Ayotriple

Maybe someone here can point me in the right direction… I’ve searched and have found people with similar issues but no one has posted a fix. I have a 92 SC400, stock motor, walbro 255 fuel pump and 12V mod

A few days ago I was driving to work and my engine just died, fuel pump turned off and the car just coasted for a bit… all the dash lights were still on… pressing down on the throttle did nothing. I put the car into neutral turned the key off then on again I heard the fuel pump prime and the car turned back on and ran as if everything was fine…

Today on the way home from work the car died on me 5 times… one second the fuel pump is doing its thing (I can hear it whining/priming) then the next second it’s off and the engine dies until I either put the car in neutral and turn the key off and on until it starts to prime again or sometimes when it dies the car just coasts for a bit until the fuel pump starts priming again and the engine turns back on. Would this be the results of a bad fuel pump? Any help is greatly appreciated. Thanks in advance.

SexCoupe

iTrader: (6)

Is the car dieing while you are accelerating or while coasting/slowing down? how is your idle?

KahnBB6

iTrader: (5)

I'm not familiar with the lifespan of Walbro fuel pumps but assuming that component itself is okay, a couple of questions about how you did the 12V Mod:

Did you use at least a 10 gauge wire from the battery positive connection with an in-line 30A fuse wired in the same gauge? And did you use a standard 30/40A relay in your circuit? And... did you retain the stock fuel ECU just for its safety control function in your 12V Mod circuit?

There have been a couple of variations of that DIY that people have done over the years which is the reason why I ask these questions first off.

Ayotriple

both, sometimes while I’m cruising at 40-50 mph leaving work and sometimes when I’m coming up to a stop sign as I’m slowing down it’ll just die

Ayotriple

honestly, the 12V mod was already done by the previous owner but he had the stock fuel pump in it. The wire he used did seem old and brittle so I just replaced it with like a 12 gauge wire but no fuse pretty much just jumped the two pins on the connector

Duck05

I may sound like a “broken record” on these types of issues, but the main ECU (when the capacitors begin to leak) should always be assessed and sent out to a reputable repair/rebuilder to test and repair. (I used SIA last year).

When I swapped in my rebuilt ECU spare to address similar (if not identical) issues the change in performance and behavior was phenomenal; car has never run better (but the troubleshooting included a new fuel pump and fuel pressure regulator but I did not complain replacing almost 30 year old parts).

Ayotriple

but if it was a problem with the ecu wouldn’t it be whatever problem is causing the fuel pump to cut off would be present at all time… I can still get in my car turn the key to on the pump primes then I start the car. If I let it idle for like a minute or so the pump stops priming car turns off then 5 seconds later it starts priming again and the car turns back on like nothing was ever wrong… if you don’t mind me asking, how much did SIA charge to rebuild your ECU?

SexCoupe

iTrader: (6)

Check the 12v mod to make sure the connection is tight. the previous owner may not have done a great job

Ayotriple

yeah, that’s the first thing I’m going to do, this time I’ll make sure I use an in line fuse

Duck05

My experience last year was similar to what you are saying and when the capacitors leak and effect the traces on the boards, all kind of strange, intermittent behavior ensues.

I was going to use Tanin but they are not as focused on ECU repair and opted to use SIA. They have a charge to perform an assessment and they call back with the full quote to address the issue. In my case, the repair was under $200; but it takes 10-14 days. I had a repaired/certified spare and now the SIA repaired/tested unit is my new spare.

https://siaelec.com/product/lexus-sc300-ecm-ecu-repair-return/

https://siaelec.com/product/lexus-sc400-ecm-ecu-repair-return/

Ayotriple

thanks for the input, I’ll definitely go ahead and get the ecu rebuilt/repaired.

CLass of 1

Electronics behave differently when they get hot as well. Your pump and your ECU may function fine for those first few moments but when they get a little heat in them they begin to malfunction.

I had a fuel pump issue on my RX7 similar to this and it was the relay. There are a lot of cheap and crappy relays. You may find just by buying a nice, new relay, you’ll fix your issue.

Good luck.

Nick

Ayotriple

Alright so after tracing my step checking stuff one at a time I re did the fuel ecu bypass and IT WORKS!!! Thanks to everyone trying to help