1988 Cressida 1uz no start no check engine light , no power to m-rel

[88sogreatv8]

So sunday last week i went to get a bite to eat. after parking sitting down eating and returning to my cressida, it wouldn't fire.
after sitting in the parking lot for 20 mins i tried to start it again and it fired so i thought my gas gauge was off and went to a gas station.

I went to the gas station and left it running , but because of the low idle it died again and this time i had to tow it home .
so the next day i started testing things . the 1st thing i found out was the fuel pump wasnt coming on when i turned the key to the run position. so i checked for fuel pressure and had nothing . I then rigged a dewalt battery to the pump circuit directly and the pump came on and i had pressure again.

so i plugged the connector back in and continued testing, the weirdest thing happened tho the key was in the run position when i unhooked then reconnected the fuel pump. the fuel pump came on with the ignition . so i shut it off and tried to restart and the pump didnt come back on. i checked the neutral safety switch fuse that i stuck in factory auto connector and the fuse was blown so i replaced it , but had the same result no fuel.

the cressida uses a main relay to trigger on the fuel pump in the run position , and that relay seems to click on when cranking the engine , but it does not come on anymore when only in the run position and not cranking.

i think im going to check all my wiring under the hood tonight , as all the wiring still looks intact under the dash , maybe ill get lucky and its just a broke connection , if anyone has had similar issue please fill free to share your story with me , it would be much appreciated

 

[numbchux]

How do you have the fuel pump wired? Cressida wiring?

My 94 SC400 - 87 4Runner swap uses the Lexus fuel pump controller, and this does not have any prime function, the pump only runs while cranking. I chased my tail for awhile testing my initial install because of that...

 

[88sogreatv8]

the wiring runs thru the cressida on a circuit open relay, before, when i got the wiring finished the fuel pump would come on in the run position and the crank position . Something has changed since this issue has occurred . the fuse was blown for the neutral safety switch , still after changing it it wont run

 

[numbchux]

I really don't like doing swaps like that. I always replicate the donor fuel pump circuit, and keep it in tact so the pump doesn't endlessly run if the engine isn't running.

So, I guess find a diagram for the cressida, get out your DMM and start testing. Start at that relay, and that will narrow down which part of the circuit is your problem.

 

[88sogreatv8]

the fuel system is run thru the factory cressida wiring . the lexus has its own module for fuel system so i cant replicate the way the doner engine was wired from the factory. i believe i found the issue. i noticed the check engine light wasn't coming on so i checked the powers at ecu. i found the b+ only has 1.5 volts , so i am suspecting the main relay. i did an ohm and continuity test on the relay and it failed. my other concern is i wired my mafs power thru b+ (thats how the cressida is wired factory) so i also suspect that the maf is shot, which may explain why my car has no acceleration when first driving . im picking up a main relay today so we will see what happens

 

[88sogreatv8]

Ok so more updates . i replaced the efi main relay, and it changed nothing. I did find however that the B+circuit has only 1.6 v at the obd 1 b+. it also has a ground. im wondering now if this wire somewhere is pinched and is grounding the circuit , which would explain the blown fuse i stuck in my neutral safety switch connector . the question is where the hell is it pinched ?/?????

 

[88sogreatv8]

Update , SO i found out the fuse box only is putting out 1.6 v from the b+ circuit directly from the fuse box. So the fuse box is shot at the efi main relay. i need to replace the fuse box and clean everything up.

So if anyone has a mx73 1988 Cressida fuse box im looking to buy

 

[88sogreatv8]

Well... updates . So got the new fuse block installed into car and it drove for about 10 miles , and after it was warmed up the check engine light turned off and shut the entire computer / fuel system down .

i was able to get it home eventually under light pedal effort , and after messing with the connector and rewiring the plug to the main relay , the fuse box eventually lost voltage again ( no check engine light ) at the pins on the fuse block . Roughly 1.4v is what it was putting out unplugged . when i plug in the connector the voltage reads 1.456v instead of 001.4v

WTF is going on???? i guess i need to retrace my steps on the wiring i did. i think tonight im going to wire a new external aftermarket relay to this circuit im dealing with

 

[Zuffen]

Why not just jump the pins on the relay socket so power flows.

It may be quick and dirty but it will prove if the relay is the problem or not.

 

[88sogreatv8]

im going to install a aftermarket relay tonight so fingers crossed . im still confident there is a short somewhere . its just hard to find

 

[88sogreatv8]

Ok.... so updates. the aftermarket relay didnt work, but i got me thinking..

So the m-relay only comes on when there is a constant power supply (which it has) , and a switched power from out the ecu that is turned on with the ignition to the run position, and a ground (which it has).

I checked to see if the m-relay wire at the ecu had voltage when i switched the car on, LOW VOLTAGE , 3.1 V ROUGHLY. After some more reading , i figured out that the ecu is internally linked to the ign switch wire that goes into the ecu.

I went ahead a made a jumper wire externally from the ign switch in, to the m-rel out and BAM, EVERYTHING CAME ON !

So what im guessing is the ecu is bad, Does anyone have any comments on this ???
i have yet to replace the ecu ,but im am very confident that this is my issue and the fuse box was only a coincidence that it temporarily worked. ihave seen this issue with supra owners , but never seen any examples on 1uz swaps

Another important question is , was this just a fluke situation with a already used ecu , or did something in the wiring cause this . I rechecked all my connections and cleaned up the wiring in the dash so it looks more uniform, but found no immediate issues.

If anyone has had similar issues with situations like this , i would love to hear your opinions on this.

 

[gloverman]

I would be replacing ecu as soon as I found no m-rel output. Same if they dont have a cel output.

 

[88sogreatv8]

so this is a common trait of the ls400 ecus to happen?

 

[gloverman]

so this is a common trait of the ls400 ecus to happen?

Not really that common, but common enough that I might see it 1-2 times a year.

 

[88sogreatv8]

fair enough.. guess im getting a ecu