Mid nineties chevy pick up that backfires every time its started, and the engine light will not go off(wait it gets better). It blew out the intake manifold, and now that its replaced it still backfires, but after it warms up it runs ok. Have had it to three mechanics, and have also done much of the work myself as well. The parts replaced includes all sensors, fuel pump, main fuel lines, intake manifold, vacuum tank, spark plugs, wires distributor....the list goes on. The check engine light states insufficient fuel to two cylinders or banks. (PS its not my truck its my brother's and I am trying to help him). He is at his wits end, and if anyone has something better to say than replacing the whole engine. Some expert help would be appreciated, and it has been to Meineke, chevy dealership, and Autozone for just a few....water pump also replaced a week ago. The vehicle has 120k + miles, and other than a possible valve problem, I dont know what to tell him. THANKS

 

Welcome to the forum...
I think you might be right about a valve issue...there are lots of good mechanics in this forum, someone will be able to point you in the right direction...

 

lean condition would be inline with back firing out the intake. possibly fuel injectors? run a compresion check, check the ignition timing. if there is someone else that has a simular truck mabye try swapping the tbi unit between trucks.

 

Does it backfire on decelleration? If he gets going about 45 in ssecond and lets the motor slow him down is it backfiring? That can happen under lean conditions, too.

I am thinking timing chain if it has a million miles. I would assume that is the problem after passing EZrider's tests.

 

timing chain is also what came to mind last night after signing off....

 

Could also be an incorrect timing advance on the distributor. Have you had it on a timing light at all RPMs to check and make sure the ignition timing isn't advancing too far?

 

Hi DAVEGS,

Welcome to the Chevy Forums.

Assuming your head gaskets are OK, I would be thinking have a look at the timing chain and gears.(many L block V8s came with Nylon gears stock)

While you're at it, it might be a good idea to have the cam inspected by a competent shop. If you don't correct the problem soon, you're cam is going to start showing wear, if it isn't already.