WJG2

Just bought a 77 targa with a 78 3L engine that had been driven only about 1,500 miles in the past 13 years. Took it for a drive last night and heard a sharp, loud backfire about 20 miles out. When we got to our destination, the car wouldn't start, so push-started it. It drove fine on the way home, but won't start this morning. It turned over fine at first, but wouldn't catch. Now, nothing. Suggestions? Thanks..

Thom Fitzpatrick

Smells like it to me. Take the cover off and see if there's a popoff valve - I had a situation once where my popoff valve popped out.
I had a cracked airbox on my '77 once, the car ran like crap for quite a while before a shop diagnosed the problem.

Bill Gregory

If it has a pop-off valve, as Thom said, check to make sure it didn't pop out of the airbox or that the wire holding the top on didn't work it's way out. If it doesn't have a pop-off valve under the paper air cleaner element, then look at the screws holding the two halves together. If the airbox blew up, the screws will be loose and if you look at the two halves you'll see that they've separated. There's an article on tech.rennlist.com under 911 engines on what's involved with replacing a blown airbox, if you need more information.

WJG2

Thanks. And thanks, Bill, for the tech piece. If the airbox is blown, would that account for the hard/impossible starting?

Bill Gregory

What a blown airbox does is create a huge unmetered air leak. CIS injection is intolerant of any air NOT going through the air plate at the fuel distributor. As a basically mechanical system, it has to know how much air is moving to meter the right amount of fuel. Since CIS doesn't know about all that extra air coming in through the blown airbox, the mixture is very unbalanced, and the symptoms could vary based on how bad the airbox is. Thom described one situation where it just didn't run real well. Others cannot start their engines at all.