Fuel Pump Issue?

OK....'89 XJ with 4.0L, Auto, 242. Quit on accelleration three times in a row two weeks ago. Fine for a week, then did it once again. Thinking TPS, I replaced it...seemed fine for a week. Then did it again, this time for good...wouldn't re-start. Towed it home. Since I couldn't hear the fuel pump run when initially turning the key, I figured the fuel pump had finally given up (only 254,000 miles!). Got a new pump from NAPA...not an exact fit, but with some modifications to mounting rubber, got it mounted up just fine. Installed and no start. Listened...not hearing pump running. Tested power to connector closest to pump/gauge sending unit. Found two outside plugs had continuity to ground and voltage betweeen center terminal and either outside terminal was 6.8v.

At this point, I hooked 12v to my old pump to hear it run just fine!!! So, guess it wasn't a pump problem after all! So, I come in for the night and search here. After search, I figure it's the relay or maybe the ceramic resister. Change resisters around to no avail. Short the resister with a jumper wire and hear the pump running when I turn the key. Only problem is that I still have no fuel pressure...doesn't even pump it from the tank if I remove the hose at the tank!!! (I don't think I have the return and supply hoses mixed up since they're different sizes).

Does the pump need to be primed or something? I think I figured out the ceramic resister block is bad...but, still no pressure, even when hearing the pump run for 3 seconds after key turned.

Any help is appreciated...and thanks in advance!!! This is my daily driver...and I can't use the company car for ever!!!

When was the last time you changed your fuel filter?
One way to check for fuel pressure is to take the cap off the fuel rail and push on the shrader valve. If there is pressure you will know it.

It's possible you connected the electrical wires to the pump in reverse order--pump will run backwards, and won't pump. The "ballast" resistor has no "in" or "out", can be connected either direction. It's there to reduce pump noise--no effect on performance to leave it by passed. I've been running my pump direct to battery for a couple of years--no problems ('88 XJ with Chevy v8).
The fuel pump is a positive displacement pump that sets down in the fuel--it does not need primed, but as you know, the pump has a sock filter on its input that could be clogged ( that should have been replaced along with the pump), and a short hose running from the pump to the pump bracket that may be loose or not connected. Both of these items must be in place to insure the pump will pump fuel from the tank. Also, as already stated, the wires on the pump must be correctly connected or the pump will run backwards.
If the pump is running, but no fuel is coming out of the tank, insure you have fuel in the tank, then re-check the items listed above.

I would say the first thing to do is to make sure you're testing for output upstream of the fuel filter. Assuming you are, if you still don't have fuel coming out when the pump is clearly running, you're just going to have to go in there and find out what is either clogged, kinked or defective. It occurs to me that if your initial problem was bad wiring rather than a bad fuel pump, it is unfortunately possible that the new fuel pump you put in is simply defective.

Lots of good advice...thanks. To clarify, I was looking for output right at the tank...before the fuel filter. Even with hearing the pump running (with the bypass in place at the ceramic resister), no output at the tank. Now, reveral of wires might be an issue...but I'm pretty sure I connected as labeled on the pump (which was backwards from my previous pump) ground to neg, hot to positive.

I guess now that I've figured out the ceramic resister issue, I'll have to pull the pump from the tank again to further chase the issue. Will let you know later tonight!

Thanks again!!

The saga continues friends. Last night I hooked 12v power directly to the pump wiring harness (at the connector by the fuel filter) and it ran great...after a little while it was pumping fuel. Hooray! Not wired backwards after all. While I'm there I replace the fuel filter and button everything up.

I use the "turn the key on" method several times to recharge the fuel system, checked at the fuel rail for pressure...all looks good. I did, however notice my ceramic jumper wire was getting warm. So, before I try to start it up, I replace it with a heavier gauge wire. Then I cranked the engine to start it...cranking for 5-10 seconds and just about ready to fire when I see SMOKE coming from under the hood over by the relays. Go to look and see two fusable links fried. Both are orange (20 ga) and both come from red wires. One is fastened to the center with an eye terminal, the other to the edge with a quick-slide type connector. (this fastening point is the starter relay...I think????).

OK...for the help. Why would jumpering the ceramic resister fry the fusable links...or did it? Is there likely a short or ??? somewhere else that is the actual problem? I've ordered (won't be in 'til Monday) another ceramic resister, but not sure mine is bad since it's labeled at 1.1 Ohm and tests at 1.5 ohm. I will replace the fusable links tonight. Another thing...I notice a very faint buzzing noise with the key in the run position...seems to be coming from the power distribution center area...but lower down. I don't ever remember hearing it before, but then I'm not usually under the hood with the key on and the engine not running. Could whatever is making the buzzing noice be a faulty part that is causing a short...causing the fuel pump to quit...eventually frying the fusable links?

Help!!! I've got all weekend to fix it...but don't want to chase phantom electrical issues if it's something you folks have heard or or know about.

Thanks a bunch in advance.

Jumping the ceramic resister would not burn the fuse links.
The buzzing sound is normal, it's the IAC setting for startup.
You still have a short to the fuel pump or the pump is wired backwards.

Well, must be a short somewhere. I was very careful to wire the pump correctly, even noticing that the terminals on the pump were opposite from my original one. It is also pumping correctly when powered by both the jeep and with an external power source (don't laugh, I used a battery charger set to 2 amps to ensure I had positive and negative correct), and connected it to the pump harness at the fuel filter.

I'm at a loss as where/how the short occurred since no work was done immediately prior to the problem. I did install a new radiator about a month ago though, if that could be related.

If it matters, I have continuity between both ceramic resistor leads, and between the leads and ground (with them disconnected from the resistor). I also found continuity between the power wire to the fuel pump and ground, but I think that path is provided through the pump motor as it showed about2.5 Ohms resistance.

Any idea where to start looking for the short?

If the wires where on the pump wrong it would cause a short when using the vehicle electrical system to run it, but would not when the power is from the charger. The pump will pump some running backwards.
The +/- wires are wrong on the pump causing the short.

I suspect Langer is right, but before you yank the pump again, you could check for a short in the harness. Just unplug the fuel pump back at the tank, and test with an ohmmeter if you have one, or just turn on the ignition and see if you can detect a load on the harness. That should be easily done by disconnecting the ballast resistor jumper. Now reconnect it and look for a spark. If there's a spark, there's a load that shouldn't be there, signifying a short in the wiring.

Problem found!!! After replacing the fusable links...and since I was fairly confident I wired the new fuel pump correctly, I unplugged the fuel pump at the harness connector by the fuel filter. Also had the ballast resistor (ceramic resistor) disconnected. Turned the key on to run...no problems so far. Then to start position... no starter, but it did started smoking a fusable link again!

This told me that the fuel pump and ballast resistor were NOT the problem (since they were disconnected). Frustrated, I sat down and tried to think of where a short might be...then remembered the only thing I had done recently was to replace the radiator and TPS. Pulled the grill and found I had pinched a wire with the new radiator...the orange/black one leading to the ballast resister and to the fuel pump!!!

Now that that is fixed, I have to tackle the no-starter problem, which I suspect is a mis-wired starter relay (since I had all four wires off at once to replace two fried fusable links.

Does anyone out there have a picture, or diagram...or can describe to me which wire (by color) goes to each of the four spade connectors?

Thanks for everyone's help...it was a short after all. Good news...I have a new fuel pump (and a spare) and fuel filter, and have learned lots in the process.

Now...for that starter relay problem....Mmmm

where is the ballist resistor located? Not to hijack but I discovered a '94 country I am building now has no power to the fuel pump and it did have power last time I started it (about a week ago).

Not sure about a '94, but on mine ('89) it's on the drivers side fender inside the engine compartment...near the front. It's a white ceramic piece about 3 inches long with a lead connected to each end.

Flyfisher said:

Does anyone out there have a picture, or diagram...or can describe to me which wire (by color) goes to each of the four spade connectors?

Click to expand...

I posted a pic in your other thread on this subject.

this exact thing is happening to me on my 94 xj country...Im going to go check it out. How did you connect the 12v straight to the pump, after the relay?

well I pulled the pump out of the tank, stuck it ovenight in fuel/cleaner, then diesel to see if it would clean out a little, then ran it backwards so it might reverse pump out some junk, then after reading around I hooked it straight up to the battery and it makes noise but no squirt. then I smacked it around with my rubber mallet and tried again...no luck.


gotta buy a new one.