rb20 weird electrical problem once engine is warmed up

[rswails]

My S13 rb20det just started acting weird once the engine warms up / gets hot. One thing is, the engine temp gauge ( using s13 cluster ), will suddenly jump up a good bit when any extra electrical load is added. Also the idle will drop a tad bit momentarily ( prolly a spike in alternator load ). This can be turning the blower motor for the heater on, or hitting brakes, etc. As soon as I let off the load, the coolant gauge goes back down. If I turn my blinkers on after engine is warm, the coolant gauge will dance up and down with the sequence of the blinker haha. Also when warm, many times when I add electrical load my radio will turn off, and turn back on. Its like a quick voltage drop or something. None of this happens when the car is cold; radio never goes out when adding electrical load.

Also, when the engine is cold now it runs kinda crappy, then all of a sudden after maybe 3min of driving engine runs fine.

Alternator is putting out 13.4 volts at the battery. Datascan is reading 12.5 volts though.

Finally, every now and then when the engine gets hot ( about 190 degrees ), the idle gets terrible and car will even die out sometimes. BUT if I fake the engine coolant sensor signal in Datascan to a lower temp ( 100 degrees appox ), the idle goes back normally.

My guess is maybe coolant sensor or knock sensor. I have already replaced one knock sensor and it didn't help. Didn't really want to spend $150 to replace the other one if there is something I can do to rule that out. Also could be a lame electrical short somewhere I guess.

Please help guys this is really annoying.

[Gabes13]

Check your grounds (block to chassis, chassis to battery) and battery connections. Maybe even add some more grounds.

I had a similar issue when I had a ground issue a couple of months ago. The temperature gauge would go all over the place; literally all the way past the "H". I know for a fact my car wasn't getting hot, bc at that temperature, the water would have been boiling all over the place and it wasn't.

Are you still using the stock alternator? How old is it? Maybe your alternator is going out?

[rswails]

I am using an s13 alternator. I don't know how old it is, I just know voltage at the battery is 13.4 volts when engine is running.

[xxsptcuztomsxx]

Sounds like an issue with the temp gauge circuit. I once insalled a water temp gauge to the factory temp sensor and noticed that it dropped the oem temp gauge down close to the bottom...probably due to the amperage draw from the other gauge... Sounds like you have a short or somethin up with the temp circuit. On a side note.. the temp sensor plays a part in idle control.

[rswails]

Ok guys it got worse. Now my car cuts out completely and all electrical devices shut off except the starter; the starter will actually engage like I'm trying to crank car with engine on. If headlights are on, they go completely dead. This mostly only happens when going over a bump, or when hitting the gas hard, so something I think is shorting when there are bumps or I drive jerky. Now since its such a huge current draw I was guessing it was a large electrical component. First I completely disconnected the alternator; after a test drive, problems persisted. Then I disconnected the small wire going to the starter, problem persisted. I don't see any melted wires. No fuses are blowing when this happens, I am stumped. Help please.

[rswails]

Ok, now for some reason the starter doesn't engage when the problem occurs. Do you think maybe it could be an ignition circuit problem? Everything is going dead (engine momentarily dies, headlights, accesories) and I hear a machine gun clicking sound. I think that is a relay(s) clicking somewhere around the drivers side dash board. A reliable way of reproducing the problem I've found is to accelerate hard, or brake hard, so I've been doing that back and forth in my drive way. As soon as the gforces of doing that stop, the problem stops. I read it could be ignition switch or relay problem. I have tapped both of these with hammer while car is running and problem wouldn't reproduce. Do you guys have any idea what this could be with this new info? I am so tired of working on this. I can't even drive it to the local Nissan expert for him to maybe fix it.

[Liquidus]

I've had that machine gun clicking sound come on when working on my car. It would happen when I was trying to start it, and my windshield wipers turned themselves on. It sucked. Found a wire for powering something on my dash touching ground.

How hacked up is your wiring harness? Does it still only happen when the car is warmed up, and not at all when you fool the engine temp sensor into thinking it's lower temp? As this post has progressed it's been hard to tell when this happens. Is the temp now irrelevant and it only happens when braking and accelerating?

It seems like what is happening is that under g force you're losing a ground, or a power wire is touching ground, causing the car to die. But also, for some reason putting the car into 'Start', as if you were turning the key to try and start it, but because of the ground issue, the starter never engages, and relays click instead, like my car did when I tried to start it.

I'd say almost certainly that it is not a relay problem, but definitely a wiring problem somewhere, probably in the ignition system considering it sounds like the car tries to put itself into 'Start' mode while it's happening.

Considering it happens under g force, I would try CAREFULLY and gently pulling on different parts of the harness and see if it happens.

[rswails]

I fixed the problem guys. Thanks for all your help. 8 hours of work tearing s*** apart and problem was fixed in 30seconds. The body to engine ground near the drivers side strut needing attaching. I found it by pure luck. The problem got worse and I noticed I could shake the car while idleing to get it to mess up. Then I noticed if I pushed back on the engine it would cause the problem to occur. My eye just happened to catch that old loose ground and I said hell, I'll try to connect it to see if that works. That ground has never been hooked up, but evidently some other ground lost connection to cause that ground to be needed at this time. Maybe my engine mounts aren't ground well anymore?