'91 Ls400 Dies While Driving, Wont Start, Starts Next Day

[JHK]

2 Seperate issues:

1991 LS400, 250K+ miles on car, 180k+ on different motor. Less than 1k miles on timing belt/ water pump, plugs, wires, etc. regarding standard tune up. Replaced fuel pump prior to this so under approx. 30k on pump.

Car has always ran flawlessly, even with high miles. This was the wifes car until fuel pump died and she lost faith in its safety. So its been a second car that family members have used when needed.

#1 - It's now started to die intermittently while driving. Most recently, drove 30-ish miles, let off throttle to exit off freeway, then back on throttle to continue on exit ramp.... No power, no rpm's with accelerator pedal pushed, drifted to stop. Tried to restart- crank no start. Towed to work. Let sit for 2 days, car started right back up.

It has done this 3-4 times prior with first time it starting back up immediatly. 2nd time had to let it sit 20 mins. 3rd time a couple hours until it was towed back to house.....as soon as it was off the tow truck, it started back up. This time, 2 days.

My first thought is crank position sensor, second is Cam positions sensors. These have never been replaced on the car. Due to age of car, I assume they should be replaced anyway, but is there a way to trouble shoot prior to throwing parts at it so I know what the issue really is/ was?

#2 - Tranny is slipping when its cold, or when its warm and on an incline. Seems fluid is slighty low (hard to tell with the dipstick on the car and my bad eyes), so I plan on filter/ fluid change, but is there another known issue that others have experienced and fixed?

Thanks in advance.

JHK-

[landar]

If I recall, this topic has been discussed several times before. I believe the issue is the ECU. Sounds heat related. Do a thorough search and it will turn up. Welcome to the club!

Here's a thread to get you thinking -> http://us.lexusowner...or-help-please/

[freegard]

Yep, no bout a doubt it. Sent of for 8 polarized electrolytics for my 94 LS400; just installed them last night; NO EASY JOB, you'd better be VERY good at unsoldering components. Putting the new caps in is easy, getting those old capacitors out is no fun. They are soldered on both sides of the circuit board. The circuit board has two wiring harnesses that are hard wired; so you MUST find a way to do all the work without stressing those wiring harnesses. Anyway, about the circuit board; the board is printed on both sides....

You must melt the solder on both sides before removing the caps. That is a total of 32 points that need to be resoldered. Of the 8 caps I replaced 5 of them were visibly damaged, i.e., had leaked. 1990 through 94 are KNOWN AND NOTORIOUS for this; the caps in the instrument cluster and the caps in the ECU, they SUCKED for some manufacturing reason.

My symptoms were:

Hunt for idle, car jerks when in gear, or has a mind of its own when in park or neutral; RPMs wander from 200 to 1100.

Engine dies at exactly 2000RPM on hard acceleration, every time without exception. This is when I said, "Okay that's it; I am contacting Mouser or Digitec and getting those low ESR, PS series, polarized electrolytics and doing this. Total cost for all 8 was $1.23 cents,

three day shipping was $12.00; it cost me 15 bucks to fix ECU issues. (Oh and about 5 hours to do it; because I am veeerrry sloooow

and I dont care that I am slooow.) My wiring harness is fine and I think the ECU is as well.

The capacitors:

1@! 16v 220uf

1@ 63v 47uf

2@ 50v 10uf

2 35v 15uf

2 10v 100uf

All MUST BE 105 temp. rated.

Fuel mileage is NEVER better than 15.5 MPG irregardless of how gently I drive.

Check engine light is on but cannott get any codes.

But a bad ECU can have many other symtoms too; they vary greatly depending on which capacitor is failing,

how severely the capacitor is compromised and so on. ME! Hey, I did the instrument cluster a year ago, and those issues disappeared

and have been putting up with these other issues since I bought the car two years ago. I KNOW the ECU is part of the

problem; it may not solve ALL the problems but I have a hunch it is going to solve the mileage, and hunt for idle issues.

And 5 to 6 more miles to the gallon; yeah that is worth 15 bucks and eight hours of my time.

I hope I did not hurt any other component fighting with those capacirots to get them out.

My ECU is 89661-50151 a California number. Though I am in Seattle the car spent 90% of its life in Sacramento.

The ECU is sitting right here next to me. Tomorrow I am reinstalling the ECU. That is a little bit of a

task too.

I will let you know the result. By the look of those leaking capacitors I know only good things

are in store, provided I did not damage any components while doing the work.

[freegard]

FIXED...ABSOLUTELY EVERYTHING WORKS NOW. For the first time in two years I do not have a CHECK ENGINE light.

Acceleration is akin to a detuned formula one car; and this car has 251K on it!

No hunting for idle anymore.

No engine failure at 2K on hard acceleration anymore. Absolutely everyhting is fine; I look for ward to twenty MPG now--yes

I will be ecstatic with twenty nevermind 22 23 or 24.

I am so grateful.

All right my ECU is hanging by the connectors (while I test drove it) I gotta go do the tedius remainder of reinstallation.

asta la vista Baby

[curiousB]

Putting the new caps in is easy, getting those old capacitors out is no fun.

They are soldered on both sides of the circuit board. (not really, this is the wicking of the solder in the wave solder process at the factory. The holes in the PCB are plated so the solder is pulled up through the hole.)

It might be easier to cut the old capacitor into pieces with sharp side cutters and get it down to the leads only on the PCB. Then using desoldering wick you can suck out the solder and pull the old lead out. Don't overheat or you will delaminate the copper layers and then its game over.

[freegard]

NO! You are wrong! This circuit board IS copper etched on both sides and is soldered on both sides.

Sure the wave soldering probably effectively wicks as you stated above, however, for our intentions

and purposes (since we are not wave soldering) you must resolder both sides of SOME, NOT ALL, of the capacitors. Using a strong

magnifying glass one can see where there is no copper and where there IS definitely copper connections

on the cap side of the board and for that respective cap to connect to!!!!

Yes, you are right, I did cut them off with cutters until only the leads were left, and still long enough to grab with needle

nosed pliers. But it was still very difficult to pull the cut-off leads out; a result of the low powered soldering iron I used.

But is is very misleading to indicate that the caps do not have to be soldered on both sides of the board when in fact

they most definitely do. I went back and tested them with an ohm meter and sure enough even where I thought

I had done a good job connecting to the copper etching ON THE CAP SIDE of the board, it in fact was still an open

circuit on one particular cap. Scraping the laminate off to expose the copper hurts nothing; it is not game over. Even if you pull up some

of the copper and rip it off the board it is still not game over. It is simply time to do some repair.

To make that connection I had to scrape some laminate off to expose that copper and resolder and BINGO, continuity.

But one better have a magnifying glass because there are also copper etchings a millimeter or two from the cap leads in a couple places

where if you do not look close you may think that those connect to the cap lead when in fact they most definitely do not!

Thank all of you for all the help and support; I greatly appreciate it.

[landar]

freegard, does your ecu board look like this -> http://www.clublexus.com/forums/ls400/597154-94-ls400-ecu-issues-running-rough.html

If so, the board appears to be double-sided with plated thru-hole via's. To replace a cap, I would normally 'wick' as much solder as I could using a copper braid with solder flux. Then, taking hold of the capacitor in one hand with the iron in the other, I gently wiggle the cap from side-to-side alternately applying heat to the connection that I what to move. That way, I can 'walk' the capacitor out of the holes without cutting the cap off of the board.

[brianmch]

This problem is not isolated to the 1st gen LS400 but also noted in the 2nd gen, which I believe is 98-2001. I've got the board pulled from mine now and am ordering caps. Will take it to an electronics repair shop I use as the guy is pretty talented with circuit boards. I'm ham-fisted with those things, but am pretty good with a wrench!