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1.5 Years ago - I finally decided to put the truck in a local shop to chase the CEL that illuminated LITERALLY a day before I was going to take it in for annual state inspection.
Several things were addressed and fixed by the shop (intake resonator box had air leaks causing lean conditions, fuel pump & FPR changed, evap canister, injectors changed & upgraded to the newer style)... I myself changed plugs, wires, distributor cap, ignition coil, water pump, and fan clutch (All were suspect - and way past time to have replaced them...
A P0300 still is a ghost that occasionally appears, though. I've narrowed it down to happening generally when the engine is under higher load. (i.e. driving up a slight hill if it's a mile or longer - the check engine light will flash, then turn off once the load has been reduced on flatter (or downhill) terrain) I picked up a scanner to read live data for the misfires, and it looks like Cyl 4 is the main culprit. (see screenshot - and I did reset the numbers while on my trip)
With cyl3 & 5 also having some misfires along with 4 - but not nearly as bad. When this happens - I feel NO change in the engine performance. No shake or roughness at all that I've noticed.
I'll do the obvious quick checks this weekend to check plug/wire and distributor cap (since firing order is 1,6,5,4,3,2 - with 4 having the other offenders (3 & 5) on either side of it's firing order... but was curious if anyone had other ideas for me to check.... Could it be PCM, if it's not the obvious spark plug/ dist. cap ?
Dec 29 2023 - Between Dallas & Lubbock Jan 2 2024 - Between Lubbock & Dallas
Last edited by Rex Smith; Jan 17, 2024 at 11:25 PM.
P0300 with counts piling up on cyl 4 under load is often ignition breakdown on the 8.1. Start with the basics: pull the #4 plug (check gap/insulator), and inspect the plug wire for heat damage or arcing?these wires love to cook next to the manifold; swap the coil and wire from #4 to another cylinder and see if the miss follows. If ignition checks out, do an injector balance or swap #4 injector, and verify fuel pressure under load with a gauge so it?s not leaning out. If your check engine light also triggered Reduced Power, clean the throttle body and check for TAC/APP codes and loose connectors at the throttle body and pedal.
P0300 - Cyl 4 - When under higher load
