Help Diagnose #4 cylinder.
Thread Starter
Racer
Joined: Nov 2007
Posts: 441
Likes: 3
From: Huntsville Alabama
Help Diagnose #4 cylinder.
I need some help to find a problem.
Motor is a new built forged motor with around 5K miles, it runs perfect, and does not seem to have a misfire. During regular maintenance, I removed all of the plugs, and found 7 of them to still look new, and #4 was Dry Black Sooty. I thought I had found a bad plug wire on that Cylinder, so I ordered a new set of wires, and also installed a new set of plugs again. Now after only a few hundred miles, I find the #4 again, Black, dry and sooty again.
I swapped the coil to a different cylinder when I changed the plugs before.
Notes,,,,
No Misfire that is detectable.
New plugs
swapped coil
Compression test show same as other cylinders
Sprayed start fluid to look for a air leak, none found.
I did last night swap the injector to the other bank, and not yet drove it to check.
Any suggestions is appreciated.
Motor is a new built forged motor with around 5K miles, it runs perfect, and does not seem to have a misfire. During regular maintenance, I removed all of the plugs, and found 7 of them to still look new, and #4 was Dry Black Sooty. I thought I had found a bad plug wire on that Cylinder, so I ordered a new set of wires, and also installed a new set of plugs again. Now after only a few hundred miles, I find the #4 again, Black, dry and sooty again.
I swapped the coil to a different cylinder when I changed the plugs before.
Notes,,,,
No Misfire that is detectable.
New plugs
swapped coil
Compression test show same as other cylinders
Sprayed start fluid to look for a air leak, none found.
I did last night swap the injector to the other bank, and not yet drove it to check.
Any suggestions is appreciated.
Drifting
Joined: Jul 2011
Posts: 1,599
Likes: 399
From: Boise, ID
2022 C5 of the Year Finalist - Modified
2021 C5 of the Year Finalist - Modified
C5 of Year Finalist (appearance mods) 2019
Do you have hptuners or comparable logging tool that lets you monitor cylinder roughness count? You might be able to use an app from your phone to do so. That would definitively let you know if you are knocking on that cylinder at any time.
Sounds like you have ruled out all leaks I'm assuming you made sure valves were nice and sealed when on the heads before reassembling?
Sounds like you have ruled out all leaks I'm assuming you made sure valves were nice and sealed when on the heads before reassembling?
