New Oil Pressure Sending unit causing Fuel Pump to run constantly (Page 1/2)
Toddster JUN 27, 04:22 PM
I'm rarely stumped, but this one has me buffaloed.

I replaced the wiring harness on my 1988 Formula with one from a 1987 GT after rodents had eaten some of the wiring. The only difference in the harnesses are the alternator, which I changed to a single wire configuration, and the oil pressure sending plug and sender unit.

With the original sender and wire, the car was fine, but when the oil pressure gauge started jumping about I knew it was time for a new sender. I took this opportunity to upgrade to the 1988 version.

I wired the Orange/Black wire to terminal C, the Tan Wire to Terminal A, and the Tan/White wire to terminal D....So why is the fuel pump running all the time now?

BTW, I changed the relay, it's new as well. One thing I noticed is water in the top of the sending unit, the rubber gasket may not have sealed very well so is it possible a short happened? Fuses are fine.

[This message has been edited by Toddster (edited 06-27-2021).]

IMSA GT JUN 27, 05:23 PM
Todd, there was a discussion on this here:
https://www.fiero.nl/forum/Forum2/HTML/145174.html


quote
Originally posted by Skybax:

I've read people doing conversion and new 1988 style doesn't last long, shorting out, or fuel pump continues to run after ignition off...

Would like to get some feedback on this from somebody who has been there is knows for sure, thanks.




I don't know if anyone on that page could assist you.
Toddster JUN 27, 05:55 PM
I found the problem....Yep, a BRAND NEW sending unit and it is crapola. I swapped it out with a unit from a project car I have and BOOM, works like a charm. I knew it could not have been ME!

Anyway, live and learn. Cheap parts are cheap for a reason.
Skybax JUN 27, 08:20 PM
All the new AC Delco 88 oil senders are Made in Mexico.
Dennis LaGrua JUN 27, 08:47 PM
If you dislike the new Mexican GM sensors, and trust your fuel pump relay, then you will not need the redundancy of two fuel pump circuits. In that case you can just use a simple two lead oil pressure gauge sensor or add the redundancy with a second relay mounted in parallel next to the OEM unit. We have seen a lot of batteries go dead with NEW defective oil pressure sending units. In some cases they pinned the needles on the oil pressure gauge.

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fierofool JUN 28, 07:38 AM
My experience with 3 different sensors was a Standard Ignition sensor blows fuses, an ACDelco keeps the gauge pegged and the fuel pump running, and another ACDelco blows fuses. New relay didn't resolve any issues except that the fuel pump would shut off with the ignition. I'm running with the sender unplugged and the gauge pegged and plan to go back to the old style sending unit.

[This message has been edited by fierofool (edited 06-28-2021).]

pmbrunelle JUN 28, 08:10 AM
88-style senders (aftermarket, not original Fiero) haven't been reliable for me, but on my Fiero the sender is catching rain from the decklid vent.

I'm going to make a rain cap for it.
Toddster JUN 28, 08:26 AM

quote
Originally posted by Dennis LaGrua:

If you dislike the new Mexican GM sensors, and trust your fuel pump relay, then you will not need the redundancy of two fuel pump circuits. In that case you can just use a simple two lead oil pressure gauge sensor or add the redundancy with a second relay mounted in parallel next to the OEM unit. We have seen a lot of batteries go dead with NEW defective oil pressure sending units. In some cases they pinned the needles on the oil pressure gauge.




It is worth consideration. however, I think the idea of redundancy for the relay is unnecessary. Seriously, how often do relays go bad? I think just keeping a spare relay and hand tools on hand (standard fare for ANY fiero owner) is the way to go. For the time being, I just put in the used sensor which seems to be working fine.

But as these parts become less popular over time we are inevitably going to end up with cheaper auto parts manufacturers taking up the role of filling the demand for the dwindling market. The results are inevitable.

hopefully someone like the Fiero store or other, will pick up the gauntlet.
2.5 JUN 28, 11:54 AM

quote
Originally posted by Toddster:

I found the problem....Yep, a BRAND NEW sending unit and it is crapola. I swapped it out with a unit from a project car I have and BOOM, works like a charm. I knew it could not have been ME!

Anyway, live and learn. Cheap parts are cheap for a reason.





Little did you know thats the best of three usual stickers found, lol

I dont know if any are made here anymore.
pmbrunelle JUN 28, 12:26 PM

quote
Originally posted by Toddster:
For the time being, I just put in the used sensor which seems to be working fine.



Does your used sensor get rained on, and it still works OK?

Or is it shielded from water?