So i got back from deployment last week and im having issues with my envoy. It was running rather rough, granted it sat for 8 months, wife drove it a few weeks while her van was in the body shop and neighbor started it every now and then, so i figured it was bad gas. It had about a half a tank so i put about 7 gallons of premium in it and some lucas fuel system cleaner with no luck. did the seafoam through the vacuum line and no luck. finally hooked my scanner up to it and it has a misfire number 6. i swapped coil packs with No 1 and stilll got misfire number 6. pulled the plug and it was wet with oil like it wasnt even firing. i cleaned the plug, put it back in and drove it, still misfire in number 6. put some vlave cleaner oil treatment in, ran it for 5 minutes and then drained the oil and put new oil and filter in. still misfire from no 6. i have a compression tester but i need to figure out how to use it. i know i could have a bad ring on that piston or a bad valve but it seems like that cyclinder is not even firing. could it be a bad injector? or something electrical not sending a fire signal to the spark plug? what options should i explore? it has 205,000 miles on the body and 160,000 on the engine. i have afm/dod. Any help or suggestions would be greatly appreciated. Thanks
NEED SOME ENGINE ADVICE
- Thread starter NORMANBD
- Start date
gmcman
Member
- Dec 12, 2011
- 4,656
Put the plug from the other cylinder you swapped coils in and see if it still stays on #6.
My guess was bad gas and it's now fuel fouled.
I would run as much fuel out of the tank as possible then fill it with 87 since there's many additives in premium fuel to resist the burn.
Then go from there, I would always advise BG 44K over the rest but do this after you get it running.
Generally fuel fouled plugs are toast, replace plug but it would be better to replace all of them once it's running again.
If that doesn't t work then I would try a compression test
My guess was bad gas and it's now fuel fouled.
I would run as much fuel out of the tank as possible then fill it with 87 since there's many additives in premium fuel to resist the burn.
Then go from there, I would always advise BG 44K over the rest but do this after you get it running.
Generally fuel fouled plugs are toast, replace plug but it would be better to replace all of them once it's running again.
If that doesn't t work then I would try a compression test
Thanks for the reply. i will try that tomorrow when i do the compression test. i didnt swap the plug because i thought they rarely went bad. i was concerned about there being oil on the plug which made me think that i had a bad piston ring or a valve. hopefully i will know more tomorrow. i paid next to nothing for the envoy but i really dont want to spend the money for a major engine overhaul repair and i really dont want to junk it since everything else is in excellent condition. i guess i have some serious thinking to do if i find something major tomorrow. thanks again.
C-ya
Member
- Aug 24, 2012
- 1,098
Welcome home and good luck with the truck. What branch and where'd ya go?
Change the plug wire after you change the plug to a new cylinder, or just move the plug to one cylinder and the wire to another. It could be a bad wire.
ETA: Saw your profile says VA, so I'm guessing Navy. I did a couple of 6 monthers and all the work ups before hand. FC1(SW) on CG69.
Change the plug wire after you change the plug to a new cylinder, or just move the plug to one cylinder and the wire to another. It could be a bad wire.
ETA: Saw your profile says VA, so I'm guessing Navy. I did a couple of 6 monthers and all the work ups before hand. FC1(SW) on CG69.
AWD V8
Member
- Jan 12, 2015
- 463
If you have a dead cylinder you need to confirm 3 things:
1) You have spark spark at the right time.
2) You need fuel at the right time
3) You have compression.
1) If you swapped the coil, wire and plug with another cylinder and the problem stays with the problem cylinder it is safe to assume that the coil, plug and wire are not the problem.
2) You can assume that fuel is getting to the engine, the other cylinders are firing.
You can easily check that the injector is working mechanically. Use a stethoscope or a large screwdriver to to your ear to the injector. When running you should hear a rapid clicking, compare it to another injector. If you don't hear the clicking the injector is bad. Now, even if it does click, it doesn't mean that it actually opening, or that it is not clogged. To test the injector itself you either need to use a fuel pressure gauge and trigger the injector while watching the fuel pressure gauge to drop indicating the injector is opening, or you need to remove or swap it with another injector, just like you did with the spark plug. You should also check the injector plug for a voltage pulse with an LED or NOID.
3) You need to check the compression on the problem cylinder. I'm not sure what it should be, guessing around 150-170 psi. Anything below about 100 psi and it won't fire. Low compression on one cylinder is often a valve train problem, like a broken spring, bent push rod, bad lifter. If I'm focused on just one cylinder I just pull the one plug and disable the ignition so I don't have to pull all the plugs. The reading will reveal a problem if there is one without removing all the plugs.
What year??? If DOD it could be a bad lifter.
If the compression is good, then it is possible that you have a bad vacuum leak in the manifold near that cylinder.
1) You have spark spark at the right time.
2) You need fuel at the right time
3) You have compression.
1) If you swapped the coil, wire and plug with another cylinder and the problem stays with the problem cylinder it is safe to assume that the coil, plug and wire are not the problem.
2) You can assume that fuel is getting to the engine, the other cylinders are firing.
You can easily check that the injector is working mechanically. Use a stethoscope or a large screwdriver to to your ear to the injector. When running you should hear a rapid clicking, compare it to another injector. If you don't hear the clicking the injector is bad. Now, even if it does click, it doesn't mean that it actually opening, or that it is not clogged. To test the injector itself you either need to use a fuel pressure gauge and trigger the injector while watching the fuel pressure gauge to drop indicating the injector is opening, or you need to remove or swap it with another injector, just like you did with the spark plug. You should also check the injector plug for a voltage pulse with an LED or NOID.
3) You need to check the compression on the problem cylinder. I'm not sure what it should be, guessing around 150-170 psi. Anything below about 100 psi and it won't fire. Low compression on one cylinder is often a valve train problem, like a broken spring, bent push rod, bad lifter. If I'm focused on just one cylinder I just pull the one plug and disable the ignition so I don't have to pull all the plugs. The reading will reveal a problem if there is one without removing all the plugs.
What year??? If DOD it could be a bad lifter.
If the compression is good, then it is possible that you have a bad vacuum leak in the manifold near that cylinder.
Thanks for all the feedback. I am Navy and i was traveling the south pacific on a sub tender for 8 months. After being on all carriers and then going to a sub tender, i never want to go back to a carrier.
So today i was able to do a compression test but i dont know if i did it right. i pulled the plug wire off (plug wire came apart, metal clip stayed on spark plug, might be my problem) and pulled the plug. screwed the compression tester in the spark plug hole, pulled the fuse and cranked her over. Now i didnt have anyone to watch the gage, but the gage pressure stays in at the highest reading. it read 120, i dont know what the spec is. didnt get a chance to compare it to any other cylinders yet. when my wife gets home, im going to get a new plug wire, i paid $70 some dollars for the MSDs and im sure they are not under warranty and im sure that i cant buy just one. i think i will wait to get some feedback from the site on if 120 is a good number before i drop the money for a new set of wires.
on another note, i have started to look at new to me cars. i dont like having a car payment or any payments so i like to pay cash. im looking at a 2003 tahoe, fully loaded, really good condition with 115k on it for $8k. i might pul the trigger on it and buy it if this envoy fix doesnt pan out an di have to do a motor tear down.
Thanks again for all the advice. i hope you guys have some good news for me on the 120 psi compression test.
So today i was able to do a compression test but i dont know if i did it right. i pulled the plug wire off (plug wire came apart, metal clip stayed on spark plug, might be my problem) and pulled the plug. screwed the compression tester in the spark plug hole, pulled the fuse and cranked her over. Now i didnt have anyone to watch the gage, but the gage pressure stays in at the highest reading. it read 120, i dont know what the spec is. didnt get a chance to compare it to any other cylinders yet. when my wife gets home, im going to get a new plug wire, i paid $70 some dollars for the MSDs and im sure they are not under warranty and im sure that i cant buy just one. i think i will wait to get some feedback from the site on if 120 is a good number before i drop the money for a new set of wires.
on another note, i have started to look at new to me cars. i dont like having a car payment or any payments so i like to pay cash. im looking at a 2003 tahoe, fully loaded, really good condition with 115k on it for $8k. i might pul the trigger on it and buy it if this envoy fix doesnt pan out an di have to do a motor tear down.
Thanks again for all the advice. i hope you guys have some good news for me on the 120 psi compression test.
Mooseman
Moderator
Search on YouTube for "ETCG compression test". He did a compression test on a similar engine where one cylinder was dead but the others were good. That should give you a good starting point.
PS: I would have done the search but my work blocks YT.
PS: I would have done the search but my work blocks YT.
gmcman
Member
- Dec 12, 2011
- 4,656
Did you try swapping or replacing the plug first?
Make sure the compression tester is fully seated, is the O ring installed?
Engine should at least run with 120 psi, sounds a little low but not sure of the spec.
Before you chase the compression, If you haven't done so. ...I would get a new wire and plug for #7 to be sure the problem is elsewhere.
Make sure the compression tester is fully seated, is the O ring installed?
Engine should at least run with 120 psi, sounds a little low but not sure of the spec.
Before you chase the compression, If you haven't done so. ...I would get a new wire and plug for #7 to be sure the problem is elsewhere.
gmcman
Member
- Dec 12, 2011
- 4,656
Sorry, I meant #6, not #7. Another member is having a similiar issue with #7 and he is getting back flow into the tailpipe which could be a sticking valve or lifter.
Go ahead and replace the wet plug which is basically toast now anyway, you pretty much can't revive it. When it's running, take an index card or envelope and hold it against the tailpipe so the exhaust flow folds it over, if it snaps back to the tailpipe then you likely have an exhaust valve not seating.
If that's the case, I would suspect loose carbon or something under the valve seat. There have been known issues with DOD lifters but since it started acting up after it sat for months with that old fuel I'm going to suspect first a bad plug or dirty injector.
Go ahead and replace the wet plug which is basically toast now anyway, you pretty much can't revive it. When it's running, take an index card or envelope and hold it against the tailpipe so the exhaust flow folds it over, if it snaps back to the tailpipe then you likely have an exhaust valve not seating.
If that's the case, I would suspect loose carbon or something under the valve seat. There have been known issues with DOD lifters but since it started acting up after it sat for months with that old fuel I'm going to suspect first a bad plug or dirty injector.
