NO start - elictical or fuel pump?

I had a different post about some fuel pump problems recently.. this is related to those problems.. and quick history is gas tank had hole in it, replaced tank, kept original pump/assembly..pump was noisy, then died 2 days later.. replaced pump.. jeep no start.. when it does fuel pump noisy again and likely going to die off again.


after i got my fuel pump installed its been a real bitch to start, jeep just cranks over and over and over, but eventually it would fire up after 10 or more tries.. so me and a friend were troubleshooting the problem.. and i was wondering if you had anything like this happen to your jeeps.

after turning the ignition on power goes to the fuel pump then cuts out, we thought it was bad ground at the tank, so we disconnected the wire harness for the fuel pump by the tank, test light shows that the power is getting cut out after about 1 or 2 seconds after the key is turned to the on position. the fuel pump relay in the box by the battery is making 2 click sounds, one when it turns on and then again when it clicks off, they are very close together, maybe a second or so apart. my thought is that the tank is grounded properly and that there is a short in the wiring somewhere or maybe that the relay itself is no good..

what confuses me is that after several sometimes 10 or more tries to get it fired up it will fire up and run fine, but turn off the jeep it does the same thing again.. could it be related to the CPS and or timing? or would it likely be a bad ground somewhere in-between from the fuse box under the hood to the wire harness by the gas tank?

also after i had the gas tank replaced the fuel pump was making loud hum sound and eventually died.. now the brand new pump is starting to make a loud hum like that and i think its only a few days before it dies again.

its my daily driver and its got me in a bind.. i am ready to walk away from it its got me so fustrated...

really appreciate your help.

the fuel pump relay May be bad.. Can you check with other relay?

The fuel pump primes for a few seconds then the ECU opens the relay (this is normal). The fuel pump relay doesn't close again until the ECU detects a pulse signal from the CPS (the motor is turning over or running). It's likely you have no spark when the pump relay doesn't close, the spark also stops unless there is a CPS pulse signal.
You could have more than one thing going on here, after Renix the fuel pressure regulator moved to the tank and is incorporated into the pump assembly. Low fuel pressure?
If you have spark while the motor is turning over, it's likely a fuel problem, no spark it's likely a CPS problem.

tried with another relay but will go buy a new one to be safe.. i am also going to test the fuel pressure and see what the reading is, what is the stock reading? i have a FSM at home so will check tonight after work.

thanks for the advice 8Mud, going to do some more tests tonight, i am thinking it is a CPS problem, will keep ya'll posted.. thanks again :cheers:

What brand fuel pump are you using. El cheapos tend to have short lifespans.

Once the pump is primed fuel pressure at the rail should be about 39-41 psi. Once running pressure will drop to 29-31 psi. The problem you have sounds like the problem I just went through for the past 5 months. The problem with mine was the ECU/PCM was bad causing the ASD (Auto Shut Down) to keep the vehicle from starting. The ASD will remove the ground to the Coil causing a no start condition. What I would check is for ground with the key on to the coil by unplugging the coil. If you do not have a constant ground look at the ECM/PCM for possible faults. Victor S.

Does the 93 have the fuel filter in the tank or is it on the frame rail like the earlier XJs? I'm just wondering if this is simply a plugged up fuel filter.

replaced teh CPS this morning no luck with getting it to start. the fuel fileter is not in the tank, just along the unibody "frame" and was replaced after the tank was replaced.. so far no luck with anything tho i havenot tried checking the ground at the coil for teh ASD.. could be teh ECm? dunno.

i bought the fuel pump at lordco which is like an autozone here in Canada, the brand i think was carter, and the only style replacement for the bosch type fuel pumps

but anyway a tow truck is on the way to bring the POS to a shop and have it fixed, i am fed up with it as this is my DD and caused too many headaches for me.

diagnose from the mechanic is that the fuel pump was a dud and is not generating pressure...

so since i just replaced it i will return it for another replacement and should be back on the road again. :yelclap:

It's disappointing to have a new part fail but it happens quite a bit actually. The factory that manufactured it may call it "infant mortality" but oftentimes it is that the reliability testing and quality control isn't at the level where it should be.

As the fuel pump for yours isn't in the tank and you have a warranty on your new pump, this one should only cost you a little labor.

Best thing to do when fuel delivery is suspect is to put a fuel gauge on the schrader valve on the fuel rail and compare it to spec. Takes only a few minutes and then can either confirm or refute basic fuel delivery problems. That's probably what your wrench did on yours....

Anyways, glad to hear yours will be running again! :viking:

well all seemsz to back to normal, there is one smaller problem that i think may be vapor lock in the fuel line..? not sure if that is the correct term or not.. basically after sitting in traffic for a long time not moving very much, jeep gets pretty hot, never overheatrs but the jeep will stall, but start up right away.. not sure what that is about.

anyway.. here is a picture of said problematic jeep.

4" lift and 30" BFG MT

You said you already replaced the CPS. Possibly a bad coil? Those seem to be heat dependant when they start to go.

lawsoncl said:

You said you already replaced the CPS. Possibly a bad coil? Those seem to be heat dependant when they start to go.

Click to expand...

i'll check the coil, it is an aftermerket accel brand, was on there when i bought the jeep so its probly due for replacement.

thanks for all the help everyone! :cheers: :: :cheers: