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check engine light comes on randomly
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Anonymous Poster
Nov 6, 2008, 2:43 PM
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check engine light comes on randomly
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2003 chevy
3500 express van
6.0
125,000
my check engine light comes on randomly during the day. when it comes on the truck runs rough(misfire). then it will turn off and the truck runs fine.
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Loren Champlain Sr
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/ Moderator
Nov 6, 2008, 2:53 PM
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Re: check engine light comes on randomly
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'96 and newer domestic cars have misfire detection capabilities. It may be that the PCM is picking up the misfire, or the misfire is causing the CEL. You'll need to pull codes. Sounds like this may be the vehicle from hell, by your posts. LOL. If your codes are P0300 (random cyl. misfire) or P0301, P0302, 303, 304, ect. , that will tell you which cyl is misfiring. P0301=cyl 1, P0302=cyl 2, ect.
Loren
SW Washington
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Guest
Anonymous Poster
Nov 6, 2008, 3:37 PM
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Re: check engine light comes on randomly
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i have had the codes pulled and it was random misfires. I replaced the fuel filter, plugs, wires, and an o2 sensor. My next thing is the pcv valve(longshot, I know but i want to start with the inexpensive stuff first). Someone told me it could be the mass air flow sensor or a weak fuel pump. Is it possible?
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Loren Champlain Sr
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Nov 6, 2008, 3:46 PM
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Re: check engine light comes on randomly
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I was reading one of your other posts where you mentioned having to cycle the key a couple of times to get it to start. When doing so, you are increasing fuel pressure. If this is a Vortec, it needs at least 50psi just to get it going. I've had several with just under 55psi that wouldn't run. Have you checked fuel pressure?
Loren
SW Washington
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Guest
Anonymous Poster
Nov 6, 2008, 4:02 PM
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Re: check engine light comes on randomly
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I have not checked fuel pressure. The truck starts fine now, the only problem is the check engine light coming on and going off. The light will come on for a little while then it will go off for hours at a time and run fine. then the light comes on and I can feel the missing until the light goes off.
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Loren Champlain Sr
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Nov 6, 2008, 4:20 PM
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Re: check engine light comes on randomly
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I'm really hoping someone familiar with the 6.0 will jump in here~ Since it's the P0300, and intermittent...Is it DIS?
Cam sensor dropping out, but I can't see that causing a misfire? Going very lean? Sticky EGR should set a code. Okay, I'm thinking out loud.
I seriously doubt the PCV is in the equation. Can you get misfire history? Are all eight cylinders misfiring about the same? Distributors are a common fault on GMs (but, don't know if the 6.0 is DIS) Wish I could be of more help.
Loren
SW Washington
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Nov 6, 2008, 4:35 PM
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Re: check engine light comes on randomly
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yes, there was a code for running lean.
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Loren Champlain Sr
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Nov 6, 2008, 4:44 PM
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Re: check engine light comes on randomly
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Then, see if you can find specs and test fuel pressure. A lean condition can be a cause of random cylinder misfire. But, for it to come and go....
Loren
SW Washington
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