Ok, So I have a 1999 Chevy Blazer 4x4 with code P0300. I have replaced Fuel Spider, Fuel Filter, Air Filter, PCV Valve, Intake Gaskets, Plugs, wires, distributor cap and rotor, TPS, Ignition coil & ignition control module. And the problems continues to get worse. It is to the point of backfiring or if it sits for a day without being started it doesnt want to start but when it does it misfires and backfires for a few seconds. Can anyone suggest a fix?

 

Have you done a leak down test, what brand parts did you use? these trucks are fussy about brands, try sticking to acdelco only. Especially cap rotor and wire. Take off throttle body and look inside for shiny areas( spider could be leaking). This a start, good luck

 

I've done all the above. Still nothing

 

How many miles are on the distributor? They can get sloppy after 150,000 or so.

 

Less than 5,000. I replaced distributor cap and rotor and plugs and wires all at once

 

I read your question. I'm asking about the distributor itself. Not the cap. The gear wears out and throws the timing off.

 

The gears didn't look worn or anything when I replaced my intake gaskets.

 

I can't suggest a fix. I can suggest some testing.

Get a fuel pressure gauge. Attach it to the Schraeder valve/test port. Turn the key on and watch the gauge. It must be 60psi-66psi during the prime cycle (when the pump runs for a few seconds after you first turn on the key). Leave the gauge attached, turn off the key. Wait 10 minutes. Check the pressure. It must be over 50psi after sitting with the key off for 10 minutes.

What is the fuel pressure with the engine running at idle, at operating temperature. At idle, fuel pressure should be 55psi-64psi.

Hook a hose up to the bleed valve on the gauge set, and put the open end of the hose in a 1 quart glass jar. Jumper the fuel pump relay. Open the bleed valve with the fuel pump running. It should fill a quart jar in under 20 seconds, or a pint jar in under 10 seconds.

Those tests are a good start. Report back and some diagnosis might be possible if anything is out of spec. More testing might be needed.

 

Have you checked your cam retard? I didn't see that information in the post. I'd be curious to know what that is...

 

Ok, so my starter went out this morning so I had to miss work and replace that and for some odd reason it fixed most of the misfire and the backfiring is completly gone, but there is still a small miss when on cruise control. The fuel pressure was all in spec also.