1990 XJ 4.0 auto trans, fuel issues or?

Along time ago this jeep was my first vehicle (14 years old just for driving around the neighborhood) I had issues keeping it running, electrical system must have suffered a failure at some point in time.
Sometimes it will pump fuel just time, other times, nothing, I have good fuel in it, and was gonna replace the fuel filter tonight, but when I turned the key with no fuel filter in, nothing, I have tested it this way before and have gotten fuel flow so its not a safety built in, any ideas? Ive been told possibly the computer, and by the numbers the one thats in it is not the original one (wrong number) but sometimes it works great and sometimes not at all. Last night it left me stranded, low electrical out put, i had a boost box, it would crank, start and then die instantly. same thing tonight with a fresh battery, except as of a couple moments ago it wont crank at all.

today I put a fuel filter in it, it starts and runs for about 1 minute and then dies out, fuel pressure gauge reads zero

please help!

Ok, modes of fuel pump operation:

Key to ON, fuel pump gets 12 volts from the B Latch relay for about 3 seconds, then the ECU cuts off the relay's ground and the pump stops.

Key to START, fuel pump gets 12 volts from the starter relay while the engine is cranking.

Key at ON, engine running from idle to just short of WOT, the fuel pump gets about 6 volts from the fuel pump relay through the ballast resistor.

Key at ON, engine at WOT, fuel pump gets 12 volts through the oxygen heater relay.

Now, when you turned the key to ON without a fuel filter you should have gotten a 3 second shot of fuel, which you did not, and that makes the B Latch/ECU/wiring suspect. However, as you said it would start and run for about a minute then die, that makes it sound as if the 3 second prime did occur, and then the engine ran out of fuel, and that makes the fuel pump relay/ballast resistor/wiring suspect.

Both suspect conditions could indicate a failing fuel pump that is presenting at different times.

I would bypass the ballast resistor (no problem doing that, it just keeps the fuel pump from being a little noisy). The ballast resistor is the white ceramic piece mounted on the driver's side fenderwell with two wires attached. Just connect the two wires together and post back results.

Hi Joe
that fixed it, thanks!

jeep<3isuzu? said:

Hi Joe
that fixed it, thanks!

Click to expand...

Heck of a lot cheaper and easier than a fuel pump, eh!

Welcome to , btw.