New MPI Relay; pump still won't run unless hotwired.

[JusMX141]

Working on a '92 Talon TSi FWD- it's a customer's car, almost identical to my white TSi FWD shown in my Avatar. The car has around 115k and it is pretty much stock.

The owner brought it to me complaining that the car kept shutting off under boost. After asking a ton of questions I felt sure it was fuel cut from a boost leak in a 15-year-old car. I patched a few pinholes in the upper intercooler neck (where they always leak) and I figured I had fixed the problem.

I took the car for a test drive and about 10 miles from home I heard the MPI Relay click off and the car died on a back road in the middle of nowhere. I pulled the radio out and beat the crap out of the MPI Relay, and it never fired. I called the little lady and had her bring a couple pieces of wire to me and I rigged up a jumper wire to the firewall to hotwire the pump and get the car home.

Brought it home, removed the jumper wire, and the car fired up as if nothing happened. Gotta love DSM's! I figured the MPI Relay was shot. Bought a new one from the dealer to the tune of $85 (wow, did they go up in the past 2 years!) Put the new relay in the car, took it for a drive. I drove it on 3 different occasions over a period of 7 days without a lick of trouble. Then, on trip #4, I was again about 15 minutes from the shop when I heard the dreaded "CLICK!" Dead. This time, I had the jumper wire with me (I made a custom wire with a spade terminal and a built-in fuse at this point.)


So the new MPI Relay obviously did not fix the problem. How come it runs fine with the pump hotwired but refuses to run on the relay?

I've searched on here and found posts where guys say there could be a bad ground to the relay....I checked that. Another suggestion was that the ECU could be at fault. I don't have a way to test the ECU, but I removed the cover and it doesn't seem to have leaking caps....although that doesn't mean there's not a problem.

But here's yet another possibility one of my good DSM buddies gave me....a bad fuel pump. He's telling me that it's possible that the fuel pump is going bad and drawing more amps than the relay will allow, which overheats the relay and clicks it off. Anyone had any experience with such a situation, or is it the ECU for sure and this theory is faux?

Thanks in advance!

 

[tqmx1]

Well you have a Polish blueprint swap the ECUs see if it follows the unit or stays with the car (my guess the CAPs took a dump). When the wifes ECU went bad every thing looked good but once the CAPs were pulled you could see the leakage.

 

[JusMX141]

I had thought about that, but I didn't want to risk there being something wrong with the car that would ruin either one of my socketed EPROM's. I'd hate to burn up a $300 ECU testing a customer's car.

By the time I drop $50 on a used ECU to test the car and risk having it turn out to be junk, I might as well have the one that's in the car rebuilt for a few dollars more and know what I have.

I was just seeing if anyone out there has some insight before I just send the ECU out to be checked.