I did some research before Im posting this, but I wanted to get a few of the 12 valve expert opinions on here. My 12 valve is a 95, just turned 72K miles. I sold my car and have been driving it to work everyday for the past 2 weeks. I started noticing a little issue.
After the truck has been fully warmed and its shutdown and cools down to about 100-140*F and you restart the truck every once and a while it will start with a rough idle/slight miss. No smoke at all, just you can feel the vibration of it not running perfectly smooth. THEN if you shut it down and restart it runs perfect again. It did it to me earlier, it starterd right up with a rough idle, and I revved it a bit and you could still feel it in the revs. I shut it down, restarted and it was fine. Has happened about 3 times to me.
Its all stock, fuel filter was changed in spring (5,000 miles ago) running white bottle of power service. I have only noticed this since the weather started getting cooler, ran it all summer in the heat and never had it happen.

Besides that truck runs perfect, no white smoke no roughness anywhere else, its only after that warm start (it will not do it if the truck is still hot, its only when it has cooled to about 140)

 

First place i wud start is the fuel filters. if you havent changed the FF in 5000 miles.....its time. i do mine every time i change the oil which right now is every 5000. (that interval will go up when i start using Shafer oil) ff replacement will still be every 5000 or as needed b4 that if i get a hold of some bad fuel. also make sure the fuel strainer in the bottom of the lift pump is clean. the other thing i wud make sure of is travel of the fuel shut off solenoid. check it for binding and full travel. also check your fuel pressure from the lift pump and your overflow valve

 

thanks for the reply. im going to change the filter, and next time it does it, im going to fiddle with the shut off solenoid and see if it snaps out of it.

 

i edited my post...check fuel psi from lift pump and also check out ur overflow valve

 

The only problem I've come across that is temperature related is a gunked up shutdown solenoid.
For some reason when dirty ones get hot they want to bind.
Some cleaning and usually a new boot is all it takes to correct.

 

Id also see if youre inhaling any air in the lines. Sometimes thats really hard to pin down. I installed a furnace sight glass in the supply line to the lift pump so I can see the air when I stab the throttle. Makes diagnosing it a bit easier.
A fuel pressure gauge may pick it up too.

 

i played with the shutdown solenoid when it was doing it, and it didnt really seem to matter. If i let it idle for 15 or so secconds it seems to snap out of it. I can almost replicate it every time by letting it sit for an hour after being fully warmed then restarting it, it will do it.

My next move i guess is to get a gauge and try fuel pressure

 

the boot is torn, i lubicated it the best at the visual pivot points and it seems to be moving better than it was. In my shop book when key is on it says theres a measurment (2.64") i believe from the pin of the bottom of the assembly to the bottom of the pump bracket... its hard to get an accurate measurment in there though.

 

Check out foster truck, they sell the boot cheap.

Yea, it is a pain to measure.........

 

solenoid seems good. truck is still doing it and its getting worse. I changed fuel filter and tighten some injector lines. I think im sucking air somewhere, its going to be tough to find. I dnt think its an injector becsaue I have absolutely no smoke at all when its running rough, even if i lay into it in neutral im only getting black, no white smoke at all.

 

Does it still start good the first time?

Another possibility, which Infidel can tell you more about is they had problems with some 94 and 95 P-Pumps with barrels being out of round. It generally is a miss, but with your low miles, who knows?

 

When the motor is cold it starts perfect.. untill you heat it up fully, shut it off, then starts the rough idle untill it cools off again. I'm thinkin it has to be an air leak somewhere, either fuel heater, or where lines come out of tank or that rubber hose that runs behind the fuel filter.

 

Doubt it is an air leak, it should bleed down and cause a hard start.

That is what makes me think a pump barrel.

Infidel?

 

Explain pump barrel to me? Not sure what you mean by that.

When the motor is hot and you start it, it will run rough (not every time though) only after it sits for about an hour. it will run rough for max a minute or so then snap out of it. or typically if you shut it off and restart, it restarts fine.

Again thanks for the help and input!

 

In 1994 and 1995, they had sporadic problems with the pump barrels on the P7100, I don't remember if it was slightly out of round, or a scoring issue, bottom line is the pump had to be rebuilt. The Barrels are the things sticking up out of your P7100 main body that are held on by the 2 nuts. There are pistons inside that reciprocate and create the pressure to deliver the fuel.

Infidel can probably tell us if I have a possible cause or just wasting bandwidth.