1993 Ls400 Fuel Pump Relay Location

[Bruno Molly]

Hi

Anyone knows where is Fuel Pump Relay location in 93 LS400?

Thanks.

<{POST_SNAPBACK}>

I have the electrical diagram for the 93. Attached the only sheet that mentions the fuel pump and ECU.

Hope this is usefull to you

I downloaded the diagram but it only show the location of the Pump and the harness which seems to disappear within the drawing. If anyone has the Electrical schematic showing the circuit, and let

me know the location of the relay so I can measure the voltage to see whats what, it would be greatly appreciated. Some models have the Fuel pump relay in the front left and it says "Fuel Pump Relay".

The particular model I am working on has this same Odd shaped box, but under the cover is says "Air Pump" but there is no relay present, as this model does not have the Air suspension. Therefore I have no idea where the FP Relay is.

Thanks

BM

[curiousB]

Parts is located here:

http://www.toyodiy.com/parts/p_U_1993_LEXU...4.html?hl=28380

I don't have schematic but there is a series resistor to limit current. It allows the pump to run at two speeds dependant on fuel demand.

[Bruno Molly]

Parts is located here:

http://www.toyodiy.com/parts/p_U_1993_LEXU...4.html?hl=28380

I don't have schematic but there is a series resistor to limit current. It allows the pump to run at two speeds dependant on fuel demand.

Ok..Thanks Curious. The thing that threw me was when i opened the cover where it says the FP relay should be it said "Air Pump", and there was no Relay present...only and empty socket.

So, I had a FP relay and installed it but the FP still won't run. The FP is brand new. Can anyone tell me what the Fuel Pump Control Module in the trunk does? Also, the Terminals where the FP relay is, there should be a way to Jumper the FP just to crank the car for a minute or 2. Other LS400's I have looked at , Pre 93, it Says "Fuel Pump" under the FP relay cover... Baffling. I would have to have the only LS on the planet with a Misprint!!!

{} {} <------FP Relay Terminals

{} {}

_____________________________

FRONT OF CAR

Which two terminals can I run 12v to to get the Pump to at least say Grrrrrr!

[Bruno Molly]

Parts is located here:

http://www.toyodiy.com/parts/p_U_1993_LEXU...4.html?hl=28380

I don't have schematic but there is a series resistor to limit current. It allows the pump to run at two speeds dependant on fuel demand.

Ok..Thanks Curious. The thing that threw me was when i opened the cover where it says the FP relay should be it said "Air Pump", and there was no Relay present...only and empty socket.

So, I had a FP relay and installed it but the FP still won't run. The FP is brand new. Can anyone tell me what the Fuel Pump Control Module in the trunk does?

Strike that last post...After reviewing some wiring diagrams from another model Lexus, it appears that the FP and FI systems receives B+ voltage from the ECM. I will check this location out today. If B+ isn't present at the Diagnostic plug then I will start looking at the ECM.

There is a Diagnostic terminal box on the top of the engine where I can measure key signals. Lotsa good info there to tell me whats wrong. I'll update and try to present this in a write up if I get lucky

and assumptions work.....

[curiousB]

Toyota_fuel_system_overview.pdf

Here's the system diagram for my 2004. It might be different from your year but maybe gives you some ideas. As can be seen the fuel pump relay is just a high or low speed selector. It switches in and out the series resistor to the FP. The C/OPN relay actually provides power to the FP.

p.s. air pump must be a location for the air supension option which I presume you don't have. That would explain the location being open.

Here is a general overview of fuel system/fuel pump and speaks to the two speed fuel pump scheme used in these cars.

Fuel_SYSDIAG_2004_ls430.pdf

[Bruno Molly]

Toyota_fuel_system_overview.pdf

Here's the system diagram for my 2004. It might be different from your year but maybe gives you some ideas. As can be seen the fuel pump relay is just a high or low speed selector. It switches in and out the series resistor to the FP. The C/OPN relay actually provides power to the FP.

p.s. air pump must be a location for the air supension option which I presume you don't have. That would explain the location being open.

Here is a general overview of fuel system/fuel pump and speaks to the two speed fuel pump scheme used in these cars.

Fuel_SYSDIAG_2004_ls430.pdf

>>>> 1993 LS400<<<<

Curious...you're the man!...Thanks. You supplied the AMO i needed to start troubleshooting.

Did some troubleshooting today before it rained on my parade and here is what I found....

Check the photos followed by some questions:

This is what I have instead of a Fuel Pump Relay. There is a Fuel Pump Controller module in the trunk. I don't know if that is used instead of the FP relay, but I don't know where else to check for

the FP relay other than here. I Ohmed the terminals of this socket just to make sure, and I got nothing at the diagnostic plug. No voltage is present when the IGN is on either.

***** Brand new Fuel Pump installed 1 month ago *******

This is the Diagnostic plug where I measured for B+ voltage and go 0 volts. I jumpered from FP to B+ and as expected, the car never started. This car ran when it was parked, has had a new FP installed, and a previous mechanic jumpered it some time ago, about a year ago, and it cranked right up. I bought this car to repair some collision damage in the front, Nothing major.Just front bumper, Hood and fender. There is no collision damage to the engine. So my speculation is if there is NO B+ voltage then the ECM is probably bad???? I also monitored for B+ voltage as the engine was cranking over and still got 0 volts. I have another ECM to try but can't open the Passenger door due to the Fender hitting the door, so i wasn't able to get to the passenger area to remove the ECM.

I will tackle this when the weather warrants a nice day to do so. I actually have bought 2 LS400's to fix up 1. One has rear collision damage which I am using to fix the front of this LS. So I still have the other to contend with. It also is supposed to run but I haven't touched it yet. So any ideas are welcomed...I have read the many threads on the ECM but can't find any quite like this problem with NO B+ present. Not sure if jumpering voltage to the FP/B+ jumper will damage anything so I didn't try that without checking here 1st. Hypothetically speaking, If you DO jumper from the + side of the battery to the FP/B+ jumper and it still doesn't start, what next? Oh It will act like it wants to start when starter fluid is sprayed into the intake but I just wanted to make sure it had spark, and it tried to run. Something is just not clicking with this fuel system. I also tried a spare FP relay in the spot where it says "Air Pump"....Nothing... With the Cash for Clunkers deal, i have access to several of these LS400's I got and ECM and a Resistor today for $25. HHHHELP!!!.

Thanks in Advance... Trying to get this car going as a Family car. Incidentally, where is the C/OPN relay that supplies voltage to the FP? Is it one of the two GREEN relays residing beside the ECM

-= BM =-

[curiousB]

I don't think you'll harm anything jumpering B+ to FP. This will cause fuel pump to run at full speed whenever ignition is on even if motor isn't running. Not a good long term solution but as a test will let you know if you can get car started or do you have additional issues to solve. Since you're focusing on fuel system it might be an idea to buy a fuel pump pressure gauge. Harbor Freight has these on sale for $8 in a small kit with adapters. I'm sure other auto stores have similar ones. Without the right tools you can do a lot of guessing and get led down false paths. $8-15 for a gauge is a pretty sound investment.

With the gauge you can confirm when B+ is applied to FP if the pressure rises in the fuel manifold and reaches the 38-42 PSI range it is intended to reach.

[Bruno Molly]

I don't think you'll harm anything jumpering B+ to FP. This will cause fuel pump to run at full speed whenever ignition is on even if motor isn't running. Not a good long term solution but as a test will let you know if you can get car started or do you have additional issues to solve. Since you're focusing on fuel system it might be an idea to buy a fuel pump pressure gauge. Harbor Freight has these on sale for $8 in a small kit with adapters. I'm sure other auto stores have similar ones. Without the right tools you can do a lot of guessing and get led down false paths. $8-15 for a gauge is a pretty sound investment.

With the gauge you can confirm when B+ is applied to FP if the pressure rises in the fuel manifold and reaches the 38-42 PSI range it is intended to reach.

Today I tested the Fuel pump with an external power source, directly to the FP terminals on the Tank. It Ran fine. There is Fuel at the motor when i do this manually but I don't know what the pressure is but it does seem normal judging the way it "Blades" out violently. I have a Fuel pressure gauge but the line I saw had a banjo bolt and my gauge is a barbed slip on type.

I Left the FP running while cranking the car over but it still did not start. Still no B+ voltage at the Diagnostic block .

Curious B, if I were standing in front of the car looking down at the Diagnostic plug, are the FP and B+ terminals at the Front of the plug or at the rear? The ECM I had to swap out was the wrong one. I'll keep looking for the right one. In the mean time, does anyone have the Pinouts of the ECM or know where I can download a Service manual??? ANyone got a photo of where to attach a Fuel Pressure gauge?

Thanks

[curiousB]

Well it might pay to get a vehicle specific service manual so you can get schematics specific to your car. You might want to join this web site (https://techinfo.toyota.com/techInfoPortal/) for 1 day and do a massive download of all the chapters of the manual for your exact model/year. They are a great resource.

I know for my car there is a fuse EFI #1 and two relays (EFI main relay C/OPN relay) before battery gets to fuel pump. It goes through the same fuse and one of the relays (EFI Main) to get to the ECU and MAF. So maybe the EFI fuse is blown or the EFI main relay is broken. It could also be a bad ECU but if you have schematics you can see when car is on if power gets to the right places on the ECU. I'd do a few measurements before just swapping out parts. That can get expensive.

[Bruno Molly]

Well it might pay to get a vehicle specific service manual so you can get schematics specific to your car. You might want to join this web site (https://techinfo.toyota.com/techInfoPortal/) for 1 day and do a massive download of all the chapters of the manual for your exact model/year. They are a great resource.

I know for my car there is a fuse EFI #1 and two relays (EFI main relay C/OPN relay) before battery gets to fuel pump. It goes through the same fuse and one of the relays (EFI Main) to get to the ECU and MAF. So maybe the EFI fuse is blown or the EFI main relay is broken. It could also be a bad ECU but if you have schematics you can see when car is on if power gets to the right places on the ECU. I'd do a few measurements before just swapping out parts. That can get expensive.

I will do that. The LS i am working on is hit in the front. It has been started several times since then (couple of years ago) and I remember reading something about an "Inertia Switch" that cuts power to the Fuel Pump in the event of a Collision. Do our cars have this? If so where is it located? I will do some more testing today. Thanks for you help Curious B.

BM

********************************** UPDATE !! ****************************************

Removed ECM to inspect... found leaky caps:

Anyone know if these are the Leaky Caps that cause Fuel Pump problems?

Before I removed the ECM I tried to generate any CEL codes that may exist. Never did a a CEL whatsoever...even when there wasn't a jumper in place and all the idiot light come on...No Check Engine insignia was present.. CEL Bulb shot maybe? This is turning into a nightmare!

[Bruno Molly]

After putting the ECm back in and bypassing the Fuel pump ECU, the car cranked and I drove it home to begin restoration. it was in a collision which only damaged the front bumper, Radiator support is pushed in slightly (about 4 inches). Today I removed all the damaged parts except the hood and Radiator support. The no start problem was a combination of Bad FP ECU, and flaky connector. Incidentally by Jumpering the FP ECU connector, is good enough to get the FP to run, and still under ECM control. I will take photos tomorrow and post them..

[curiousB]

Incidentally by Jumpering the FP ECU connector, is good enough to get the FP to run, and still under ECM control. I will take photos tomorrow and post them..

Jumpering FP to B+ isn't a good long term solution. The pump will run at high speed all the time even when only idling which will put premature wear on it. Also when engine not running but key on the FP will run full speed. Again wear and tear. Lastly this disables safety features like inertia switch (collision shut off) and other such protection measures. So just as you plan to restore the body you'll need to restore the FP circuits to operate as originally designed. Anyway congrats on getting it running.

[Bruno Molly]

Incidentally by Jumpering the FP ECU connector, is good enough to get the FP to run, and still under ECM control. I will take photos tomorrow and post them..

Jumpering FP to B+ isn't a good long term solution. The pump will run at high speed all the time even when only idling which will put premature wear on it. Also when engine not running but key on the FP will run full speed. Again wear and tear. Lastly this disables safety features like inertia switch (collision shut off) and other such protection measures. So just as you plan to restore the body you'll need to restore the FP circuits to operate as originally designed. Anyway congrats on getting it running.

Yeah...Boy did I strike Gold today. Went to one of my Cash for Clunkers Grave yards.. Found a 93 LS400 inline for the Crusher. Talked the guy into to putting it aside and saving it for last or until I get what i need off of it. Got a Fuel Pump (Extremely clean!) Shifter, Fuel Pump ECU, ECM, Headlights, corner markers, Instrument Cluster, Alpine 6 disc changer, oxy sensor, Good Battery.....cost? 12 pack of Budwiser and a pack of Camels. Thank god for bad habits! Came home, tried the FP ECU, car cranked right up!. Now the Fuel "Pimp" starting problem is SOLVED! couple of other Quirks I need to work on while waiting for the 1992 LS to get here next week so I can strip it to rebuild the 93. The Ignition keylock won't release the key unless I disconnect the Battery. Ignition key Interlock solenoid is intermittent. I will post another thread on that problem. Curious B, youre a great help man. I really appreciate your help. When i first started with this car, I knew absolutely Peanuts about a Lexus...now its totally clear.