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Really Need A Gm Tech Here, Please Help

mark111

By mark111
in Ask A GM Technician

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mark111 Enthusiast

mark111

Posted
Posted

I have a '98 3500, 4WD, Vortec 5.7. Noticed bad power loss and pinging (spark knock). I just noticed my exhaust manifold was glowing red after I shut the truck off. I am assuming it is running lean. I had a scanner put on it and there is no trouble codes in the history. I have no check engine light, I don't know what to do next. Do these trucks even have a map sensor? Can this be caused by the mass airflow sensor? Do you know the correct timing procedure? I am not sure if the procedure on the vortec is to disconnect the wire for the distributor and set it on a scanner. If so, do you know where the wire is on this model? Sorry for all the questions but I am really stumped here and need the truck desperatly. I am afraid to run it this condition. Thanks for any help you can offer.

Mark.

bobcat5544 Enthusiast

bobcat5544

Posted
Posted

If the manifold is glowing red. It means one cylinder is not firing or too much fuel is being dumped in...

 

On the manifold is it just one spot that get red or one part of it is more red than the rest of it?

mark111 Enthusiast

mark111

Posted
  • Author
Posted

Thank you for the reply. I'm not sure if it sure if it hotter in one spot than another. If you think it is ok to drive, I'll take it out tonight and then look at the manifolds. I thought a lean mixture would heat the manifolds. I will also check to be sure all cyls are firing and then get back to you. I won't be able to check the cylinder firing until the morning, but I'll leave a post as soon as I do. (And the scanner also didn't show a misfire either.) Thank you again for the response, I am really stumped here.

Mark.

bobcat5544 Enthusiast

bobcat5544

Posted
Posted

lean means more air than fuel, rich mean for fuel than air... when the manifold glow red it means unburnt fuel is being burnt in the manifold...

 

Far as driving it. I would sugget it unless you are doing test on it, but I leave that up to you.

 

one of the best things you could do is plug the spark plugs and let me know what they look like or if possible take pics of them and post them. That would help a lot...make sure you write down which cylinder each one came out of.

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