sicwhip

OK I have looked and done my research ...

I was having a fuel pump no start / intermittent problem ... on real hot days I couldn't even get the car to run at all or for 2-3 minutes before shutdown again ...

I have a walbro fuel pump so I didn't hear the pump turn on and knew something was odd ...

So I tried replacing the pump ... Did not fix the problem
Tried replacing efi relay (could be sticking open on hot days) ... Did not fix problem

After that ... I did some checks at the pump connector but every time I would disconnect it and reconnect it pump would start up again ... then I did a back probe and waited for it to happen again ... sure enough I am only getting like .5v instead of the 12v or 9v I expected to see at this point I am suspecting the Fuel Pump ECU (FP ECU) which is a known problem (read pattern failure) on the sc300/400 ...

The FP ECU was hot to the touch (not a real hot day) ... and just to verify this was the problem since I had it all open ... I decided to go ahead an test my theory ... with Key On Engine Off ... I could hear the pump running ... I got out my Heat gun and hit the ECU Heat sinks with some heat ... sure enough 30 second of heat and Fuel pump shut off ... exactly the problem I am experiencing ...

So now that I have located the problem now comes the fix ... the way I see it I have 3 or 4 options ...

1. replace with used FP ECU (Could be just as bad as mine being its 20 years old)
2. replace with NEW FP ECU (cost prohibitive and NEW stands for Never Ever Worked)
3. Do the 12v Mod (I think this has both pros and cons to it ... please weigh in and correct me if I am wrong)
4. Attempt the fix I am proposing (See below)

As for option 3 I may end up doing this if my fix does not work but some pros cons I can think of:
- pros
- better response if I do end up getting a turbo
- no more issues with overheating ECU
- cons
- constant 12v all the time (premature pump wear)
- fuel maps not tuned to use extra fuel at idle (ie will run rich) (not sure about this one)

So finally my proposed solution (option 4):

I was thinking this thing has a huge heat sink on it ... and heat sinks are designed to air cool a component by conducting the heat away from the unit ... well I'm thinking this is in a quarter panel (sealed) with little to no air flow ... So I think if I get a small (50mm) 12v case fan for a computer and mount/zip tie it to the heat sink and tap into the 12v (its only .14Amps) it will be able to dissipate the heat better ...

So please ring in on this and let me know what the community thinks ... Its a cheap fix (if it works) ... approximately $12 for the fan and a couple of wire taps (temporary) will solder if all is good and a few zip ties ...

Any thoughts / comments are appreciated ... I used the following links as my references ...

https://www.clublexus.com/forums/per...tures-faq.html

https://www.clublexus.com/forums/per...ed-help-4.html

O. L. T.

iTrader: (17)

As long as my car, and the other millions of SC's run without issue with a stock ecu, you have not located the problem. The ecu has a job, the fuel pump has a job. If the fuel pump has too much drain then you would simply wire a relay into the system and the ecu would kick the relay. Simple.

Clean400

iTrader: (2)

Just do the Fuel Pump ECU bypass and be done with it. You're looking way too much into this.

sicwhip

Thanx for your replies ... A few questions ...

OLT:
I do believe the problem is more prevalent than you think ... it is my Fuel Pump ECU not the main ECU which is why I think people do the 12v bypass when they experience this problem ... And if this is not my problem why does the fuel pump shut off when I apply heat to the heat sink ... just as if its a hot day (I live in florida) ... I do not have a schematic for the internal workings of the Fuel Pump ECU ... but I assume it has some sort of thermistor/bi metallic strip in there to prevent circuits from frying ... as it cools the unit continues to work as advertised ...when the unit fails I can also do the diagnostic port bypass and car runs again ... I am not sure of your suggestion could you clarify ... what do you mean by pump pulling to much drain (are you referring to amperage) ... and if so add a relay ? can you explain how this would help ? ...

Clean400:
"Just do the Fuel Pump ECU bypass and be done with it. You're looking way too much into this. "

As OLT has pointed out already "The ecu has a job, the fuel pump has a job" So the engineers who are not dummies ... from what I hear ... put the Fuel Pump ECU operating at two speed in for a purpose (what that purpose is I have no IDEA) ... bypassing it just means liability if I were working in a shop or ignorance on my part for not being informed enough to make that decision ...

Thus the reasoning I am asking for opinions on this topic ... Give me the pros and cons so I can make an informed decision ... Again I appreciate your input ...

estomax

iTrader: (2)

most cars don't have a fuel pump ecu, the purpose of it is to slow down the fuel pump to reduce noise and wear on the pump when low throttle conditions are present 99% of the time. This is a reliability / luxury trick the engineers did, and it is perfectly fine to bypass and have the fuel pump function like many other cars on the road (full speed all the time). It is worth a try, if you are having issues driving the car with it present. if you have a stock exhaust and the fuel pump whine gets to you, then maybe look for a new fuel pump ECU.

Marko

sj408

iTrader: (6)

As stated before, your looking WAYYYYYYYYY too much into this. Do the 12v mod and be done with it, Before i knew how to do my own stuff a lexus/toyota specialist (head mechanic at lexus of las vegas for quite some time) performed the 12v mod on my car and has performed flawlessly since , though i have since upgraded to a TT pump for more fueling.


Id assume the fuel pump ecu was built 2 stage to keep noise at low speeds down and to help prolongue pump life. But honestly who knows by how much, i ran my 12v mod for like 4-5 years on the oem pump from 1993 before i replaced it so i doubt youll ever see the "cons" your worried about.

Clean400

iTrader: (2)

This thread gets created a billion times on this forums so sorry for not being more thorough when I responded to your question. I was just trying to save you the headache of looking into it more.

The fuel pump ECU is there to put less wear on your fuel pump by lowering the voltage so it's not running at MAX voltage all the time. Also probably keeps the inside of the car quieter but the difference is probably not even noticeable. The fuel pump ecu is an over engineering choice by Lexus and it's not even needed. Most cars don't even have one.

I had this same issue a couple years ago. I did the fuel pump ECU bypass and my car has worked great ever since.

If you want your car to be 100% factory then buy a new fuel pump ECU. Simple as that. I would just recommend doing the bypass. It's a 5-10 minute fix and you can put this whole problem behind you. There are probably thousands of forum members who have done the bypass without issues.

Vrank

iTrader: (4)

The difference in noise is noticeable if you have an old walbro. If you're not chasing huge power just bypass the fp ecu. Maybe throw in a new pump while you're at it if your car has a million miles on it for insurance that increased load doesn't push it's already worn state over the edge. If the car is lower miles with fairly regular maintenance and has always used good gas in a timely manner, don't worry about it.