The unfixable mystery problem
 

I have an 88 n/a auto supra from california, that has all the extra sensors and other goodies, with a faulty speed sensor. Other than that, the car runs fine except that if you floor it, the car will rev up to 4000k and then stop and not go any higher. If you push the pedal down 3/4 of the way, it will rev above 4000 up until redline. I have the car in at a mechanic that has knowledge of these kinds of cars. They've checked the fuel pressure, the distributor, they looked for some sort of rev limiter, they've looked for vacuum leaks, and nothing. I have no more ideas (nor does the mechanic) of what could be wrong on this car and it's really starting to frustrate me. If anyone has any clue as to what could be causing this, I would greatly appreciate your input. Thank you very much!

P.S. I have another car that is the exact same as this one from Canada that I'm using as a parts car. The mechanic suggested I get it towed there for random part swapping and I'm thinking I will have to resort to this but I'm hoping not.

I have a 87 turbo that is doing the same thing..... if any one know's what can cause this please let us know so we can get it fixed...

I have the same problem I just decided to swap out the engine and disasemble the old one but i couldent find anything I think it had to do something with comprasion and fuel cut off not sure tho

Luckily I do have a spare engine... however, that is a last resort. Perhaps I'll get a compression test done to see what it's doing. As for fuel cut, I don't think that's an issue as the mechanic said that when the engine is bogging at 4-5k, the fuel pressure is actually increasing. The TPS has also been ruled out... There may be a vacuum leak, but I'm unsure if it would cause that much of a problem. If anyone else has any ideas, I would gladly entertain them.

????
 

I had a similar problem and it was actually a misfiring at high rpm.(this is not what it felt or sounded like.) New valve cover gasket, plugs and wires solved the problem for me. Oh i changed original fuel filter (88 turbo). took me longer to do the filter than the gasket, plug and wires!

if it is a vac leek get some newspaper and light it on fire keep it away from the filter and run it around the vac lines and if you get a blow or suck of air cheak around that air for a leek

Just for an update, I guess the mechanic tested compression and said it was very strong. He's going to check the timing belt for missing teeth as he said that could be an issue. He also didn't think that a vacuum leak would cause this problem.

hmm, I know on my '88 supra I'm using as a donor motor for my '87 in much better shape that it had some old hoses and lines on it that were all split and it completely sucked the power right out of it.

That is a good suggestion, however, that is not the case with this problem. The car will run fine with lots of power up until 4k. After that, the car simply feels like it is not getting more power. If you depress the accelerator to about 3/4, you can rev it to redline. If you put it right to the floor, it will stop revving at 4k.

Sounds like their is some kind of limiter on your electronics end. Have you checked into the fuelcut? I know HKS makes a fuel cut defender (FCD), you could look into this. It might solve your problem.

I've definitely heard of them. I've also heard that they may not be so great to use as you can potentially bugger up your engine. I suppose that only happens if you're doing something super retarded though. I know that the mechanics have looked for a rev limiter in the ignition system and such and they haven't found anything. I guess the only way to know for certain would be to swap the other engine I have to see if it does the same thing. I'm about ready to throw in the towel and live with it for now, but we'll see what happens (I should know later today.)

First place I would look is the throttle position sensor - but to tell you the truth I don't even know if the supra has that. Alot of high performance shope sell a bogus "power enhancer" that is a throttle position switch that tells the computer that you are at full throttle - when you are only at 3/4. doesn't really add power - the petal still goes full - just no gain after3/4 throttle.

This problem sounds like the switch is working backward for some crazy reason! Like I said - it's a shot in the dark - but if someone burned a performance chip and it got screwed up - this could be the issue!
AFAIK - The Rev limiter on this engine is burned on the ECU chip! ( we hit it on occasion in the lemons racecar!)

Carl Johansson

Well, to tell you the truth, the TPS has already been looked at. Unless the new TPS they brought in was screwed, it's working fine. Thanks for the suggestion though.

sorry,
didn't read all of the posts carefully enough. So if the TPS is OK - does this thing have a stock chip in it? Have you tried switching out the ECU with the one on the parts car?

Yes, I knew I forgot to mention something! The parts car is a manual, but the ECU works fine with the auto and I think it shifts slightly better with the manual ECU. On a side note I'd like to point out that I started having these problems before I put the other ECU in, so I doubt it's the reason.

So I talked to the mechanic today. Timing belt is fine, cams are properly aligned. Honestly, we are completely out of ideas. Since combustion requires three things: air, spark, and fuel, it's either not getting one of these things or perhaps it's something else. I know it's getting air, I'm reasonably sure it's getting spark (new wires, plugs, distributor has been checked, as has the coil wire,) and there is plenty of fuel pressure. Is there any way it is remotely possible that the tranny is dying on me? I mean the oil doesn't smell burnt or look brown and there are no metal shavings in it... The only tranny error code I'm getting is the speed sensor 2 error. So unless someone else has a revolutionary idea or something, I think I'm SOL.

Have you looked at the throttle cable? have someone sit in the car and floor it = while you watch the cable - maybe the cam lobe broke off or something stupid like that - so it's going back low throttle -

compare that to watching when you are at 3/4 throttle and it revs to redline.

I assume you took the fuel pressure after the fuel filter right?

It almost sounds like it's getting to much fuel at full throttle - did someone change the injector sizes? and isn't there an adjustable fuel pressure regulator? To much fuel at full throttle could be choking it off - while 3/4 is allowing enough air! It used to be a fairly common problem in carbed cars!

Just throwing out ideas - I don't know!

Carl Johansson

Sorry for the long delay, was out of town and only had access to a dialup connection... Anyway, I don't think it's the throttle cable since it'll redline in neutral and park when you floor it. As for the fuel pressure, I wasn't the one checking it, so I don't know but I'll find out. I don't believe that anyone changed the injector sizes, but that could be a possibility. It was running rich at one point before I changed the AFM. The car is initially from the Los Angeles area, and now the car is definitely at a higher elevation here in Saskatoon, but you'd think that the other car that I have would run the same as this one if that were the case unless there's some elevation tuning differences that I don't know about. Apparently the mechanic had no clue about the speed sensor problem until I told him about it today... so basically he's going to see what all it controls and if it's causing the ECU to go in to 'limp mode.' It's a long shot, but I'll try some of the stuff mentioned here as well as the speed sensor issue and see what happens.

try doing a smog check and ask to check ur vacume lines if it dosent pass the smog ull at lest have a better idea of wut it is and im pretty sure thell tell u whats wrong

mystery problem
 

i had the same problem after i had my 7mgte rebuilt. the shop couldnt figure it out so they took the motor out tore it apart and put it back in the car. It turned out to be a bad throttle body and mass air. hope this helps

Well, today I picked up my supra from the shop it's been at. The mechanic has officially given up on the car. He can only think that there may be a bad connection in the wiring system, but he's not sure. I also bought a speed sensor off of www.rockauto.com , but it does not fit in my car. So now I'm stuck with a broken car and a speed sensor that does not fit. Luckily I can return it. I've been having a hell of a time trying to find a speed sensor for that car. I basically want to replace it before I try anything else with the car since it's the 'easiest' to get at. The part number is 89411-30090 and upon further investigation, apparently a 30091 would work as well... If anyone knows where I might be able to obtain this part, it would be greatly appreciated. Aside from that, it looks like I may have to take a peak at the throttle body.

P.S sorry for the long delay in updates... I was on holidays and was only able to steal a wireless highspeed connection a couple times

For anyone interested, I have uploaded a couple videos on youtube. The first is of the car running fine up to 4000 RPM and then as soon as you try to floor it, the engine starts cutting out: http://www.youtube.com/watch?v=DfHrL3gNaJ0

The second is of the car cutting out and how it will not go much past 5k even with it floored. Notice that the speedometer is not rising very quickly: http://www.youtube.com/watch?v=9p67-hROA-k

I hope this helps in diagnosing the problem that I'm having.

Could it be the box?

Good suggestion, but I'm thinking if the engine won't even rev past 5200 RPM that it probably isn't it. I forgot to add that when you leave it floored for a bit you can begin to smell raw fuel when the windows are down.

what about a leaky injecter or a crack in the manifold

Im just throwing out ideas see if anyone clicks

It sounds to me that the air entering the engine is not being metered properly. I haven't seen much discussion of the possibility of a bad mass air flow sensor in this thread. If the sensor is bad, or if the wiring has been reconnected improperly, your computer will not be receiving an accurate measure of air and will not add the proper mix of fuel, therefore resulting in a loss of power (stopping you from increasing your rpm's with various loads). Note that you will still be able to rev in neutral or park as there is virtually no load on the engine, thus requiring little power to rev.

I tried finding a pinout of a N/A mass air flow sensor, but have failed in the search. Colored wires should be the same on similar year supras, so you might be able to cross reference that way. I say swap your Canadian MAF for your CA one and see if that helps.

So I took a look at the wiring, and this is what I found.

The camera wouldn't really focus properly, but the yellow wire is bare at the beginning of the connector in this pic :
Attachment 2234

In this one, it shows two brown wires spliced into one. I'm wondering if this might be the issue:
Attachment 2235

Let me know what you guys think. I may be able to pull off the harness from my other car to fix it. Also, the maf was bad on this car so I have one from the US now that I got off of ebay. Both run fine on my parts car.

Yea that looks a little dodgy man if you really want to you could change the looms or take it down to an auto sparky and get them to have a look

Yeah, I would check the wiring on your parts car's MAF sensor plug. Wire colors will probably be the same, and if so I would cut the connector off of it and splice it onto the Supra you're trying to get running. I'm pretty sure those 2 wires shouldn't be spliced together, but I can't say for sure as I don't have a N/A that I can easily go check the wiring on...

Hopefully that's your problem though. Would like to see this thread end with "I got the car running" sometime soon...

ancient thread, i know.
 

I had been having this prob since i bought my supra. I tried the tune-up (dist cap, rotor button, wires, plugs), changed the gear oil in the tranny and rear diff., tested the igntion coil/module, and changed the oxygen sensor.
Then, i blew a head gasket.
After rebuilding the engine (pressure tested the head/cleaned/crack tested block/milled/decked/bore/hone/new pistons/ground crank/re-bushed rods/new bearings/metal Headgasket/arp studs/ port & polish/ new clutch/ new headers/ replaced EVERY vacuum line on the ENTIRE engine/ fuel filter/ cleaned injectors/ cleaned fuel rail/ new air filter/ OHM tested fuel pump relay/ igniter/ coil/TPS/ and all 3 pick up coils)
dropped in the engine. SAME PROBLEM!!!!!!!!! W.T.F!?
Next is ECU. idk what else to do either. I like the idea of replacing the mass air flow sensor.

Funny you should revive this thread. I actually managed to fix the problem. What it ended up being were the injectors. I had a donor supra, so I swapped out the injectors and voila, problem was solved. My theory was that they were injectors for a turbo model in my NA model. I don't know if this will help you, but I would definitely check to see if the electrical resistance on your injectors are consistent for your model.

God. Bless. YOU! but only if it works for me. :)
 

Thanks a lot gettarobo!! if that turns out to be the solution, i will come and find you wherever you are, i will anoint your head with oil and wash your feet with my hair. LOL

Possible Solution
 

I have a 1989 turbo with recent mild modifications, a slow work in progress. The car backfired badly a few weeks ago at speed, the check engine light came on and I had similar symptoms, would not rev above 4,000 rpms. Checked everything, changed TPS, etc., no luck. Finally found a simple cost free problem. The lower intercooler hose had come off, huge vacuum or pressure leak. Re-attached it and made sure it was secure, problem solved. One possibility. Hope this helps.