KEEP WISHING

Like the post says, they are back and with a vengeance. Lets get started... yesterday I decided to replace the fuel pump. 4th in 3 years. After getting it installed I went to crank it and didn't hear the normal hum of the start up. It would crank and run for about 3 secs before shutting down. Decided it was time to find my ole friend the multimeter. I started at the fuel pump and had .07v with key on and 12.2 cranking. Wires looked to be in good shape so I went under the hood. At the splice where the ballast used to be it was the same .07 on and 12.2v cranking. Next was the relay... jumped 87 and 30 and the pump kicked on. Tested 87 and the current was steady. 85 with the key on would start at 12.4 and after a few secs go down to 11.6. 12.2v when cranking. 86 nothing .04v.
Went over to the starter relay and got 12.4v from the cable from the battery and .07 at the fuel pump terminal in the on position. 12.2v when cranking.
Before I headed to get the matches and gasoline I decided to jump the relay one more time just to hear the pump run. Hit the key and the darn thing cranked up and ran until I shut it off. 15 mins or more. Turned the key to the on position and heard the familiar sound of the pump buzz.
VICTORY!!! Put the tools up and tried again no buzz and would crank then shut off after 3 secs.
Could this be a ECM issue or am I just missing something? Should have 12v at pump with key in the on position right?

KEEP WISHING

I have replaced and cleaned all the grounds I could find under the hood. Forgot to add that....

Firehawk068

Sounds like a relay issue to me..........................
Have you tried new ones? Maybe try swapping them around?
I may not be certain, but doesn't the ASD circuit shut everything down if it doesn't receive a signal from somewhere?
Someone with more knowledge of the ASD will probably chime in...........


Also, have you ever dropped the tank and flushed out all the rust and sediment? Could be the reason you are going through so many fuel pumps.

steelybill

I haven't checked the wiring diagrams in my service manual yet, but most cars have the fuel pump fed through an oil pressure switch after start, to prevent pump from running in the event of an accident, with engine not running.
I'll have to look that up for the Jeep....

Bill
Well, I haven't figured out how it's powered yet, but the ASD ( auto shut-down relay) is in the mix too....

KEEP WISHING

Thanks guys, I switched all the relays around and still get the same results. It still has no power to the pump with the key in the on position. I guess that would be the prime when it buzzes before cranking. Does the 1990 have the asd relay? If so where would that be at?


Just got me stumped that it would crank and run until I shut it off.(15mins of perfect idle) After I shut it off I turned the key to the on position and here the pump prime, then walk away from it for 5 mins come back and now no prime.

freegdr

If ignition key is kept turned slightly forward after starting will it stay running I wonder ?

KEEP WISHING

You may have something there... I replaced the ignition switch about 3 years ago. Right before this happened and the jeep was running perfect my intermediate wipers would only work sporadically. They would always work on high. Do you think this could be a steering column issue? Also my right side HID headlight will work when it wants too and my oil pressure gauge and temp gauge will go crazy from time to time.
Dash Ground maybe? There has been a lot of stereo equipment shoved under the drivers side dash. Bluetooth handsfree box ect...

freegdr

After install did you adjust it ? Cant hurt to try a , ignition switch can do funky things if its not getting good contact !

cruiser54

Have someone wiggle the ignition switch around in the On position while you test for power.

Also, have you done my Tip # 3?

KEEP WISHING

I didn't know you had to adjust it.... lol. Thought it was a plug and play. We may be getting somewhere now.

KEEP WISHING

Nice write up Cruiser. Looks like I have a Saturday project.

cruiser54

A half hour one anyway!!