1981 FI Tailpipe Backfires

[trent]

Last week I fired her up in the garage and got a very loud POP(!) out of the tailpipe. Now this parking garage- not the home garage- so a few heads turned rather suddenly- including mine! This is the first time, though when warm I've always heard a little popping and canning during downshift so I'm not really surprised that it backfired.

I've looked for air-leaks, and things look pretty good (no gaps, hoses in good shape) and the car generally runs just fine. After replacing the vac-advance, it's smooth as silk up to 4500...

Where to go next? What's the next step for troubleshooting?

[rlux4]

It may not be ther cause, but the first thing that popped into my mind was leaky injector(s). There is still pressure in the fuel rail after the pump stops running (engine off).
The second thing it may be is the trottle position sensor. When you take your foot off the gas the signal the ECU gets is to stop pulsing the injectors. If the TPS is out of adjustment it could cause the puffing backfire on deceleration. A TPS adjustment technique can be found in Brad Artigue's maintenance manual.
http://www.artigue.com/fiat/books/Artig ... 124_MM.pdf
Ron

[carl55]

You might have a leak in your exhaust. Check from the exhaust manifold back. Should be a small one.

Carl

[trent]

Will look at both! Thanks for the replies. I had thought about the injectors (or worse, the whole FI system) since it seems undetonated fuel is escaping into the exhaust manifold.... Well, it made sense in my brane.