Random misfire

[Timc9516]

Ok so when I bought the truck a few years ago I would randomly get a p0300 code I'd feel it occasionally but not bad enough to be concerned. Plus I had alot of other repairs and maintenance to do. Well when I got my truck back from the trans shop I noticed the miss alot more and it's been consistent sence then. So I bought plugs and wires. Both acdelco and yes I used the iridium plugs according to the tsb. When I pulled the plugs the previous owner put autolite double platinums in it
Also I found that cyl 1 was loose which scared the crap out of me. But luckily it tightened up just fine. Unfortunately even with the new plugs and wires I can still feel the misfire. I'm gonna try and put my bosses scanner on it today after work to see if there's any codes in it anything else I should look for. Also some info for you guys. I've already replaced fuel pressure regulator, intake manifold gaskets, oil pressure sensor, camshaft sensor, valley pan gasket, knock sensors and harness, valve cover gaskets and grommets since I bought the truck. Ik there's a relearn for the crank sensor. Is there one for the camshaft sensor?

 

[Fless]

After you do the crank variation relearn, and besides looking at codes, view live data and the individual cylinder misfire counters to narrow down the contributing cylinder(s).

 

[Timc9516]

That's the odd thing is the misfire counters all show 0.

 

[Timc9516]

Ok so I've got some more info. I checked the fuel trims and long term were at 10 and 12. I cleared the random misfire code I got while decarboning the engine. And my fuel trims went to 25 and dropped down to 10 and 11 again. Before this I was getting 10.5 mpg on my way home after doing that I got up to 13.5. It was fairly warm that day (enough to have the shop doors open) this was Tuesday. Yesterday when I went to go home it was chilly out and when I started the truck it was idling really rough. I drove down the street to the red light and it was idling fine. To me that sounds like a intake manifold gasket. So has anyone replaced there gaskets with the fel-pro permadry plus gaskets (part #ms98016t) and had them leak shortly after? I really don't want to throw parts at this. But with the price of gas here in Illinois I gotta figure this out

 

[MassHoe04]

If it were me, I would wait a bit and see what happens. The roughness could be the computer re-learning and re-adjusting. I would give it a little time and some more drive time under different speeds and conditions. Maybe, it will smooth itself out. I would give it a try, before jumping into gaskets or other things.

 

[Timc9516]

Sounds good. I'm headed up to Wisconsin this weekend so it will get some good miles on it. I'll see if I can borrow a scanner to check fuel trims when I get there and when I get back

 

[rockola1971]

Ok so I've got some more info. I checked the fuel trims and long term were at 10 and 12. I cleared the random misfire code I got while decarboning the engine. And my fuel trims went to 25 and dropped down to 10 and 11 again. Before this I was getting 10.5 mpg on my way home after doing that I got up to 13.5. It was fairly warm that day (enough to have the shop doors open) this was Tuesday. Yesterday when I went to go home it was chilly out and when I started the truck it was idling really rough. I drove down the street to the red light and it was idling fine. To me that sounds like a intake manifold gasket. So has anyone replaced there gaskets with the fel-pro permadry plus gaskets (part #ms98016t) and had them leak shortly after? I really don't want to throw parts at this. But with the price of gas here in Illinois I gotta figure this out

If you think there is a possibility that the intake gaskets are leaking, thats an easy check. Just spray some starting fluid along gasket/head/block mating surfaces and see if idle jumps up or not.

 

[InterceptorF]

Replace the intake gaskets. Those intake gaskets are notorious for causing p0300 misfires in cold weather. Since I replaced mine (at 280K miles) the cold day start is no longer an issue with bucking and misfires.

 

[Timc9516]

Sorry it took so long to reply. Been super busy lately. Well like I said I took It to Wisconsin and back. 2 and half hour drive one way. Used half a tank there half a tank back. Fuel trims were the same when I got there and when I got back. I took some carb cleaner (all I had on hand) and sprayed everything. Intake gaskets, throttle body, map sensor, vacuum line from valve cover to intake, vacuum line from intake to fuel regulator, all the plastic caps just incase, fuel injectors, and the vapor purge solenoid. No change in idle. I looked at the exhaust manifolds and flanges. And don't see any soot and I can't really tell if the trans shop had them off or not. I'm really not sure what to do next.

 

[Fless]

I would document the O2 sensors and how much they are reacting. Also, it's not clear what the short- and long-term fuel trims are for each bank, if you could revisit and retest, it might help point to a source.

The crank-cam correlation relearn is one test, there's not a separate one for the cam. Perhaps if you're feeling a misfire but no counts are showing up, there is still something wrong with the tranny slipping or some such thing.