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Discussion Starter · #1 · (Edited)
2000 Prelude Base

A good bit of background info is possibly necessary for this. I've had the vehicle for tad over two years, engine blew 11 days after obtained.
Shell has sat for the two years. I've spent the time slowly rebuilding the engine. fully built block blah blah, not what post is for.
Dropped engine in few weeks ago, wired up the engine bay harness. Using P28 ECU w/ S300, simple OBD2 ->1 harness.

Day 1 crank up attempt; Key works for accessories, primes fuel pump, does nothing in ON. Green-key-light giving me weird mixed results.
Immobilizer key light readings, just for reference.
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I jumped the starter off with the battery directly, to make sure it was good. Turned over the car instantly, sounded like it properly cranked with fuel+air, then suddenly cut off anyway in a very instant halt. The key was in and clicked forward ofc. So I needed to fix the key issue before being able to figure out why the engine seemed to turn off by itself.

First I thought it was the main relay, but the board was in very good condition. I still ran through some of the troubleshooting with it.
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I stopped once I reached the point where I was needed to start putting the key to the third click, because the car was already so broken. Everything before that was flawless. The board I cleaned off anyway, and resoldered a few spots that just seemed like it didn't have enough. Sadly I thought I had taken a proper photo of it when I had it out, but this is all I've got. If anyone thinks I should get a better pic, I can certainly take the time to get it back out.
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So, since that did nothing to help, as I had tried again a few times, it was time to discover more of, and bypass, the immobilizer system.

I already have ECU portion of immobilizer system "fixed" since I have the P28. So during searching, I came across this thread.
This is the Starter Cut Relay circuit. Poster said to ground the LT BLU wire, which goes to immobilizer.
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So I cut the LT BLU, and spliced it into another wire's ground nearby, used for one of the gauges.
I spent a while looking into it, should be perfectly fine to do. Wire gauge was thicker than stock by a bit, and even combined total peak amps, should be fine.

Well, lo and behold, I go to crank the car, and I'll be damned, it turned over with zero hesitation! Huzzah.
Except it would just keep turning over, and not properly start. I know for a fact I have spark at all four plugs, as I had individually tested each one previously.
But then, cluster lights suddenly goes out, then my gauges. Car dies completely. Check the battery, like lower 4 volts.
Uh, was not just from me cranking the starter a few times... Charges up the battery with other car, disconnects jumper cables, checks voltage, high 11s.
Goes back to car, clicks accessories on, before I can get further than that, everything dies again. Oh boy. Go back, check battery, voltage lower 4s again.

So now I check out the immobilizer circuit properly.
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I also then found this post from other site, Says to just splice A3 to A2 together, which would be exactly what the original post said to do, except instead of directly grounding the SCR's LT BLU wire, you splice it to before the clutch switch, which only grounds the LT BLU wire when clutch is pushed down, rather than directly draining the battery the moment the ignition switch it on.
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But this would still technically start draining the battery the moment you engage clutch, right?
Although it also says to leave the plug undone from the Immobilizer entirely.

So, I undo the direct ground, and just kinda clamp the LT BLU wire back together.
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I am aware you normally use splice connectors for two wires, but it worked well enough for a quick fix to the LT BLU for now.

So I started working on depinning the Immobilizer's plug.
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Also; If you can tell me what that yellow cable is for, that would be cool.
The car has a quick release system, but the airbag plug does seem to be right up near the release.
This yellow cable pretty farther down. the steering column.

I did depin it successfully, just taped the LT BLU + GRY for a test.

Charged vehicle up again, check voltage while charging, good high 12s or something it was.
Undo the jumper cables, check it again, we down into 10s and dropping fast. The key is NOT in the vehicle at ALL now.
I haven't even gotten to test immobi bypass attempt #2.
So I went ahead and undid the tape, installed the pins back in, and plugged it back into the immobi.
Now everything is back to exactly how it was before the battery started magically draining. Yet it still does it now.

So, here are the two videos of me testing out wtf the battery is doing.
First one mostly shows how it dies and charges by being hooked up or not.
Second shows how there is lingering voltage in the frame that I am picking up between positive terminal and frame.

Don't hose me for the missing negative tip, literally broke off like half an hour before I recorded these videos.
I absolutely despise the fact YT decided to automatically force my first video into a "shorts" format because it was less than a minute long.

So does this mean that there is a short literally anywhere on this mf? I still haven't even gotten to turn on my brand new engine 馃槶
Any ideas where to even begin? I don't understand why this became a problem after the starter cut relay test, because I put everything back to normal.

OH YEAH, also I have the negative terminal grounded above the passenger headlight, and down where that bracket that comes off the transmission is.
This is correct, right?

4 Posts
Discussion Starter · #2 ·
Oh also I made sure the aftermarket jank radio wasn't having any poorly done wires touching the frame behind it. I did redo a few wires, and even redid the front speakers' connection. but it's still having no difference in issues.

4 Posts
Discussion Starter · #3 ·
Yesterday night I had someone mentioned it could just be the battery, went and got it tested, 9 CCA, didn't have enough energy to print the ****in' receipt lmaoo
And I had left the house with it as a supposed like 11.8v I had tested it at with the meter beforehand.

It was indeed just the battery, I'm seriously such a fool haha.
I've spent so many days focusing on so many other wiring issues, and the battery was new, so I didn't think anything of it at all.
But I probably blew up the battery cell(s) from how intensively I had been testing the system over and over, jumping it off to full charge, using it all up again shortly later, repeat.

I just fixed the immobilizer system properly. Also important to be noted; When I stated
which only grounds the LT BLU wire when clutch is pushed down, rather than directly draining the battery the moment the ignition switch it on.
This is wrong. That is not how the battery, or grounding on a vehicle works. I was severely mistaken, and probably too tired haha.
Grounding it like that will not begin draining the battery.
Although I still chose to connect the two LT BLU + GRY pins from the immobi, I jumped off the clutch switch to bypass clutch anyway. Resulting in the same exact scenario of the SCR's LT BLU always being grounded. No freak battery drain.
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