SC400 1993 - Less than 170k km

I shipped off my ECU for repair and ended up receiving a different repaired ECU. I've confirmed that this ECU functions properly (tested in friend's SC400).
The car sat around for a yeah while I was waiting on the ECU from delivery issues. Upon installing the new ECU, I received a Code 15 CEL. This is an ignition fail code.
There is nothing wrong with the ignition. We have spent all Spring & Summer trying to get the vehicle running. It will turn over no problem, then cut off seconds after the ignition (electrically).

Several people have looked into this, here is a list of what has been tested.

• Ignition - For sure working properly. All aspects tested from the parts to the leads to the electrical. Engine keeps running with a little contact cleaner spray in the air intake. Clearly running all 8 cylinders.
• Fuel - No problems here.
• Fuel pump ECU bypass - Tried this, no help.
• IACV - Cleaned.
• TPS - replaced (both the standard TPS and the trac. TPS).
• MAF - No issue.

I would like to add, that there was an aftermarket looking box which was tapped into the ignition power wire, fuse box positive, and battery's positive terminal. We noticed there was a fuse connected with this box which had melted the plastic of the fuse. We pulled out the fuse, which actually got the car running. I drove it for 2 days, and it would randomly shut off while idling (same Code 15). We decided to take the box out, to find out that this was the fix for daytime running lights. Unfortunately taking the box out returned the vehicle to it's original Code 15 state of not functioning. All the electrical testing for the ignition was done after this event. The box remains removed.

I'm starting to think that this is some sort of anti theft thing kicking in since I swapped the ECU, but I have not heard of this on the 1st gen of SC400s, nor have I been able to find much info on it.
This has been a huge battle, I would love to drive this mint car again and keep it on the roads. Any help is GREATLY APPRECIATED.

Hoping for the best!

 

I could be wrong but I believe a CEL 15 for SC400's and LS400's refers to a second igniter for those engines?

You could have a faulty igniter that needs replacement (if so, order a new one from MyLParts or Amayama to save on cost for an OEM one). Usually igniters don't fail (although any of them can after 30+ years of service... but usually they do not) but one thing that can make them fail is some issue with one of the factory ground wires on the ignition circuit that the igniter is attached to or any way in which the grounding points of that circuit are being inhibited by something.

This happened to me for a while with my 2JZ-GTE engine swap until I figured out that my igniter failure issue (again, igniters should rarely if ever fail) was related to a missing ground cable. The same basic principle of how a Toyota igniter operates and can have an issue will be the same for a 1UZ-FE V8 engine.


However... I think these two threads are worth reading first since you mentioned the odd aftermarket wiring that was (or still is) in your car.

https://www.clublexus.com/forums/ls-...-new-coil.html

https://www.clublexus.com/forums/per...l#post11321030

Also, check the ignition circuit diagram in the TSRM and then check all your plastic connectors on that circuit and all the terminal wires in them for any signs of compromise, fraying, etc. But you did say you have already checked all those so... as a last suggestion you should just make sure that the connectors all flow their proper +12V and Ground for each appropriate terminal.

Reason I bring this up is that once I had a weird issue once tracking down an injector misfire on my engine harness. I tested every single connection and finally found that one injector connector was putting out less than +12V on the positive terminal wire and +3-5V on the Ground terminal. I pulled the wires out of the plastic connector and they put out clean +12V and Ground signals. I put them back in again and once again got the previous readings. I ordered a brand new OEM connector and installed the terminals into that and.... suddenly now I get clean +12V and Ground readings on that connector.

The connector wasn't broken in any way. It was just old. None of the other old connectors on that circuit were affected in the same way. I can't explain how the plastic of that one old connector was able to conduct electricity between the two isolated terminals but it did... somehow. Installing a new OEM connector solved that issue.

For what it's worth, that sort of thing can happen so if the info in those two threads doesn't point to a solution, just double check to make sure the same issue with an unbroken yet still faulty 30+ year old connector isn't affecting your ignition circuit.

To be clear, that which I've described about my weird connector fault issue is also something *extremely* rare to ever happen. But in the spirit of problem solving it's good info to be aware of as a last, last, last resort test while you're troubleshooting.