nonotford

I am a novice here, so I am asking what might end up being a dumb question. I'll put on my flame retardant suit in advance.

My 1990 XJ 4.0L starts fine, fuel is going to the cylinders. But then it just cuts out after a couple seconds. If I start it while giving a lot of gas, keeping the RPMs high (>4k), it'll hang out for a while. But as soon as I dip down, it cuts out.

My current hypothesis is that the fuel pressure is too low when the RPMs are low, which might tell the ECU to cut things off. But, it is only a hypothesis. I am replacing the fuel pump as we speak (the one in there now is some Bosch pump that totally does not match the OEM pumps at Napa - related to that, it shows it was made in Czech Republic, meaning it was not OEM since that country didn't exist until '93). I am praying that the new pump does the trick. Failing that, I am out of ideas. It seems that ignition is fine because it sarts right up and runs for a few seconds.

I'm a little bummed that this engine control system is not OBD compliant, meaning I can't get codes from the check engine light - which doesn't even seem to exist.

Any ideas out there??

Thanks in advance.

longtravel1

sounds exactly like what my 89 did. I replaced everything than as a last resort I replaced the fuel pump and viola! it was fixed.

capndoodles

This certainly does sound like it could possibly be a fuel pump problem

93XJRay

X2 i would check that out...

offroadnut36

I have a 90 jeep 4.0 too, and when I was putting in my new fuel pump I noticed that my old one was a Bosch 12V, which is weird cause they are supposed to be 14V. Guess what, my new pump didn't fit in the old assembly so, I ended up buying a 20 gal tank with a new pump and assembly. Now everything works great.

nonotford

OK - it runs!!

However, I have no idea what it is we fixed. We replaced the fuel, which seem to improve things *slightly*. Instead of running for 2 secondas and cutting out, it would run for about 10 seconds and cut out - woohoo...

But, standing there with beers next to the open hood, I happen to glance down and see a loose wire. I found its terminal, brushed it clean, reconnected it, and voila! The connectors were corroded so we replaced them, and it ran like a champ.

My current question is: what the hell was that? My Chilton manual is basically worthless for finding the answer to this one. Look at the image below and tell me what you think....



Thanks again for everyone's input.

bishop letov

thats the fuel pump resistor. It basically lowers the fuel pumps woltage after crnking and starting has happened. when you turn the key on and engage the starter it allows the full voltage to the pump. It allows the fuel pump to "recharge/repressurize" the fuel rail in case of a leak down situation. after the starter is diengaged the voltage is routed to the fuel pump resistor to run the pump at a reduced voltage to extent the pumps life. Once the fuel rail is pressurized it only needs to maintain the pressure and thats where the volume of the pump comes into play. Im surprised it wasnt suggested in the begining. Its a common thing for corrosion to effect the terminals. make sure to put dielectric grease on it after you have cleaned them up and if you have enough wire then loosely wire tie a loop in order to secure the connections and keep them from falling off again. cheers on figuring it out.

nonotford

Thanks BL! That certainly explains a lot!

bigjamez21

i think thats the ballast resitor