Hello, I recently purchased a 92 sc400 from a family member. I have a supra as well so the main new thing is the power plant itself.
It has been running fine but this morning, it would fall flat on its' face and bog down when accelerating at all under load(in gear). I had a hard time getting up to 30mph to even get it home. If I simply rev it in neutral it is smooth to redline with no issue. There are no engine codes. I know this sounds like a fuel filter in my estimation but it was only replaced a few years ago, along with plugs, wires and the AFM to name a few related items. There are a few threads related to this but I couldn't really find a definitive answer considering it is fine when not in gear.

Hope somebody has a bit of insight on this...thanks!

 

Is your check engine light coming on? If so, you can do the CEL pin bypass at the diag port (I forget which pins it is, but there are several threads discussing this) which will have your CEL flash a code at you that you must count. It's very easy to do and will help us diagnose your issues!

 

Hey, thanks for the reply...
No check engine light at all. I tried to pull the codes(TE1 and E1 just like the supra) and nothing.

I let it come up to operating temp again just now and even when just holding the brake and giving it throttle in gear it runs like absolute garbage, lurching and basically doing nothing under load. Also doesnt matter if I leave it in drive or just put it in 1st manually. Reving in neutral/park is still smooth

 

Usually breaking up under load is an ignition issue or possible airflow sensor. I'd start w/ pulling the distributor caps & spark plugs & take a look.

 

Failing ignition coils are a common cause if hesitation, but usually at a specific RPM range in my experience.

If it's just completely bogged down throughout the range, it could be in limp mode due to a knock sensor signal. Have you verified that the CEL is actually working (lighting up at key ON)?

 

You should get some blinking doing the jumper in the diagnostic port, like t2d2 said check to see that the light works at key on, it should come on for a second or two and go away.
If that light works but won't come on when you jumper the pins, with the other symptoms I would lean towards an ecu gone bad and getting worse.
Has been happening more and more on the older models as they fail with age and can happen faster even depending on stuff like humidity, garaged or not, etc..

 

Thanks for all the input guys! I did pull out the ECU to check the capacitors and they look ok just doing a quick visual. I did spark tests and am getting it on all 8 cylinders. The driver side coil has been replaced previously but not the top one. I have to emphasize NO engine light.. and when I do try to pull, it doesnt even flash. I tried this on both the diagnostic box in the engine bay and the one in the cabin. The CEL comes on solid when on accessory as it should. Just to check, I unplugged the AFM and it came on right away...not sure why it's not responding to pulling the code.

Anyways, I also took apart the distributors and both of them basically look like below. I know that clearly the rotors and caps should be replaced but is it potentially able to cause such a severe issue as I am having? Can't even make it above 2k rpm...but only when under load(in gear...any gear).

 

Ok I'm back with more!
The TE1 wire had a crimp that was going open under the diag box, got that sorted out. I am now able to pull the codes. Stored codes were 14, 24 and 31. However after clearing them and replicating the issue, no codes are coming up.
I replaced the caps and rotors as well as the ignition module that had not already been replaced.
I also did the tests on the AFM and it falls within spec.

I took a video of what is happening. And at the end, you'll notice it is smooth when not under load:


I am not even sure where to go from here, so i hope somebody has some wisdom! Thanks

 

So i took the ECU out again and went over it more closely. Low and behold...at least 1 cap going bad. It feels like it is really loose and obviously the 2 pins are touching eachother with all the corrosion.

Does anybody have any experience with what capacitors can cause which issues? I am going to order the replacements either way, but i am hoping this is the root of it all...