once a gunner

I 've got a 99 GMC saffari just changed the coil, plugs wires, cap and rotor all with AC Delco parts.....but I'm still getting a p300 code. When I accerlate from 0-20 kph no problems....20 -40 kph I get hesistation spurting but after 40 kpm no problems everythings good....could a faulty TPS cause a p300 code. I understand that the TPS should throw it's own code but is possible that it could also create a p300 code. I live on a military base where the max. speed limit is 40 kph. So there is quite a bit of driving in that range of 20-40 kph Could that range have worn out the TPS in that area and that is why everything is good after 40 kph...also If I step on it from a standstill and push threw to 60kph no hesitation...any advice would be great

Don Smith

old_master

The TPS circuits are monitored 100% of the time when the ignition is in the RUN or START position. If there's an intermittent problem with "drop out" in the TPS, it would instantly set P0122, which is "low voltage detected". P0300 indicates the PCM detected a random misfire. If no other DTC's are present, more than likely the problem is either secondary ignition, (plugs, plug wires, distributor cap, rotor, ignition coil) or fuel delivery related, (fuel pump, fuel lines, fuel pressure regulator, fuel filter, or fuel injector).

The fact that you've replaced all of the secondary ignition parts with good quality parts, and the problem is still there, I would suggest checking fuel pressure and leakdown rate. Key on, engine off, fuel pump running: pressure must be 60psi to 66psi. Pressure must remain above 55psi for 3 to 5 minutes after the fuel pump shuts off. Post your results.

once a gunner

just to follow up on this....I had 2 poppetts that were bad in the 4th and 6th cylinders....as well as a bad distributer....all is fixed and works great but now I have a new code but I'II bring that up in a new topic!