# SR20DET Alternator grounds and other electrical questions.



## theCanucklehead (Oct 24, 2018)

Hello, I'm currently having trouble with my battery on my 95 240sx not charging. It has an sr20det blacktop swap out of (i believe) a kouki s14. I recently just swapped alternators and the battery still wont charge so I want to go through all my grounds and check them. I cleaned and reattached the 8mm ground on the back of the alternator but still no luck. I only just notice that there is another wire hanging free in the engine bay, seeming to come from the same harness as that small ground on the rear of the alt, that to me looks like it has to be a ground as well (first picture seen below), although i could be wrong, wiring is for sure my weak point.

https://imgur.com/LdpSjMn

The next issue is something more obscure that ive been having a lot of trouble finding much of any info on. When I first had the car a few months back, i was picking over the engine bay and decided to replace some fuses to see if things would work better. I ended up destroying the main 100a fuse because i didn't know it was bolted in. Long story short, in the process of replacing that 100a, i ended up losing one of the two bolts (the right hand one connecting directly to the positive battery terminal).

https://imgur.com/fLbv75G

So what I did was just use a random bolt from my interior that happened to fit (thats the silver one, maybe from the inside of my door when i was removing speakers, I cant really remember). Anyway, after I installed that, the next time I drove it was when the car first showed signs of charging issues, so I feel like having a bolt made of the wrong material could be doing something fishy? again wiring is really not my strong suit so i just dont know whats plausible and whats not. Either way, I'd like to replace that bolt with one that is designed for this purpose, but i need to know what exactly I'm looking for. Its a 10mm from what I can remember but what material should I look for? Is there any rating system for how much current it can handle? any help with either of these issues would be much appreciated, This car is so close to running and i just want to get it fixed up for summer at this point.


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## theCanucklehead (Oct 24, 2018)




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## smj999smj (Jan 1, 2006)

That's a pretty big ground cable! It looks to me like the end of the negative battery cable that bolts to the engine, which would explain why your alternator isn't charging. As far as the fusible link bolt, it just holds the cable to the metal plate on the side of the fusible link box. Any steel bolt will do just fine as long it's the correct length. The bolt you have in there has a 10MM head, by the looks of it, so it's probably 6MMx1.0 thread. The original bolt wasn't very long, IIRC; maybe 10MM long?


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## theCanucklehead (Oct 24, 2018)

smj999smj said:


> That's a pretty big ground cable! It looks to me like the end of the negative battery cable that bolts to the engine, which would explain why your alternator isn't charging. As far as the fusible link bolt, it just holds the cable to the metal plate on the side of the fusible link box. Any steel bolt will do just fine as long it's the correct length. The bolt you have in there has a 10MM head, by the looks of it, so it's probably 6MMx1.0 thread. The original bolt wasn't very long, IIRC; maybe 10MM long?


Yes the original bolt was much smaller and i think made of bronze-silicon. But as for that big ground cable, where would be the best place to mount it? I know there are several points both on the body and the engine but my bay is pretty cramped so if i coukd ground it as close to the alternator as possible that would be great


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## theCanucklehead (Oct 24, 2018)

Okay so a bit of an update. I went out and grabbed some bolts to ground that big wire. The bolt was a perfect fit for the holes in the block just below the intake manifold, but slightly too large to fit through the mount on the cable (that tells me it may not be supposed to be mounted there, but I figured a ground is a ground and its better than having it flopping around all over the place). I used a rasp to slightly widen the hole and it bolted right on. As soon as I went to start it, my starter died (unrelated, id been having issues with it for months and had just tried to rebuild it with a ka starter because i was told it was easy, but not a single part fit so i put the original back on, must have made a mistake rebuilding it cause the solenoid wouldn't even click) . So, got a brand new starter, hooked it up and went to start it. It cranked over like new, and idled well. Also, my battery light wasn't coming on on my dashboard, so I was hoping for the best.

BUT, after letting it warm up for a few minutes and going to take it up and down my road, i quickly noticed that the car wouldn't let me rev past 3 grand. I left it for a day or so, then hooked a booster pack up to it and started it just to let it idle for a while and see how it ran. On startup, my air fuel ratio was 14.5-14.9. It'll rev all the way to red line with the booster hooked up. Afr leans out to about 12 flat if i rev to about 5000-5500. Seems to run fairly smooth overall, although I did notice that none of my gauges light up, but they do function as intended otherwise. (ive removed them before, easily couldve messed up a connection). As soon as I take the booster off, I can hear the engine start to run more sluggish, and my air fuel ratio also slowly rises to mid 15s, sometimes jumping as high as 17. I always shut it off as soon as it starts creeping this high. 

These are similar symptoms to what was happening before I had replaced my alternator, but with some slight differences. Mainly, beforehand if I charged the car for a while, it would run well until the battery got low, then it would go into 'limp mode' and only let me rev to 3000. the gauges also would stop working at that point and the car would buck under any hard acceleration (hard for limp mode at least). Now, any time the car is running off excess power (booster pack, jump starting it, etc) it runs fine. Revs strong, smooth idle, reasonable afr (definitely needs a tune but its runs well in perspective). The gauges also all work, but if i do something that requires extra power (lights, radio, my radiator which is hooked up to a switch) the tac will dip 100 revs or so, although the engine sounds like its holding steady. As soon as I take off the booster, it'll keep running but slowly degrade, as if the alternator is almost charging the battery but not quite(it is a used alternator, same output as the original). I haven't kept it running in that state long enough to see if it'll die. I'm sort of at a loss because I'm really bad at most things electrical, but I do have some things available to me that i could try.

I've been looking at high output alternator kits and swaps, or just aftermarket ones, but don't want to spend a bunch of money and time hooking one up if it still isn't gonna charge the battery. Its also occurred to me that my battery may just be too small (it is a low profile one because my intercooler piping encroaches on my battery tray). And lastly, I'm sure this could be something to do with a sensor, but looking at my ecu its actually missing the light that flashes the engine codes (i can literally look through the hole into the ecus internals). So I cant read the codes unless I get an actual reader which i do plan on looking around for. What I do have is a piggyback that came with the car. Its a Perfect Power SMT 6, which isnt made any more and I can find almost no info on. The previous owner said it has a tune on it and just needs to be hooked up to "run perfect" (his words). Its crossed my mind that the limp mode could easily be the ecu getting some strange data from any number of sensors seeing as the engine is moderately modified but the ecu is stock, but A, I have no clue how to wire it up and B, even if I could I feel like it wouldn't make a difference because of the apparent charging issues.

If anyone has any ideas, or could at least point me in the right direction it would be a huge help.


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