.4L there are packs on cylinders 1, 3, and 5, and a wire that runs from each of those over to 2, 4, and 6. so the mechanic thought that since the corresponding cylinder to number 2 wasnt missfiring, that it couldnt be the pack since it would affect them both. but ill still have 'em check that.

 

[kustomkhaos]

Take it back to the dealer and have them hook up the scan tool to read the fuel injector duty cycle. We have been getting a few cars in with water in the fuel since this fuel change that has happened. Take a fuel sample and look for traces of water at the bottom.