Is it normal to backfire on deceleration?

[davemccorkle]

Since I just got my car back from it's 3 year restore I am noticing that no matter what gear I am in, when I take my foot off the accelerator I get slight backfiring. Is this normal? I did read that I should hook up the vacuum line to the distributor but did not know if that was it or not. And I am sure to never slow down is the answer! lol

Just wondering what I could do.

[steely]

I got them all of the time the past couple of years when I would decell in the 'hood.
I just figured it was part of the experience until I fixed my ICV drive (found in the process of trying to fix a cold start issue), and now I don't get them near as often(!?)

I don't have a clue as to the connection.
I sort of miss them.

[butzi73]

I always have one decent sized boom if I am decelerating from very high revs in a higher gear. I also get small gurgly pops on occasion. I know it's not an exhaust leak because I've replaced the header gaskets and checked everything out in that area. A number of experienced individuals that I've asked about it just chalk it up to my 2-out sport exhaust and other mods. I've always kind of wondered if it was normal or not, but after years of dialing in everything I think it's normal for my car, with my exhaust, carb, cam setup, which isn't a stock setup of course.

What is the setup of your car?

[john walker's workshop]

you probably wouldn't hear it if the exhaust was stock.

[davemccorkle]

So true! I have the 2-in, 2-out Dansk and thought as much! It runs fantastic jsut pops a bit at times on deceleration. Therre are certainly worst things to worry about!

[PorscheGAL]

This not my video, but it has normal "backfiring" sound when on decel. Is this the sound you are hearing from your car? If so, that is from a modified exhaust. I like it

YouTube - Porsche 930 - RarlyL8 exhaust & K27 turbocharger upgrade

[davemccorkle]

That is the exact sounds it makes! Awesome!

[dshepp806]

I never hear anything other than the engine revving downward everso smoothly!!!!!!! For many years now!!!!

Doyle

[PorscheGAL]

You may find your car even doing this(watch video) on decel. Good times!

YouTube - Porsche 930 Turbo Flames

[T77911S]

perhaps too lean, the exhaust could make it lean out too much when you let off the gas, also retarded, (not enough advance) timing will do it.

check your timing, make sure the advance is working and it is set properly and you could remove the retard.

[twin plugged targa]

If you car is a 930/turbo, then I would say it is probably common.
If it is a 3.2 Carrera (trubo look/supersport), I would say it is not normal
If it is a car with carbs, then I would say it is not uncommon unless the carbs are tuned 100%

[Porsche-O-Phile]

More likely it's an afterfire, not a backfire per se. It can result from (among other things) too rich of an idle setting. Common on motorcycles, very noticeable w/ loud exhausts

[kach22i]

Originally Posted by Porsche-O-Phile

More likely it's an afterfire, not a backfire per se. It can result from (among other things) too rich of an idle setting. Common on motorcycles, very noticeable w/ loud exhausts

Interesting, I've not read of this before but seems to be very plausible.

Normally I would agree with what T77911S said, then again this is a turbo and I know very little about them.

It will be interesting to see the final outcome on this.

The afterfire/backfires in the video did sound Hot Rod cool though.

Is the car Talbot Yellow?

[T77911S]

i missed where it was said it is a turbo. is it? 2 in 2 out on a turbo? i think someone put in a confusion factor above.

timing , or the exhaust making it lean out too much.

the exhaust has caused my brothers 930 to backfire like that. started when he put on an aftermarket exhaust, well, just the muffler, the rest is still stock up to the turbo.

i wollard out the cat on my BMW, now it does it. O2 sensor is before the cat.

[spuggy]

You need to explain what the car is and any mods. I don't see a turbo or wastegate in the photo above and the mufler doesn't look like a 930 one, but the photo isn't great for identification and the car is wide-body.

If it's a 930 with CIS, it's quite normal for them to "cackle" on the overrun. With an open exhaust, these backfires can be very loud - with a stock muffler, just pop and bangs. You can reduce or eliminate this by holding the throttle just slightly open on the overrun, rather than letting it sit on the idle stop. But then you won't get any flame balls if the turbo is hot.

If it's an N/A car, it probably shouldn't do it - although an SC with CIS might.

[WIL84911]

If you have a LOUD pop then I would check for header leaks.

Otherwise enjoy the sound... wish I had more of it.. I make my car do it every so often specially during slow traffic... lol

[kach22i]

Maybe the yellow car at the top of this thread is not a turbo, I was reacting to the video I suppose.

At one time my car was making little farting noises when I let off the gas. I increased the spark plug gap from .028 inches to .030 inches and solved the problem. Hard on the coil if you re-gap too large though.

[T77911S]

i personally dont like it.
one muffler my brother had on the 930 did not do it, i also think that one had a much better tone, dont remember what one. the tone sounded much deeper with this one.
the one on there now does it, it is one most put on the 930, i dont think the 930 sounds as good with the popping on decel. kinda takes away from the "class" of the car. also makes it sound like truck with a hole in the muffler.

[WIL84911]

So I think the answer is NO it's not normal.

But if you have an exhaust manifold leak then you will get loud pops.

Also if you remove the cat then definitely there will be noted backfiring during deceleration/throttle lift.

[davemccorkle]

Sorry guys/gals mine is a 2.7 RS, carbs, solex cams, not a turbo.