Hello SC fellas,

I have a 92 SC400 with 160k miles on it and I have been having a strange problem. One day I took her out and went in to the store, when I came back out she wouldn’t start and I had to tow her home. Did some electrical tests and solved the problem by replacing the Ignition control units. When I went to start her, she started fine but cylinders 2 & 8 were misfiring, with inconsistent and low idle. After a while of working on it I had something really strange happen- at night I ran the engine for a second and smoke started coming from my passenger exhaust manifold, so I looked at it and it was glowing BRIGHT RED HOT, illuminating everything around it. So I immediately cut it off and called it for the night to start doing some research. Any idea what the problem is? At this point I am lost and Its starting to drive me nuts.



I have been testing, cleaning and replacing things: I have replaced both ignition coils, ignition wires, all spark plugs, alternator, passenger camshaft position sensor, both distributor caps and rotors, all intake related gaskets (manifold, egr, throttle, ect), fuel injectors, egr temp sensor, (all) O2 sensors, tp sensor, maf sensor, cleaned intake manifold, cleaned fuel rails, cleaned idle air valve, new fuel filter and new fuel pump. Since then, I have also done compression tests and all cylinders are within 140 psi +/- 10psi. Oil is healthy (no leaks, no coolant or sparklies). This is my first 1UZ and I have had it for about 6 months, but I am relatively familiar with the common problems. This week I plan on opening up the exhaust and seeing whats inside- and am thinking the next thing I should do is get the ECU rebuilt?



Anyone who can help me would be greatly appreciated.

 

The misfire you're getting on 2/8 is causing an excess amount of un-burnt fuel to enter the exhaust and is then igniting after the fact causing it to heat your exhaust system up to that point... You may have melted the catalytic converter on that side at this point which is something you may have to replace. You'll want to diagnose what's causing that misfire ASAP before running the car further and causing any more damage to the cat/exhaust system. Double check your spark plugs, plug wire routing (it's easy to confuse on those engines) etc before going too crazy. An ECU rebuild isn't out of the question but double check the work you've done first before moving into spending more money.

 

Hey brotha,
Yeah, thats definitely it- Ive been at this issue for a few months now. I cant help but feel that since 2 & 8 fire one after the other on the passenger side distributor, I cant help but feel they are definitely connected, I have replaced almost all of the ignition system at this point. Maybe it jumped timing? I dont know how though I dont drive it often, and I definitely dont beat it up when I do. Or ECU is dumping fuel at the wrong time 🤷‍♂️. I cracked the ECU open and everything looks clean.

 

I don't think your timing is off, but I would definitely check your firing order and make sure you have your wires run correctly. After that, inspect the wires, cap, and rotors closely to make sure nothing has a short somewhere. It could be a bad ECU, it could also be fuel injectors that are stuck open perhaps. Are you getting any CEL codes?

 

I would side with the ignitor on the top of the engine, that is bank 2's ignitor. I cooked both of my cats last year, but only ignitor 1 was noticeably damaged. I replaced both of them, and got to move the car around. I enjoyed it 3 days, before the next issue, but again I would check the top ignitor for either proper seating or would swap it with the driver side one and see if the misfire changes sides. You didn't mention replacing ignitors, but everything else you did, so you should be good to go after replacing that.

 

No, no CEL codes which really doesn't help me diagnose. The injectors are new any reason they would be stuck open?

 

I must have missed it, yeah I replaced both of them. It cant hurt to try though, I did that test before I replaced them. Its the name of the game when you own a 30 year old car, you only go 3 days before something else comes up, lol 😂.