If only it turned on...

[zdiehl12]

Ok guys so here's the deal; I just recently purchased and 1996 240sx with a Redtop Sr20det swapped into it. The guy who sold it to me said it was an s14 redtop, but the ECU says S13 redtop on it... He wasn't much of a techy though and the guy who owned it before him was the one who had done the swap and he was a mechanic. Anyways, he showed me the car and started it right up with a battery jump and it ran very nicely. Well once I got it home I went to jump the battery again and smoke started coming from the top of the jumper leads SO I just replaced the battery with an old battery that I had before in a different car, well without checking I was a moron and reversed the terminals... I tried starting it with the terminals switched and quickly realized I had made a careless mistake, I checked all fuses and there was a fusible link and the 100amp engine fuse I believe blown. I replaced them and bought a completely new battery and when I went to start the car now it just cranked... I heard rumor of the CAS going bad quickly so I replaced that, still nothing, just cranking... I don't believe it's the ECU because when I turn the key to the "on" position all my dash lights come on, radio works, head lights work, a/c works. I tested the current at the coil pack harness with an ohm meter and it read out at like 1.2 on the positive pin, .4 or something on the pulse and all of my grounds are good. I've run through all the fuses in the engine bay and under the dash and all are good. What am I missing here guys? My mechanic said to run through all the fuses again because one of them must be blown somewhere. Anyone have any ideas at all? Any help would be great. (also I have searched around through the forums and really haven't come up with any answers for my situation)

[Hijacker]

Just because you're dash lights and stuff works doesn't mean the ECU is fine. They're all on their own separate circuits from the ECU's power leads.

TBH, when you cross the terminals like that, you can dry a whole lot of stuff. So it's difficult to tell you what exactly to look at. Are you certain you're getting spark and fuel? I would get a noid light to check you're injectors to make sure they're pulsing properly and if you have a way to check for spark, do that too.

Lastly, terminal crossing can fry wires and melt sheathing. As a last ditch effort, I would also consider going over the harness looking for areas that have melted.

[zdiehl12]

Hijacker, I'm getting fuel but NO spark, I know that just because my dash lights work isn't necessarily a determinate of if I have or have not fried my ECU, I guess I will also check into it. I was thinking that I would probably pull the harness and see if I happened to melt something. Mostly I was just wondering if anyone had done such a thing as I had and what their findings were.

[Hijacker]

Are you getting 12v at the coil packs? If not, double check back to the ECU 12v supply and check it for 12v (most conversions tap this circuit to supply the coil packs). If you're getting 12v on the common supply at the packs, then the issue is in the ignitor or ecu.

[zdiehl12]

Ok so two things happened to me... I tested and got 12v from each coil pack BUT when I go to crank the car now it cranks over but slowly starts to die and when I try to crank again the engine doesn't turn and all electronics go out....

[zdiehl12]

I have a working ignitor I'm going to borrow from a friend and try tomorrow, I guess tomorrow we will know if it's the ignitor or the ECU

[zdiehl12]

So, I did forget to mention something... when I turn my key to the "off" position there's like a buzzing noise that comes from the ecu? Only happens for a second but it's pretty audible, also upon further investigation I realized the ECU led never lights up. Should this info lead me to believe that it's the ECU that is bad? haha

[blkvrtswp]

Slow cranking = low battery juice or compromised starter wiring. It's probably not going to be anything else. Buzz comes from low battery juice, I've had that happen a bunch of times.

Resolve the probable dead battery before trying anything else.

I've seen a crossed jump blow out an ECU several times, try sniffing/smelling the ECU right by the plug. If it smells burnt, open it up and look at the end where the plug is to see if there is a melted spot on the circuit board kind of near the corner.

[zdiehl12]

I replaced both battery and ECU just to see what would happen. I now have the car cranking over pretty quickly but of course, no start. When I did duck my head into the passenger footwell I see that there are some burnt wires. I had let a family friend who is a mechanic look at the car and he patched together a few wires but clearly not all of them. The wires that are burnt out are on a connection that is white? Not sure exactly how to describe it... Thanks for the response and maybe you'll know something more about this?

[zdiehl12]

I know just what it is... Its the damn F3 plug and there's a few wires on top of the plug that are like totally melted out... WOOO! I think I found the true problem, I just need to figure out how to re-pin it all...