Miata256

In my 92 SC400, I was having the issue the title states. Few moments on Google later , I sent my ecu off to tanin. They stated mild corrosion but it functioning in their test car. I selected to continue with the repair as it was already there(same day option was actually same day, impressive). I recieved the ecu back , quickly plugged it in and recieved the CEL with the key on, and a running vehicle. A shortly after warming up, the car began to die. Unable to restart as there was no cel. Randomly wrenching led me to realize the efi relay being removed would cause no cel with key on. Used a jumper wire and car ran great for an hour. Replaced relay same day and had a running vehicle for a week. Currently have no cel with key on, a non running vehicle , even with the efi relay wire jumped.
List of items replace or trickery tried :
-tanin ecu
-Efi relay jumped, and replaced
-12v mod , and also undone
-new negative terminal and cable to body, and new cable to engine ground . 2ga wire ,copper lugs.
-new battery alternator


My question is , what else is in this circuit and would cause these symptoms ? I'm new around a voltmeter but I can take simple instructions well.
Thanks for any advice.

KahnBB6

iTrader: (5)

Hmm. Though very rare to happen normally... with stock SC300's or GTE engines the issue could be a bad igniter... but that always triggers a standard CEL 14 (aka "Bad IGF signal or too many inconsistent IGF pulses within a set number of firing cycles). Also, once an igniter burns out it can happen while you're driving causing engine shutdown and of course a CEL 14.

And since you have no CEL let alone no CEL 14 I don't think that would be it. Only in exceptional circumstances or with very extreme age do Toyota igniters go bad anyway. And even the old ones tend to last under normal conditions.

Your problem appears to be localized to startup unless you failed to mention the car died even once while you were driving. And again, the only thing that would get the car going again if an igniter was at fault would be another new or good used working igniter.

Does your starter motor at least engage when attempting to start your SC400?

When you first turn your key to the "ACC" and "ON" positions *before* attempting to crank over you should see a solid CEL light until the SC's engine comes to life. If you do not see that and all the factory wiring for the factory CEL light function is working anyway then there still might be an issue with the ECU.

What Tanin can do *usually* fixes ECU issues by replacing the old capacitors with new correct type ones and cleaning up and/or repairing any board issues. And testing the ECU out in one of their shop cars is part of their QC process. What they probably can't account for is any deeper irregularity within the chips of these ECUs but that is what their on-site QC test cars are there for. But if they just tested it and it worked fine for them it would seem to rule out the ECU at the moment.

And you replaced the battery and alternator. I once had an ECU (2JZ-GTE) electrically damaged by an old overcharging alternator and it gave me a similar no-start condition every so often by burning igniters. But... in my case I always had a CEL. And in your case you replaced the ECU capacitors and the alternator and you have no CEL.

Tell me, at which point in this diagnosing process did you replace your alternator? Before you had the ECU sent to Tanin and tried your car again or after? It's a really long shot question but I'm curious.

Miata256

Thank you for the reply. Car had a cel on start up this morning (go figure ). The car HAS attempted to die directly after the tanin repair . By attempt I mean all loss of engine function. Keeping rpm about 4k would allow the engine to shut off and then appear to catch itself and go back to 4k. When I finally let it die, I would not have a cel with key on, engine off and would not be able to restart. Could let set a few hours a repeat the process and even managed to catch the cel.blinking before staying lit, key on engine off. The alternator replacement was pre ECU repair. Battery was replaced at same time, and again post ECU repair.

Miata256

"When you first turn your key to the "ACC" and "ON" positions *before* attempting to crank over you should see a solid CEL light until the SC's engine comes to life. If you do not see that and all the factory wiring for the factory CEL light function is working anyway then there still might be an issue with the ECU."

correct. I'm definitely aware that the cel needs to e present for the car to start. I'm also aware that other things can prevent the circuit from being complete and causing a no start no cel condition (efi relay as an example )


And to answer, yes the starter does attempt to start the vehicle no matter what. Thank you !

Miata256

Another small coincidence that has recently upgraded to clue status......everymorning when I get off work (7am) and the temps have been mid 50s the car has had a cel with key on and been able to crank. Every evening (high 70 mid 80), no cel no cranks. Has repeated this 4 days straight.

Miata256

Any tips on what relays would commonly fail ? Perhaps a link to wiring schematic (not that I would know what I'm looking at )

scsexy

iTrader: (1)

Check the crank position sensor you should be able to ohm it for a good reading

Miata256

"ohm it" what exactly should it read ? Sorry. New around voltmeters but will check this TODAY.

scsexy

iTrader: (1)

it should read 2-300 or 2-3000 i forget which

Miata256

Sorry for not honoring the today that I capitalized . I made some rookie mistakes with the voltmeter and needed some youtube help. Anyways......


according to the copy of service manual I have, its expected to be 835-1350 cold. I read 1100. The sensor also does produce ~180mv when triggerd. Thanks for any further advice .

Miata256

Large green IG2???? Relay failed continuity test between pins 4&5. Ordered two "guaranteed working, 90 day warranty" ones from an individual. Not sure if pulling that relay will cause the no cel symptom with the key on car off....if anyone wanted to ease my tension. Relays get here tuesday

Miata256

Relays were a bust. Still no CEL! Looking for guidance .

Miata256

Okaaaaaaaay so . Rebuilt tanin ecu was confirmed GOOD today. Swapped into a different car, fired right up. Swapped back, no cel ,no crank. Open to suggestions.

Miata256

In my sorrows, I plug in my confirmed ecu to be greeted with a cel with key on. Turn the key fully expected the car to start,instead nothing. Forced to jump the starter relay, the car ran on it's own for nearly 20 minutes before dying out and losing the ability to have a cel with the key on , car off. Open to suggestions.

Miata256

Car is still:No cel key on, and now forces the starter relay to be triggered in order to attempt to start.

Broke out the the voltmeter today
At the ecu plug , key on
IGSW has 12.5v
Unable to get reading for +B unless my efi relay was rigged (is this normal?)
+b1 showed 12.5v


Continuity checked out on e1 circuit

No cel with key on,can watch it flicker a moment when moving to the on position.


Irregardless of the the cel being on or off during key on stage, im able to start the car via jumping the starter relay and it does run.......extremely rich..


TR-125 in the lexus manual requests an ignition switch check. Any easy way to reach the connector/switch without pulling the dash apart ?