Where to begin? My diamond in the rough is being a big old bitch, She is a 99 3.9 2wd 5 speed regular cab with 175,000. For starters I know I have a bad fuel pressure regulator or some would say none at all, My fuel system holds absolutely no pressure what so ever once the truck is turned off, Instantly drops to zero, I prime her a couple times before every start and that works great except for the first start of the day she gets real lippy, Starts fine but like clockwork after around 12 seconds of running smooth she stumbles real hard and finishes off with a backfire from hell, sounds like a damn shotgun sometimes and she smooths right out. The fact it is like clockwork when it begins to stumble makes me think think there is more going on. last summer I replaced the tps, iac, both coolant and air intake temp sensors, both 02 sensors, new cap and rotor, tons of spark plugs, and new wires. all this because I bought a faulty ignition coil from napa and began this love hate relationship, After that she never ran better. about 3 months later she started running like complete ****, hard to explain but like it was just trying way too hard when rpms were above 3 grand, and other times she screams like a banshee and runs like god himself which shows me her potential, My mpgs are horrible, like 16 mpgs and i drive highways 95% of the time, she was getting 22 before this nightmare, and she also pings like crazy in 3rd gear and up, and now that it is getting cold as hell out, when i push the brakes my rpms shoot to 2300 unless i double tap that ****, and if i pump the brakes 5 times the release the rpms will drop to like 400 and she stumbles for like 5 seconds, these are my thoughts on what is going on but its time for some thoughts on other owners that know these trucks better than themselves.

-I need a new fuel pump for sure im just not looking forward to it, could also be a leaky injector

-iac is going bad even though the one I put in was the best napa had but they gave me bad parts before

-I dont think its the plenum, completely removed the throttle body for a deep clean and there was no major oil pools and doesnt burn any,

-possibly bad alternator or some thing electrical, maybe dirty contacts, I removed the battery posts and cleaned them real good and it ran excellent for like 3 days and then ****ty again,

- a leaky booster, My brake pedal is very spongy and it hits the floor if i push hard enough, but when she is off the pedal is hard as a rock if i pump it a couple times,

- I do have a newer cat, 10 or 15 thousand miles ago,

-Timing could be off causing the pinging

- I run full syn oil and change every 2000 miles, (dont ask why)

-new spectre air filter,

Please guys, any input would be greatly appreciated, I have spent way too much money and bloody knuckles to throw in the towel,

 

Almost forgot just put in a new map sensor and no improvments, still acts like pulling a monster load when excellerating

 

what is the rear gear raito? for mostly hi way i would go with a 3.55 or 3.23. i just changed a 3.9 auto trans from 3.55 to 4.1, gained 3 mpg. only cause i drive ONLY in town. what it does is kick over to the top gear at 35 mpg, gear ratio drips down 1400 rpm. i really didnt think it would pull that load, but it pulls the load fine. course its at low speeds.

 

Yeah mine has a 3.21 and it's a five speed so it should be a lot better on gas. When I first got her at 150000 I would hit 200 miles at the 1/2 mark on my fuel gauge, now I'm lucky if it is 130. And it's a 15 gallon tank