Anyone else? Fuel pump failed 7 times now in a year

88 cherokee 4.0
Before you ask. It was not Airtex, but the ones from Napa, a few were the bosch ones, too.

This is my first post on here, although I have been on cherokeeforum.com for awhile.

Anyone else had multiple fuel pumps go bad in a short time? I really want to like this cherokee but she makes me so mad. Since I've had the thing, I;ve gone about 10,000 miles. I had to replace the fuel pump once near the beginning of the ownership, and since then I've had to replace it about 7 times. I've replaced the filter every time.

At first I figured it was because of a dirty tank... So I cleaned it, twice (removed, emptied out stuff, sloshed cleaning agent in there, scrubbed, dried, etc..). It still eventually failed again. I'm starting to get good at replacing them at this point.. I start to notice a pattern that it fails after excessive bumping around on dirt roads (WTH, jeeps are made for this stuff!), washboards, etc, so I thought it needed some new wires inside, new connectors... Put those in, and here it is failing again. 10 psi at the rail. It's been about 700 miles since the last one.

Any ideas? I mean, I keep getting free pumps from napa, and the process isn't hard to do, but why!?

Today I checked the voltage at the connection by the pump, it said about 4 V during crank. Is that the correct number?

Thanks a lot in advance.

Jamey

Check the ground wire at the sending unit connector and see how much resistance there is.

My best guess, is the real problem was never the fuel pump. Check the flow rate at the fuell rail, measure it and time it with a gallon jug. Either the fuel pressure regulator is bad (overworking the pump), or there is a damaged fuel line between the rail and the pump.

Choice two is a wiring or wire connector issue. Salt water or just dirty water splashing on damaged wires will cause a voltage drop.

NO 4 V is not high enough. Should be around 10 V or higher

Maybe your relay is going bad?

I had a similar problem with a Bosch pump from NAPA. It had good pressure while the pump was cold, then the pressure would drop as the engine warmed up. The problem turned out to be the line between the pump and steel nipple inside the tank. Instead of trimming the new rubber hose to fit the nipple, I tried to push the hose past the taper and clamped it there. After I trimmed the hose back and clamped it on the smaller diameter nipple, it held pressure.

HTH

I threw installed an upgraded bosch pump from carquest a few years ago, and I have never had any problems with it. I'm not sure if walbro makes a drop in replacement for the cherokee, but I have had really good luck with those in my other vehicles.

If you have 4v at the pump during cranking that is your problem. The pump will never reach pressure. Or if it does reach pressure it wont put out the volume to keep it there. Check your ground for the pump. Check after your relay and see what the voltage is. If its okay. Use a new wire between the relay and the pump. See if that fixes it. If it does then replace that wire.

You are changing the filter sock while you're at it, right? You probably are, but just not overlooking the simple stuff.

I had a similar issue. Engine would start, run for a few seconds then stall. See the following post...

http://www.naxja.org/forum/showthread.php?t=1083220

There's a ballast resistor on the fire wall. It's embedded in ceramic. There should be a resistance value (in Ohms) printed on it. Check the voltage going to it (should be about 13.8 VDC) Check the voltage coming out of it (shouldn't be less than 12 VDC). This feeds power to the fuel pump. After that check voltage at the pump connection, should be 12 VDC.


Ken C.

I've had a few issues with pumps in the past, never actually had a pump fail, but had everything else fail... As Electric said, check the ballast resistor, it's a big white thing, bolted to the inside of the engine compartment on the drivers side (should be right on top). You don't need to do anything except connect a multi-meter to the leads (might try cleaning them while you're at it). If that reads ok, turn the car to the "run" position, if you get a friend to help you, when you just turn the car to "run" the fuel pump should energize for 3secs when the switch first turns to this position. Check voltage here, if you put your negative to either battery negative, or chassis ground, and you check both leads, you should get 2 numbers, the higher one is the input, the lower is the output. The spec voltage for the lower should be 10V or so not 12V (higher is ok, but means you will get fuel pump hum). If it passes this test, that means you've got a busted connection between the ballast resistor and the fuel pump and will need to chase it down. If it doesn't pass this test, it means you have a busted ballast resistor, which should be an easy fix. If you find the input voltage to the ballast resistor (the higher number) is not the same as battery voltage (12.4-12.8 with the vehicle not running) This means the problem is higher up the stream. If it is further up the stream, locate the fuel pump relay (should be labeled on newer, in the repair manual if older). Check supply voltage to relay (should be battery voltage, if not, problem is further up) if ok, check resistance between relay output and input of ballast resistor, if greater than 50ohm, replace wire. Another test you can check, is jumper across the ballast resistor and see if you get battery voltage at the fuel pump connector (under the car). hope that makes it easier.

Loose connectors at the ballast resistor can cause issues also. Sometimes the little female terminals on the wire don't grasp the male terminals on the resistor tightly.

FWIW, any ballast resistor I've tested for voltage had battery voltage at one end and about 10.2 volts at the other. It's sole purpose was to reduce the voltage so the pump ran quieter.

I thought the reason for the resistor was to reduce the alternator voltage (13+ VDC) down to 12 VDC to prevent overvoltage to the fuel pump which is designed to operate at 12 VDC.

Ken C.

Electrichorseman said:

I thought the reason for the resistor was to reduce the alternator voltage (13+ VDC) down to 12 VDC to prevent overvoltage to the fuel pump which is designed to operate at 12 VDC.

Ken C.

Click to expand...

There was a TSB in 87 and/or 88 to address the noise issue. A ballast resistor harness/kit was provided to us Jeep dealers to address customer complaints of noisy fuel pumps. The resistor became a running change shortly thereafter.

4 volts is not enough, the ballast resistor would be my first guess as the culprit. Remove the ballast resistor and splice the two wires together and call it a day, even if it doesn't turn out to be your specific problem. One less thing to go wrong miles from home, the only side effect is a little bit more fuel pump noise. None of the 87's ever had it, and I've removed it from every XJ I've ever owned and never had a problem.

NotMatt said:

4 volts is not enough, the ballast resistor would be my first guess as the culprit. Remove the ballast resistor and splice the two wires together and call it a day, even if it doesn't turn out to be your specific problem. One less thing to go wrong miles from home, the only side effect is a little bit more fuel pump noise. None of the 87's ever had it, and I've removed it from every XJ I've ever owned and never had a problem.

Click to expand...

Not bad advice at all.