I have a 1999 3.9L single cab 5spd manual sport. I bought this truck about 7 months ago now with no problems but a rusted out water pump and no power steering. After having it sit for about 2 months without being run i replaced the water pump and removed the thermostat and put a restrictor in place of it, registered, insured, and put it on the road. After sitting for those couple of months it started running funny, it would hesitate sometimes and when i put the pedal down it would surge. I didn't worry about it much at first but then it became worse over the course of a few months. It's gotten to the point where it hesitates badly, and it doesn't surge anymore when i mat it, it just cuts out completely and then comes back once i let off the gas, its misfiring on cylinder 2, and when this is at its worst sometimes i can't even get the truck over 10mph. I can't get the truck over about 2500 rpm in each gear most of the time because once i get to those rpms it seems like im starving for fuel and i have to shift. I did a fuel pressure test and at idle my pressure flucuates rapidly between 25-50 psi, and when i press the gas my fuel pressure drops down to steadily almost to 15 psi. The weirdest part about this all is sometimes it doesn't do it, and it usually runs better in cooler/cold weather. One day i had the battery disconnected for about an hour and I reconnected it and the truck ran absolutely fine for almost 2 days and then returned to it's slow, crippled status. I read the codes a little while back and got a code for misfire on cylinder 2 and a po138 code. Sorry for the lengthy read I tried to provide as much info as possible, If anyone has any insight on where I should start to diagnose and fix what is making my truck run so poorly it would be greatly appreciated. Thank you.

 

installed a restrictor? Why thats part of your problem I think is the coolant temp sensor on/in and working have you checked the plugs?

Are you running coolant or just water? You may have a bad vacuum leak?

 

sounds like fuel pump. fuel pres should be a rock steady 49psi at the rail, maybe 40-45 under heavy fuelling.