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· Registered
1 Posts
Discussion Starter · #1 ·
Hello friends, i’m posting today because i’m having some electrical issues with my s13. The car has a sr20det swap. This thing keeps toasting 62 redtop ECU’s and i’m trying to get to the bottom of it. I’m no stranger to working on my cars, but know very little about how electrical systems work. If someone with knowledge on the subject could give me some pointers, that would be much appreciated. I’ve been researching for days but haven't come across any articles on my situation.

I’ve owned this s13 for under a year and taken it to one track day. The car ran fine until after an hour of driving, I spun out and the car would not run. It would fire up, run very rough, and die. After troubleshooting every component, the car started up totally fine when I replaced the ECU. After speaking with one of the previous owners, he said the car had gone through many fried ECU’s for the same reason. I’m trying to figure out what could be causing this.

The shop that sold me this car gave me an entire vehicle harness to replace. However, after closely inspecting, it seems this new one is quite a bit different. I can sense disaster if I rip my existing chassis harness out and replace it (it’s a little over my head). For starters, the engine harness and the rest of the chassis harness are intertwined when it runs by the fuse box down through the front of the car. On my current one, they are separate(wiring specialties sr20 engine harness). Also, my replacement harness has a smaller ECU pin connector (maybe a KA harness?)

I am wondering if there are troubleshooting steps I can take to try and solve this ECU frying issue without having to replace all the wires in the car? Use a multimeter to trace where the electrical surge is coming from? Try to find loose wires that could be grounding out? Would little messy exposed wires cause enough surge to kill my ECU time again?

On a possibly related note, the car has a very severe parasitic draw. The battery will go dead in 15 minutes. That draw goes away when I remove the 75A linkable fuse in the fuse box. This is labeled the alternator fuse. The car will run without this fuse, but no electrical components will work (tail lights, radio, gauges, etc..). I’m thinking that this draw could be caused by a bad diode in the alternator? Allowing the electrical current to flow backward when the car is shut off? Or maybe something else? Could this in away way be linked to the ECU killing issue?

Thank you very much for any advice!

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· Administrator
2,120 Posts
Hi there,
I'm sorry you're going thru a bunch of ECUs. Honestly I don't really have much advice to give you besides getting the FSM and going through each connection.
I personally went with a wiring specialties harness for my swap and it seems to be holding up.
I'd definitely check out each and every ground first.
Then I'd go and check out the harness for any evidence of rubbing near the fenders (where your tire would rub at full lock)

That wiring job doesn't look clean so I suspect two wires are shorted to each other that probably shouldn't be.

Another thing would be to approach it as if you were wiring the SR swap for the first time using the factory harness for your car. There's been a few wiring guides out there that you can use, that way you can go down one by one as if you are wiring it for the first time.

Or you can buy one of these. I don't know what an sr ecu costs today but I'm sure the days of $50 ecus are long gone.

· Registered
s13, galant v4, e30, datsun roadster
5 Posts
Assuming the harness grounds are all good:
Check to ensure the engine block, head, alternator and starter all have good clean grounds to the chassis/battery negative. If you run the battery in the rear run a min of -4ga wire from the battery ground to the chassis, Alternator and starter.
Be sure your cylinder head, block all ground to the same point as the -4ga wire you run from the battery negative.

When there is not ample grounding the ECU can be shorted out and damaged. This most often happens during cranking/start but can also happen from the alt or coils not being grounded properly.

· Registered
8 Posts
You need to remove all the tape and inspect every single wire for flaws including the ECU plug. I would replace the entire engine harness also. DO not use an aftermarket harness like wiring specialties, I've found issues with their harness such as ECU pins that don't plug in fully to the ECU causing intermittent issues with spark for example. Get an OEM harness and pull all the tape off and inspect for damage and flaws. Do not use any butt connectors. Only make soldering connections with heat shrink. Learn how to cut and solder wires properly. Make cuts inches apart so the soldering don't over lap. Put double heat shrinks and shielding cable over important wires like MAF TPS CTS etc...

Use the FSM and ECU pinouts to trace every wire. Go through them step by step using a multi meter and visually inspection. Use continuity testing and wiggle the wires during the test to find flaws. Make sure you test THROUGH the fuel injectors, i.e. from the ecu plug, through the injector, to the other side of the injector to it's power source wires. It is time consuming ofc I spend 40 hours going over my electronics. But when its done its done right and you can drive forever
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