1UZagoo

Been working on a 93 LS400 that is claimed to have sat 10 years. It was drained of fuel and fresh put in, paperwork suggests a new pump was installed.

Anyway, I've narrowed it down to the EFI relay isn't energized when the ignition switch is turned on, but everything else comes to life. I've put the ECU in another 93 lexus LS400 I have, and it worked fine in that car, so I don't think it's the computer. The instrument cluster does have the flashing back light problem, could this effect the EFI relay?

If I manually jump the pins the EFI relay jumps, the engine will stumble a little. With about 80% throttle while cranking, it sometimes gets enough rpm to almost idle. If I jump B+ to Fp to force the fuel pump to run at high speed, it starts weakly and dies. Giving it gas while cranking with the pins jump doesn't help things.

I've looked over the fuses, and didn't see any bad ones.

I've bought 2 day access to the Toyota TIS site, so I have the complete car wire harness diagram. I've worked around Toyota pickups quite a lot so have a fairly good understanding of the main wiring theory.

The car did have a Circuit Opening Relay sitting on the seat when I bought it, does this LS400 have one of these or was this possibly from a different model? There's some ES300 (I think) parts sitting the car from the last person trying to fix it including the wrong ECU with no case. The COR, Fuel Pump Control ECU and the engine ecu with no case.

I'm currently working on going though the wire diagrams following the power from battery to efi relay to attempt to find where the problem area is, but any thoughts or advice would be great. Car only has 148k miles, and I bought it mainly for the engine and plans to part the rest of the car out to pay for it, but I want to get the engine up and running before I start listing parts for sale.

Oh another question, from the ECU there is a MREL wire which is black/orange which runs to the efi relay (coil side). I don't fully understand why/how it functions since the efi relay needs to be on to give the ecu B+ power, so does the power for MREL come from the BATT pin that has +12V all the time?

Thanks for reading!

Yamae

Depending on the DC supply problem at the instrumental cluster, the driving transistor which makes MREL signal is inhibited to work and you can't start the engine. Fix the instrument cluster first. I worry about the DC voltage regulator there is not working right.

1UZagoo

I'll swap clusters and hopefully the EFI relay receives signal to turn on.

I've replace bad caps on pc motherboards before, so I have some caps on hand, but not the smaller ones (low ripple, low esr, high temp (105C)).

Thanks for the tip, since there's a DC voltage regulator in there, I'm pretty sure that would make sense why things are not too happy about running.

1UZagoo

Update, swapped the instrument clusters from the other car that runs fine, and same issue except the back lighting and such are solid and working well. This cluster was rebuilt based on the warranty sticker on it, the other with the problem does not have any indication of being rebuilt. Check engine light is still off with key on and efi relay isn't receiving signal to turn on.

The car does have security, I'm not sure what characteristics show up when it's in lock out mode. Most domestic (USA) made cars will start then die right away.

I'll continue researching, but any more ideas are always welcomed =).

Thanks!

EDIT:

Oh I did a sanity check and the black/orange wire at the coil and #1 injector have battery power with key on.

EFI relay has good ground connection at pin 3. Pin 2 has battery power. When I jumped pins 2 and 4 a couple days ago, that's when I got spark and the engine tried to start, so I think the problem relates to pin 1 not receiving power from the ECU (MREL). Is there by chance some sort of flow chart or list of items required for MREL to provide power? When I get a chance I'll double check the ECU has battery power at A14 BATT. I know +B and +B1 have no power since it comes from the EFI relay.

Wiring is a possible problem area on this car since a person that didn't know what they were doing was working on it before I bought it. Besides that, the driver's window and main window switch are missing and moisture has gotten into the car for an unknown length of time, guessing around a year. Trunk seal was bad as well, the spare tire was swimming in water, I've drained the trunk. So far water damage has been visually minimum but I know electroncis and wiring does not like that. Water damage is on driver's seat track (rust), and the dash frame behind instrument cluster was rusted as well. The tape holding the cluster wiring is pealing apart too, but the wires looked in good shape yet. Terminals in the connectors looked good.

Since I've swapped clusters out, I don't want to cause any damage to the good one since it is needed for a project down the road. Is it safe to manually jump the efi relay pins, and B+ to Fp to test start with the current setup? I suspect it's safe but never hurts to double check.

oldskewel

iTrader: (1)

My '91 drives just fine with the instrument panel (combination meter) completely removed. I know the 93-94 clusters are very different, but in my thinking, that would be a bad design if a problem with the cluster would prevent the engine from running.

BTW, after reinstalling the cluster, one of the warning lights (airbag?) stays on, but is easily turned off with wires and a paperclip. (for my 1991, at least)

1UZagoo

I had several blown indicator lights, I think I took the air bag light and moved it to the check engine light. I found 4 blown bulbs. As for the air bag light staying on, based on my research it's code 41 or 43 from memory, and requires the wire dance in the diag plug. The code is thrown when the car is started with the instrument cluster removed. When I swapped mine, I set the steering wheel down and all the way out, and disconnected the battery for the swap to prevent the code from being thrown.

I'm glad both the cars I have are 93's so I know the parts are basically all interchangeable. The one I'm working with has the cd changer and sun roof, but I think the rest of the options match each other (traction control and such). I double checked the cluster's part number before I swapped them and they were a match.

I'm thinking about going through this list and finding what has power vs no power at the ECU. This is part of the wire diagrams I saved for this car.

I've back probed the ECU before on a T100 to diag a start/die issue (ignitor was bad) after an ECU swap and repin (auto vs manual trans), so this should be a fairly simple process of elimination to find the problematic item/circuit. Besides blindly checking the above voltages, I'm also studying the wire diagram relating to them to better understand the wire design and other possible points of failure.

Thanks!

1UZagoo

Another update.

BATT at ECU does have power.

I looked over the wire diagram and saw no reason jumping the relay and B+ to Fp would cause any issues, so I gave it a shot. This whole time it's been basically starting and dieing, so that makes me think ignitor or mass air flow meter (old pickup experence). I remember reading the 3.0L pickup ignitor is the same part number, so I grabbed a known good one, and it does match both ignitors on the LS400. Swapped out the one you can't normally see the part number (secondary I'm guessing) and found an interesting pattern, with it floored for one cycle it would stumble 500-700 rpm and die, and the next start with out touching the gas it would fire up like normal to around 1500 rpm and die. Before it would get around 900rpm at best so I think the igniter is bad.

Next step I took was since I have been having to jump B+ and Fp in the past, I jumped them again with the ignitor swapped out, and the engine fired to life. Sounds pretty healthy for sitting 10+ years. I still have the problem with the EFI relay not getting a signal to turn on, and I have to dig into the fuel wire diagrams to see if the mass air flow sensor/meter on this car is like the pickups where it can effect the fuel pump from running while engine running. This is basically a parts car, so I don't really have to fix the issues, but I'd kind of like to know what's bad for when I part it out. The engine and maybe trans will probably be used in a pickup/play toy down the road.

Neromax

Hi, did you fix the problem? my problem ( SC 400) :

Opening the door with a key, an alarm came on, and the car won`t start.
The EIF does not have adequate voltage. for "1" pin only 9V for "2" the same as the battery. When I connect artificially sockets 1 and 2 (efi) everything works. Where does the tension go to slot # 1? With ignition or ecu? why did the car won`t start when the alarm turn on (I turned it off by turning the ignition switch)

Moarpower

The circuit opening relay is mounted on the ecu and this will affect the efi relay and in turn, the pump itself. I was getting no start from the fuel pump. Manually tripped the circuit opening relay and the pump worked. Issue was the pump circuit was bad.

Neromax

Could an alarm be triggered by a lack of voltage on the pump? How to disable it? Computer reset has not helped