avalon42

iTrader: (1)

So my friend tells me that his (my old) LS400 has been acting up. Doesn't throw a code period. So I borrow it for a couple of weeks, and low and behold, it did it.

At first, the problem only happened when after a really long, long drive, and especially if the weather/engine is hot, but now I notice it does do it all the time, albeit hot weather/engine antagonizes the problem.

Hesitation
Struggles to accelerate
Feels almost like pulsing..

I checked the cats, they are not glowing red. Pulled both coils, tested their resistance, for the heck of it, just replaced them anyways. Plugs and wires are fine, correct gap and test within resistance range. Checked for arching and pinching too, that's not happening. Read on a thread here that sometimes the camshaft sensors will go bad. Tested them and they were well within range today. Tested and swapped IACV just in case, same effect. Swapped TPS and MAF off a working vehicle. No change. Changed the fuel filter, ran 3 bottles of Chevron Fuel System Cleaner (spread out over a week and half though), running 91 octane. The ECU is not throwing any type of code.

It's almost as if the timing is being retarded intermittently.

I know its not the trunk wire harness either, I fixed that and elongated all the wires myself with solder and new wires.

My cousin thinks it's one of the fuel injectors on its way out, but I wanted to throw it out there and see what you guys/gals were thinking.

PureDrifter

iTrader: (10)

ECU checking out?

deanshark

I would lean toward the ECU. There have been alot of threads with the same symptoms and a couple have been fixed after changing some caps in the ECU. But it really sounds like the AFM is bad, sometimes it doesn't throw a code. When you changed it with the (known???) good one, did you test it with an Ohm meter? The problem could be intermitent b/c of the Intake Air Temp sensor inside the AFM. I'm not sure if the IAT can be tested seperately. Did you try unplugging the AFM and drive it? My 93 had the same symptoms until I unplugged the AFM and the ECU goes into fail-safe mode and runs extremely better, but very rich.

ImWildBill

This is what my 1990 LS400 is doing. I'm getting about 12 mpg, no power at all, fells like it's surging also and I hear popping at times from the engine bay (like a quiet backfire thru the intake) and when I disconnected the AFM it ran worse.

avalon42

iTrader: (1)

Thanks guys who posted. It's the darnest thing though...it only happens intermittently, the pulsing is at random, there is loss in power but the fuel economy is pretty darn good. Just got 100 miles on 1/4 of the tank. Unheard of for an LS400.

Which leads me to believe that the fuel pump may be on its way out. I guess I should check the fuel pressure and go from there.

BTW: I did check the very easy crap (air leaks, PCV blockage). If the exhaust was plugged it would run like crap all the time. So my quest continues.

avalon42

iTrader: (1)

Check the resistance in your coils. You're probably dumping the unused fuel into your exhaust, killing your cats in the process. SEARCH and you will find the specs to test resistance.

From checking the driver side coil, that sucker is just way too damned close to the driver side exhaust manifold. These Japanese engineers are just hilarious sometimes.

fluxedup

when i replace my ecu, I think I'll add some dielectric heat sink compound prior to installation, it will be interesting to see the results......

avalon42

iTrader: (1)

Wow, I was totally off on this one...I am now leaning towards the transmission shift solenoids going to crap...basically putting the ECU in fail-safe mode. This guy posted on a different car site and its starting to make sense based on the symptoms of the car. The coils, wires, everything checks out. Not losing fuel economy. My guess is that the solenoids can fail without sending out a readable code. After reading the Toyota factory service manual for information, it only affirms my suspicions.

Reading on this forum, I think Och also had this problem on his LS400, based on a few of the posts I was able to follow. Don't know if he ever solved it...couldn't find more information on it.

My friend are going to pull off a few solenoiods from junk cars and try them out. Hopefully, we'll get one that works fine and will solve the problem. Tranny Filter and Fluid was changed 30k miles ago, used T-IV stuff.

https://www.clublexus.com/forums/sc-...placement.html
https://www.clublexus.com/forums/ls4...or-softer.html

Found these links also, just wanted to post and keep them on this thread. I will do the work tomorrow, confirm results this Sunday. Wish me luck guys, this LS400 has been a trip.

----------------FROM CARGURU SITE------------------
http://www.cargurus.com/Cars/Discussion-t16041_ds50496
The problem you are describing sounds alot like what I was experiencing. I have a 91 LS400 with 242,000 miles. The car starts right up and runs exceptionally smooth. When I first start off from a stop it runs great then no power. I put my foot to the floor and it very slowly starts to gain speed but no real power to speak of. Well I found the problem. The shifting solenoids in the throttle body of the transmission were malfunctioning. When this happens the computer sort of goes into a failsafe mode and shifts from 1st to either 3rd or 4th depending on the malfunction. The car had been doing this for better than 6 months even though I had no codes at all up until about 2 weeks ago when my Overdrive light on the dash started to blink. I bought some new solenoids (they come in pairs) and replaced them last weekend. Now the car feels like a brand new car. LOTS of power and solid shifts all the way through the range. Hope this helps.

dr gtr

I dont know if we have knock sensors but when knock sensors go. The ecu does not get a signal so it goes into safe mode by retarding the timing and running richer to protect the motor.
Hence the slugishness and the pulsating which is the timing being retarded.

avalon42

iTrader: (1)

All I can say is WOW. After spending nearly a couple months trying to diagnose the problem, I think we may have stumbled onto it...the charging system (both alternator and battery) are bad. Had the system tested twice, thank goodness Autozone has that lifetime warranty on their crappy alternator. Since 2007, this replacement will be #5 all on their tab. All bad indicator lights for alternator finally turned on after the Autozone guy tried to test the charge from the alternator. Sure enough it failed. Even though the battery is at over 12V and 100% charged, the test came back with a bad cell. Hmmm....ok.

However, I am not entirely 100% sure it is the issue but will post and let you guys know. Will be delving into that tomorrow, will post when I am done.

BTW, we didnt spend Sunday doing the shift solenoids, we actually spent the day taking apart the timing belt again, under consideration that it may have "jumped". Had about 4 ASE mechanics friends standing around arguing with different diagnosis over the car and it was hilarious. They spent more time drinking beer and smoking cigarettes, I spent more time taking her apart and making sure everything lined up again.

PureDrifter

iTrader: (10)

most rebuilt alternators dont have the voltage regulators replaced, hence your issue.

avalon42

iTrader: (1)

Closer analysis revealed power steering fluid discreetly tracking its way down and slowly dripping on the alternator. P/S pump, alternator, and battery were toast. Cell in battery was bad, had to check it TWICE for about 2-3 hours before it was determined to be bad.

Car is back up and running, however, getting a slight shudder upon acceleration. No codes still, but going to check the usual suspects: EGR, mounts, then driveshaft.

avalon42

iTrader: (1)

Ok, so it seems that my problem is a TWO-PART problem. The transmission is OVERHEATING, I know this for 2 reasons: 1) the base of the shifter is HOT, I put my hand down barely and it felt like someone was putting the kettle on. 2) SMOKING after a long drive. I know its not the valve cover gaskets/spark plug tube seals or even the P/S fluid because all were checked while the car's engine was running and have been changed a while back.

The P/S pump was leaking fluid and it was trailing back, so once I put the new P/S pump on, I cleaned everything off with a pressure washer and engine degreaser, so it's a clean slate. Double checked my work, and it looks solid.

But the transmission overheating is the culprit here. ATF is at correct level. I want to re-visit the solenoid problem, but was wondering if any of you guys had an ideas thoughts on what it might be....there is not CEL or O/D lights or codes, but I know 100% ATF is spewing out after a long hot drive.

There is an aftermarket oversized transmission cooler that I put on a while ago and dual electric fan setup on the car. Thank God I put them on there, otherwise I would have been stranded on the side of the road.

PureDrifter

iTrader: (10)

if something's smoking it may be the return or high pressure hoses for the PS. it can spray fluid right onto the cats.

avalon42

iTrader: (1)

But I've been driving for a while and there is no fluid loss from the P/S system...I double checked that PD...forgot to say Thanks for replying btw, kinda frustrated with this car. I told my friend to look into retiring the vehicle through BAR, but now that I've stepped back into it, its almost like an addiction to work on the ole LS again. Unfortunately, like a drug addiction, since its hitting my wallet running around getting the parts and driving the ole V8 again!

https://www.clublexus.com/forums/ls4...-strainer.html

Found this tidbit through searching, gonna keep digging on here and into the transmission pan tomorrow to get this sorted.