Good Fuel Pump, Bad FPCU?

[desertq45]

I put a new fuel pump in my 1990 Q45 3 years and 30k miles ago. It has been fine until just the other day. The symptoms were classic as per all the posts in this forum, and I bypassed the fpcu with a ground and the pump ran fine.

I pulled the fpcu and opened it up to find the square capacitors? (the black square electronics screwed to the side of the unit) burned up/melted. This is the original fpcu.

I had a spare and put it in and the car starts and runs fine now. There is no humming (other than when the key is turned initially and the pump builds pressure) and the pump is as quiet as can be.

So I'm wondering if the fpcu just finally had had enough of hhe AZ heat and failed w/o the pump contributing to it?

Is is possible for the fpcu to smoke if the pump is good?

Anyone have any thoughts on this? I searched about 20 threads and couldn't find anything other than "always replace both at the same time" which I obviously didn't do with the last pump (same fpcu) and it may be my problem.

Thanks,

[3Q Jay]

those would be the power transistors. the often fail as a secondary to the undersized capacitors.suggest you change your fuel filter, as the additional strain to maintain spec pressure is probably what caused your previously overstressed (original) FPCU to finally die.hold on to your blown one, i'll fix it for you cheap in a few months---all my stuff is in storage right now.

[desertq45]

Ok, at least I was on the right page there... I changed the fuel filter when I swapped the fpcu thinking that it may have become clogged/restricted and put load on the pump and hence the fpcu.

The car is running great, but I just wanted some confirmation that I was on the right track with my assumption that the fpcu died independent of the fuel pump. The first pump went 140k miles, this current one has less than 1/4 that and the tank was cleaned when it in.

So it is hard for me to believe the pump could be bad, thus killing the fpcu. Also, there isn't the tell tale humming/noise I have read about over the years (although it was present when I replaced the original pump-- yet at the time the fpcu wasn't burnt and looked fine when I opened it up-- so I left it in).

My assumption is that the original fpcu may have been stressed with the original pump as is was failing, but still lasted another 3 years and may have finally been pushed over the edge by the heat in AZ and perhaps a restricted filter. The fpcu I put in isn't new, bought it years ago as a spare from someone on this forum... but electronics are electronics so it should be fine I suppose. I just don't want to lose another one if it is ALWAYS caused by the pump.

Finally, I wired a toggle switch to the white ground on the fpcu connector that is used to bypass the fpcu... to a known good ground. My logic is that IF the fpcu fails again, my daughter who is taking the car to Tucson tomorrow can flip the switch and limp it back to Phoenix... any issues you can think of with this arrangement? I assume with the switch open, the additional 14ga wire from the connector to the switch won't change the resistance to the pump?

Anyway, thanks a bunch for the reply... and I'll send the original fpcu to you to rebuild when you are ready.

[3Q Jay]

yes, that should work. did you hear the pump speed up to full rpm when you threw the switch to test?

drove thru scottsdale/phx on 05 aug this year---in the afternoon with the silver 94. registered 117°F on the outside temp gage. when i stepped out at IoS, felt like my lungs were burning. the g50 did fine, though.....

[desertq45]

Yep... worked like a charm.

This summer in Phx was BRUTAL. It started nice with a mild June but got even in July and August. 117 was a common high and not at all fun.

FYI IoS is moving to a new location in North Scottsdale off the 101 and Frank Lloyd Wright... much more convenient to yours truly. I've been getting the emails advertising a "clearance sale" for a week or so now. IF you brave the heat and come back they will be in a different place...