Well My truck has officially stumped me. I have a drivability issue I cant seem to track down. It only accure once the truck reaches a ECT of 202*. Its is a random miss fire that is not ignition related as the pcm shows nothing under misfire data. Its recently started happening. There are 0 codes and it passes all self tests. Here is some hard data. When cold the truck pulls 23 in lb of vacuum. But one it reaches operating temp it will no longer pull more than 15 in lb of vacuum. When the problem first started, I replaced the plugs, boots, cleaned the maf, and TB. It didnt show its nasty head for a few days. Then It start happening more vigoursly. SO I test the fuel system. I foun the fuel pump was weak, and 3 out of the 8 injectors were measuring high resistance than what is specificied at operating temps.

So to summarize, I have a major multiple cylinder missfire under load only at operating temps. When the truck is cold it runs like a bat out hell. Here is the list of recently replace parts:

Injectors
Mass air flow sensor
Fuel pump
Injectors
Plugs
Coil pack boots

If its the coil packs I think i will lose it, as they arent cheap.

 

You sure there's not an intake leak or crack in the manifold somewhere?
(Shows up once it gets warm and expands)

 

That's what I was thinking too. The only other temp related thing I can think of is fuel line vapor lock. Try brainstorming all temp. variables. If I think of anything else I'll post.

 

Most likely a cop give it a little more time it will show itself

 

Well speaking of the devil it showed itself this morning on the way to work. I just got home and going to let the truck cool down. It triggered a hard miss fire fault with the flashing check engine light. Checked the codes and I have 2 codes. P0307, and a P0308. Hopefully just COPS will fix it. But I'm thinking it has more to do with the injectors. I switched to EV6 style injectors and had to use adapter which add about 1" of height to the pigtails. I'll check it out and report back. As far as the intake being cracked, that is not a possibility as I have a 99 PI aluminum manifold. No plastic junk here.

Well after checking the truck all I found was a injector came unplugged along with one coil pack unplugged also.. So we shall how it performs tonight..

 

Good to know.
I'd also think you'd see a lean code with a big vacuum leak.

 

Ok so just a update so if anyone else has a similar issue this may help. I have successfully have put around 125 miles on the truck with no problems. I ended up retorquing the intake manifold after the truck had cooled down last night. Everything seems good to go. I would have flipped out if one of my COPS were bad, as they are aftermarket and are high output EFX stage 2 coils. The main cause was a injector coming unplugged, along with a coil pack plug that was not locked correctly.