Replacing NEC K591 Transistor in FPCU - 1991 Q45

[RZV500R]

Replaced new fuel pump and filter after pump started humming loudly about a month ago. Car ran fine for a couple of weeks and then stopped again. Took the FPCU out and the noticed the solder on the IC board where the NEC K591 contacts were charred, not bad though. Also, one of the K591 transistors had signs of melting and ash around it on the FPCU body. Has anyone replaced these on the IC board with success? The pump is good which I checked by grounding the lower left contact on the FPCU connector to the bolt which holds the FPCU unit.

How risky is it to drive the car with the fuel pump grounded this way and operating at full capacity until I get the transistors to repair the unit? Previous older posts on this topic, especially the very informative post by tangalora on 10-12-2003 were extremely helpful when I replaced the pump on my Q. That post states:

"Note: I drove the car for more than a week (about 200 miles) with thisalligator clip shorting the fuel pump to ground bypassing the three-position ([email protected] to 5.7 volts, [email protected] to 8.1 volts, & fast@11 to 14 volts battery voltage) fuel pump control unit settings. Note: Online mechanics estimate the old fuel pump might last a few weeks(running full speed as it is when jumpered to ground); while a newfuel pump may last a few months in this temporary full-power state. Note: It is recommended the fuel tank be kept full whenever operating the Infiniti Q45 in this state as the fuel pump is cooled by the gasoline in the fuel tank. "

Can anyone confirm this? I don't want to risk having to buy another fuel pump, but at the same time need to have the car for short distance local runs until I can locate the parts to have the FPCU fixed.

BTW, does anyone have a used FPCU for sale, or a source for the NEC K591 transistors?

Thanks much!

[maxnix]

Tangalora was a meticulous poster, so I am not sure what your question is.

Not a good idea to run at full power all the time.

Look for used ones (may be good, may not be) ones in the marketplace Forums.

You can't possible know if the pump is "good" without measuring fuel pressures at idle and WOT.

[RZV500R]

Sorry, pump is brand new from Infiniti of Scottsdale. The transistor on the IC board is burnt out. I had 2 questions:

Has anyone on the board repaired the unit by replacing these transistors? A known source for obtaining this would also be useful.

I guess you answered my question on running the pump at full power. I don't like doing this either, but wife needs the car to pick and drop kids off at school and run errands, so have to go this route for a week or so until I can either get the unit repaired or get a new one.

Thanks!

[qship96]

Used fuel pump control modules are listed on ebay everyday for $40-60.

search posts from member "jesda", a previous Q owning gringo who replaced his transistors and documented the process.

[RZV500R]

Thank you qship96. Just ordered one off eBay.

[Q451990]

Has anyone on the board repaired the unit by replacing these transistors? A known source for obtaining this would also be useful.

I know you ordered a pump, but here's a link to the thread where I researched a source and cross reference for the parts, as well as Jesda mentioning that he fixed one this way.

zerothread?id=92777

Might be worth doing to have as a spare - but I have a few failed ones in my garage that I have never done, so I understand not taking the time to actually try it.

Heath

[RZV500R]

Excellent, thanks for the link. Prices are still the same today as in your post from 12/6/2004. I'm going to order a couple of the NTE 2985 and the 960 and try it out on the old board. Will update this thread on how that works out.

[Q45tech]

The 97 and later FPCU have a high wattage resistor bypassing the circuitry to take some of the current load off the transistors.

Even 1.0 amperes [off loaded to external resistor] could require a 15 watt resistor.................... 8 amperes x 4 volt drop =~ 32 watts............hopefully members understand why things are big and finned for cooling.