93 LS4 Fuel pump won't run....

[Lex-Luther]

1993 LS400
Anyone have a link to a diagram showing the Fuel System and how it interfaces with the ECM---Fuel pump controller ECU (module)?
Also, Which terminals are FP and B+ on the diagnostic plug, the Front two outer terminals or the two outer terminals in the rear of the plug?

Looking at the sticker, are the terminals as the sticker says or like when you flip the cover over which would put the FP and B+ in the back.. It would have to be Me to confuse this...






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Thanks

Lex luther

 

[MX73 V8]

Dood, the sticker is as it is printed. You have Fp and +B labelled correctly.

(PS the diag connector is not symmetrical, look at where IG- and WA/WB)

 

[Lex-Luther]

93 LS400 fuel pump

Ok..gotcha. In that case, I have measured for voltage at the B+ terminal with the key on get 0 Volts. Does this mean the ECM is bad? I have checked every Fuse in this car (Inside under the dash drivers side footwell and under the hood) and they all check out. I have Swapped the EFI relay under the hood as well with no change. Where should I look next?

LL

 

[MX73 V8]

+B should be +12V anytime the ignition is on. It is controlled through the efi main relay. It is fused through the EFI fuse. If it isn't 12V with ignition on then there is some issue.

Did you remove the fuse and check each one with a multimeter? (I have been caught out before with a fuse which looked fine but was broken).

If that checks ok. Then you need to check the wiring to the efi main relay. There are four pins, (assuming same colour codes as 93 ls400) there will be a black yellow wire which should have 12V at all times, black-red which should have 12V with ignition on, white-black thats earthed and black-orange that is 12V with ignition on.

The black-orange wire is the output of the ECU which turns on the EFI main relay, if its not 12V with ignition on then make sure the IGSW pin on the ECU is at 12V when the ignition is on. If the IGSW pin is 12V and the M-REL (black-orange) is not 12V then it would suggest to me the ECU isn't wired correctly or is faulty.

Is this a conversion you are working on? Or the original engine/car. Has it been running in the car?

 

[Lex-Luther]

Fuel pump issues.....

+B should be +12V anytime the ignition is on. It is controlled through the efi main relay. It is fused through the EFI fuse. If it isn't 12V with ignition on then there is some issue. Yeah I got 0 Volts on B+

Did you remove the fuse and check each one with a multimeter? Yes

(I have been caught out before with a fuse which looked fine but was broken).

If that checks ok. Then you need to check the wiring to the efi main relay. There are four pins, (assuming same colour codes as 93 ls400) there will be a black yellow wire which should have 12V at all times, black-red which should have 12V with ignition on, white-black thats earthed and black-orange that is 12V with ignition on. So should it be that these wires are the same colors at the ECM? I check which plug and udate so everyone else knows.

The black-orange wire is the output of the ECU which turns on the EFI main relay, if its not 12V with ignition on then make sure the IGSW pin on the ECU is at 12V when the ignition is on. If the IGSW pin is 12V and the M-REL (black-orange) is not 12V then it would suggest to me the ECU isn't wired correctly or is faulty. Definitely will check this one....

Is this a conversion you are working on? Or the original engine/car. Has it been running in the car? This is not a Conversion but in the Original Car that has been sitting for about 2.5 years, just had a new fuel pump installed a couple of months ago. Also the Guy who worked on it about 3 months ago had to Jumper from FP to B+ to get it to run. So after that event, and sitting up for 3 months, It does Nothing. The pump will run though but only if I put 12v on it directly at the pump terminals behind the seat.

I took the ECM out to check visually for problems and found a couple of Leaky caps:

The world of ECM repair is seems to appear as a "Secret" as is the "ABS" module the Volvo world...but I have more time than money to easter egg parts. Junk yards are High as H3LL here!

Not sure what these control but I will replace them anyway.
Not sure what Pin or Port # M-REL is as the Unit's ports are 34P 22P 16P and 28P and apparently are the number of pins for each connector.
What Connector # has M-REL, B+?...I guess that will be the same as the wire colors you stated if they go the complete path without a a color change eh?.. I am collecting this info and creating a log so when I write this up the next guy should be able to breeze thru. My guess in my case is a Dead ECM But the adventure continues.
Thanks MX. Your's and Anyone else's ideas are Welcomed.

 

[Lex-Luther]

FP ISsues..

Update...Made major progress today. Replaced the Caps and installed ECM. Still no start. Troubleshooting revealed a flakey connection in the Fuse box under the dash, the IGN 10A fuse. Moving the fuse from side to side gives intermittent connection. So i wedged in a matchbook to keep pressure on the fuse and got all the voltage to the required neighborhoods...Fuel Injectors, ECM, Coils, all that. Still no voltage to the Fuel pump. Later troubleshooting revealed what I think is a bad FP ECU and a voltage drop of 5v between the ECM and the connector on the Green / Black wire from the ECM (FP-C). I have 9.8 volts on this wire @ the ECM and only 4.5 @ the connector on the FP ECU. There is only 9v coming out of the FP ECU on the Green wire that is supposed to feed the FP. However, the wire going to the FP is Blue / black. Not sure why. The diagram says green all the way to the Pump but such is not the case. It got dark on me so I had to stop. the car is at a friends house. So now I have to figure out how to bypass the FP ECU and run 12v directly to the pump which is how I got the car to run.
In order to get the car to run I had to run 12v directly to the pump from and external power source (Portable Battery booster) as I have just bought this car and it has been sitting for 3 years. It has a 1/2 tank of bad fuel and ran like a kangaroo when I first started it up.Siphoned the nasty turpentine smelling junk out of the tank, new pump, New gas with FI cleaner and after a couple of minutes of spitting and skipping the engine cleared up and purred like a Kitten! I first suspected the ECM module but I have all the correct voltages (That I know of) in order to get the pump to run, but not sure why I get the voltage drop. Reading a thread on another site for SC400 lexus's has given me the insight to do the inevitable!!! BYPASS!!!! (But....Just to get it home)
Since the fuel ECU delivers three states, OFF/LOW FEED/HIGH FEED, this is determined by the running conditions, if the engine is stalled the ECU would go to OFF, with the bypass in place this option is not available, so in worst case scenario if you had an accident and killed the engine or fractured a fuel line the ECU would not be able to go to OFF and would continue to pump fuel round the system or into the engine bay or just dump it onto the road. So its not a Long term option. Once I get the car home to my shop, i will still try to locate the voltage drop because I wanna know why it does. But it is a good thread because I have always wondered if bypassing the FP ECU would be feasible. According to several people this is a Mod on a Supra website and also can be done on Lexus. I understand the function of the FP ECU is control the speed of the pump under not so demanding conditions but on the flipside a pump with full 12v all the time does no harm to the system as the pressure is regulated by the regulator but still not safe. (I am sure there will mixed opinions on this mod) I don't think it will shorten the life of the pump. But, today was a joyous day as I got to hear the car run and purr like a kitten after the FI cleaner did its job. I see a good oil change and a dose of Seafoam or Auto-RX in the near future and chase this voltage drop down. Hope this was helpful information to someone out there. I have spent countless ours learning the Lexus / Toyota engineering process. My experience is typically from working on BMW's and Volvos and dealing with the 750il Over engineered system.. A completely different Engineering universe.. I will update when I make more progress

 

[Thermactor]

Hi Lex, I can tell you that I've enjoyed reading this thread and hope to read more as you update us on the situation.