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Fuel Pump not always priming

Tenny

NAXJA Forum User
Location
Houston, TX
Alright, so this has been an on-going problem for years now. Finally "really" trying to solve this.

Basically the Jeep would eventually start if I kept trying to crank it over, but sometimes it'd take a few minutes. If I used starting fluid, it would generally always start pretty easily and run just fine. Once it started, I could start it back up within the next few hours pretty easily. I thought at first it was the fuel draining back into the fuel tank, thus the FPR / Filter / Additional check valve was installed. That didn't fix it, so I installed a new fuel pump figuring the old one was just going bad at this point.

Well that didn't work obviously. So I bought a fuel injection pressure tester. What I've determined from that is sometimes it primes the fuel system, sometimes it doesn't. I would say it's every few key turns the fuel pump primes (and primes to about 51psi). If it doesn't prime it flashes the check engine light (I think five times). Even if it doesn't prime, but it ran recently it'll have enough fuel pressure to start and turn on just fine.

It was holding at 40psi after being off for about 2 hours earlier. The problem is I don't really drive this vehicle often. Right now it's probably only started 3-4 times this year, last year I used it for towing for a few months and it did pretty well during that time. Before that it probably moved 10-12 times a year.

So far I've replaced:
  • Fuel Pressure Regulator
  • Fuel Pump
  • Fuel Filter
  • Added additional Check valve in fuel line

Additional "swaps" I've done that didn't fix it:
Swapped the fuel pump relay and the A/C Relay (A/C hasn't worked for years so I don't know if this is a valid test).
ECM/ECU or whatever is near the driver fender (Had a spare)
 
Hard initial start plagues obd1 xjs. I don't think I've ever seen a fix. Although mine primes every time, if it's been sitting for a few hours it has to crank 20 seconds or so before it fires. Good luck.
 
Do you have a "known good" relay with which to repeat the relay swap test? Condition of terminals inside fuel pump relay socket?

Have you checked the Fuel Pump Ground inside the driver's side quarter panel?

Do you still have the fuel pump ballast resistor (white, on driver's fender a little rear of ECU)? If so, is it in good condition?
 
Do you have a "known good" relay with which to repeat the relay swap test? Condition of terminals inside fuel pump relay socket?
Terminals look good inside, but don't have a known good relay without buying a new one.

Have you checked the Fuel Pump Ground inside the driver's side quarter panel?

Had to google where it was, but just looked at it (visibly, didn't check continuity or anything) but it looked in good condition and has not been tampered with.

Do you still have the fuel pump ballast resistor (white, on driver's fender a little rear of ECU)? If so, is it in good condition?

Doesn't have one.
 
Regarding the , you can always test the one you have - apply 12V to the two terminals for the coil, and you should hear it click. Leave the 12V attached, and check the other two terminals for continuity.
 
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