Backfiring problem

[boston914]

Hi guys.

I have a '76 2.0 that gives me backfiring trouble on deceleration.

The problem is most apparent under 3000 rpm.

The car has an aftermarket exhaust system (not sure of the brand).

I had the car tuned recently, and the shop told me that the best way to stop the backfire would be to install a factory original exhaust system.

Does anyone have any ideas?

[SGB]

Did it just start or has this been a problem since you got the car? My experience with carburated 914s, and FI on other cars (but not same system as 914) has always shown backfiring to be a result of leaks at the manifold or elsewhere in the system. I can whack out the mixture on the webers on my car and it will go *popapopapop* but i'm pretty sure the car wouldn't get out of the driveway like that. Is your problem disabling or just loud? If yer still running OK, it almost has to be a leak. Those copper gaskets on the manifold at the exhaust ports leak sometimes.

[Paul_Heery]

Originally posted by boston914
Does anyone have any ideas?

First of all, find a new mechanic. I would run from anyone that would tell me to replace an entire subsystem on a car without first offering some alternative course of action.

Now, to help with your problem, we need to know a little more about your car. Is the fuel injection system intact or do you have carbs? Are there any other modifications?

On a car with FI, there are two places that are normally the source of this problem and they both involve leaks. As SGB stated, go over the entire exhaust system looking for leaks. You may find that some things need to be tightened or you may need some new gaskets. The other place to look are all of those funky hoses that are part of the FI system. I chased a backfire down for a while and fixed it when I repaired the vacuum leak caused by a faulty hose.

Good luck.

[boston914]

Thanks for the advice. The car is FI with no mods other than the muffler.

The car runs fine, it is just loud on decelleration.

I looked at the FI air fileter case. There is one nipple with no hose attached to it. I cannot see any loose hoses anywhere.

Does anyone know where I can find a diagram of the vacuum hose setup for a '76 2.0 ??

Thanks again!

[JohnB]

When I replaced my muffler I had this same problem. Earlier advice is correct, new gaskets at the heat exchanger/muffler flange sealed things up and cured the problem. Might work for you, 2.