Engine/Transmission (1998.5 - 2002) 98.5 engine missing at higher rpms

[KMott]

Hey, new to 24 valves here. I picked up a 98. 5 24 valve with 236,000 km. The VP44 has a 'remanufactured' tag on top. The truck starts good and runs good when first started. Runs smooth up to 3000 rpm, but once truck has run a few minutes it starts to miss bad and smoke white past about 1800rpm. If i put the pedal down it wont rev past about 2400. (this is all being checked under no load in the shop) It still starts good and idles nice when warm. I checked supply pressure by hooking a gauge to the fuel filter canister (take out a 1/4" npt plug) and the truck is running about 5-7psi, and it drops down a bit when revving up. It has the lift pump in the tank. I thought the problem was fuel pressure, but seems like someting else since it runs ok when cold. Anything electronic that could cause the problem? Not sure if there is a way to reset computer. Just hoping the VP isnt going bad. Thanks in advance for any help.

 

[JLandry]

Are you able to pull up any trouble codes using a good code scanner and is the check engine light coming on?



Is that fuel pressure you reported taken when the engine is stumbling?



John L.

 

[KMott]

Thanks for the quick reply. I dont have a scan tool here, but the check engine light isnt coming on (unless the bulb is burned out!) Im only running the truck at the shop, not on the road since its not plated and has no box on it right now. Fuel pressure at idle is around 5-7 and drops down a bit when stumbling, maybe as low as 2-4psi. When the engine is cold the fuel pressure acts the same, but the engine doesnt miss. There is definately fuel pressure to the pump because if i crack the banjo bolt on the output line of the filter canister fuel sprays out pretty good. I changed a lift pump on a '99 24 valve a couple weeks back, and that truck was running fine and had no fuel pressure at all? Thanks again

 

[JLandry]

I wouldn't be so sure there's isn't a fuel supply problem.



I say this because those are very low fuel pressures to start with, and since you're measuring the pressure pre-filter, you really don't know what the pressure is at the VP44 fuel inlet. The symptoms you've mentioned are very similar to fuel starvation.



My recommendation would be to measure the fuel pressure directly at the VP44 inlet to rule out fuel starvation, and also buy or borrow a code reader to check for trouble codes.



Please keep us posted.



John L.