1993 q45. Picked it up in November for a tinkering toy. Car stalled when I put it in reverse the other day. No start after that. Cranks but no start
No sound of fuel pump priming at ignition. Fuses fine. Relays all clicking and fine. Tried the FPCU bypass trick. No work. Randomly cranked and started today. Started it 4 or 5 times. Cranked and idled fine. Went out a few hours later. Cranked again. Ran fine. Few hours after that no crank. No signs of pump humming or on it's way out. Possible FPCU malfunctioning? Idk in stumped. Not much info here but idk where I'm at before I dive into the gas tank at this point

Replace the FPCU first. Good luck finding one.. I got one and it shipped from MA, so you might be in luck. I bought the FPCU and pump and later found out it as just the FPCU.

BCC93QT wrote: ↑

Tue Jul 09, 2019 6:08 pm

No sound of fuel pump priming at ignition.

This is the key in my view. you'll always hear the relay click 'off' (both of mine do) when it's working properly. Do you have a 5/16 pressure gauge that you can see what the pressure is going into the rail (after the filter)?
what is the part number suffix on a 1993 (92 build?) FPCU? the u00 are the suspect ones. the u01 hardly ever fail (circuit design improvement).

it's a 60u01. If I bypass it with the alligator clip it cranks idles and drives fine. then plug it back in and restart it. Runs and drives fine again. just sometimes it wont engage or something. I'm stumped. I'm trying to locate a used FPCU. If anyone has one up for grabs I'll take it off their hands just let me know how much

the 93 probably has the green relay in the trunk, behind the right side finisher? could be going bad.
RELAY NISS#25230-C9965

FPCU failures are usually (almost always, maybe always?) caused by a worm fuel pump pulling too much current. You run a real risk of toasting a replacement FPCU if you install it without replacing the pump at the same time.

Has 140k miles. Signs point to the fuel pump has been replaced at least once. I don't think it's the FPCU or the fuel pump itself at this point. It hasn't been an issue in 3 days and I have yet to recreate the issue. Could be heat related with a relay stuck or something. I replaced the blue relay with a known working and I have a green one in route

Fuel filter replaced frequently? One tank of bad gas can take it out.

Filters replaced. all fluids flushed over winter. still hasn't been an issue. Have not been able to recreate the issue. I have all possible relays on standby if it happens again. Have a fuel pump still in box for years.