facime

So Im a long time hobby mechanic. Ive worked on everything from boats to bikes to cars. Im in jam and could use some help. I speak mechanic so dont feel the need to dumb down any replies you might have for me. One of my main problems is I dont have a manual for this car and cant seem to find one online that I can use.

The car is a 92 SC400. I bought it a couple months ago with a bad water pump and needing a timing belt. I did those repairs and the car has been great for a month or so since. I went to drive it today and its running fine as usual until about two miles up the highway. (seems to me, right about the time it reaches full operating temp perhaps). I notice its shuddering under load pretty bad. Seems to run a little better higher up in the rpm range but trying to roll into it from about 45 it shudders pretty bad. No codes thown, idles okish, revs ok but I can definately feel a miss in it.

The thing stinks out the back pretty bad. I can actually smell the cats and there is an obvious rich condition out the tailpipes. Now that could be weak spark still but Im thinking its sensor related telling it to go pig rich.

After reading some threads here I suspected the DS coil. I would have tested it, but during some investigative poking around I believe I pulled the main coil wire and shorted it out anyway, so I just replaced it. Back to square one, new coil, same original issue.


Sooooo...Using the search engine here I managed to find the manual pages for the MAF, the TPS and the IAC. I ran out of daylight today, I will check those in the AM but Im kind of obsessive about this kind of thing. I wont be able to sleep until Ive researched it to death.


Any ideas? Does this sound like something anyone has seen before and solved it with anything other than a coil, fuel injection treatments, or fuel pump ecu mods?


What I would really like is the FSM page on backprobing the ECU. Also if anyone could assist with probe testing the O2 sensors at the diag block, I'd like to start with those things.




TLDR:
car shudders under low rpm load.
no codes
pig rich out the tailpipes/cats stink


Things Im sure of:
DS coil replaced
no vacuum leaks
new plugs/wires recently
new timing belt a month ago
Im freaking broke so I wont just throw parts at it.


Wish list:
FSM pages for backprobing the ECU
Info on testing O2 sensors IN the car
a hummer from an asian chick

facime

Found a manual, so I now have some diagnostics to follow.

AFM unplugged doesnt alter the issue.
Fuel pump ECU bypass doesnt help.


Im fairly convinced now its an ignition system issue. I ohmed all the plug wires and they are within spec (under 25Kohms). The plugs were all replaced recently and they look good and clean still. I found an ignition rotor in pretty poor shape, filed it down a bit for a clean contact point and its definately improved but still has a slight miss.

At this point this is probably more for my own benifit to keep my thoughts organized, but it anyone wants to chime in, Im all ears.

Ali SC3

iTrader: (10)

in the past those sysmptoms turned out to be a bad coil/ other ignition ecu, or even a bad ecu.

for ecu confirm you see the check engine light come on when you turn the key one click over, you know where all the lights should come on. IT should go away after a few sec or if you turn the key to on. if it doesn't light up at all that means the ecu is not responsive or acting funny, if it comes on and stays on then it means you should pull the codes. if when you go to pull the codes it doesn't blink at all, then that means the ecu is once again not acting correctly. even with no check engine light, when you jumper the diagnostic terminals to check codes, it should blink out a pattern. if any of those are not doing what they are supossed to that means the ecu is suspect and should be opened for inspection.
The toyota method for checking the responsiveness of the ecu is via the check engine light, its somewhere deep in the manual.
also if all of those fail verify the bulb works on the cluster by swapping with another tested one. once the ecu gets leaky capacitors all sorts of wierd things tend to happen, but the most reported symptom is alot of fuel being injected, which fits your symptoms with the smell.

More likely though it is an ignition issue. I would check the other coil also, unplug it while the key is out of the car, and then try and start it and see if there is a difference. do that with your new coil also, many people have gotten some replacements from aftermarket places that simply do not work out of the box.
also if the ignition rotor is in poor shape I am guessing the cap is as well, and both haven't been changed. You are going to want to do that anyways then, the 2 caps and rotors being in good shape is vital to the 1uz and thats about all you need for a good tuneup, plugs caps and rotors and working coils.

facime

the caps looked pretty new and looked like aftermarket jobs. The electrodes were still shiny with just a bare minimum of evidence they had been run. (Ive only had the car for about 2K miles). The rotors on the other hand looked pretty old and had quite a layer of dead corroded material at the ends. They were genuine Denso parts so god knows how long theyve been in there. (car has 225K). I filed them down clean and put them back in. In an effort to be thorough I replaced a couple slightly questionable vac lines only because they were a tad hard and didnt hold on to their nipples as welll as I would like. (giggity).

Took it for a drive and 95% of the problem was gone about 90% of the time. 9% of the drive I had a slight hesitation in low rpm range with heavy load. During the last 1% of my test pulls it chugged enough to make me think I hadnt fixed anything. I was ready to start throwing parts at it.


I live out in the country 30 miles from the nearest town. I put in an extra large bottle of Techron fuel system cleaner and went to town to run that through it. I went to pick up new rotors and caps, a fuel filter, and a set of NGK's to replace the ****ty Autolite Plats the P.O. put in. Within the first 5 miles or so I noticed a difference. Cautiously optimistic I made it to my parts store, bought what I needed and headed home. Not one stumble or misfire that I can tell. It has its power back and ran great all the way home.

In the morning Im going to go ahead and swap the caps and rotors anyway, and then put all the beauty covers back on and see how it goes from here.



TLDR: Rotors seemed to fix it mostly, but a Techron treatment finished it off. Miss gone. I still havent gotten my "hummer"

Deeztha1

so basically you replaced the ignition coils, dist. caps and rotors, spark plugs, and wires?

sounds great, cause my 92 sc400 just dropped power after a afternoon of Southern cal traffic.
i didnt notice anything when i got home but later in the evening when i went to the store, as soon as i fired it up there was a considerable power-loss. it felt just like the exhaust was blocked and the exhaust was glowing directly behind the manifolds.

so i think ill try the tune up before i throw alot of cash at the exhaust.

i know in Oregon that if your car is over 20 yrs old then you dont need cats in the exhaust or if you live in a county that doesnt require them.

but i dont know if california has the same laws?

Ali SC3

iTrader: (10)

thats good news, you will want to replace those rotors though. the filing job will make the contact clean again, but you may have increased the gap too much, and when they get older the more gap, the more air resistance the spark encounters, and that creates a weak spark, and eventually it will start to arc and well not fire correctly (if you had a 2jzge with the cam and crank sensors in the distributor you would find the jumping arc killing your distribotr pretty quickly, good for you on the v8 they are separate sensors.
Cap and rotors, always toyota/lexus. I have used a parts store one and had misfires before, its a hit or miss kind of thing.
the fuel cleaner may have also helped, sometimes the sc4's have injector issues, sometimes you can tap on the side of them while operating to loosen up the debris, but if its working its working.

the glowing manifold is usually a sign the coil has gone out.
caps and rotors should be done periodically with the spark plugs. the stock wires are fine to keep unless they are pinched or something unusual.

Deeztha1

Awesome thanks

juanikun

iTrader: (3)

How's your gas mileage since the problem occured?

facime

Actually, if I were a betting man Deez, I would say you had a rich condition due to a bad tune (similiar to my issue) that melted one of your cats when you got stuck on CA traffic. Ive seen cats melted in those condition before and will have to be punched out our replaced, and at the same time fix your tune problem.


As for my SC400, I sold the car. I did replace the rotors before I sold it and all was well with it at that point.

I decided to go back to my roots and bought a mk2 Supra that may or may not get a 2JZ (GE only) swap in it.


p.s. I agree on Toyota parts for caps and rotors. Nothing beats the quality of genuine tune up parts in those cases.