Help diagnios Cylinder #4
#1
Staging Lane
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Help diagnios Cylinder #4
Guys,
I am stumped, and need opinions. New Supercharged, forged LS engine with 5-6K miles on it. Runs great, with no issues. I just removed the plugs while doing some maintenance, and found all plugs to look new, except for #4, and it is Dry, Black Sooty. Here is everything I have done so far.
Installed 8 new plugs
Installed new wires
swapped the coil to other bank
swapped the injector to other bank
compression #4 test show same as other cylinders
Sprayed starter fluid for air leaks.
After all these changes and test, the plug #4 repeated.
Not sure where to look now other than pull intake to inspect, then head, then piston????? ANY SUGGESTIONS is appreciated.
I am stumped, and need opinions. New Supercharged, forged LS engine with 5-6K miles on it. Runs great, with no issues. I just removed the plugs while doing some maintenance, and found all plugs to look new, except for #4, and it is Dry, Black Sooty. Here is everything I have done so far.
Installed 8 new plugs
Installed new wires
swapped the coil to other bank
swapped the injector to other bank
compression #4 test show same as other cylinders
Sprayed starter fluid for air leaks.
After all these changes and test, the plug #4 repeated.
Not sure where to look now other than pull intake to inspect, then head, then piston????? ANY SUGGESTIONS is appreciated.
Last edited by Mastif; 10-23-2015 at 01:10 PM.
#4
Staging Lane
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Thanks
Thanks for the suggestions guys, I will get back on it in the morning and see what I can find.
I am posting a pic to give you a better idea of what the plug looks like, and like I said, 7 look great, and only the #4 pictured on the right is a issue.
This is dry sooty, not oil.
I am posting a pic to give you a better idea of what the plug looks like, and like I said, 7 look great, and only the #4 pictured on the right is a issue.
This is dry sooty, not oil.
#6
TECH Resident
Wow no drivability problems with a plug like that. I agree with a leak down test first. Testers are cheap if you don't have one. Compare #4 with some others as a basis. Have you had any oil consumption? The plug sure looks like fuel fouling though. You can check dwell with a multi-meter on the injector and compare with others as well. A quality spark tester would let you know if the ignition system is up to snuff. Every cause I can think of would cause a drivability concern, lol. Good luck!
#7
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Thanks for all the input guys, I am now in the process of doing a leak down.
Question, If the rockers are off of the the engine, can the leak down test be done with the piston in any position, or does it still have to be TDC?
Question, If the rockers are off of the the engine, can the leak down test be done with the piston in any position, or does it still have to be TDC?
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#8
TECH Resident
TDC should not matter with the rockers off. Leak down is done with minimal pressure, but it still may push the piston down. The results would be credible either way, barring a cylinder wall flaw low in the cylinder (very doubtful).