Secondary air woes

[69-]

Just a couple days ago, my LeBaron (318-4) started to have detonations in the muffler when I got off the gas. That was really annoying and loud... Checking the muffler for leaks, but only some very minor hole (approx 1/10"). Then, thought over the whole thing and removed the belt of the smog pump.

Tada - detonation gone.

Obviously, the vac-switch turning off secondary air at high vac (when getting off the gas) is gone. I'll see if I can get a replacement.

 

[BudW]

The A.I.R. system is always supplying air to the exhaust (via the AIR pump), but depending on engine temperature, it either injects the air at the cylinder head or when hot, to the rear-most catalytic converter via a tube.

I suspect you might have a cylinder misfiring (or not firing) maybe, and loading the exhaust with unburnt fuel.
BudW

 

[69-]

As far as I understand the service manual, that's the job of the diverter valve. In deceleration situations (sudden throttle closure), the (high) manifold vacuum operated diverter valve closes air injection to the exhaust (and releases the air to the outside), to prevent such misfires in the muffler. Carburated engines always have a short "too rich" situation in this case (Most likely followed by a too lean situation, which tends to release further unburned fuel through the exhaust, as ignition might not fully catch up "early") .

After finishing my 1979 Dodge Camper's front axle, I'll check that diverter valve.

My 318 is a non-catalyst (export)
version. Even in 1979 european exhaust checks were not able to handle US catalytic converters... Hasn't much changed, considering the Diesel debacle...

 

[Aspen500]

You are correct. On decel the air should vent to atmosphere or you'll have what you have, popping in the exhaust. Also, make sure your aspirator check valves are good. Should allow air in, but not exhaust out.

 

[Justwondering]

I will definitely have to read up on what you are talking about...
I've come to learn the value of stocking up on fiddly bits while they are available instead of assuming I can get things in 10 years.

JW

 

[Aspen500]

We run into that problem at work on cars much newer than our F, M and J bodies. Certain "fiddly bits" (and some that aren't so fiddly) are made of unobtainium. It's worse when it something that the car (or truck) needs to be driveable. No part, there it sits.

 

[69-]

So we are happy with our old iron - which still runs if you remove the belt for whatever

 

[Aspen500]

In my part of the country (north central Wisconsin) there's one problem with trying to drive old iron year round, it'll turn into old iron in short order (i.e. RUST and corrosion) and collapse on itself from all the winter road salt and I hate seeing old cars in the winter, covered in salt. There's only so many of them left and they need to be preserved. Newer ones rust also of course (we've seen as new as 2017 with pinholes already showing up over the rear wheel openings at work), but it's not the same thing.