Anyone getting exhaust popping with factory air injection? - Team Camaro Tech
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post #1 of 10 (permalink) Old Jun 9th, 15, 08:44 AM Thread Starter
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Anyone getting exhaust popping with factory air injection?

My 69 big block car still has the factory air pump, lines, etc., and it is all functional. It also has the stock dual exhaust with the transverse muffler. As long as I have owned the car, it has exhibited a little bit of backfiring or "popping" out the exhaust on deceleration. I have always attributed this to the air injection pumping air into the exhaust stream, which is igniting unburned fuel that has gone out the exhaust during deceleration. Has anyone else seen this with the factory, functional air injection system on their car? I know a lot of people remove the vanes and block the lines off on their pumps to "dummy" them up, but I'm sure there is someone out there with a survivor car and a 4-speed who can comment on this. I suppose I could have something else causing this. The carb has been rebuilt and the car runs well otherwise. This is more of a curiosity to me than anything else - I don't really think it is a major problem.

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post #2 of 10 (permalink) Old Jun 15th, 15, 03:25 PM Thread Starter
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Re: Anyone getting exhaust popping with factory air injection?

Hmmm, 118 views, no responses. I guess either everyone has no air injection on their car, or they have theirs dummied up, or no one has encountered this issue. Oh well, carry on.

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post #3 of 10 (permalink) Old Jun 15th, 15, 03:58 PM
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Re: Anyone getting exhaust popping with factory air injection?

The only vintage car I ever drove with the AIR still hooked up (we normally removed them literally on day 2) was a 1969 Z. And it back fired just as you described.

When I spoke with Jerry M about this a few year ago, and mentioned that I may install my AIR system, he quickly stated: "We normally just gut it and dummy it up, as there is no way to keep it from backfiring.

Now, having said that, my 69 Z with the factory carb, running factory original size jets and power valve STILL backfires occasionally on deceleration. Not nearly as bad as the Z I drove with the AIR hooked up and functional.
I have slightly re-curved the 111480 distributor and hooked VA up to manifold vac, and small diameter long tube headers running through flowmasters.

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post #4 of 10 (permalink) Old Jun 15th, 15, 04:30 PM
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Re: Anyone getting exhaust popping with factory air injection?

Probably a faulty diverter valve. Pull the vacuum hose from the diverter valve and plug it with a golf tee. A short drive around the block will show if that is the problem or not.

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post #5 of 10 (permalink) Old Jun 15th, 15, 05:24 PM
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Re: Anyone getting exhaust popping with factory air injection?

I'm no expert in A.I.R. systems but seem to remember that there were changes made to the Carburetor tunes and maybe the timing for vehicles equiped with these systems to prevent performance issues but that is sketchy at best. I do know that most Chevrolet lines stopped using smog pumps in the 70 model year when TCS switches arrived to retard advance for 30 seconds or more at certain RPM's.

Like so many my system was removed by the original owner the second the car was off the lot as the unfounded perception was that these systems robbed raw horsepower.


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post #6 of 10 (permalink) Old Jun 15th, 15, 05:40 PM
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Re: Anyone getting exhaust popping with factory air injection?

I agree that the diverter valve is worth a look.. My 302 did this a lot. The diverter is not working on mine so it does not block the output of the A.I.R pump which adds too much air when you let off the gas. The exhaust ends up being rich for a few seconds and will backfire with the added air from the pump. There is a good explanation of this on the Camaros.org site.

In my case, I must have a hole in the diaphragm as it will not hold vacuum. When you let off the gas the high manifold vacuum shifts the plunger in the diverter valve to divert the air out of the muffler on the valve.

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post #7 of 10 (permalink) Old Jun 15th, 15, 08:11 PM Thread Starter
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Re: Anyone getting exhaust popping with factory air injection?

Thanks for the replies, guys! John, I was running a carb for a while that did not have a vacuum port for the diverter valve, so I was essentially doing what you suggested, and it made no difference. I guess based on what some have said this is normal behavior. I guess I was more curious than anything. I am going to replace the pipes from the manifold back to the muffler soon, as they are starting to rust out, and this might help to quiet it down a little. Doesn't really bother me actually - kind of gives it a little bit of a snarl like a track car.

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post #8 of 10 (permalink) Old Jun 15th, 15, 10:06 PM
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Re: Anyone getting exhaust popping with factory air injection?

mine does the same and my valve and pump are in good shape. some times a small exhaust leak will do that also

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post #9 of 10 (permalink) Old Jun 16th, 15, 01:09 PM
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Re: Anyone getting exhaust popping with factory air injection?

FWIW, this was a common occurrence regardless of application. 40+ years ago I had a Chevy II with a 194 I6 and 3 on the tree that was an original California car with the A.I.R. setup and it popped through the exhaust all the time and that car had only 40,xxx miles on it.

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post #10 of 10 (permalink) Old Jun 19th, 15, 02:10 PM
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Re: Anyone getting exhaust popping with factory air injection?

Yes ,my all original 69Z still has the 302 & all the smog equip. in good working cond.,it pops & cracks thru the exhaust system on decelaration just like it did when new, I am not going to change anything since I don't want to change the originality of the car. I love the sound & the rpm's on the street cruising.
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