C3: Smog pump sonata

[Dan Pepper]

My '69 350/350 coupe has most of the stock k19 system intact - albiet with a service replacement pump. The car runs fine with a little popping thourgh the exhaust on deceleration which I expect with the k19 system. Here's the rub: there is an odd muffled popping/rattling sound that emits from the smog pump diverter muffler and it's driving me nuts. To a passerby, the noise sounds like a waterpump on it's last legs - but it's all coming from the smog pump diverter muffler. Is typical for '69 era a.i.r. pumps/diverter valves?

[Joe L.]

Re: C3: Smog pump sonata

Dan-----

The sound that you describe is not normal, at all. However, are you sure that it's coming from the diverter valve? A sound as you describe is a lot more likely to be originating from the pump, even though it may seem like it's the valve.

If you really think that it's the valve, then remove the valve from the pump. Shake it to see if there's anything obviously loose inside---there shouldn't be. If that's ok, then apply a vacuum source (like a MityVac pump) to the vacuum nipple on the valve. Observe that the piston moves back and forth by looking into the hole in the flange.

If the valve is bad in any way, it's pretty hard to get it repaired. The only one that I know of that does it is Don Dorfman and I don't know if he does it any more. Bill Hodel may get involved with repairing these valves; I'm not sure if he does that, or not, though. He advertises in the Driveline.

An NOS valve for your application will set you back $500, or more.

[Harmon C.]

Re: C3: Smog pump sonata

Dan Diverter valve will cause the popping on deceleration as Joe said. The check valves or diverter valve may cause your the noise at idle.
Lyle

[John H.]

Re: C3: Smog pump sonata

When the diaphragm in the diverter valve fails (as they all do eventually), two things happen: 1) You'll get "popping" in the exhaust on overrun, as the valve fails in the open position so the pump is dumping air into the exhaust manifolds 100% of the time, and 2) You'll have a vacuum leak from the signal line to the diverter valve, which is now open to atmosphere. Plug the source fitting for the signal line or stick a BB in the hose to stop the vacuum leak.

[Dan Pepper]

Ah ha!

Evidence points to the diverter valve as shot. I've been trying to pin-down a stumble/hesitation at higher RPM's. Based all of the observations above, sounds like a vac leak through the signal line. I'll block the hose and see if that takes care of the problem.