fuel issue

[Dave90ranger]

ok i posted a while ago about powers loss over 3k and well i dont think i explained good enough. now as i accelerate my fuel pressure starts to go down from about 30 psi and then if i go full throttle fuel pressure drops to about 10 or 15 and wont increase and the truck stops accelerating and sputters then if i let off the throttle a little bit to about half way or so it will start accelerating and go father than 3k and fuel pressure will go up to a certain point and will stop accelerating. pretty much the truck is acting like its running out of fuel to keep accelerating and thats why i think its a fuel problem.

i have replaced tps sensor, act sensor, map sensor, fuel pressure regulator, fuel filter, and a new gas neck since it was broke apart and leaking, the fuel pump is brand new also. new plugs, wires, coil, cap and rotor, and air filter. im about out of ideas of whats wrong all i know is its a fuel delivery problem. im hoping someone else has this issue and has a solution to it cause i cant stand it since i cant accelerate into traffic at all.

fuel pressure KOEO: 39 psi
fuel pressure idle: 30 psi

its a 1990 2.9L

 

[BillupsOMally]

I'd go for a good drive around the neighborhood and make it act up as much as possible with as little regular running as is reasonably possible before parking and shutting off. Then check plugs, if they tell you it's running lean then it's fuel pump/filter/FPR. If they tell you it's runnin rich, then it could be any host of things that make the computer think it's running too lean and dumping in fuel.

The only time I left a fuel filter long enough to cause flow problems the truck would die instantly like I'd shut the key off when I matted it. And when I had an O2 sensor fail it ran too rich, it would sputter and miss and shake and slowly gain RPM (apparently I was even puffing black smoke like a diesel on hard shifts).

 

[RustedRanger]

Since you changed the FPR and the pressure still drops it almost sounds like a clog in the fuel line somewhere. The fuel pressure tester I used (my cousins) had fittings so the pressure could be checked at various places in the fuel lines. Did you change the gas cap? Try loosening it and see if it does the same thing. It could be the gas tank is not getting vented right.

 

[dirtymike]

There is a fuel accumulator between the high pressure and the tank. It hat two lines(high pressure and return. The return is the smaller of the two. This accumulator becomes clogged with particles over the years. The easiest way is to bypass with a fuel filter. I just used a splice kit a picked up at a local auto parts store. This little black gismo caused me two burnt pumps and alot of time.

 

[RustedRanger]

There is a check valve that get messed up in that accumulator also,when I took mine off thinking it had a filter in it the check valve was sideways in the hole,I drilled it out.

 

[Dave90ranger]

ok so far havnt figured anything out but i think my tps circuit has issues and the sensor is brand new. got codes 53 tps circuit above maximum 4.6 volts and 63 tps circuit below minimum 0.6 volts. now my truck doesn't have an accumulator/filter at all just an in tank pump and a filter on the frame rail. both are new not even 500 miles on them. also the gas cap is fine so that isn't the issue.

now heres my thinking of the issue, since the tps circuit has issues i think the computer is thinking the throttle is at a certain spot and its not and its dumping in more fuel than it should causing pressure to go down. now my dad said he could smell gas when it was sputtering and doing its thing. so im going to diagnose further into this tps issue and hopefully figure it out. i was thinking maybe my computer is shot which i hope it isn't but if it is oh well.

 

[RyanL]

Did you back probe the TPS sensor wires (pretty easy to do with a digital multimeter, although analog meters with a needle are better for such things where you can check the sweep). I think that the signal wire is in the middle, the 5V power is on the bottom and the 5V computer ground is the top wire. Either way, it should be easy to figure out which wire is which. Check to see what you're dealing with. If you've reset you're computer since you replaced the TPS and you're getting the proper voltage, then it seems as though you have a wiring or computer problem. There might also be a slight chance that the TPS isn't on there right. When I was checking mine out, I think that it was just like a flat head screw driver tip which pokes into the sensor; maybe it was turned 180* already when it was installed? I'm not sure if this is even possible, just an idea of something easy to check out.

 

[RustedRanger]

If the FPR is working right then the pressure should stay about the same no matter what the ECM tells the injectors to do.

 

[Dave90ranger]

ok well i checked out my tps which is working properly and correct voltages, now the wiring is also fine i checked all that now im almost positive my computer is shot. now i disconnected the battery(when i put the new sensor in a while ago, i reset the computer to clear codes) it was doing its hesitation thing before i disconnected it, now after i checked the wiring and all, i put it back together and so far no hesitation. now me and my dad think its a computer issue and our tech at goodyear i work at also thinks the same thing as we do. my dad used to be a mechanic also so he knows all about this stuff also.

now i know fuel pressure should stay constant but since its not and ive done about everything to the fuel system and stuff ive pretty much diagnosed it to the computer being shot.

 

[RyanL]

ok well i checked out my tps which is working properly and correct voltages, now the wiring is also fine i checked all that now im almost positive my computer is shot. now i disconnected the battery(when i put the new sensor in a while ago, i reset the computer to clear codes) it was doing its hesitation thing before i disconnected it, now after i checked the wiring and all, i put it back together and so far no hesitation. now me and my dad think its a computer issue and our tech at goodyear i work at also thinks the same thing as we do. my dad used to be a mechanic also so he knows all about this stuff also.

now i know fuel pressure should stay constant but since its not and ive done about everything to the fuel system and stuff ive pretty much diagnosed it to the computer being shot.

I hear a lot of conflicting methods around here on how to reset the computer, but it seems like the best way is to disconnect the jumper wire while pulling codes: http://www.therangerstation.com/tech_library/OBD_I.html. I only mention that because maybe your computer wasn't reset or there is the possibility that you're computer needed time to re-adjust to the new TPS. If everything seems fine for now then drive it around a bit to see if it acts up at all. If all is well, then maybe your ECU is fine.

 

[Dave90ranger]

I hear a lot of conflicting methods around here on how to reset the computer, but it seems like the best way is to disconnect the jumper wire while pulling codes: http://www.therangerstation.com/tech_library/OBD_I.html. I only mention that because maybe your computer wasn't reset or there is the possibility that you're computer needed time to re-adjust to the new TPS. If everything seems fine for now then drive it around a bit to see if it acts up at all. If all is well, then maybe your ECU is fine.

thats what i thought on how to reset the computer but i did it once before and it worked for a little bit like not even 20 miles or so and then acted up and i have done it twice so im 99% sure that the computer is the issue right now. but if i replace the ecu with a different one and still nothing then ill most likely look into diag more or a better pump or something.

 

[Dave90ranger]

ok so i have basically come to the point where my computer is shot. while i had time at work the other day i hooked it up to our scanner and it was randomly throwing codes that i know have no issues and the codes went away seconds later so ive pretty got to replace the computer now. which i was surprised isn't much compared to other cars.

 

[BRUTUS_T_HOG]

low pressure comes from a restriction or a bad fuel pump. new doesn't always mean good.

if you haven't replaced the high press. pump on the frame rail you should do that. if the truck only has 1 pump and its in the tank then you should replace that.

before you do check for bent lines/hoses. if you can pinch off the return hose and get the pressure to rise you know the pump is weak.

is the fuel pump(s) getting good power and ground? test with the pump(s) running to put load on the wires

 

[Dave90ranger]

ive already checked all that and everything is good (and yea new doesn't mean good but the chances of getting something bad, new are slim to none). anytime i reset the computer like disconnect the battery for a half hour or so it runs fine for about 30 miles then starts acting up at higher rpms then gets down to the 3k rpm and thats as far as it goes. ive told everyone at my work and they thought the same thing at first and then i did the computer codes with our scanner and ran the self tests over and over again and it popped up one code then i erased it and ran it again then popped up another code and i did it one more time and it did another code. so my computer is throwing random codes that have no issues. so now they think what i think now(i work at goodyear and our tech and everyone says its the computer).

 

[BRUTUS_T_HOG]

i've gotten bad maf sensors 5 times in a row new, switches a few times in a row and a couple bad fuel pumps new. it happens and chances are pretty high when the partys come from china. its frustrating as hell, but you're only wasting your own time by assuming.

there is no sensor that changes fuel pressure, you need to make sure the fuel pumps are not losing voltage when hot and affecting performance. you say this only happens hot? and ONLY after resetting the computer? that almost sounds like a dead O2 sensor to me... but i've never seen a computer compensate to the point it was holding the injectors wide open to cause a drastic drop in pressure