bigwhite

Thanks, but its a new battery, I can drive for 5 days and it runs perf. and starts perf. Usually when I walk off and leave it for an hour, all the sudden I loose 12v. to the fuel pump. Guess I need to look at a wiring schmatic to see from where the old fuel pump ECU was, where does the wire go to until it reaches the battery. I know through the key switch and main EFI relay. Those are both new.

bigwhite

So I was just looking at a wiring diagram on google and it shows the main ECU has to send power to the main relay for it to work. It does so after the computer sees cam and crank signals, which I no are good because I can bypass the main EFI relay and car runs perf. So it seems the prob to be the signal from the main ECU. I know rockauto does not list the main ECU, any suggestions where to get a good deal on a good unit?

bigwhite

I have to ask my own question, if the main ECU takes over after engine starts, maybe thats not my prob, because I have no initial start.

turbodremz

iTrader: (18)

I dont think it would be the primary engine ecu as those signals are sent to the fuel pump ecu and one for the 12v to the efi main, however it is possible and worth a borrow and test from someone local. Worst case spend the $$ and get an ecu from Aliga, and if its not the issue you have a spare on hand in the even of burnt ecu capacitors..or sell it.

When looking at the wiring diagram, once the fp ecu is bypassed all you are left with is 12v switched from the efi main and the common ground. There are two other wires that could have an ill effect on the 12v switched that is tied in to the diagnostic box under the hood. (properly labeled "FP" and the other +B) So I would safely assume that if you dont have power at the pump, you wouldnt have power at that FP pin either, but would be worth stabbing with a meter.

+B or +B1 comes from the main ecu, taps the 12v switched signal for the efi main and fuel ecu, then leads to the diagnostic box. However FP runs from the fuel ecu to the fuel pump and has a tap running back to the diagnostic box. So with that said, and having already done the 12v mod, the only 2 problematic areas I can see on the diagram is either FP from the diagnostic box, or +B/+B1 from the ecu going to the diagnostic box.


Hope that makes some sense. Here is the pic I have been eyeballing for reference:

bigwhite

I got 5 min. with a respected pro mechanic that I know to run my prob. by him. 1 what was the circuit opening relay mentioned on rockauto? He said was prob. the same as the main EFI relay. 2 what about the fuel pump inertia switch listed on rockauto? He said he had never seen one on a Lexus in the 90s. His advice after all the parts Ive relp. was to look into the theft deterrent, which if malfunctioning might disable the fuel pump or injectors. If anyone else has knowledge on these 3 subjects, especially location and easiest way to disable the theft deterrent please advise, as I will be looking into theory and design of that system. Thanks for posting the fuel pump wiring turbodremz, thats the same one Ive been looking at.

bigwhite

The theft deterrent / door lock ECU is above the steering column, not easy to access.

bigwhite

No two cars are the same and everyone is going to have differing problems. I just went out and unbolted the theft deterrent box which sits at the bottom of the steering column under the dash, on top of the column, held on with, 2 bolts. Unplugged the shorter of the 2 plugs and my fuel pump is running fine and my power door locks still work. The box will be silver on the bottom side but black plastic on the top side and say theft warning on it. Dont worry about someone finding this box and unhooking it to defeat your theft deterrent because its so hard to get to and hard to unplug the connectors, no one would do it. I could have backed up to it with a rollback easier and quieter.

bigwhite

Drove car to work today, starts immediately and is running like a champ. When I unplugged the small plug from the theft ECU, I now have no power windows. The correct fix would be to by a new theft ECU, will keep my eyes open for a good used one. More than the cost is how hard it is to get to and unplug.

bigwhite

So I drove the car to work and to the store, then the next morning, no fuel pump again. So I plugged my small p[lug of theft deterrent back in and have my power windows back. Called a guy that does mobile auto computer diagnostics to make a service call to check the car out. He said dont pull the computer, he wants to check it on the car and not running the fuel pump.

bigwhite

Low voltage at the main EFI relay, rewired to another keyed power supply.

larsbars44

any new info? i am having the same symptoms of my fuel pump not getting power on warm starts intermittently. Please update

Bankswood

I know the fuel pump mod has been posted to death but here goes. When I first got my 400 it would crank when cold and run fine. After it warmed up it would not crank. Had to wait for it to cool down then it would crank. Tried all the suggestions, clean iacv valve, replace coolant temp sensor, replace TPS, test AFM. Finally ran out of ideas and did the mod. Never had a starting problem again. That was two years ago.

bigwhite

My jumping power to the efi relay caused it to start and run again, but then it wouldnt turn off until I pulled the efi relay. So I undid the jump and bought a good used ECU and now all is working good. I owned the car for 3 1/2 years prior to having this prob. and it always started and ran dependably. Sometimes it would crank longer than I thought it should on cold start. The fuel pump bypass did help that. Just like our home computers, the one in our car is not going to last forever.