BACKFIRE, ENGINE STALL, FAILS TO START = EXTREME FRUSTRATION

[flippingloser]

Good morning. I am at a complete loss here with regards to my 83 Spider and would appreciate some guidance.

Situation: I was motoring along in light traffic, third gear, accelerating upwards to 45 MPH when the engine suddenly backfired resulting in immediate and complete power loss. Coasted the Spider into a parking lot, checked under the hood - AFM/ airintake housing blown completely off. No joy with restart, towed the car home.

Present Tense: In an effort to find/fix the problem, I have installed new plugs, new coil, new distributor, new rotor, new control module. Replaced the distributor after finding the shaft gear pin missing - related to backfire? Not sure. No damage to the camshaft or cam tower.

I pushed the car in fifth gear to TDC lineup, lined up 4th cylinder with rotor cap and attempted to crank the car. Same result: big backfire, blew AFM housing off. Rechecked, rehooked, restart - backfire. Stopped work for fear of causing major damage.

I am a nominal gearhead, no Fiat mechs in mys area. Any suggestions or recommendations would be much appreciated.

Thanks, Sam

[rlux4]

Not sure what you are calling the intake housing. The air intake has four major components: filter housing, air flow meter, intake boot and intake manifold. In a back fire situation I'd assume that the AFM flap has gotten damaged. If so, I'm not sure you could repair it. It may have gotten bent and because the tolerances in it's plenum are so close you may not be able to rebend it well enough if that's the case. If you're very lucky it's not damaged. It wouldn't hurt to check your valve timing, could be the belt has skipped.
Ron

[flippingloser]

I was referring to the intake boot or "piping". I will check the AFM flap for damage. Any ideas on why/what caused the initial backfire? Thanks.

[So Cal Mark]

if the pin is missing from the dist gear, it may have turned and changed the ignition timing causing the backfire. Usually backfires in the intake indicate incorrect timing. I'd start over, lining up the crank and cam timing marks, then verifying the distributor installation

[rlux4]

That's what the valve timing suggestion was for, you may be getting exhaust pressure through an intake valve that should be closed at that point in the cycle. A backfire could also be caused by unburnt fuel. The throttle position sensor (TPS) is tasked with shutting off the injectors upon deceleration. If it's not calibrated it may not be doing this correctly.
These are just ideas that come to my mind off the bat. Someone else may have other (perhaps better) suggestions.
Like Mark's, for instance.
Ron

[azruss]

my first thot was you dropped a tooth or 2 in the timing belt. was your dizzy drive gear rotated or was it still lined up with the pin hole. blowing the plenum off sounds like you have an intake valve open when a plug fires. i would also be prone to pulling the cam covers and rotate the motor by hand to make sure all the valves look like they are doing their thing okay. check your cam timing as well.

[131]

My biggest concern would be "where is the distributor pin", unless it fell out when you removed the distributor, it has to be in the engine somewhere. I would surmise that the distributor pin falling out has caused the backfire and there is a good chance the cam timing is now out as well, causing your ongoing starting issues.