random missfire
08-19-2008, 07:21 PM
#11
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A stopped up converter can cause this and will give you missfires. Just unbolt pass side exhaust flange and see if it goes over 4000 rpms. A bad injector will not hold the engine back to a certain rpm.
08-19-2008, 08:23 PM
#13
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how do i check to see if its my converter? and how does a converter get clogged?
and when i put a new fuel injector in it lowerd the times it missed but then it said cylinders 2,5,6,8 where missing too now. maybe my friend will chime in if i forgot anything.
and when i put a new fuel injector in it lowerd the times it missed but then it said cylinders 2,5,6,8 where missing too now. maybe my friend will chime in if i forgot anything.
08-19-2008, 08:33 PM
#14
You can check for a plugged exhaust with a vacuum gauge or by disconnecting the exhaust in front of the converters and seeing if the misfire goes away and if the truck will rev above 4k. A couple of things can cause converters to fail...rich a/f ratio for one, but sometimes they fail on a perfectly tuned vehicle. I believe that certain additives in the gas will play a role in a converter's demise...
08-20-2008, 07:54 PM
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Im the service manager and a Chevy dealership and we see the converters fail all the time, and yes, missfires will go over 4k rpms. Failures of converters can be because of fuel trims and of engine oil that has a lot of metal in it. New oils now have to hardly any zinc(metals) to help with premature failure of converters. I run Valvoline VR1 racing oil due to the high concentrate of metals to bond to the internal engine parts to help control engine wear, and yes my converters are gone.
08-21-2008, 12:03 AM
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If he has P0308(misfire on cy#8) he needs to look for something that is cylinder specific not things that are common to all cylinders(fuel pressure). Fuel or spark to #8 is a good starting point. Do a leak down or compression(or both) on #8. Do you have good sealing on #8? It's easy enough to swap the coil packs between the drivers to passenger side on a CNP system. Since you've already done the ign. and fuel stuff try pulling the rocker cover and look at #8 rockers and pushrods. It only takes a few minuters to pull the rocker covers on #8 to check the pushrods and examine your rockers. Spin the crank while your in there and watch the intake and exhaust rockers as you turn the crank over.
Last edited by eallanboggs; 08-21-2008 at 09:03 AM.
08-23-2008, 01:54 PM
#19
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its not just missing on 8 anymore i changed out the coil packs it still misses. actually when i changed the coil i got three more misses. now it misses on 2, 5, 6, 8.
08-24-2008, 02:38 PM
#20
What about the crank sensor??? Just saw this issue On an 02 van with a 4.3L V6. Had a check engine light on and It was throwing 4 codes when it came in 300- random missfire 301 302 303cylinder 1-2-3 Misfire. Also after takeing some readings the MAF was not Reading properly and the up stream O2 sensor was going out B1 S1. after replacing the MAF and O2 Sensor I cleared the code and ran it threw a few drive cycles. showed code 301 ( cylinder number 1 miss fire In the stored codes. Went back to the computer and looked up some info on All Data....
It Turned out on there was also a TSB on the miss fire code about the crank sensor sitting to close and causing a missfire issue. I did not see any signs of contact but replaced the ruber gasket with a thicker one to shim it out and give it the extra clearance the TSB called for... I think it was 1/2 a mill
I know the 8.1's had a crank sensor issue too.... My old boss had simillar problem in his dualley. He spent over $1000 at the dealer trying to fix it replacing injectors on those cylinder and coils . It would run fine at first on the relearn but a few days later it started doing it again. He took it to a local mechanic and they fixed right. Being the crank sensor....
Hope this Helps....
It Turned out on there was also a TSB on the miss fire code about the crank sensor sitting to close and causing a missfire issue. I did not see any signs of contact but replaced the ruber gasket with a thicker one to shim it out and give it the extra clearance the TSB called for... I think it was 1/2 a mill
I know the 8.1's had a crank sensor issue too.... My old boss had simillar problem in his dualley. He spent over $1000 at the dealer trying to fix it replacing injectors on those cylinder and coils . It would run fine at first on the relearn but a few days later it started doing it again. He took it to a local mechanic and they fixed right. Being the crank sensor....
Hope this Helps....