Extrudedco

I recently purchased a 1991 LS400 as a project (turning someone's beater back into the car it should be), but I'm having trouble identifying the cause of the running issues.

Things I've replaced: valve cover gaskets, distributor caps + rotors, spark plugs, spark plug wires, one ignition coil, battery (swapped with known good one from other car), spliced new wire into trunk hinge harness, PCV valve, radiator cap, assorted hoses

Things I've cleaned: EGR valve, throttle body, idle air valve, decarboned combustion chambers

Symptoms: The trac off light is on (I'm assuming this is a symptom of the rest of the problems). It's rough and slow to start, idles very poorly, stalls or doesn't accelerate under light throttle, and blows some black smoke out the exhaust during startup. Engine speed wanders at all throttle positions (haven't tried full throttle, but I would rather not drive it with how it's currently running). Before I replaced all the ignition components, it would stall whenever it dropped to idle (yes, the previous owner was driving it this way, along with the about to burst tires on 19" chrome wheels). 236k miles on it.

I plan to check the voltage output at idle next to verify the alternator is working, bypass the fuel pump resistor, and block off the vacuum lines to and from the power steering valve. I'll probably grab a fuel filter if I get a chance today as well.

Any thoughts as to what else I should look at? I'm starting to think it may be a fuel supply issue, but I don't have a pressure gauge to check.

Neofate

iTrader: (1)

You've covered alot.. I would be looking into fuel myself at this point and maybe ECU. Have you pulled codes?

Extrudedco

Alternator is putting out about 14v at idle. Not great, but should be adequate.

Plugging up the power steering vacuum lines definitely improved things, but I'm still seeing stalls, running rich, and wandering engine speed.

There's no CEL, so I assume that means there's no codes stored...but I could be wrong.

Extrudedco

Well crap. Fuel filter replaced, and the idle is almost where I would expect it to be. It's still a little rough, but not any more than I would expect from a little carbon buildup or dirty injectors, and stalling doesn't seem to be an issue any more (in park at least). Bypassing the resistor didn't have any effect.

Now that it's running somewhat better, other issues are becoming more clear. While in park, revving the motor up to 2200rpm results in it surging up to 3000rpm and back down continuously. Suddenly releasing the throttle causes the engine speed to dip below idle before coming back up into the 600-800rpm range.

I'll mess around with the car more tomorrow, but as I was closing things up and testing it I noticed the surging went away when I had the MAF disconnected, leading me to believe that the MAF might be toast.

Extrudedco

Worked on it some more today. Tested the TPS, found out it was bad (resistance increased relatively smoothly as throttle increased, but on throttle release resistance would spike before dropping back down). Replaced the TPS and identified a couple damaged vacuum lines. Replaced them even though they didn't seem to be leaking.

The surging is gone, but the rough idle and stalling have returned, along with a slight miss. Disconnecting the MAF didn't seem to have any effect.

Only things I can think of looking at now are the fuel pump, possibly the other ignition coil.

Extrudedco

Tried to pull the trac code since I was out of ideas, noticed the CEL light wasn't illuminating at all. Turns out several bulbs had been pulled out at some point, and two more were burned out. Engine is throwing code 13. Time to see if the newish looking timing belt was installed wrong.

Edit for updates: Checked ignition coil resistance, neither matches up to what little I've been able to find online about their specs, but both the new and old ones have the same resistance. It looks like the passenger camshaft might be off by one tooth (which would explain the code 13), I'll get everything lined up and check again when the rain stops. Looks like I'll probably be tearing it down to adjust the timing belt tomorrow.

Extrudedco

Hah, starting to feel like I'm talking to myself here, but I figure I might as well document things in case someone else runs into a similar situation.

Checked the timing belt today, it was clearly off. Once I had everything lined up, the passenger side cam was off by about 8 teeth. So much for 'one tooth'. I tore things down and got the timing belt lined up properly again. Only issues I had were from not pulling the spark plugs (air spring effect complicated getting things lined up properly, but less effort than actually pulling the recently replaced plugs) and getting the tensioner back in (used larger bolts from distributor housing to get things locked into place, then swapped the smaller bolts back in). It now sounds like a Lexus V8, instead of an old beater!

I still have a bit of a rough idle, and the check engine code 13 is still there, but it looks like I should be able to get it registered and through emissions once I get tires safe enough to drive on.

I also need to get the interior cleaned and put back together, new speakers installed, dash lights, fluids changed, windshield replaced, and other odds and ends bolted back together, but there's now a light at the end of the tunnel.

I also need to get the alternator swapped in my Millenia so I can sell it!

tomtheslac

Wow, you seem to be as stubborn as I am...seems like all is well in hand. Have you checked your fuel pressure? I have a 91 as well, so you can bypass the low pressure 9v (low demand) cycle on the fuel pump to full 12v (high demand). Just use a paperclip to bypass the fuel pump resistor under the MAF..see if that cures your rough running...easy to try.

Twista4004

Let's bring this old thread back to life!

So I just bought myself another LS. This one a '94. I bought it as a parts car for my '93 but decided I'd try to fix the issue to see if I might end up with two good cars then figure out what to do from there.

Issues:
Horrendous idle
Serious Misfire
Dies when shifted to drive (only lasts about 6 seconds in drive when it doesn't die immediately)
No power (was able to drive it for a 1 minute length of time once. barely accelerated then promptly died immediately after getting to about 25 mph; which was a struggle)

Just bought the car two days ago and have been busy working and such. I've only spent about 1 hr on the car so far. I noticed that there was no AFM on the intake after I got the car home. I went to the junk yard and pulled two. I tried on of the two I pulled. No change. Didn't have anymore time to spend on the car since so I haven't tried the other yet, nor have I checked to see if the harness is getting any power either.

There's a blind history on this car but I have the feeling it's something electrical and easily fixed. Any thoughts?

Thanks In Advance

dicer

With all the talk of ECU capacitor problems, and after checking the most obvious things, ecu should be next on the list.

Twista4004

Yeah, Think i'm going to pull the ECU from my good LS and try it in the new one.


**Also, I spoke to the previous owner last night and he (not mechanically inclined) says that he had someone working on the car over and over with no progress. Just a couple hours ago, I figure I'd check the distributor. I pull the covers off of Bank 1 (driver's) only to see cylinder #1 plug wire is literally cut. It's a clean cut too. Clearly done purposely.


****Check these shady MF'ers that are working on your cars causing you to dump money then eventually jack it up so bad that you just decide to sell it to some guy like me for $200.****


*I put a new plug wire on it and now the car actually stays running. It's progress.

*Idle is still like cuddling a bull though it does stay steady at just about 1-1.2k
*There is no power to get past 15-20mph.
*Will only rev to 3k if it's feathered. If it's WOT, nothing past 2k.

dicer

Wow, wonder what else has been goofed up? Sad thing is that sort of thing can happen anywhere you take a car to get it fixed.

Twista4004

Well, I pulled the valve covers off and saw that one cylinder was literally flooded with water. Another cylinder just did not look right.

So this car when I drove it home was running on no more than 5 or 6 cylinders.

Furthermore, I found that the damned plug wires were in the wrong order on bank 2

1UZ= greatest engine ever lol smh. I'm amazed that this thing would even run.

----



My goal with this car since it is a spare was really to make it a menace to society...or at least a menace to AMGs, M3/5s, anything non Lexus LS really.

You guys think there's any hope in this motor?

Rolled and pulled front fenders. Yes, I know they look ****ty. Rolled rears.





Full header back dual exhaust. Got the car with them on there. Sounds raspy but maybe that's because the engine is in rough shape.








White one is my daily. Much cleaner, more comfortable. Gold one is pretty hard.

TREYFIGGS

Lets bring it back to life AGAIN!!! Did you ever figure out the idle problem? By the way I love the gold one. That thing is nasty. My LS is running really rough at idle. No matter if in drive or park. Think the IAC valve may be an issue. I am ignorant to when it comes to these motors. Thanks in advance.

Trey