Random misfire - very intermittent

Hi I’m looking for some ideas on what else to check on my 2008 4.7 with 208,000km (125k miles) that has random misfires. In August when I got the truck I was getting p0300 and sometimes cylinder 3, 5, and 8 misfire codes. Funny enough, there never a change in how the truck ran or sounded. Which is weird for a misfire. Checked and cleaned all engine block grounds and replaced the spark plugs in September and the lights stayed away until today. (No engine lights for 6-7 weeks).

Long, steady, uphill acceleration from a stop seems to do it. That’s what caused it back in August, and that’s what caused it again today. Though it did did it again on flat. The whole dash lights up like mad, (engine, traction, vac and 4lo flashing) but the truck drives and sounds 100% normal. I cleared codes and it has not been back.

I will also note that 2 weeks ago after a quick trip the hardware store, the truck would not start after being parked for 10-15 minutes. It would crank but not fire. I left it along for 15 minutes and it started up with no codes or history.

I’m thinking I might have a fuel delivery issue. I think I’ll run a can of injector snake oil through for the hell of it. I also think I may test fuel pressure if there is a way I can rig it up to see it when driving.

Any idea on what to check next? Should I load the parts cannon for a fuel pump or anything? Lol

 

You should first figure out what's causing the misfire, before you load the parts cannon. Start by swapping out coils to other cylinders before you buy anything. Inspect those specific spark plugs for any kind of wear, damage and gap. If spark plugs have never been changed, it may be a good time to do it. I do believe the OEM sparks were good for 100k miles.

 

if you carefully read the my post again, you will see it’s not that simple. I already changed the plugs (oem spec denso) and the misfire is on random cylinders. I’m looking for other areas to check.

 

Inspecting wiring would be the next step, including grounding points. borescope all cylinders in case you have a valley coolant leak.