Need some advice on my newly aquired car.

[coheed]

Ok so I just picked a 1987 Supra non-turbo for $300. The car wouldn't rev past 4000k rpm. So went through the ignition system, new plugs, wires, cap and rotor. Still wouldn't go over 4. Figured out the woodruff key sheared itself. Got a new key and balancer, still wouldn't go past 4. So I reset timing on the cams and distributor. I set the ignition to 10 degrees BTDC, which I'm pretty sure is where it's supposed to be. The car will rev all the way up to redline now, but afterfires (shooting fire out of the headers) all throughout the band. The fire is apparently so frequent that I took it for a 2 min drive down the street and the catalytic converter almost caught my floorboard on fire. I'm completely lost at this point because all the timing is good and I cant find any vacuum leaks. It isn't throwing any codes either so I'm stumped. If anyone can help me out here it would be greatly appreciated.

Also checked the AFM and the TPS and both are good.

[fnkngrv]

wow dude...not that my post here is useful at all, but I would love to hear the answer as well! Seems bizarre for sure!

[yarisugi]

Remove cat and see if its melted, blocking exhaust gases? Banana in yo tailpipe?

[coheed]

Pulled the exhaust to check the cat and the honeycombs are still white as snow. There is no clog in the exhaust at all. The fire is coming from the engine.

[CTScott]

Check for vacuum leaks and check for fuel flow, particularly fuel pressure being low.

[SailDesign]

Originally Posted by yarisugi

Remove cat and see if its melted, blocking exhaust gases? Banana in yo tailpipe?

That would have been my guess, having done it on a VW before.... (The "cat" thing, not the banana...)

[coheed]

Originally Posted by CTScott

Check for vacuum leaks and check for fuel flow, particularly fuel pressure being low.

No vacuum leaks anywhere. And why would low pressure be causing fire?

[yarisugi]

If it's shooting fire through the headers through all six cylinders, the only thing I can think of is that the timing is way off. So what's happening is your spark is igniting the fuel when the exhaust valves are open, therefore seeing fire exiting out of the headers. You might need a Supra repair manual to find out the correct position of where the cams are lined up when the #1 piston is at the very top of the chamber. Person may not have aligned the timing belt correctly.

[coheed]

I have a factory service manual and a Haynes. The matchmarks on the cams line up where they need to be at TDC. You can look through the oil filler cap and see the alignment mark on the intake cam. It lines up with the sight hole, so I'm assuming the exhaust cam is in good time. Wont know for sure until this weekend. I'm going to replace the timing belt and tensioner along with some misc gaskets.

[yarisugi]

piston #1 also at TDC? crank also at 0 degrees? Hopefully this weekend you'll find the real culprit. Keep us updated.

[Yar Is Word]

Here?
http://www.toyota-supra.info/forums/

[CTScott]

Originally Posted by coheed

No vacuum leaks anywhere. And why would low pressure be causing fire?

Running crazy lean from low fuel flow or pressure can cause significant backfiring as well.

[coheed]

Originally Posted by yarisugi

piston #1 also at TDC? crank also at 0 degrees? Hopefully this weekend you'll find the real culprit. Keep us updated.

Yea crank and piston at TDC.

Originally Posted by Yar Is Word

Here?
http://www.toyota-supra.info/forums/

On a couple supra forums. No definite answer from them yet.

Originally Posted by CTScott

Running crazy lean from low fuel flow or pressure can cause significant backfiring as well.

Huh... I didn't know that. I know these motors run rich from the factory though. All the resistance values when checking the AFM are in spec though. So I doubt the AFM is cause a lean/rich problem. Not entirely sure how old the o2 sensor is. Probably gonna replace it this weekend too because its only like $25.

[*MAD DOG*]

Originally Posted by coheed

Ok so I just picked a 1987 Supra non-turbo for $300. The car wouldn't rev past 4000k rpm. So went through the ignition system, new plugs, wires, cap and rotor. Still wouldn't go over 4. Figured out the woodruff key sheared itself. Got a new key and balancer, still wouldn't go past 4. So I reset timing on the cams and distributor. I set the ignition to 10 degrees BTDC, which I'm pretty sure is where it's supposed to be. The car will rev all the way up to redline now, but afterfires (shooting fire out of the headers) all throughout the band. The fire is apparently so frequent that I took it for a 2 min drive down the street and the catalytic converter almost caught my floorboard on fire. I'm completely lost at this point because all the timing is good and I cant find any vacuum leaks. It isn't throwing any codes either so I'm stumped. If anyone can help me out here it would be greatly appreciated.

Also checked the AFM and the TPS and both are good.

I think if you buy a 25 year old car for $300, don't expect anything but problems.

[coheed]

I knew going in this thing had problems. I'm not an idiot.

[Lux]

Coheed, You might be in luck... I know the these cars practically inside-out.

If you have the equipment, check your fuel pressure, verify that it is 2.3 to 2.8 bar. The backfire is from rich mixture and/or incomplete combustion, could be caused by excessive fuel pressure. The fuel system is not monitored by the ECU, and the MIL trouble codes are not much help due to their simplicity of that era. These engines are also double-spark-- they fire twice per combustion cycle-- which accelerates spark plug wear by twofold; check your plugs and replace as necessary. Proper AFM and TPS testing requires a professional lab scope across the full range, but if you checked them by voltage test at low, mid, and high ranges, then I guess it should suffice.

Verify your firing order as well, because that much fuel igniting in your exhaust system makes me think that some cylinders are just pumping wet (fuel, but no spark).

**edit: sorry, I just noticed you have the 7M-GE, not the 7M-GTE. The fuel pressure for your model is 2.7 - 3.1 bar. Your ignition system is a single-fire only, as well.