Hello all, I need advice on a random no start. Fuel pumps get no power. But when I jump fuse 4 to any other hot fuse car runs fine.

what Ive done: changed computer, changed frp(tried 4 different ones) new cps
swapped ignition amplifier and coil(although this seems fuel related)

All of the above made no difference, and I have checked grounds. Where do I go next??

Thanks in advance for your responses
dhall

I just pulled out my wiring diagram book and tried to track this down for you. As always don't take my word for it but double check what I'm saying.

The first thing I would check is the underhood 25amp fuse located near the battery. I recently had a problem with this fuse and found that the small white fuse holder had degraded to the point of being a fire hazard. Power to this fuse holder comes directly from the battery so the condition is extremely important and extreme caution should be exercised.

The power to fuse #4 appears to come from the main relay located under the glove box which in turn looks to get its power from the under hood 25amp fuse.

The main pump runs off fuse #6. Fuse # 4 powers the tank pump and fuel injection.

I do not thinbk the 25 amp fuse is used in the '93. It is not in the '91 I have.

rhaire you are correct. No 25 amp fuse. But connected to the positive terminal is a connection for four new plastic case fuses, one for the A/c, ABS
Ignition and main. I replaced all of these fuses and the battery terminal and all was well for a while (don't know if that was just a coincidence) I have most recently bypassed the main plastic fuse mentioned above and gone straight to the battery -- no difference.

There is power to the big red wire at the relay -- its just that the power is not making it to the fuse panel and hence the pumps will not run. When I jump
fuse 4 to any hot fuse car starts and runs fine.

I also check pump wiring and It was intact. Should I try yet a 3rd 951 comp.??

thanks
danny

"There is power to the big red wire at the relay."

Are you talking about the main relay? I would probably suspect a bad main relay next. Relays that supply fairly high currents tend to fail first. The main relay supplies power to Fuse #4.

The wiring diagram manual I have is a little confusing. On the fuse box diagram they show the main pump running off of #6 but if you look at the diagram for LH2.4 they show the main pump running off #4. So I'm not exactly sure but it sounds like its #4.