What's wrong with my Chevy?

Question

I have a 1998 Chevy Silverado extended cab short box with a 5.7Litre 350 with 421,000km. The problem is the truck seems to have a mind of its own, Some days it starts and runs like a champ, but most days it doesn't catch and makes this thumping sound like it's misfiring or running on 2 cylinders but won't actually run. I've replaced the crankshaft position sensor recently, the starter, battery, alternator. The fuel pump was replaced a few years ago. Would this be the coil needing replacement?

Update:

This truck runs fine after it sits for a week or so.

Mike S · Accepted Answer

1st thing to check, is the coil wire. Not the wire from the coil to the distributor, but the main power wire. They very often corrode, or even melt into the connector itself losing contact. They can often be fixed, by using a small knife to pry to connector apart and spread the connectors wire retainers and clean the contact of the retainer also. 99% of no start problems on chevy's from 98-2004 is this problem.

2nd Check the fuel pressure at the test port on the back side of the engine facing the drivers side. You should have 55-60 lbs of pressure. anything less, the pump is bad. If the pressure raises then drops back to zero when cycling the key off, then it is either a stuck injector, or faulty fuel pressure regulator.

anotherredman · Answer

It doesn't sound like a coil problem but it could be.  It actually sounds like a timing chain about to go.  I think you need to take it to a good garage to have it checked out.  There are so many things that need checking to diagnose a problem like this that unless someone is very lucky they just aren't going to be able to guess what is wrong.

Anonymous · Answer

when is the last time you checked the fuel filter.  sounds simple but you would be surprised how many I've re paced in my shop doing what you are describing.

What's wrong with my Chevy?

3 Answers