Here's what this 1992 LS400 with real 170k on it is doing now and what I have done to try and fix it. NOTE - I have checked mutiple times and the car is not throwing any codes. Car starts, rev's very slowly. When reving engine accelerates very slowly. When reving to high rpms the drivers side cat becomes cherry red. Car has no power, can not go above 15 mph. Here's what I have done.
1 - Pulled drivers side oxygen sensor and left big gapping hole open in exhaust system. Started car. No change or even minor improvement. Nothing. So I don't think exhaust is plugged.
2 - replaced both coils one at a time with known good coil. No change whatsoever.
3 - replaced MAF sensor - No change whatsoever.
4 - replaced fuel filter and fuel pump. No change whatsoever.
5 - Finally decided to take a vacuum reading at idle - solid and steady 15 inches. According to gauge, This indicates late timing.
6 - Replaced ECM with known good ECM, No change whatsoever.
7 - Checked timing at idle with timing light . Solid 10 BTDC.
8 - removed covers from both camshafts and checked timing marks with engine at zero degrees on main pulley. Marks are perfectly aligned.
9 - replaced throttle position sensor - No change whatsoever.
10 - pulled 2 of the 4 plugs on drivers side and they look fine.
I am baffled.

 

Your car is running too rich with either too much fuel being dumped or not being burned properly

Take all of your spark plugs out to check them. I imagine some of them will be burnt

Your spark plug wires should be checked. You should be able to find a resistance spec on this forum. Check if all of your wires are in spec and replace if not. If they are out of spec, it may not be a bad idea to do new plugs and coils as well, since bad wires could put stress on the ignition system

The other thing to check is leaky injectors. If the ignition system is all fine and the ecu is good,, it could be a bad injector (or more)

https://www.clublexus.com/forums/ls-...o-power-2.html

Long story short, more diagnosis is required

 

So I pulled and replaced with new all 4 plugs on the drivers side. While I was at it, I measured resistance of wires. Coil was 5k. Coil on other (passenger side) was 4k. The 4 plug wires, going front to back, were 5k,14,.15k,11k. The odd thing is the plug porcelain with wires 5k and 11k came out black and dry. The 2 higher resistance longer wires came out perfectly normal looking but they are fed by the passenger side distributor. Hmmm. Would it be worth draining the cooling system and pull the distributor cap on the driver side ? Is there any known issue with these distributors?

 

I don't feel like it's worth pulling the distributors yet. They can fail, but you'd get a misfire condition

Your spark plug wires sound like there were all in spec based on:
http://www.lexls.com/tutorials/ignition/sparkplugs.html

Check the passenger side when you have a chance

 

Pulled passenger side plugs today. resistance front to back was 5,14,14,8k. Plugs that had the 14k wires this time were both black and dry and fed by the drivers side distributor, just like the other side. The 5 and 8ks were normal white but fed by the passenger side distributor. I did not have extra plugs to replace them with so I put the old plugs back in. Everything seems to point to something in that drivers side distributor.

 

I do believe (although I find it unbelievable) I have finally found the real problem. First I pulled the drivers side distributor cap and found the rotor worn and cracked. But certainly not bad enough to explain this. I replaced it anyway because of the cracks radiating from the screws. Restarted car, no change. Then I decided in bed one night to ground the high tension coils of each distributor individually and try and start the car, To my surprise, after grounding the drivers side the car would NOT start, period. But grounding the passenger side had no effect, car started and ran poorly just the same as if it was connected. So I tear into the passenger side distributor and find the rotor completely disintegrated. See pictures. Is this a known issue? I can only guess that the last mechanic overtightened the screws, they both cracked and the one just eventually came completely apart. The question now is how many of the timing belt covers do I really need to remove to get all the debri out ? I'm thinking I really should remove the bottom timing belt cover as the steel top pin is still missing!

 

Don't know how I missed your last reply. Good find

Brittle distributor rotors deteriorating is known but it's not a common issue. Part of it could be over tightening, but age of the plastic also could have made this problem worse

Everything is probably at the bottom of your timing belt by the crank. I would start by removing that one first, but you'll need to pull the harmonic balancer.. That will require a puller tool and a special tool (or some ingenuity) to remove the crank bolt. It would be ideal to be at top dead center before you start. You'll be part of the way to doing the timing belt job at that point..

Check out some other threads and videos about the timing belt job before proceeding further

Alternatively, you can try to clean out what you can and replace the distributor rotors for now

 

Yeah, they tend to crack right at the screw holes (as you can clearly see). Get in there every few years a put your eyes on them. And do not over tighten! I think it's like 8 ft/lb or something in that ballpark.

 

Thanks for all the reply's. It's running great now until it reaches operating temperature/ Then it stumbles terribly trying to accelerate from 40 to 50. I guess something else is still wrong. But strangely cold rums fine.

 

If you feel like firing the parts canon this can cause your issue
https://www.amayama.com/en/part/toyota/8942220010

Don't buy aftermarket. Are you sure the intake has no leaks anywhere?

 

I have sprayed a ton of carb cleaner all over the engine and no change in rpm, so I don't think it is a vac leak. I have also plugged the egr valve, no change in poor performance. Next I plan to dummy the temperature input with a 2k resistor and see what happens. This should tell the computer it's running cold all the time. Will let you know what happens.

 

Funny, but as I read what you did already in the first post, my first thought was "no news on the distributors?" and thought that's where I would've looked next. But then, I do have the advantage of having seen these exact ones, the orange colored ones fail slowly on my car. First they crack, so your timing is a bit off, then they crack some more, and finally you get what you got in that picture - and if your other side is working, you get to drive home on four cylinders, which I don't recommend. The orange distributors are sold by virtually every company - all branding them as theirs, including BOSCH. They are all made by one and the same company (don't remember which one any more), and are BAD quality. They cannot last as long as your timing belt, no way, unless you happen to be incredibly lucky. So plan on replacing these aftermarket distributors at around 45k, otherwise, you'll end up stuck somewhere when you least need it. Oh, and once one side fails, the other will fail too, within weeks if not days, provided they were replaced at the same time.

 

Ok, thanks to all for your replies. Just thought you might like to know the final disposition of the stumbling issue and putting a dummy resistor accross the computer terminals :
3k resistor - Problem gone, idle in drive ~800 rpm but idle in neutral after warm up 2500rpm!
2k resistor - same as 3k but neutral idle 2200 rpm
1k resistor- same as 3k but neutral idlw 20000 rpm
500ohm - stumbling issue is back
750ohm stumbling gone, idle in gear still 800rpm, idle in neutral 1300rpm. This is acceptable to me for now, so that's where it will stay for good.
Thanks again, this saved it from the junkyard.