A fuel pump flummox

Hey all,

I'm rapidly approaching wits end with my MJ's fuel pump problems and wonder if anyone has any insight. Here's the deal: A couple weeks ago my recently acquired 89 mj died on the side of the road. I checked the harness at the pump and found voltage so I swapped the pump from my wrecked 89 xj and it ran. so, a few days later it died and this time there was no voltage at the pump so i examined the wire harness under the hood and found a bad connection to the latch relay.fixed it and it ran. couple days later it dies on the way to work, I find voltage at the pump, test the original pump on the battery and find it works. thinking that the bad connection caused my first problem, I swap the old one in and drive about a half mile before- it dies. so, I check voltage at the pump and it's about 11.9v or so. pull the pump out and its got some crap in it (its missing the sock filter) and i figure ok, thats gotta be the problem so i go get a new one. put it in and it works---for about 3 days.

yesterday leaving work it doesn't start. I have close to 12v at the pump but no pumping. I used a jumper wire to bypass the latch relay (so I can check pump voltage) and while i'm scratching my head i notice the ballast resistor on the fender is smoking. so, i don't want to buy a new pump but it looks like i have to so i want to find out what killed this one. the smoking resistor has me thinking bad ground. also, the pump assembly doodad isn't in the best shape. when i first took it apart i noticed that the motor is grounded to the return tube which is attched to the round part which seals against the tank which is where the ground wire into the harness goes. on mine the return tube had broken free of the round part so i moved the ground and attached it to another part of the assembly. that appears ok but the wire which goes into the harness is pretty small and rather corroded. im thinking i want to somehow ground directly to the frame, can this be done or will it create a problem with the computer?

this is killing me as its my only ride and I've been dealing with it for a while now.

any thoughts?

thanks,
DAN

Yeah, bypass the ballast resistor, it has probably been the root of your problems.

Yes. And refresh all your grounds since this Jeep is new to you.

seconding what's been said above. definitely ditch the ballast resistor. also, pull off the left tail light and check/clean the ground wire that lives behind it. many people do not know about that ground on the mj, it seemed to be the source of some weird intermittent fuel pump issues on my mj.

Thanks guys.

The ballast resistor is as good as gone, so that's done. The dipstick ground point and the one by the temp sender seem solid but i guess it wouldn't hurt to clean 'em up. Are there any others I should check? And how about the idea of running my own ground from the pump assembly to the frame? I was under the impression that the fuel system knows when to turn on by the computer completing the ground. Is this correct? I guess that my knowledge of the system is lacking in a few areas. For example, I don't quite get why the resistor would burn up. If anyone cares to just go on a lengthy lecture on xj/mj fuel systems, I'm all ears.

thanks again.

Dan

edit: Hellbent you beat me to the punch! that ground is total news to me

You can ground the pump directly to the body. The fuel pump ground does not run through the PCM.

Excellent, but will this prolong pump life? I'm thinking the ground may have been the reason for the smokin resistor, at least I hope so.

Those resistors are ceramic coated, and designed to dissapate heat. Over the years they break down and dont dissapate as well and eventually turn brown or burn up. they are cheap but not always required. many have bypassed it like as mentioned. unless you want an under the hood cigarette lighter