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2007 chevy vin u 6.0 has misfire on #7 & 2 at...

Resolved • Response time -56 minutes

29 Dec 2012

2007 chevy vin u 6.0 has misfire on #7 & 2 at idle only above 1000 rpm goes away. Have traded plugs/ciol/injectors also had valves done on motor 105,ooo on motor. Have lab scope injector coil ckeck ok I do known in the fire order 7&2 are next too each other Any help would be nice thank you dale I have over 40 yrs in this feild of diagnostic
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29 Dec 2012

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Chevy Mechanic's response
29 Dec 2012
Gary
Gary
can you feel those 2 cylinders dead at idle?or just the misfire is showing those 2 cylinders ?
29 Dec 2012
Customer reply
29 Dec 2012
you can feel like dead cylinders runs ruff at idle smooth above 1000 rpm going down the road runs good fuel trims are very good all the time 3 to -5
29 Dec 2012
Customer reply
29 Dec 2012
also did compresson test ok
29 Dec 2012
Chevy Mechanic's response
29 Dec 2012
Gary
Gary
can you connect a vacuum gauge to manifold vacuum line and when its skipping at idle tell me what its reading and tell me if the needle is bouncing a lot on the gauge ?
29 Dec 2012
Customer reply
29 Dec 2012
a steady 18.5 vaccum at ilde in gear dr it skips 16 to 14
29 Dec 2012
Chevy Mechanic's response
29 Dec 2012
Gary
Gary
no needle jumping at all ? if not the next step will be to do a fuel pressure drop on the fuel injectors and see when fired if they all drop the same PSI OR you can swap # X with # X injector and see if the skip moves to cylinder # X
29 Dec 2012
Customer reply
29 Dec 2012
fuel test done 60psi also runnig at 60psi did a injector test on all they drop the same to 38psi on all 8
29 Dec 2012
Customer reply
29 Dec 2012
also swap injectors and coils tested power at coils/inj ck ok
29 Dec 2012
Chevy Mechanic's response
29 Dec 2012
Gary
Gary
well you eliminated spark ,fuel and compression. Now we are down to 2 things. Possibly the crank sensor or cam sensor is sending a wrong pattern to the PCM we can also do a running compression test on each cylinder one at a time with the little valve removed in the bottom of the compression gauge so you can see the psi going up and down and see if all 8 testing them one at a time are the same
29 Dec 2012
Customer reply
29 Dec 2012
also did this test showed running at 70psi all 8
29 Dec 2012
Customer reply
29 Dec 2012
did at lab scope only on crank showed good pattern If the cam had a bad signal why only at idle
29 Dec 2012
Chevy Mechanic's response
29 Dec 2012
Gary
Gary
well I have never seen this before. Lets see if any other experts have seen this. Hang on let me open this question back up to the other experts.no need to reply back to me another expert will reply to you hang on
29 Dec 2012
Chevy Mechanic's response
29 Dec 2012
Mazda Ed
Mazda Ed
Lead Technician
Hi Dale! Let me see if I can help. First things first I want to make sure we are shooting for the right cylinders. Please don't get insulted, I just don't want to miss something easy. Cylinder 2 is passenger side front and cylinder 7 is driver side rear. Is that what cylinders you are troubleshooting? Also when you swapped coils, injectors and plugs... what cylinders did you swap with or did you swap in new parts?
29 Dec 2012
Customer reply
29 Dec 2012
hi #7 and 2 are misfiring at idle Yes i swap injector on the motor THE SWAP WAS form 4 to 2 3 to 7 also coils where swap. At this piont ask anything I will not get insulted I have also lab scope crank sensor good pattern did not scope cam because it runs way to good off idle I am at my wits end my boss and cust: Are not happy we me because i said a valve job would take of problem
29 Dec 2012
Customer reply
29 Dec 2012
valve job done new plugs and still #2 #7 misfire I do not know what I miss I smoke at 5psi in #2 #7 the intake valves show smoke on intake side exhaust ok
29 Dec 2012
Chevy Mechanic's response
29 Dec 2012
Mazda Ed
Mazda Ed
Lead Technician
Are any other cylinders showing a misfire but not setting a code yet? Are you saying those cylinders show smoke through the intake? Are they the only ones?
29 Dec 2012
Customer reply
30 Dec 2012
no other or cyl. 2;& 7 are showing codes the only code come and goes is p0300.The other cyl are okay. to clear a statement 2 & 7 never gave a code only showed a misfire at idle on the scanner But off idle runs great./ at idle runs ruff but not setting a code but every now & then p0300 pops up and goes away fuel trims are good 02 are reading good But in gear at idle runs really ruff like 2 cyl are dropping out
30 Dec 2012
Customer reply
30 Dec 2012
the only thing i just thought was pull #5 plug wire see how it effect # X the reason why is fire order 18436572 what do you think
30 Dec 2012
Customer reply
30 Dec 2012
because 7 / 2 are next to each other in the fire order
30 Dec 2012
Chevy Mechanic's response
30 Dec 2012
Mazda Ed
Mazda Ed
Lead Technician
Ok, I did have a problem once that was similar to this but I can't remember the exact year of the truck. Even though all test passed I removed the fuel rail and all injectors. I found that because of the way the fuel rail was designed all the crap would accumulate at the end of the rail by #7 and by #2. I was able to shake some of it loose by spraying carb cleaner in but ultimately I ended up replacing the fuel rail. I don't know for sure if this is going to help you, but when you swapped the injectors did you do a through examination of the fuel rail?
30 Dec 2012
Customer reply
30 Dec 2012
okay I see that at the end of the fuel rail is 2 7 but I had injector out with a glass jar one at a time I energ: the fuel pump and draw aline on it so I could see exat amount on 2 match same amount 4 amount of fuel in glass jar If you think another fuel rail would help I"ll change it Can you think of test at idle to see whats happen in 2 7 misfire please advice open to anything
30 Dec 2012
Chevy Mechanic's response
30 Dec 2012
Mazda Ed
Mazda Ed
Lead Technician
It was a weird occurrence for me... Everything seemed normal during testing. Injector flow, fuel pressure, etc.. My thoughts were the debris was causing some kind of cavitation effect and disrupting the steady flow while the truck was running. When you mentioned the smoke test before... was that before or after the valve job?
30 Dec 2012
Customer reply
30 Dec 2012
before and after heads install 2 7 still misfire I did a running compression test 70 on both cyl a couple other cyl the same 70 psi to see if okay they where at 70 also
30 Dec 2012
Chevy Mechanic's response
30 Dec 2012
Mazda Ed
Mazda Ed
Lead Technician
You said you did a smoke test... Are you still getting smoke through the intake valves of those 2 cylinders?
30 Dec 2012
Customer reply
30 Dec 2012
no test good
30 Dec 2012
Customer reply
30 Dec 2012
also pass on cyl leak down test
30 Dec 2012
Chevy Mechanic's response
30 Dec 2012
Mazda Ed
Mazda Ed
Lead Technician
Is this truck equipped with the AFM (Active Fuel Management)? If so, some of those trucks were having lifter problems. One of the fuel management cylinders is #7. I'm wondering if this could be part of your problem...
30 Dec 2012
Customer reply
30 Dec 2012
as I know when the intake was off i did see any fuel management or in the scanner pids
30 Dec 2012
Customer reply
30 Dec 2012
if it where how would i know or find out looks like no elec: on lifter
30 Dec 2012
Chevy Mechanic's response
30 Dec 2012
Mazda Ed
Mazda Ed
Lead Technician
I would think that this would show up on a compression test, but it could be possible that right now it is a minute difference that you are recognizing on the gauge. If you open the glove box there are RPO codes listed. Look for one of the following codes on the sticker. RPO Codes L76, LC9, LFA, LH6, LMG, LS4 and LYS
30 Dec 2012
Customer reply
30 Dec 2012
thank you I will look at this monday morning to see If it is are thier any tbs to prove this problem I have I dentfix did look for tbs saw nothing If you have tbs on this problem I would like to know
30 Dec 2012
Chevy Mechanic's response
30 Dec 2012
Mazda Ed
Mazda Ed
Lead Technician
Also, have you done a Crankshaft Position Relearn and verified that it was successful?
30 Dec 2012
Customer reply
30 Dec 2012
yes and it verified
30 Dec 2012
Chevy Mechanic's response
30 Dec 2012
Mazda Ed
Mazda Ed
Lead Technician
Check GM bulletin 08-06-01-018C also engineering information EI08245. It wouldn't hurt to do the CKP relearn again.
30 Dec 2012
Customer reply
30 Dec 2012
have done 4 relearn no diff in misfire thank you on tbs Dale
30 Dec 2012
Customer reply
30 Dec 2012
I will get back to you on monday Have a nice day
30 Dec 2012
Chevy Mechanic's response
30 Dec 2012
Mazda Ed
Mazda Ed
Lead Technician
Did you install new intake gaskets when you did the job?
30 Dec 2012
Customer reply
30 Dec 2012
yes all gasket new fel pro also smoke intake both before and after okay the fuel trins are good also 3to -5 o2 switch plus pull o2 out no diff in misfire
30 Dec 2012
Customer reply
30 Dec 2012
i try looking up tbs 08-06-01-018c found no tbs on i dent fix advice on it
30 Dec 2012
Chevy Mechanic's response
30 Dec 2012
Mazda Ed
Mazda Ed
Lead Technician
Basically it says you could have a lifter tick noise, an engine misfire or a check engine light on. It would be on cylinder 1, 4, 6 or 7. It is caused by a collapsed active fuel management lifter. They want you to replace them in pairs. I was thinking maybe the lifter is weak and won't pump up at idle causing this misfire.
30 Dec 2012
Customer reply
31 Dec 2012
found the problem let the motor run at idle loosen rocker on # X and the miss when away So been said gm has a lifter and cam problem thank you for all the help Let me know what you think about this I will on next one how to prove the problem fast have nice new year Dale
31 Dec 2012
Chevy Mechanic's response
1 Jan 2013
Mazda Ed
Mazda Ed
Well I'm glad this mystery is solved. Please don't forget to rate me! Have a Safe and Happy New Year!
Mazda Ed
Mazda Ed
Lead Technician
Avg. question only $28
ASE Master Technician, Mazda Master Technician, GM and Ford factory trained. 15 years experience.
1 Jan 2013
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