Mtilton24

Regular Member 391 posts Posted 4 hours ago · I saw a mention on another web site about a guy finding lots of vacuum in the fuel tank when the fuel cap was removed. There is supposed to be a check valve in the fuel cap per the LS400 manual. OBD2 would not have that because of the self vacuum check the system does. So if the fuel tank is not letting air in that could be a problem for fuel delivery after a 15 minute or so run time. Just something to keep in mind. How would i check this? I have noticed that when i remove the gas cap there is a lot and I mean a lot of air that comes out.

Sorry it has taken me so long to post an update I've been really busy but thankfullymy LS is back on the road! What i ended up doing was running a wire straight from the battery to the fuel pump. I included an in line 20amp fuse as well. And I had previously tried to jump the Fp and B ports in the dlc both under the hood and under the dash on the drivers side and that didn't work for whatever reason I dont know. I know this shouldn't be a permanent fix but I was wondering wiring it this was is the regulator still telling the pump how much to pump? I jumped the battery to the wires that are on the outside of the gas tank cover.I thought the regulator was part of the fuel pump assembly located inside the tank so it would be getting poweras well but not from the fuel pump ecu or ecu so i dont know how it would know how much fuel was needed. Also now I'm having another issue where my heater is not blowing any hot air. Any suggestions add to what might cause this or how to troubleshoot it. I wish i had a workshop manual but i can't find any for free online. Anybody else have any luck finding one? Thank you for all your replys and help it is much appreciated . :-)

Update

Ok so update i connected the fuel pumps i got straight to the battety the test light lit up so there's power going through it but it didn't even try to engage. So I'm thinking maybe my problem is the fuel filter is clogged or there is a problem somewhere else and the fuel pump has already pumped enough gas into the line so that's why it won't turn on

Ok i put the relay i had in and using a test light touched it to the wires and no light so either the relay is bunk or there is no power going to the fuel pump

And where is the circuit opening relay? I think I by passed it when i went straight to the battery and I wired it to the cigarette lighter so it would go off when i turned the car off.

Ok so I tried to read the trouble codes by jumping the per the diagnostic port under the hood by jumping the Te1 and E1 with a piece of wire and a paper clip I also tried the one near the fuse box on the drivers side kick panel and I got no codes. And yes I had the car in neutral od button pushed in throttle valve fully closed etc. No codes. And I also tried jumping the Fp and B+ to run 12v straight to the fuel pump still wouldn't run. I know where the fuel pump relay is in the engine compartment I meant I can't find a replacement. I even called my local lexus dealer to get the part number and they couldn't find it. I ran 12v straight to the battery by splicing the wires from the fuel pump to a battery charger with a cigarette lighter adapter on it and plugged it into my cigarette lighter port on the back of my center counsel. I know but it worked for a few weeks and now nothing. I even tried running the wires straight to the battery and I can't even hear the fuel pump come on. I just went to pick and pull today and got a new fuel pump out of a 96 ls400 and a relay from a 88 Toyota that looks the same as mine and it's 12 v but it was for the dimmer lightsso I don't know if it will work. Fingers crossed.

I just recently bought a Lexus LS 400. When I bought it it had no obvious problems. It has +200k miles on it but the previous owner had a good record of all the scheduled maintanence he had done and seemed to take pretty good care of her. So I'm driving one day and all of a sudden she starts sputtering and eventually stalls. I cranked the engine a couple times and eventually I managed to get home but it seemed like I was in "limp home mode". This problem persisted for a few days until eventually the engine wouldn't turn over at all. I sprayed starting fluid into the intake and it started but wouldnt stay running so I diagnosed it as a fuel problem. I checked the fuel filter and gas tank for rust or any other viable issues and found there to be none. I also pulled the gas linegoing to the fuel filter and there was gas flowing from it so without having any proper testing instruments I could only do so much but I decided to check out the electrical aspect of the fuel pump. When I pulled the relay it looked kind of black and sooty so I put it back in but without the cover and tried to start it with the starting fluid and noticed the circuit opening relay was not closing as it should be. So to check and see if it was electrical I wired the fuel pump straight to the battery and it started right up and ran just fine for a few weeks and now I'm dead in the water again. I have been trying to find a new fuel pump relay but with no luck. I don't know what the problem is. Should I have put in a fuse or my own relay somewhere between the positive side of the battery and the pump? Is my fuel pump shot? Somebody help!