Hi Ya'll Greetings from Tx,

I just picked up pretty good '96 LS400. Drove great on the test drive and ran well for about 3 days. After a few days of driving I noticed that when cold, my tach was jumping around and the vehicle was slipping into neutral or changing gears erratically. Initially, I suspected a transmission valve body, but now I am a little more confused. I have documented the problem with this video:


(Note that the problem has really quickly progressed rapidly and gotten worse over the last week)

I am no longer convinced that I have a transmission issue. I think it might be something else. The only code I am throwing is a P0420 which is a bank 1 catalytic converter. Now, normally, I could drive this thing for years with that code (my county's emission standards don't require me to fix it to pass inspection). I suppose that it is possible that the catalytic converter is just so bad that that I am getting poor performance, but I can't possibly figure that that converter is causing a tach surge.

I can't imagine it is a crankshaft position sensor and it is unlikely to be just the tach needle, because the car is acting funny like it is missing or bogging down or shifting erratically. I have ALL the service records and see that the ECU fix was performed by a professional shop about 10 years ago. Without any codes I just don't know where to go. Any suggestions?

Brian

 

You need to real time monitor engine RPM with a scanner to see if the engine is really jumping revs. I'm guessing no but the ECU thinks it is which is messing up shifts and general drivability.

 

The engine isn't surging. Just the needle jumping around.

Brian

 

I think you have to run down the trouble code. Might be a failing oxygen sensor confusing the ecu. My other thought is a wiring problem or bad ground.

 

Recently I acquired a 1996 LS400 with 220k miles. Test drive went well so I paid $2900 cash but I suspected the seller wasn't telling me everything. After 2 or 3 days, I felt the transmission acting strange. The Tachometer was randomly jumping around and she was shifting strangely. I posted a thread and didn't really get any good clues.

An old tranny guy suggested 4 oz of Trans X be added and driven for a few days. I have driven over 1 million miles in first gen LS400s. I was horrified. I have NEVER put any additives in my transmissions so I was hesitant. The service records on the car indicated the leaky capacitor issue had been addressed in 2012.

I went down and bought 6 quarts of Toyota type 4 at fluid. I added 4 oz of trans x and drove it 50 miles. Then I let the car sit for a week. Then I bought a 2quart bucket and started cycling tyranny fluid. 2 quarts out, 2 quarts in. Drive 20 miles. Then repeat twice till I cycled all 6 quarts.

Fluid out was visibly dark and had a slight burnt smell.. after 6 quarts it regained a little pink.. My problem healed itself and car seems to be performing well now. I just purchased 6 more quarts. And will periodically repeat the 2 quarts out 2 quarts in for the current oil cycle.

Hope this helps. Only try at your own risk.. it may be too late for you, but it wasn't too late for me.

Brian

 

It's good news that the trans is working properly again.

From your description it sounds like you did three fluid exchanges. The dilution calculator says that you got about 54% new fluid mixed with whatever was initially in the unit. Eighty-four percent new fluid will occur sometime around the 7th exchange. This is all theoretical, of course. Drain/fill is a PITA process. You might be better off taking it to a dealership and having them do a fluid exchange (not a flush).

 

Very cool. Thank you.
Brian

 

i'm still hesitant to put anything other than toyota type-iv ATF in there, but glad the trans is better!

 

You can have the instrument display rebuilt for the jumpy tach.