P0300 + backfire

[Mongoosekeith]

Ok, first a little background... this is a 99 c1500 with vortec 350 273,000 miles on it, truck has new plugs, wires, cap, rotor, and ignitor/ignition control module, the truck needs both catalytic converters and b1 s1 O2 sensor, have been chasing this code for almost 2 months. Thought I had finally got rid of the code until today... l had done some running around and stopped off at my dad's and left the truck running we were sitting outside talking and I heard my truck backfire out of the exhaust. Threw his scanner on it no new codes.... my question is could the O2 sensor be causing a rich mixture/backfiring or is this a timing issue? Thanks for your help in advance!

Keith

 

[Mongoosekeith]

Today we did the 2 front O2 sensors and replaced the spider.... still backfiring through the exhaust does anyone have any ideas what to do next?

 

[aaronb]

The gear on the distributor may be worn.
You will have to pull the distributor and inspect it.
If it is, I'd replace the distributor.
Also check the firing order on the cap. Make sure you don't have #7 and #3 plug wires in the wrong terminals.

 

[slowburb]

Also could be a valve sealing issue. I'd run compression and leakdown tests before spending any more money.

 

[Mongoosekeith]

I'm hoping tomorrow we can get it on a good scanner, not a hand held pos like the parts stores use and will go from there, I can get the cam sensor and coolant temp sensor for $23 so I may replace that and that will be last parts thrown at it

 

[Slimpickens]

Curious if you found anything out. I have a buddy with the same issue. I've searched like crazy and have yet to find a solution to the problem.