torque converter

[Guest FBody Addict]

the backfiring is still there, and i'm thinking there maybe a connection to the tc

 

the problem really first started when i put the junkyard tranny in, one from an astro van, which is a vehicle used for carrying heavy loads and is a heavy vehicle itself (~5500) so the tc would be different than one placed in a pony car which weighs less and would need a different stall speed for desired performance

 

i think that the computer is set with programming for the original tc stall speed, and sends the signal to lock up the tc but the tc is not yet to or past stall speed and all the parts are not yet spinning at the right speed to lock and has trouble locking up while the computer thinks it is locked and adjusts timing and fuel accordingly

 

in class the prof. said the wrong tc could cause engine problems

 

would an astro van have a stall speed ~ 2000 and my car ~ 1100? or the other way around? either way does this make sense to anyone?

 

at wot there is no backfiring and she pulls rather well, so i think the tc locks pretty well when i floor it and above 2000

 

hopefully this makes sense to someone

[desperado]

As far as stall speed, the V-6 convertor will have a HIGHER stall than the one for your car.

 

Now, as far as the convertor causing it to backfire, I would have to doubt it, backfiring is caused by either a rich mixture not burning off in the cylinder, getting into the exhaust and then being ignited by the hot gasses in the exhaust. It can be caused by a bad plug or wire not lighting the mixture in the cylinder, letting it end up in the exhaust and then being ignited.

 

Lean backfire can also occur, but that is up through the intake. The cylinder gets overly hot from being too lean and the mixture ignites as it is entering the cylinder because of the additional heat, but this again is ONLY up in the intake. Exceedingly late timing, carbon buildup, and bad valve sealing will also cause backfiring through the intake.

 

As far as the convertor doing it, I can't see how. Even if it was the wrong lock up point. You would only lug the engine, or over rev the engine but backfiring would still be caused by something else and the convertor stall and lock up points would only be agravating the problem, not causing it to begin with.

 

You said at WOT that the backfiring goes away, that leads me to believe that it's a rich mixture issue, especially if the problem goes away at WOT. This is more of an indication of a rich mixture at part throttle. Have you changed the computer with a 350 computer on that motor? Are you running any sort of piggyback FMU (Fuel Management Unit)? Are the O2 sensors still on the car and operational? As you know the O2 sensors are what keeps the fuel system in tune. The other posibility is that you have a bad injector that is allowing fuel to pass even when its off. This will run the mixture WAY rich and cause it to backfire out the exhaust. If it's a TBI motor, you can turn on the key and look at the injector and see it leaking, if it's a tuned port car, typically it will ONLY backfire off one cylinder bank if you have a bad injector as it will only make one or two cylinders rich. Reading the plugs is a good way to find out which one. With a new set of plugs, fire the motor and run it around a bit then pull the plugs, find the black one and you will have found your bad injector.

[Guest FBody Addict]

well, i saw all the plugs a few weeks back and they were all nice and clean except for one, which the gap had closed due to carbon build up (which is why i was checking the plugs) i believe this is from oil leaking in somehow, but will a bad injector do that?

[desperado]

It can, it can also cause backfiring if the plug is fouled and not firing. The fuel/air mixture will burn off in the exhaust if it's not burning off in the cylinder. As far as an injector causing that level of carbon buildup, I would have to doubt it. I would run a compression test or better yet a blowby test to see what the condition of the cylinder is. If the numbers are good then it's most likely the injector, or posibly an intake manifold gasket. If the cylinder has alot of blowby, or low compression, then the rings are a better bet.

[Mattsv8]

keith do you still have the tube chassis s10? im starting a s10 car club in columbus!!

[desperado]

Yep