[jeepunlimited]

welll ill try to explain this as best i can, sometimes i turn the key and the pressure primes to 36 if im lucky, othertimes it will prime to 30 on average, but i have days where it only primes to 15-20 psi and if i prime it again, it primes to 30, it still has the long start though, i have a new CPS soo i dont think its that . WHen it primes to 15-20 , i crank it and it instantley shoots to like 30 psi then starts and runs at 32 psi all day long. but sometimes when it primes to say 30-35 ....ill crank it and the pressure will drop to like 15-20 and then jump back to 32 when it fires up.

i think i might need a new fuel pump but im not entirely sure, do you guys think i shoudl check the injectors ?? could that be any sort of a problem for my long starts and my low power ??

i just wanna get to the bottom of it , cause i have felt the power the 4.0L has on a good day, so i know its capable of pushing that power out all day, but something, fuel or electrical related, is holding that power back .

what do you guys think i should do in this position ?

[rxl]

Have you checked your cat and muffler?

May sound strange, but and old chevy I had would near die on steep inclines. I knew the cat was getting bad but didnt know a piece of the crap inside choked off flow as I got vertical.


Uh huh....true story.

[jeepunlimited]

well my muffler is new, and i dont think its the exhuast system at all cause i took it in for emissions testing in october and it passed with numbers 1/2 of what the limits were, i was very impressed, i think its sensor related

soo far i have replaced the MAP, TPS, CPS, coil, IAT sensor, o2 sneosr, cleaned the throttle body and IAC ,k+N drop in filter, new plugs, cap, rotar , wires,

im at my wits end as to whats left to change

im thinkin fuel pump but it runs at 32 psi all day long, idle is a bit rough but i think my motor mounts are bad,

im really at my wits end as to what the hell could be causing my weird power problem ...

coolant sensor maybe ?? my gauge works fine, but is there a seperate sensor to the ECM?? bad cam sensor ?? i hope not cause i dont wanna remove the distributor, and yes you HAVE to remove ito n the 1993 models. ...i was thinkin cam sensor, becuase on one of my stalling occasions , i held my foot right to the floor to try to keep it running, and the jeep started popping out the exhuast, then sputtered and died.

could my cam sensor be garbage ?? causing my low power ?? like is it in any way possible ?? also could that be whats working in conjunction with my ASD relay to shut down my fuel pump at times ??? it feels like my timing is being pulled out causing low power ?? there are no codes and i think the cam sensor is orignal. could this also cause my rough idle and long starts by chance?? i work on jeeps all day at work (chrysler dealership and every 4.0L i work on takes 2-3 cranks and VROOM , mine is like 9 or 10 and its starting to make me thing something isnt righ and i wanna fix it ASAP!!... anything you guys can suggest i would be up for it ..thanx

any other opinions guys ?

[jeepunlimited]

can anybody help me figure this **** out !! ..thanx guys

[-Joe-]

If you work at a dealer why not hook it up to a diag machine and monitor the engine while its running? That would have saved you from buying/replacing all those sensors.

It should throw a code if the camshaft sensor fails to send a signal.

Theres 3 coolant sensors.. 1 for the gauge, 1 for the fluid level and 1 for the computer.

[jeepunlimited]

where is the one for the PCM located ?? my gauge works, my low coolant light ISNT on but maybe the PCM is getting signals that its running way to hot ?

[greasefingers]

The coolant sensor for the PCM is the one on the thermostat housing.

[nitecop]

Originally Posted by jeepunlimited

well my muffler is new, and i dont think its the exhuast system at all cause i took it in for emissions testing in october and it passed with numbers 1/2 of what the limits were, i was very impressed, i think its sensor related

soo far i have replaced the MAP, TPS, CPS, coil, IAT sensor, o2 sneosr, cleaned the throttle body and IAC ,k+N drop in filter, new plugs, cap, rotar , wires,

i work on jeeps all day at work (chrysler dealership and every 4.0L i work on takes 2-3 cranks and VROOM , mine is like 9 or 10 and its starting to make me thing something isnt righ and i wanna fix it ASAP!!... anything you guys can suggest I would be up for it ..thanx

any other opinions guys ?

Ok here is the way I would look at it. The problem you have comes and goes which rules out a lot of mechanical problems. The fuel pump is a mechanical device( its either on or off). While a chunk of converter media in a converter or rusty steel in a muffler that does not sound like it to me since it has got so bad it died once, right? I would look at things that can effect the computer output. I would focus
on things that put a input into the computer that are variable. (the crank position sensor does not put out anything but a steady output. with every turn of the crank it puts out the very same thing.) Did you keep the old sensors you replaced?
If the engine it at a normal 190 degrees but the coolant temp sensor tells the computer it is at 260 the computer will back off timing to cool the engine when it is not needed. Variable out put sensors are what i'd look at. ( MAP, CTS,... )It is something that can "fix" its self and work right when it want to. these are the things i'd focus on. very few mechanical thing can fix themselves.

I have had the very same problem with my 99 TJ. But I have narrowed it down on mine. Once in a blue moon mine will get very lean at part throttle between 1500 and 2400 RPM .sometimes it gets so bad as to backfire back up the intake. It has not done this in months. I still have no clue as to why.

[jeepunlimited]

yes i kept the old sensors, im still thinkin fuel pump but maybe not, i just bbought another set of MOPAR plug wires today but i still have the long cranking issue ....i was thinkin about trying the coolant temp sensor next. .....what does everybody think ?

[greasefingers]

No I do not think that the cts would prevent normal starting times.

[-Joe-]

at this point why not.. your taking a brute force effort on it by replacing everything in hopes it fixes it..

just because the sensors are replaced doesnt mean the wiring is good either.

i would test the sensor before replacing it.. but then again my approach would be different..

we did have a saturn which had hesitation on throttle.. it turned out to be a coolant sensor messing with the injection timing.

----------------------------------

Engine Startup-mode

Open loop mode

the pcm receives inputs from:

battery voltage
engine coolant temp sensor
crankshaft position sensor
intake manifold air temp sensor
map sensor
tps
starter motor relay
camshaft position sensor

the pcm monitors the crankshaft sensor, if no signal received within 3 seconds of cranking the engine it will shut down the fuel injection system.

[jeepunlimited]

Originally Posted by greasefingers

No I do not think that the cts would prevent normal starting times.

i replaced the cap today with a spare my brother had from his old 93 ZJ 5 years ago , its new and never installed on a vehicle. now my ZJ starts amazing, quick and accurate , no more long cranks

gonna try the coolant temp sensor next for the power issue, if thats not it, i give up and ill keep driving it the way it is .

[greasefingers]

If it ends up being a $ 12 part then I will scream

[jeepunlimited]

start screaming man ....a mechanic at the dealership i work at had one in his toolbox, spare from his old 4.0L grand cherokee winter beater...he gave it to me to try, told me if it works, you owe me a bottle of pop and we call it even , real nice guy, just popped it in, WOW what a difference, great power, no stumbling, great acceleration.....feels like a new 4.0L ....im taking it for a drive tongiht to double check everything is good but i think that was my problem all along....THANX JEEP FORUM!!!

[jeepunlimited]

success !!! all my power is back for sure, it was the coolant temp sensor !!!! 15 bucks later!!! ...

but of course, fix one thing, another goes wrong, fuel pump is dead, pressure fell to 10 lbs, got home just barley .....when i turn the key i hear the pump buzz but it doesnt sound like normal, it sounds like if you left your cell phone on vibrate !!....not a whining more of a vibrating sound.....its totally screwed.....geuss ill be spending my sunday putting a fuel pump in !!