GokieKS

Hello CL forums! Have a question that I hope I can get some helpful answers on. But first, a little bit of background:

I bought a clean and low-mileage 92 SC300 5 Speed last year, and then put it in storage over the (terrible Michigan) winter. The car was originally intended to be a summer and project car (eventually doing a 2JZ-GTE swap), but due to a possible work relocation, I've been putting off any modifications and instead planning to DD it and sell my other car, a 2005 Saab 9-2X Aero (aka Saabaru, as it's mechanically a WRX) that was my winter driver. Anyway, I didn't drive the SC too much before putting it in storage last Nov, but it seemed fine.

But when I got it out of storage earlier this year (end of March), it ran fine until suddenly it just died and refused to start, leaving me stranded in a shopping center parking lot. After determining it wasn't a battery issue, I had it towed to a local shop, and their diagnosis was a bad fuel pump ECU. I wasn't too familiar with this (apparently somewhat common) issue on the SCs, so I did not know of the FP ECU bypass mod, and just had them replace it with an OEM part.

Fast forward a little over a month to yesterday, and the same thing happened again. The symptoms being the same, I obviously suspected the FP ECU again, and with the new unit only being a few weeks old, I had it towed to the same shop. They looked it over and confirmed it was indeed the FP ECU again (which I more or less knew after doing the Fp / +B jumper trick that I came across while doing some research), but they said that the cause of it going bad again was the fuel pump itself, drawing too much current. I was then told that they would be able to replace the FP ECU under warranty, but would have to replace the fuel pump itself as well to get warranty on the FP ECU from the Lexus parts warehouse they got it from. The cost of the FP itself would be about $530, on top of the $500+ the FP ECU cost me last time, and that's not including labor.

Obviously that's money I'd like to save if I can at all help it, so my question now is, if I perform the ECU FP bypass, would this (apparent/supposed) higher current draw by the FP itself cause any problems? The shop obviously won't do the mod for me, being an non-factory and "possibly unsafe" work, so I'd have to do it myself, but I want to be very careful that it won't cause any issues before taking this risk on my own. So any help is appreciated.

KahnBB6

iTrader: (5)

GokieKS, welcome to the forums!

I cannot speak from experience on the Fuel ECU bypass as well as other members can (haven't tried it yet myself) however I can suggest that you go to Denso's own online sales website where you can buy the same factory pump kit from them directly for a much cheaper price.

The Fuel ECU unfortunately is Toyota/Lexus only. Further, one or two members have already tried sending those units to Tanin Auto (who perform engine ECU capacitor service/repair) and they were informed that the units were not serviceable/repairable even when cracked open.

I believe there is a slight update to what the 12V Mod basically is but now involving a relay setup of some kind to make sure the fuel pump is shut off when the engine stalls or fails in the event of a wreck. I do believe that has been the chief concern when doing the 12V Mod the traditional way. However, the best up to date source of information on that modification is in the thread itself. I believe that Ali SC3 had some thoughts on it recently.

Ali SC3

iTrader: (10)

it was not the factory fuel pump (unless you dropped a gte pump in there), it was the fact that the "new" fuel pump ecu has been sitting on a shelf for many years meaning the components were just as old and failed after a couple uses. it happens.

if you bypass with the 12v mod it will work, but you loose safety cut off of the fuel ecu, as in the fuel pump can run with the motor off and in case of an accident that is not a good idea as you can imagine and could be life threatening... that being said people do it all the time... but personally I would never do it the quick way without a relay.

correct thing to do is to replace the fuel ecu with a working one, or replace with another working one AND then do the 12v mod with a relay so the current isn't going through the fuel ecu and you get 12V (good for gte swap) and retain safety features (good for you know... living).

the last options means you need a working fuel ecu, and do the 12v mod with the relay. generally though if you can just find a good used fuel ecu then that would be the quick fix.
I have been turbocharged for years and I use the fuel ecu still. if you find a good condition one it will last a long time.

I am surprised Tanin cannot fix it, I thought when it was opened in that other thread they saw the capacitors inside... maybe its not readily available or that wasn't what was failing, hopefully they will chime in and let us know what the deal was.

GokieKS

Wait, the 12V mod with relay requires a working FP ECU? I was looking through the 12V mod thread and I thought this was the instructions for doing the 12V with relay mod, and it doesn't seem to indicate the need for the FP ECU:

Or are you talking about doing something different?

I'm not against getting a new (old stock) FP ECU, per se. It's just that considering the apparently common problems with them, that the shop may not be able to get a replacement under warranty without a new fuel pump (even if we don't believe the fuel pump is an issue), and that they may not be able to get it even with a new FP if it's not ordered from the same place (per KahnBB6's advice I looked at sourcing the Denso FP online, and now I'm wondering if I shouldn't maybe just get the GTE fuel pump in preparation), I'd feel pretty annoyed to throw more money at it instead of bypassing the problem altogether.

Ali SC3

iTrader: (10)

if you are getting a denso TT pump then replace fuel ecu with the stock n/a one and do the 12v relay mod, cause the TT pumps will burn the fuel ecu out when no relay is used.
You can also swap to a TT fuel ecu unit that requires some wiring or run the 12V mod with a relay so the fuel ecu doesn't burn out.

what mitsu guy said uses a relay but it still turns on and off with car's power (not the output of the fuel pump ecu like I was saying), so you would still have to pull the key in an accident cause the fuel ecu gets power as long as the key is not in the off position.
the only way to retain the safety functions is to have a working fuel ecu, or a standalone ecu that can control the relay to turn off when rpm's are 0.

you can bypass the problem altogether without the relay, just as long as you are aware that the safety stuff is bypassed.

I know its a common problem, and lack of good options makes people bypass all the time, but I worry how many people out there have no idea that their car could burn down in an accident rather easily. After seeing how Paul walker went out, I rather not mess with anything that can cause fires. normally when you add more power you add more safety features, not disable them completely. If you are knocked unconscious in an accident that also causes even the tiniest fuel leak I can guarantee you in hindsight you would have paid any amount of money to have a working fuel ecu.

TaninAuto

It's not that we couldn't, we just aren't going to attempt it. The effort involved vs the cost of used replacements on the market doesn't make sense from a labor standpoint. From what I remember the whole thing was potted or had some type of glue over everything so it was not as simple as taking out components and putting new ones in.

GokieKS

OK... so I assume the Denso NA pump would need to be replaced (with either the Denso TT pump or something like the Walbro) when doing a GTE swap, correct? In which case it really doesn't make much sense to replace the pump with an NA one if I'm going to need to replace it again down the road.

And to make sure I understand the 12V relay mod that make use of the FP ECU:

FP ECU Power -> Relay Control + (86)
FP ECU Ground -> Relay Control - (85)
Battery Positive Terminal -> 30A Fuse -> Relay Input (30)
Relay Load (87) -> FP Positive
Vehicle Ground -> FP Negative

Does that look right? If so, seems reasonably straight-forward, so I'll probably just buy a used NA FP ECU and do that.

Ali SC3

iTrader: (10)

I think you have a couple pins switched around but you have the basic idea.

RXRodger

iTrader: (2)

Hey Ali, I guess those that have done this have not had trouble with the relay staying picked up when the ecu cuts to 9v since that is the signal being used to fire the relay?

Ali SC3

iTrader: (10)

9v is above most automotive relay switching points so it shouldn't cut off.