Burnt out ECU?

[LuckyX2]

So I was driving my 240sx back in the fall before I left for college and as I was driving I suddenly lost power. The lights dimmed when the power went and It didn't want to rev above about 2500rpm so I couldn't go much faster than 15mph or so. I was only about two blocks away from where I park the car so I pulled it in there and shut it off where it sat until I just came home from college recently.

When I got home I pulled the valve cover and everything in the head looked fine, also the compression test read 175 across all cylinders but the plugs were black when I took them out. I cleaned the plugs, put them back in, started it once, pulled the plugs again and they were just as black after the one start. When it runs, it runs so rough that the engine actually shakes from the super rich conditions.

So where I'm at now, I'm thinking that there may have been a short which blew something in the ECU. Everything in the engine seems to be fine mechanically so I'm thinking it's an electrical issue. The lights dimming when it went also signifies to me that something electrical happened.

I now have a Haltech Platinum Sport 1000 ECU that I was planning to upgrade to anyway but I want to make sure it's safe before I hook it up. The wiring harness for the ECU is cut up a bit from the previous owner's installation of a S-AFC II so I'll start there by cleaning up that wiring and doing it nicely. Also there's a single wire on the ECU plug that is cut and nothing is soldered to it; it's just cut and not even cleanly I might add. It's a yellow wire with a green stripe, is that supposed to be cut? Aside from cleaning up the ECU wiring, what other precautions should I take before hooking up my new ECU? I don't want to possibly burn that one out too.

TL;DR: My car is running so rich that the engine shakes violently when at idle. I think my ECU is blown. I have a Haltech unit to replace it but want to make sure it's electrically safe before I ruin that too.

So what could be the reason for this and is it safe to install my new ECU and start trying to diagnose it then?
Thanks guys.

[PyR0NiAk]

Green/Yellow is A/C Output..

[LuckyX2]

Well I guess that solves the cut wire problem... Thanks

But should I still be worried about hooking up my new Haltech ECU?

[zachattack_5491]

Green/yellow is not the same thing as yellow/green. Yellow wire with a green stripe is the signal from the speedometer to the ECU, but it's just about as important as the AC wire.

I've read before that incorrect MAF wiring can cause the ECU to get fried. Check over that wiring. I wouldn't plug in any new hardware until you're pretty darn sure everything has been sorted out.

[PyR0NiAk]

I definitely read that as Green/Yellow... My bad.

[LuckyX2]

Well my speedometer has always worked fine, it's my tachometer that hasn't worked since the sr swap but I was told that was due to going from a sohc ka to the dohc sr and that the stock tachometer would only work with a sohc engine. Should the speedometer still be working with that yellow/green wire cut?

And also I have checked into the MAF wiring. I have a Z32 MAF currently and I have the two black wires connected to ground, the black/white wire going to the 12V pin and the White wire going to the 0-5V pin as per the diagram on Jim Wolf's site. The only thing I could see was that the connections weren't sealed as best as they could have been and possibly could have shorted if some water got to them.

I'm going to be eliminating the MAF anyway when I go to the Haltech's MAP sensor so it's kind of a moot point.

Is there any other specific place I should be looking in the electrical that's semi-common for it to short and cause an extremely rich situation? I'm really not looking forward to going through the whole harness but that might be necessary

Maybe I should just put down the $275 for a new one from wiring specialties? I just don't know. Thanks again for the help guys, please keep the suggestions flowing.

[PyR0NiAk]

Maybe I should just put down the $275 for a new one from wiring specialties

I got tired of dealing with my maf and how ugly my wiring looked, and did just that..

[LuckyX2]

The more I think about it, the more I'm thinking it is something with the MAF. This whole thing happened maybe my first or second drive after putting in the z32 MAF, having the ecu tuned for the MAF and putting in new spark plugs.

I drove it maybe a total of 30-60 minutes after putting in the MAF, ECU and new plugs before it went...

Does that seem about the length of time it would take for a MAF to fry an ECU? Because I've read that it's not instant but that it will burn the ECU out after some time running. I was also driving pretty hard for 15 minutes or so before it broke so the MAF was outputting higher voltages than just at idle or normal driving.

[zachattack_5491]

If you've got the cash, most definitely go with the wiring specialties harness. You can be 100% positive that all the wiring is legit, and that's the best feeling ever.

[LuckyX2]

I'm gonna test the MAF hopefully tonight or tomorrow with a multimeter and by unplugging it at idle. If I unplug it at idle and then it idles better it should be the MAF that's causing it then right?

If unplugging the MAF doesn't fix the idle then I'm gonna go ahead and replace the harness. If I find it is the MAF tho, I'll save my money and use the stock harness.

I'll update once I've gotten to test the MAF. Thanks again everyone.

[PyR0NiAk]

Good luck. Keep us updated.

[LuckyX2]

Hey guys, I just read the MAF lines with a multimeter and here's what I got:

3V on the 0-5v signal at idle
http://i45.tinypic.com/2ibhhe0.jpg

and 22V on the 12V line
http://i50.tinypic.com/28kj8qp.jpg

When I read the lines without the MAF connected then it still reads 22V on the 12V but 0V on the 0-5V

So basically the MAF is overvolted and is also outputting about 3 times what it should be at idle. Also, it idles the same with or without the MAF so I think the ECU was permanently broken by this. Could this still be a wiring issue or is it the MAF for sure?

Thanks again.

[zachattack_5491]

I can't imagine how it could get 22 volts. Terminal E should be the same as battery voltage. Unplug the connector from the MAF and test with ignition on. Terminal B should be .8-1.5 volts at idle.

Actually, nevermind you already tested with MAF unplugged. That's wrong for sure. I would lean towards wiring, or possibly the ECU causing the high voltage because it's messed up.

[LuckyX2]

well scratch my last post, turns out the multimeter was busted, seeing as how it read the same 22V right off the battery terminals while the car was off...

I did find a few things here and there to take care of first before I start diagnosing again. I'll update once more then.

[LuckyX2]

So it's up and running now, running well actually...

I was trying all sorts of diagnostics with no success until yesterday when I finally decided to read the codes off the ecu. It flashed some codes but I was too slow to catch them. So I tried to read them again but it only showed 55 which is the code for no faults. I thought if I tried to start it then it would get the codes again, so I went to do that and what do you know; it started up first crank over and it idles beautifully, even revs fine now too.

Unless I did something in the process, it looks like the ecu just needed to be reset. I'm a little upset it took me so long to get to this point but at least it wasn't anything bad.

Thanks for the help guys.

[Mysteryimpt]

Hello Sorry I am having the same issue here. I was wondering if you could kindly clarify how you fixed the issue in your last post. I understood you started your car to clear the code 55 but then what happened? lol sorry been working at the car issue for whole darn night it wont rev pass 3000k. Please help