I been sick sucks,but going to go out tomarrow morning and mess with it,going to test the FB & +B on the motor with my multimeter and see if they are good like buddy stated and if good that means i dnt need to check other relays and fuses from what he said,im doing alot of reading, where the EFI MAIN RELAY & CIRCUT OPENING RELAY? I want to check on these next and check it

 

92 ls400 the fuel pump wont prime in the on position with key,i bypassed the fuel pump relay and it was priming good but when i turn the car over it wont start with the fule pump running???

 

Most fuel pumps only run enough to bring the pressure up for initial start, then to keep running there needs to be a tach signal meaning the engine is firing and running for the fuel pump to keep running.

 

So do you think it could be a ecu the computer maybe???

 

I was thinking bad ignition maybe???

 

Proper trouble shooting has nothing to do with THINKING ITS THIS OR THAT. Its testing those this or that's to see if they do what they are suppose to do.

So if the relay is plugged it does the fuel pump initially build up fuel pressure when you do the start process and turn engine over? The relay is good? Have you checked the capacitors in the ecu? I would be checking the cam and crank sensors too.

 

I understand what u are saying,i had 2 machanics look at it and they gave up and even took it to a shop they couldnt figure it out either so its very frustrating so i feel lost right now, its not building pressure because its not comming on until i bypass the fp relay,wheres the ecu located? And how do i check the cam and crank sensor? I sewar all this happend right after my wife broke her front drivers lower ball joint while she was driving it??

 

Its been awhile on this one, why not just go back to the original post on this car, I had a whole check list to do and what the problem could be. Did you ever try a new fuel pump relay?



Here I found it for ya.
https://www.clublexus.com/forums/ls4...driving-2.html
Read through that thread and here is what I posted in it at one place.
And since I switched the first 2 steps around from what the manual said, just do 2 first then 1 and goto 3.
Do this and leave in the fuel pump relay when doing it.


Here is what the manual says.
Though I am switching around the first 2 steps, since I don't think its a good idea to jumper it with the ignition on.

To check fuel pump operation and to also check the fuel pressure.

1 Jumper the FP and +B terminals of the check connector found on top of the engine on the driver side front.
2 Turn ignition on
3 Check for pressure and or hear fuel return hose. 38 to 44 PSI
(this is how to turn on the fuel pump without the engine running, otherwise there needs to be a signal from engine to run it)

If you have nothing, then here are the causes.

Fusible link
EFI main relay
Fuel pump
Fuel pump resistor
ECU
Fuse EFI (20A) Ign (7.5A)
Circuit opening relay
Fuel pump relay
Wire connections
And added by me (Bad wires)

Okay so the relay is not clicking did you test it like I said? In my list from the manual most of those Items will '
cause the fuel pump relay not to work. You spend too much time ignoring all the good info me and others post here and it already cost you an unnecessary fuel pump and the hassle to change it. Have you even checked fuses, and the connections like the other guy here mentioned? What about the fuel pump resistor? Did you check it? Really your first thing is to obtain is the instrument to check the items listed. And really in the end your fuel pump money would have been better spent on someone that KNOWS HOW TO DIAGNOSE THE PROBLEM. I get a bit grumpy when I go spend time studying for a problem someone else has with their car and then ignores everything I post. Though it does help me if I ever have the problem

 

Well the first machanic fixed it at first he said he just wiggled the fuses under the hood and it cranked right up and my wife been driving it for a week then it cut off on her again on the highway,she been telling me it feels like it doeant have power or feel the same when shes on the gas? Im wante to start a fresh thread again,i dont have all the tools etc to diagnose these problems,im going to write all these down and tomarrow morning and pass ot along,
Going to have the car towed to another shop and see if they can fix it

 

Well took it to another shop with the list u gave me,hope it can be fixed

 

Any news from the shop?

 

No nothing yet,will keep u posted for sure

 

I hope the new shop has a skilled mechanic. Sorry to say that many mechanics don't understand the fuel control system of a LS400. I often have seen that they have changed units/parts next to next and still they couldn't have fixed the problem. They were like changeneers.

There are different reasons why the fuel pump doesn't prime. The problems related to the circuit opening relay are sometimes not easy to troubleshoot.

Anyway there are 3 important fundamental items you need to know.
1, The fuel pump resistor is only reducing the current to the pump while the engine load is not heavy.
2, The fuel pump relay is only bypassing the fuel pump resistor when the engine needs extra gas judged by the ECU.
3, The circuit opening relay inhibits fuel pump to work when the ECU detects abnormalities.

The ECU is related to 2 and 3. That may be the reason why mechanics are not happy with this type of problem.

 

Any news yet?

 

I guess the shop is still fooling around with it huh?