Goesta

Hi, I've been trying to fix my 1994 LS400 for about 2 years now and I'm so close to just sending it to the junkyard and buying a bike. This might be a long post, but I will describe what caused my issues as clearly as possible, what I've replaced and how the car is acting at this moment.

It started with me accidentally trying to jump start the car with 24 volts (not noticing that my uncle had changed the cables and didn't put them back for 12V). This absolutely destroyed my ECU (at least).

Since then I have changed the ECU and had it rebuilt with new caps, I have changed a TPS sensor, O2 sensors, MAF-sensor.

Now the car runs exactly as it should for about 15 minutes, but then the CHECK ENGINE-light comes on along with the TRC-light. The car won't shift gears, is slow and stalls at sudden stops. After this happens, I have to give it gas to start the engine. It feels like it's misfiring at this point and the exhausts smell like gas. The engine bay also seems abnormally hot, but I can't say for sure because the gauge shows it as working temperature. Sometimes the check engine light and TRC light flicker, as if theres a bad connection somewhere, engine rpms also fluctuate when they do. When I read for codes, the only one I get is TRC 51 meaning "problem in engine control system", which is so incredibly vague.

I've had mechanics try to get this car going, but it never lasts more than about a week.

I would really appreciate any help!

paulo57509

1. When you start the engine and it runs well for 15 minutes, does this time interval begin with the engine cold? By cold, I mean the engine has not been run for at least over night.
2. I think the car not shifting gears seems to me a symptom of something else malfunctioning. On a basic level, the transmission shift is determined by throttle position, engine RPM, engine vacuum, road speed.
3. TRC 51 - I don't know what this means either. Does TRC mean "traction control"? I do know that when an engine electrical issue is detected, traction control is disabled. I don't know if "TRC" and "CODE" mean different things. NOTE: A lot stuff on the internet regarding specific traction control trouble codes is so old that most links are no longer active.
4. I searched and found another meaning of a Code 51: Switch Condition Signal. This definition came from the attached document (I wish I could find this document with better resolution). Open the document and scroll down to "Code 51" and read through the diagnostic tree - notice that there are electrical checks for three sensors.
5. Related to (2) and (3) above; are you reading the codes thru the DLC1 connector (jumping terminals) under the hood or do you have a scan tool? Does your scan tool show live data? If you can read live data, look at what data the sensors are reporting (to the ECU) and compare them to normal readings (sorry, I don't have those). You should be able to tell if something is way out of range; example - if the coolant temperature shows 20C but the engine has been running and should be 95C.

This is confusing. You say that the engine runs bad after 15 minutes. But there are times when the engine will run OK for a week?

1. What have the mechanics been doing that makes it run well for a week?
2. Is the car being driven the same way for that week and differently for those 15 minutes?

Related to connecting 24 volts to the battery - have you checked every fuse and fusible link for opens?

Goesta

1. It doesnt have to be from cold. Today I went for a test drive after changing the MAF, and the car was great for about 15 min then the problems began. Then after like 30 minutes with the hood open I could drive another 15 minutes before it came back.

2. I was thinking it might be in "limp home"-mode or something, altough I don't know if that's what it does. I can feel the transmission engaging when I select P, R and D. The gauge cluster also shows which I'm in. But when the problem arises, the engine can't run under its own steam so to speak, and it reacts to throttle strangely.

3. The TRC is traction control. Makes sense it would be an electrical issue after the 24 volts, but car electrical systems may as well be witchcraft to me.

4. I am using the DLC1 with a small wire. If it were ENGINE code 51 condition switch would be the correct code, but this is a code from the TRC light, meaning "problem in engine control system". I don't have any better scan tool for this unfortunately. Maybe I should check the computer responsible for TRC if I can find it. But it's strange that it's intermittent and simply "goes away" after a while and then comes back.

Yes it's very confusing, but I haven't really used the car that much since I can't trust it anymore. But sometimes it has worked for more than 15 minutes, I'd hate to pay for another tow truck.

I don't quite get what you mean by "fusible link for opens" but I have checked all the fuses that I can find. Thank you for responding, means alot.