Frustrating 1992 Ls400 !

[BangEmBoy]

I have a problem with my LS that I posted in the new members forum (Introduction), but no one has gotten back to me as of yet . Thinking that I may have put my problem in the wrong place, I am submitting it here for your help.........

Earlier in the year I bought a 1992 LS with the insurance money from my 1990 LS that got totaled . I got a good deal on the car because the previous owner had problems with the ignition system and wanted to get rid of it; the car had been sitting up three years . Being a mechanic, I figured it wouldn't be a big deal to fix .

I got the car home, changed all the fluids, gave it a COMPLETE tune up (plugs, wires,caps & rotors) and changed out the fuel pump as well as the related filters . When I tried to start the car, it wouldn't .So I attempted to put the computer into diagnostic mode, and then found out I couldn't because it didn't have an ECM . I purchased one, ran a diagnostic and found out that one of the coils wasn't firing . After I replaced it, the car ran just fine, and became my daily driver . On my way to work one day, I noticed white smoke coming out of the tial pipes . I pulled over to get a look see, and found out that the vacum pressure switch on the p/s pump had malfuctioned and was letting the fluid get sucked back into the intake manifold . I blocked off the lines and headed to work . On the way home, the car started loosing power, I couldn't get it to go over 40mph . I had it towed home . The next morning when I started the car, I ran just fine; but on my way to work, it started to loose power once again, and I noticed the low coolant light come on (bird cage with a ball on top) .

Since then, the car idles just fine, but when you give it gas,it bogs down and shuts off . I have done a leak down test, a compression test, a fuel pressure test, replaced the timing belt, the water pump and bought another computer; but its still doing the same thing .

Can anyone out there offer any advice concerning this ? Thanks

[landar]

Sorry to hear about all of the problems. The first thing to do is to stop throwing so many new parts at it in a 'shotgun' attempt to hit the root cause. That costs a lot of unnecessary money and could even introduce a new problem. You need to take a more disciplined approach to diagnosis.

Ok, so the engine will sometimes bog down and die when you give it gas but idles fine, right? If it will do that in the driveway, I would buy a can of starter fluid and spray some into the intake snout WHEN it starts to bog down. If that revives the engine, then you know you have a fuel problem. Else its spark. But it is a simple, cheap way to begin diagnosing.

[BangEmBoy]

Thanks for that bit of advice, but I do believe that my problem is alittle more complicated than that . I would like to clarify and state that contrary to what you may believe, I am not using a shot gun approach, the repairs that I have done were already going to be done anyway . I concientiously take care of my vehicles; that fact that the LS sat up for 3-4 years before I bought it, demanded that I perform the repairs ....

But you're right, I do have a fuel problem, but not in the sense that you are thinking; I am running way too rich, not lean . Secondly, eventhough my car idles, giving it just alittle bit of gas stalls it, and the only way that you can get it to run and idle again is to pull a spark plug out, turn the engine over a few times, reinstall the plug, and then it will run again .....

I just came in from checking the IAC valve, and while I was at it, I kicked the computer in diagnostic mode . I am getting codes 14(ignition no. 1 signal) & 31(air flow meter signal) . Anyone familiar with those two(2) codes ? .......

Am hoping that someone out there has been where I am at now and can advise me as to my next step ...... Is it possible that when the p/s pressure valve was letting gas be sucked back into the intake manifold that it stopped up my cats, and I am getting too much back-pressure ?

[landar]

Maybe I was too quick to call your shotgun approach as I really don't have first-hand knowledge of your situation. We just get lots of owners on here who needlessly replace parts.

If your engine is running rich, I would think you would be seeing some 'black' exhaust and perhaps smelling some raw fuel as well. Typical problems in that area are bad or intermittent sensors, such as a temperature sensor. You do not mention if the symptoms get better/worse when the engine is cold or hot. That could reveal a lot.

As concerns the codes...you mentioned that you already replaced a coil. Which one? Maybe the other is on the way out. Or perhaps a rotor/cap is not on properly even though you replaced them. The air flow could be the MAF sensor. Did you clean the throttle body? Have you checked the air flow sensor for proper operation? You can 'ohm' it out. And maybe there is an intermittent connection to the sensor. That happens quite often with older cars.

You probably already know all of this so I am bowing out now. Best wishes.

[BangEmBoy]

I really appreciate you taking the time out to advise and help me; thanks .

I have a running LS(1990) that I use for a daiy driver, and all the parts that I even thought were bad has been swapped between these vehicles . So now both vehicles have new everything on them lol (The 90 LS runs perfect) . But to get back to your question, it doesnt make i difference if the car is hot or cold, it still idles the same; and yes it is running super rich .

I have been told that my ECM is in limp home mode because the ECM is not getting a rebound(confirmation) signal from the no. 1 igniter . I was given a diagram that showed which pins to check for that signal, but it was wrong because none of the connections that plug into my ECM have ten(10) pins. Can anyone help me with a diagram ? Gonna go clear the ECM and switch the igniters to see if the ECM throws the code to igniter no. 2, and post my findings .

[fsuguy]

Hi,

You could do a test on your TP sensor. Landar has given you good advice, and I think some of the symptoms sound like TPS failure.

By the way, If you can post some instructions on how to post a diagram on this site, I would be able to upload a picture of the correct diagram from my repair manual (mine is a '92 as well).

hope this helps.

[BangEmBoy]

Ok I'm back from working on the Demon Spawn lol, what a day ...

I started by swicthing the igniters, the TPS, and the whole MAF assembly . Car still runs the same . Kicked the computer into diagnostic mode, no codes now . Took the parts from off the 92 and put them on the 90, the 90 still runs great, so I guess that I can rule out those parts as bad . I did find a broken wire (white/black) in the trunk wiring harness, soldered in back together, but it didnt make a difference to my problem.

My mind is telling me that I have a blockage in my exhaust system somewhere, but since I'm no Lexus expert I will await some feedback on that thought . If anyone out there has any suggestions, advice or help; please feel free to post it . All post will be taken very seriously . Once again, thanks to everyone for your help concering this matter .

[Daniel091]

Try switching the ecu's. Worth a try.

[Daniel091]

Try switching the ecu's. Worth a try.

[1990LS400]

It still sounds like it could be one of the damned trunk hinge wires. You might recheck them and especially to see if there are other breaks in the black/white wire. A broken truck hinge wire is often accompanied by the Reverse indicator light in the cluster flashing intermittently while driving forward. Your symptoms sound exactly like what happened when the trunk hinge wires separated in the 90 LS I drove for many years -- like someone stuffed the exhaust pipes with corncobs.

[BangEmBoy]

Thankx for that bit of advice, I will pull the wiring out again and do another check for broken wire's ......

Once again I would like to thank everyone for thier advice and help with my problem . We haven't gotten it figured out yet, but with my skills and your input, we will get right ,or it's going to the junkyard lol .

Here is an update on what I did today on the Demon Spawn...... I had gotten feedback telling me to check out the IAC valve, so I took it off today and ohmed it; the readings that I got say's that it's bad . I had a spare, ohmed that one out, and it's bad too; but before I spend the money for a new one (have you seen the pricse for those things !), I'm gonna take the one off of the 90LS and see if it works first . I also disassembled the upper intake so that I could properly clean the throttle-body, because I had gotten feedback on that being a problem area as well . I'll put everything back together tomorrow and post my findings here ...... One other note, I have gotten alot of feedback about the possibility of the ECU being bad, well we can rule out that therory . When I puchased the car, it didn't have an ECU, so I bought one for it; and I also bought a just in case spare . But you and I both know tha they can go bad at the drop of a hat, so to rule them out as being the problem, I took both ECU's and installed them one at a time into the 90LS and it ran like a champ . I then installed the 90LS's ECU into the 92LS and it still ran the same as before .

So as you can see, I take everyone's suggestions very seriously, so keep em coming and help me to lick this problem . Thanks again everybody .

(Note : To all that's reading this post, keep in mind that if I give the car any gas It stalls out, and the only way that I can restart it, is I have to remove a spark plug and let it run with it out before I can relace it and get the car to idle again)

[LemboMods96LS400]

The map sensor was not all the way put in after fixing the p/s vac' problem.. sounds like map. An yes same characteristics of TPS problems

[BangEmBoy]

Thankx for your feedback, am going out now to work on the Demon Spawn lol . I will definitely pay close attention to that . Actually, I'm gonna switch the intire Upper Intake from the 92 to the 90 and see how that works .

[fsuguy]

this is a long shot, but how are your battery terminals? I had been having power issues with my '92 and when I looked under the terminal cover, the positive terminal was all but corroded off. After replacing it, everything was back to nice and sweet!!

[BangEmBoy]

Brand new battery and terminals, thanks for the feedback though ........

I worked on the Demon Spawn yesterday, what a d#m day ! Started out by taking the intake back off to mack sure that there was no broken wire's or improper grounds . Upon installing the intake, stud after stud broke ! Got new ones today, and will get back to work on it tomorrow . i also bought another Idle Air Control Valve and fuel regulator, even picked up some injectors for a good price . When I get done tomorrow, everything on the top of the engine will be new . Hopefully with everything that I have done, this will cure my problems . Once again, thanks to everyone for your feedback and help .

[Daniel091]

Wow. Thats alot at once.

[BangEmBoy]

I definitely have a back-pressure problem thats stopping the car from cranking . Is there anyone out there that has experienced this problem ? If so, what steps did you do to fix it ?

[BangEmBoy]

First off I want to thank everyone for thier input and advice on my post . I have found out what my problem is, but not what's causing it . I have so much back-pressure that it blows off my vacum lines ! I have a cap on my intake that blocks off one of the ports, and at every turn of the engine, that cap blows off . All of the thing's that I have done to the LS needed to be done, so I aint mad, I just want it running again . Do you think that when the p/s pump valve went bad and was sucking the fluid back into the intake that it burned a valve, or stopped up my exhaust system ? Looking for help and advice on this . Thanks

[fsuguy]

Hi,

This may be out of line with your coolant light coming on (in your original post), but have you had occasion to check your fuel pump resistor? If that thing is on the blink or acting up when it gets hot, it may be affecting your fuel pump/fuel supply after some time of being active and could be causing the symptoms you described, especially since you have replaced the coils and ECU. If you have a set up to test your fuel pressure after the engine is warmed up, you should be able to rule the possibility out at any rate. If you don't have the pressure testing equipment, I believe there is some way you can bypass the resistor temporarily to test the fuel supply circuit. My understanding (and that is subject to correction by the much more knowledgeable crowd on this forum) is that the resistor is active during normal driving and bypassed during higher demand conditions, but it may be the other way around!!

HTH

Oops, just saw this second page, so you can safely ignore the above...

[BangEmBoy]

I want to thank each and everyone personally or thier feedback to my post . It is rare that I get stumped on a vehicle . I have been in the automotive field for many years, and if I would have used my mechanical common sense, this problem would have been licked some time ago; but by me not being Lexus familiar, I chose this forum for help .

Now that i've had the time to analyze thing's to the fullest, I believe that I have a stuck valve, collasped rings, or a blown head gasket . My reasoning ? I have way too much back pressure on the engine, and also when I did my leak down test, # 8 was leaking substantially . Eventhough there is no water mixing with the oil, I'm leaning heavily on the head gasket therory because I noticed today when I had the car idling that steam was coming back out of my intake opening when I took off the MAF tube, and the fact that I have to take a spark plug out to get it to run .

I could be wrong, so therefore I am asking the community to give me thier feedback once again .

[SRK]

What do you mean "back pressure"? Exhaust back pressure? Easy to check with a rag over the tailpipes and get someone to rev the engine - if no exhaust gas flow, blocked cats. If you do mean exhaust back pressure I'm at a loss to understand how you could think a stuck valve, or collapsed rings, or a head gasket would cause that. None of them can.

If you mean crankcase pressure then the diagnosis leans towards cylinder compression and leak-down, and that's easy enough to check, because the only thing that can cause excess crankcase pressure is piston sealing.

You said you checked fuel pressure, but have you monitored it while trying to rev the engine? A weak pump can make pressure but not volume, or volume but not pressure whereas a good pump can do both.

You have used a complete shotgun approach so far, and then defended your replacement of parts as "needed doing anyways". Mechanics like that put me in business thirty years ago....

Diagnose it. Stop throwing parts at it.

[landar]

Ok I could not stay away and I have a 'burning' question. You have said in several posts that "the only way that you can get it to run and idle again is to pull a spark plug out, turn the engine over a few times, reinstall the plug, and then it will run again ....."

That makes almost no sense to me. Can you just pull any old plug out? Or one in particular? Is the plug wet with fuel? The engine should run on seven cylinders (albeit a bit rough). If you are consistently pulling one particular plug, then that could be a clue. If any plug, then you are being fooled and it is just coincidence.

And if the cats do happen to be plugged, could you not just temporarily drop the Y pipe connections and see if it improves? That is not a fix, just a help in diagnosis.

[BangEmBoy]

Instead of replying to the negativity of the recent posts to my issue, I'm gonna be the mature one about this and just say that after tearing down my engine today, I had a blown head gasket between the no. 6 & no. 8 cylinders .... Anyone with any kind of mechanical apptitude knows that (1) if you have a stuck valve, when the engine come's up on the compression stroke on that cylinder it's gonna blow the compression out of the cylinder because the valve is stuck open; (2) if your cats are stopped up, everytime the intake valves open up, compression is gonna leak back into those cylinders, because it has nowhere else to go (3) if you have ran a car hot enough to the point that the ring's collapse, you are gonna get crankcase back-pressure that's gonna come back out of that cylinder as soon as that valve opens up, and (4) if you have a blown head gasket between two cylinders, the pressure from the compression stroke is gonna leak to the ajoining cylinder and out the valve's as soon as they open .

I learned a long time ago that if I don't know something, I ask; I don't jump to conclussions or tell someone else that they are wrong, just because I don't have or know the answer . I get me a book , or lean upon the knowledge and experience of someone that's more knowledgeable than me . And just for the record, I am an ASE Certified Master Mechanic with shop's (Supreme Clientel) in two (2) loacation's (Alabama & Florida), and have been in this field for over 30 years, but that doesn't make me the smartest or the best mechanic in the world, nor does it give me the big head to think that I'm too good to ask for clarification of an issue that I'm not familiar with .

Before I go, I just want to let everyone here know that, It's best to fix a problem than try to put it off, or patch it; because it will come back to bite you . Some people say that I took a shot-gun approach to my problem, if thats your opinion, then that's on you . I know my skills, abilities and bank account lol . When I bought the car, It had sat up for 3-4 years . I didn't know it's history, and I wasn't gonna take the chance of just patching a problem that could possibly lead to another problem . That's why I fixed everything, I would rather be safe than sorry; my wife and daughter will be driving this car . I care more about them than somebody's opinion . (Remember the old saying about opinions lol) .

My new heads (shot-gun ? lol) will arrive at my shop in Alabama Saturday morning, by Saturday evening I will have the car back together and driving it to my daughter in Florida . I'll keep you all posted .

I want to once again thank the people that offered me advice and feedback concerning the issue that I presented in this forum . I learned alot from you guy's/gal's . Special thanks goes out to Mark, thanks man for everything today .

[SRK]

I have done a leak down test, a compression test, a fuel pressure test, replaced the timing belt, the water pump and bought another computer.

Can anyone out there offer any advice concerning this ? Thanks

So you did the leak down and compression test but forgot to tell us that it failed miserably? No wonder the water pump didn't fix it......

[BangEmBoy]

If you would quit being an a-hole and read the entire post, you would know that the leak-down and compression test's failed . The water pump couldn't fix what was already broken . Go find you a Barbie doll to play with and leave me alone !