I have a naturally aspirated 1994 supra. Unfortunately, I ran into some car trouble the other day. My father and I have tried a little bit of everything, but can't figure out the problem. I was wondering if any of you car buffs could maybe help diagnose the problem.

Car was running fine, when all of a sudden (thursday), it just died. When I started it back up, a bunch of black smoke came out the exhaust. The car does not idle, but will die if you don't keep your foot on the gas. It feels like the car is in "limp mode". The car has very little power, and trouble going through the gears because of that (it's an automatic). Still plenty of black smoke.

We figured out that black smoke means too much fuel. We reset the ECU, have looked into whether or not it could be a catalytic converter problem. My dad has hypothesized that fuel is only getting to a couple of the cylinders and the rest aren't firing- hence the rich mixture (black smoke) coming out of the exhaust as raw fuel is being dumped in the motor but not igniting.

It can't be just one fouled plug (would have to be multiple). I know what it's like to have a cylinder miss. It feels like three cylinders aren't firing here. Dad also thinks it could be the fuel filter- like it being clogged. I don't see how that can be, as the black smoke would seem to indicate too much fuel.

Anyhow, there's the problem. I'm thinking the ecu itself might have to be replaced or maybe an O2 sensor went bad. I would love to think it's an easy fix like replacing the fuel filter, but I'm not that optimistic.

Let me know if you all have any suggestions...
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Timing belt? I had a 78 Datsun 280z that did something similar.
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Hmm. That's another thing we went over. You know, now that I think of it, the car itself is making a clicking noise when idling. It isn't knocking (the sound of a cylinder about to go out).

Car has had plenty of lubricants and just put a quart of oil in it about 3 weeks ago...
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sounds like what happened when the idle air control valve went out on my mustang
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That would be something to look into. Even jumping one tooth on the gear could have big implications to how it runs.
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Timing belts usually do jump when the vehicle is shut off or goes to idle after acceleration.
That said, they typically don't over fuel as a side effect of bad timing. The black smoke is a clear sign of too much fuel.
Pull the plugs. Are they all black or darker than usual? Or just one?
If they're all darker than normal, it is a general problem affecting all cylinders.
I'm not familiar with that particular vehicle, but I would start by checking the air temp sensors and coolant temp sensors. Also, if it mas a MAP (Manifold Absolute Pressure) or MAF (Mass Air Flow) sensor, check it for proper operation... Usually, you will have one or the other, not both.

Back to pulling the plugs. Which one is black if they all aren't? If just one is odd looking, you can narrow it to a single cylinder. If that is the case, look at plugs, wires, coil, injector for the affected cylinder.

This is a hard to diagnose remotely kinda problem.

All that said, timing may still be the culprit. That should be easy to check.
You should be able to pull the valve cover or timing belt cover, whichever yuor car has that covers the cam gear/sprocket.
Rotate the crank pulley to top dead center (there should be a mark (dot, arrow, line...) on it. Look at the cam sprocket/pulley is it's mark also top dead center? If not, rotate the crank 360 degrees and look again. The Cam should now have its mark at TDC. If it isn't, you gots a problem.
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Thanks for the info Stu. Im by no means a mechanic, just citing personal experience. I never did find the exact issue with my car as i sold it unfixed to a scrap yard. Years later talking with a coworker about it, he thought that may have been my problem from the sypmtoms described, some of which were similar to what Tecnorobo's having. However, I didn't have the black smoke like he's having.
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Another thing to look at is your coil pack I think the Toyotas of that age have a coil pack where all of your plug wires end up I would make sure that all of the cylinders are getting spark.
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Thanks for the replies fellas. I'll look into all those things. I don't believe it's the coil pack, as it was replaced 20,000 miles ago or so.
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You say it makes a clicking noise while idling, but NOT like a cylinder about to "go out". Does that clicking noise increase in frequency or speed while the engine is running at a higher RPM (more importantly can you tell if it is still there?). Furthermore, you mentioned you just added a quart of oil...how often do you have to add oil? Generally it is not uncommon to add several additional ounces to an engine after an oil change, but adding a quart is a lot of oil.

Early 90's Toyota's with the 3L I6 all had one of two things in common that involve loss of oil:

A)The M-engine model developed bad lifters/rockers after about 90,000 miles. This was a direct side effect of the head gaskets cracking (sometimes barely, sometimes blowing catastrophically), which they often did because almost all of the engines came from the factory with the head bolts under-torqued from improper specifications.

B)The J-engine model would suffer from turbine failure in the turbos, or have a faulty 1-way valve on the head that would cause turbo failure, OR would get oil vapors into the seals on the exhaust side and cause the seals to fail. Lots of issues were corrected with the 2nd-gen J-engine, but I think the valve issue remained.



Have you hooked it to a code reader to see if there's a diagnostic code showing? Most chain auto stores have a reader they can hook up for you for free.
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The car burns a little oil, but I certainly don't have to add it often. Before I added that quart, I wouldn't be able to remember the last time I had to put oil in it. We've tried hooking a code reader up to it, but the model we own doesn't work on my car.
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Advanced Auto will read the codes for free, if you can get it to a store.
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How many miles are on the vehicle? (don't think I saw that posted.)
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Good question. It's a higher mileage vehicle. I believe it's sitting around 157,000 at the moment.
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Ok. Has the timing belt ever been changed?

I ask because if the belt IS worn out you could be hearing a valve tapping on the top of a piston. If this is the case, one more tooth out and your entire head will need to be reworked. See, timing is very critical in these types of motors. As the timing belt stretches it begins to hop or skip making the timing become more and more out of synch. The last straw is when the piston is at the top of the stroke and the valve(s) are completely open which causes total havoc.

I will make a call right now to a buddy and ask what a common problem is with those motors and report back.
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Says they are common for burning up exhaust valves. He said to do a compression check on each cylinder. Black smoke is fuel.

If compression checks out, check the turbos.
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Thanks for calling your buddy.
One thing to note is this motor is the Naturally Aspirated version...
So no turbos
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To answer your previous question, yes, the timing belt was changed around 97,000 miles.
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Compression test. He's guessing the burned exhaust valve(s).
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I had a similar problem once and it turned out to be the Mass Airflow (MAF) Sensor. Over time/miles it gets gummed up. When they fail they send bad data to the ECU, which in turn gives an improper fuel/air mixture ratio.

My car wouldn't idle at all, I had to keep my foot on the gas to keep it running. Not easy when trying to park or move short distances at slow speed.
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