Mtilton24

92 LS 400 fuel pump problems

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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!

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And the problem could be the fuel pump resistor, the relays are available.  The easy way to by pass and direct wire the pump is at the data port on the engine.

So how did you wire the pump directly?  If it was not turned off when you turned the engine off then yeah the pump is probably toast.

The circuit opening relay is on the side of the ecu under the glove box.  Or did you mean the fuel pump relay?

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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.

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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.

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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

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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

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There is a much better and simpler way to jump the fuel pump, at that under the hood data port, I think its by jumping Fp and B.

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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.

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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 . :-)

20160220_180058.jpg

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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.  

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Air pressure is better than vacuum, the check valve is supposed to let air in and stop air from going out.  What you should do when you get time, is go to the Toyota site and look at the service manuals, tech bulletins.  Did you ever check continuity from the fuel pump relay to the fuel pump?

Downloading the info here for a few day membership deal is way cheaper than trying to buy a manual.

https://techinfo.toyota.com/techInfoPortal/appmanager/t3/ti?_nfpb=true&_pageLabel=ti_home_page&SMENC=ISO-8859-1&SMLOCALE=US-EN&SMAUTHREASON=0&SMAGENTNAME=%24SM%24mT%252bGLraBu9CwUVnZg4mEDzB2kysT90hgbwsWgdZzNOc%253d&TARGET=%24SM%24https%3A%2F%2Ftechinfo.toyota.com%2F

 

The first thing to check for heater problem is the valve just above the passenger side valve cover up on the fire wall. If you have some one turn on the heat and off you can see if its working. Other wise could be an air lock from low coolant and or a restriction from a bad hose.

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post-41820-0-03922500-1439034313_thumb.j

Landar originally posted this here.

http://us.lexusownersclub.com/forums/topic/87225-engine-quit-has-spark-electric/#comment-487797

Maybe the efi main relay  is not letting power through? If memory is correct that circuit opening relay is mounted on the ECU on the right hand side when your sitting in the seat.  Also check power at the efi fuse that feeds the efi main relay. Check for power at ig2 at the efi relay.  This is for your fuel pump problem.

During normal low load with engine running the power for the fuel pump goes through the resistor. Even if the ecu was not powering up the fuel pump relay the fuel pump should still run because it looks like the relay is set to bypass the resistor when starting, and also does that for full throttle and acceleration. Its a 2 speed fuel pump.

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I have a similar problem like this one. Hope someone can relay me to any solution. My LS problem is when I turn the ignition key ON (not starting), the fuel pressure reads zero. When I crank the engine, car turns over and runs, but with heavy smoke. I troubleshoot the circuit at On positio to see if circuit opening has any voltage, it does not. The control line is FC from the ECU seems not working. 

The way I understand is when the key is on, EFI main relay is on, Power run to Circuit Opening and the FC (from the ECU) will turn on the Circuit Opening relay to allow current flow to the pump relay. In my case, the Circuit Opening Relay does not give any output, so the pump does not build up initial pressure.

Now, when I start the engine, the car runs (with smoke), in that sense, it appears the Circuit Opening Relay is working (otherwise the pump doesn't work). Is it safe to call the ECU is bad so it did not turn on the pump when the ignition is at ON position?

Measuring fuel pressure, it should be between 38-44 psi, mine reads 38. Should I just blindly replace the pump because it is at the borderline?

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What color is the smoke?

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Black. But for a few minutes so I won't worry about it too much. 

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Black smoke usually means too much for in the exhaust. I would definitely do something to fix the issue because the cats are probably taking a pounding.

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10 hours ago, sha4000 said:

Black smoke usually means too much for in the exhaust. I would definitely do something to fix the issue because the cats are probably taking a pounding.

Thanks SHA4000. I agree and am investigating the fuel system.

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