Electrical signal not reaching fuel pump

[pwpanas]

Originally Posted by A.BuckShort

OM PART # 89661-14580
Understand interchangeable with same configured 1992-95 Supras, 1992-05 Lexus 300s (and possibly Lexus 400s)? Is that correct? If so would the Lexus units have same OM part # 89661-14580?

Yes, he’s baaaaaaaack..........!

Greetings. You may remember me, the hapless bozo who first checked in here 2 whole months ago, inquiring if anybody knew why aforementioned vehicle kept stalling and not starting because of no electric signal getting to fuel pump.

Got some good advice here, including that problem may be in fuel pump ECU (the smaller, dedicated one), how to test for that, and also a feasible workaround with a fused direct wire ignition-to-fuel pump. (Had already replaced the fuel pump, fuel pump ECU, cleaned throttle, etc. – nada!) Further testing suggests it’s the MAIN (larger) ECU—which I understand may be common in Supras.

Seeming confirmation: shipped ECU core to Cardone Industries in Philly for rebuild and return. Came back as “ECU cannot be repaired.” No reason given, but my understanding is it’s the ones with fuel pump signal, circuitry, or fuel injection issues that are irreparable.

No great success finding a replacement unit, so far. Now understand can also take rebuilt or salvaged ECU from the years 1992-95 for above, as well as Lexus SC-300 and possibly SC-400; so still looking. Leads on unit or where to look are appreciated.

Since I don’t recall losing any other ECU-controlled functions at the time fuel pump quit, it looks like we may be able to get by with the existing crippled unit combined with the workaround suggested by Phil, for fuel pump portion. However, if possible, first would like to take another shot at maintaining the integrity of the structure with a replacement ECU unit from Supras or Lexi. Leads appreciated on available unit or even good places to look, and also would the applicable Lexus ECU have the same OM part #? Or would I at least have to determine if also automatic, nonturbo, non-Cal. emissions?

(FYI, have Googled/eBayed some possibilities. Tanin Auto Electronix (rebuild/return service in Racine, WI) says they will try to help look for a working replacement, but understand that may be kind of pricey if found.

Also tomorrow planning to contact ZK boys (aka SIA in Illinois) who have listed 1993 Lexus, naturally aspirated, SC300 ECU – but unsure yet if that’s for an auto trans, without Cal. federal emissions, or even it’s not actual unit available, but another inapplicable rebuild-return situation, as most of these turned out to be. Emailed inquiry Monday to OEM Auto Computer Parts in Miami, but have not heard back.)

I really appreciate this forum.
I can also be emailed directly at reb1000@sbcglobal.net.
Thanks.
Roger Burke

[Those gangsters in the supermarket parking lot who kept asking if I wanted to sell this sucker are now starting to look like a real missed opportunity ]

The workaround should be fine. Here's why. That fuel pump ecu's only job is to switch the fuel pump to 9v (vs 12v) under vaccum (i.e. no boost). This has two extremely subtle and nearly useless benefits:
1) on really long trips (200mi+), the fuel can warm up a bit ... which can affect the accuracy of the fuel pressure regulator to a very small degree. At 12v, the fuel pumps more volume, which means fuel takes more trips through the return line...eventually warming the whole tank of fuel up a bit. If I recall correctly, you'll run slightly leaner with a warmer fuel pressure regulator...which will actually improve your gas mileage. Conservatively, just don't push the boost to the max during a very long road trip if you're using the workaround.
2) running at 12v full-time consumes a bit more electricity on average, which is very slightly harder on the battery & alternator...and of course consumes a very slight amount more fuel.

Contrast that with many single turbo supras that run 2 or even 3 fuel pumps full time at 12v. I'm almost 100% sure there are no upgraded fuel system kits available for the Mkiv that provide for 9v ... especially on pump#2.

Oh, and for what it's worth, some aftermarket fuel pumps provided with aftermarket upgraded fuel kits actually can't even reliably run at 9v (eg. Walbro).

As most know, I bought my '94 Mkiv TT new in December '93. I'm as much of a 'purist' about keeping factory features/functionality (as much as practical) as almost anyone -but- I sincerely think the 9v fuel pump ecu/feature is superfluous. My advice: trigger a relay to run a new (fused) fuel pump circuit off any other circuit tied to the ignition and don't give it another thought.