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Author Topic: Working smog pump system  (Read 656 times)
sixt9x33rs
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« on: November 29, 2013, 11:35:53 PM »

I have a smog pump system on the Silver Z that I recently bought. I am told the smog system was removed years ago when the car was fairly new. Now the smog system seems to be working well as installed. When I compare the exhaust smell of this car against non smog cars I have or cars with smog where the pump has been "devaned" there is a big difference. The Silver car just does not "stink" like the others. However, the car does have an exhaust "pop" when you let off the gas at medium or high RPM. Any ideas on how to solve the exhaust popping noise?

Lawrence
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JKZ27
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« Reply #1 on: November 30, 2013, 10:51:42 AM »

I think the popping is a characteristic of the AIR(smog) system pumping air into the exhaust to continue burning any unburnt fuel. Thus, the different exhaust smell. Kind of cool yours is working.
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JohnZ
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« Reply #2 on: December 01, 2013, 11:50:39 AM »

However, the car does have an exhaust "pop" when you let off the gas at medium or high RPM. Any ideas on how to solve the exhaust popping noise?

Lawrence


That "popping" on over-run is the classic symptom of a failed diverter valve diaphragm - when it's working properly, on over-run, the high vacuum level to the diaphragm closes the diverter valve and dumps the air pump output to atmosphere instead of sending it to the exhaust manifolds. When the diaphragm fails, the valve defaults to "open", and sends air pump output to the exhaust manifolds 100% of the time; air pumped into the manifolds on over-run causes the "popping" in the exhaust system.
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JKZ27
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« Reply #3 on: December 01, 2013, 01:53:08 PM »

Yeah...what JohnZ said is quite a bit more accurate. Sorry.
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69 RS/SS Cortez Silver, L48 MC1
68 RS Ash/Ivy Gold 327EFI M20
79 Z28 Brown LM1 M21
04 SRT 10
sixt9x33rs
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« Reply #4 on: December 01, 2013, 08:37:44 PM »

However, the car does have an exhaust "pop" when you let off the gas at medium or high RPM. Any ideas on how to solve the exhaust popping noise?

Lawrence

John, other than the "pop" is this damaging anything?

That "popping" on over-run is the classic symptom of a failed diverter valve diaphragm - when it's working properly, on over-run, the high vacuum level to the diaphragm closes the diverter valve and dumps the air pump output to atmosphere instead of sending it to the exhaust manifolds. When the diaphragm fails, the valve defaults to "open", and sends air pump output to the exhaust manifolds 100% of the time; air pumped into the manifolds on over-run causes the "popping" in the exhaust system.
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'69 RS Z/28 Olympic Gold, 711
Flat hood no spoiler, black top, endura, 4:10
POP 39,000
69 X77 Z/28 69 711 Original Paint Unrestored
'69 X66 Convertible Cortez Silver 712 black top Endura, auto, bumper guards, am/fm rear speaker 44k miles
JohnZ
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« Reply #5 on: December 02, 2013, 10:54:46 AM »

<< John, other than the "pop" is this damaging anything? >>

No, not really - it's more of an annoyance than anything else.
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