Question about Chevrolet Blazer

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Has fire fuel on new plugs will run about 3 days not very good. black smokes. Idel rough stumbles when you give it throtle seems better at 1500 rpm. When it wont start as soon as you turn the key off it will fire a plug and every so often engine off key on it will just fire the plugs about 6 times real quick. Shows o2 not enough switches multiple random missfire just recently showed system too rich. Showed one time o2 heater malfunction. It seems as if there is something shorting out causeing the injectors to pulse possibly other sylonoids. Key on engine off you can hear a high pitch noise. Tested ignition module vent sylonoids changed map sens checked vcm gnds sens gnds ect changed fuel pres regulator got worse does seem intermitent but getting worse.Primed furl rail no leaks. On scanner shows fuel trim to the negative short -31 % long -13 to-15 % 1500 rpm trim comes up some but at idle just negative symtoms everywhere this thing is driving me insane any advice please about to junk its sad is a very nice truck. Thanks

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  • brakenit Dec 28, 2010

    98 chevy blazer 4.3 I have checked the EGR for carbon deposits new gasket checked didnt seem to have a sign of a short Checked MAF cleaned seems to show proper readings at idle and under load

  • brakenit Dec 30, 2010

    I did suspect the crank sensor because I did see a abnormal response on the timing seem to change an awful lot when I gave it throtle. Was also wondering about the cam sensor but was uncertain of the exact condition these faults could give. Very good point about the crank sensor intermitent short throwing the timing slightly. Will check this and let you know the results.

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Hi

You certainly done your home work on this fault so I sure you know what your talking about. I would be tempted to say this is an EGR fault or maybe combined with MAF sensor, can you give me the exact model and engine size and the year of the truck.

Regards

Dan

Posted on Dec 28, 2010

  • Dan Doherty
    Dan Doherty Dec 28, 2010

    Hmm, I'm not sure then, what about the crankshaft sensor?

  • Dan Doherty
    Dan Doherty Dec 28, 2010

    A dirty crank sensor may cause a intermitent short, which would throw the timing slightly and rough under 1500rpm, or it could be faulty.

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