'93 truck stumbling on take off. (Long Read)

1993 Toyota 2wd 5-speed 160,000+ miles.

I recently noticed that my upper alternator bracket (from the motor) was broke and the lower tab on the alternator was oval-ed out. A friend of mine gave me an alternator and bracket off of a 1991 truck and we put it onto mine. Then I found out the plug on the back of the alternator was different, so we spliced the plug from the '91 onto my '93 harness.

We started the truck, let it idle and it was charging so we thought everything was fine. I go to leave my friends house and as I accelerate the truck starts to stumble and bog down and the check engine light came on. I pulled back up to his house and it smells like it is running rich. So we put my original alternator and plug back on my truck with no change in performance. It will run fine idling and wide open but stumbles at approximately 1000-1500 rpms. (guessing because I do not have a tach)

The next day, with the help of some other friends we try to troubleshoot it. We replace the plugs, plug wires and coil/igniter because the plugs were saturated with gas. Gaped the plugs at 32. No change.

I drive it to a local mechanic to try and find out what threw the CE light and he tells me that my diagnostic port is fried and he can't get a code off it. I really don't trust him.

As I drive back to my friends shop it starts to smell horrible and the floorboard is extremely hot. So we assume the cat is clogged and cut it off with no change. Except for now sounding like a dirt track car.

Next we replaced the O2 sensor still no change.

We removed and cleaned the air filter and Mass Air Flow sensor. It will run slightly better with the Mass Air Flow sensor unhooked, so we replaced it with one from a running truck with no change again. I did however notice that the center pin on the plug is corroded so we tried to clean it as best we could. Still no change.



Anyone have any ideas? Could I have fried something by putting a '91 alternator on a '93? Or could it be something simple that's unrelated? I feel like we are chasing our tails on this one. The truck is 100 miles away from me right now so I won't be able to do much until this weekend.

fuel filter?

no idea whats goin on there, but the question i have is how the hell does your truck run without the mass air sensor hooked up, i've never heard of such a thing.

sounds to me like you have a wire in the wrong spot were u spliced it.

check the EGR sounds like it is stuck wide open thats why all the fuel..

judging by the fact that the obd port wont "jack up" it sounds like the ecm (computer) is fried.

you need to go back and check what output the alternator is/was. sounds like it blew too much juice so to speak and fried something or like james said, you got something "mixed up" when wiring it and there again - fried the ecm!

either way it sounds electrical in regards to the ecm. keep in mind that the ecm control EVERYTHING! o2, egr, fuel mixture blah blah blah (all mentioned above!). it will make EVERYTHING go ape shit!

i know some places around here will check the ecm and/or the aalternator for free. you should be able to test either/or and see whats up.

keep this in mind too, if you get a new ecm from anywhere it will be nonrefundable so do your homeowrk before buying one!

you can also pm jsondrops on here. he works at a yota dealership and can get you diagrams, etc if you need it!

it sounds like lucky is on the right path i have never heard of a yota or any maf sensor vehicel running with out it being hooked up. the maf simply tells the computer how much air is bing drawn into the engine and tells the computer how long to open the injectors meaning more or less fuel. with the floor getting extremly hot the cat was over heating meaning that you are getting way to much fuel through the motor and it was still burning in the cat with all that being said the coumputer could be in a fail safe mode also know as get me home mode befor buying a computer try to disconect the battery for 15-30 min this can reset your computer while the battery is disconected check all the wiring you spliced also check all the wiring in your harnesses coming from your computer you might have pinched rubbed through a wire causeing you computer to fault hope all this helps

Thanks for all the help.


We got the codes off the computer over the weekend (code 31) and tried a few things.

1. Replacing the ECU with one from a running truck.
2. Replacing the MAF.
3. Other random things.


Ended up beings a broken wire at the MAF plug. So simple that I felt retarded for spending almost a week troubleshooting it.