2005 2500HD 6.0 - Troubleshooting P0300 Codes

chev78fan · January 31, 2015

Truck has approximately 125,000 miles on it (odometer doesn't work). CEL is on and flashes above 2500 rpm. Truck also falls on its face above 2500 rpm. I am the original owner and truck is stock.

Changed plugs and wires. Checked the coils with a spark tester and they all have good spark.

After a 2 mile drive i checked the exhaust with an IR gun.... 410F and 350F at the inlet of the cats / 390F and 350F at the outlet of the cats. (i don't think they are clogged). Good flow out of tailpipe.

Fuel pressure after sitting all night (below zero) was at 0psig / key on goes to 50psig / start it goes to 62psig / shut off goes to 56psig and slowly drops... down to 28psig after a half hour.

I have Lucas fuel injector cleaner in the tank.

idle is smooth.... when i pull a plug wire off to check for spark there is no noticeable difference in the idle.

Any thoughts or suggestions?

chev78fan · February 1, 2015

Thanks for the replies. Filter is in the tank. The truck also has the returnless fuel system with the regulator as part of the pump assembly.

I'm going to try and drive it with the fuel pressure gauge attached - I think the gauge hose is long enough. If pressure is good I'm going to pull the front O2 sensors (unplug the exhaust) and drive it.