Jakester71

So I traded my sc400 for an ls400 I had the car for about a week and then the battery died. So naturally I bought an alternator and got my battery tested, the battery checked out and was supposedly fine so I installed the new alternator. I turned the car on drove it around and everything was fine. The next morning the car started and then died on my way to work since then the car has basically been sitting in front of my house. I have a voltage reader and for some reason the car will charge when I have it in park, the voltages drop but still stay at 13.9 when in reverse but when I put it in drive it will rapidly drop and stop charging. So today I bought a new ecu hoping that was the issue and when I plugged it in everything seemed to be working correctly until I tried to start it. The car would turn over but not start. I now have the old ecu in so it will start and run but it does what it did before, charges in park charges in reverse but in drive drains the battery and kills the car rapidly. NOTE: I’ve checked the fuses and they are fine, I also checked the pig tail connection to the alternator and they are fine. I’ve also check the wires the go directly to the positive connection right by the battery.
Please send any advice you can this is my daily and I need to get it fixed asap

oldskewel

iTrader: (1)

Weird problem.
What year is your LS400?
Did you check voltage when in N or L (or others)? Weird that it is different for D vs. P or R.
Are you measuring voltage with one of those cig lighter gauges, or with a voltmeter at the battery?
Does turning the headlights/window heaters/AC on/off give any different weird behavior? Those are ways to instantly increase the electrical load and could be useful info for troubleshooting.

Yamae

Are engine mounts OK and harnesses are not damaged?

The reason why I ask you this is that I had a bit similar experience at my local shop. It was not a Celsior but my local shop owner asked me for a help to diagnose an intermittent engine halt problem using my tools. I'm an electric guy and I have different kinds of tools for E.

According to the owner, the problem was first happened when the customer was running at a very rough road. But restarting the engine, he was OK to drive again. A few days later he had the problem again but this time it was at his house when he started the car and shifted the AT lever.

Using an oscilloscope with a clamp current prove, I measured the current at the battery cable and I found a big current spike when the AT lever was shifted. At the same time I also found an unexpected big engine movement/shift. It was caused by the shot engine mounts. The movement damaged the harness, the shop owner and I understood. I was busy on that day and without analyze the problem more, I left the shop. The shop owner informed me later that he replaced the harness and engine mounts and there was no more engine halt problem.

CLLEXUSS

Yes could easily be a short somewhere unrelated to the ecu, this was my first impression as well, it's just a matter of tracking it, its shorting somewhere my guess as well