1983 - metal tubes from exhaust manifold

[kishy]

Hey,
I did the intake manifold and valve cover gaskets yesterday on the '83 (302, Motorcraft 2150 factory carb). While those missions seem to have been successful, in the process I discovered something I'm not familiar with. On the passenger side, running up over the valve covers there are two metal lines. Both are approximately the thickness of brake line, one may be a bit thicker.

One is fixed to the exhaust manifold, possibly with a flared threaded fitting (by feel since visually it's just a ton of rust) and connects directly to the underside of the choke thermostat.

The other is just dangling, but I found what feels like a broken off flared fitting further down on the exhaust manifold. The other end of it makes a 90-degree L on top of the valve cover and becomes a rubber line that goes to a nipple on the side of the thermactor valve on the passenger inner fender.

Can someone please explain the roles of these lines? I know carbureted thermactor systems are supposed to have a mechanism for killing the injection based on specific exhaust conditions (to prevent blasting fireballs through the cats I believe) and I'm wondering if that relates to the broken one.

[marquisman]

They are for the choke and thermactor. One will feed the choke, other feeds to thermactor. Once the heat from the exhaust hits the vac temp switch, it should turn the thermactor air pump off/divert the pump air flow. The one for the choke is needed as, it helps to heat up the choke element.

[kishy]

I figured the choke thermostat would get an exhaust temperature off the one (which is connected and intact). The other one which goes directly to the thermactor diverter (it doesn't go via any other switch or regulator, it's directly connected to the diverter valve) was the concern since it's broken off. I'm thinking the only way to fix that is removing the manifold and trying a screw extractor, if it is in fact a threaded fitting then the drilling is already done for me...

From the various photos I've found of other thermactor diverters I can't find one that looks exactly like mine, so I wasn't sure if that was a vacuum control port or what...seemed to me that under certain conditions a brief exhaust vacuum would exist (e.g. immediately letting off of WOT) and that could be a vacuum control for the diverter, but IDK. Shop manual and EVTM don't really touch it at all, I'm guessing it's covered in the all-Ford-models emissions book that I don't have.

[85crownHPP]

There is a vacuum actuated flapper valve in the exhaust between the drivers exhaust manifold and the down-pipe. I'm not sure exactly what its for, but my 85 ran fine (for CFI) without it.
I'm pretty sure that's what the brake-line-that-gets-vacuum is running to.
The other doo-dad indeed looks like a thermactor air/smog pump diverter valve.

[kishy]

Hmm...might have a clarity issue on my part.
In the pic of the diverter valve, notice the thin rubber line that looks like vacuum hose. That line is what goes to the metal tube that has broken off of the exhaust manifold - it's a direct connection from the passenger side exhaust to the thermactor diverter.

I'm just trying to understand the function of that - basically what that extra nipple is for on the diverter. Autozone has this troubleshooting guide for thermactor systems (working with what I have available online until the emissions book shows up), none of the diagrams seem to show exactly what I have going on here. I 'get' the idea of how the system works, but don't 'get' what that line is doing if it's supposed to be connected to the exhaust. Starting to wonder if perhaps something else is supposed to be in line with that tube but has been removed in the past.

(this is arising from me trying to resolve whatever is causing a cloud to appear over the passenger side exhaust after the engine heats up - coolant and oil have been resolved, but cloud persists, and am wondering now if it's pre-cat exhaust getting out the hole in the manifold because it sure smells foul)

[gadget73]

The flapper valve in one manifold is to force exhaust across the intake to the other side. Its used to keep the carb (or CFI unit) from icing up by warming the manifold with exhaust gas. When thats not being used, the same passage is where the EGR draws from.


The diverters operate from engine vacuum, not exhaust. Its most probably a simple thermostatic vacuum valve. When the engine is cold, it likely diverts air to the back of the heads to warm the cats up faster. When the engine warms, it usually directs it to the converters only. There is probably another valve in there closer to the pump itself that is used to dump air to atmosphere instead of through the cats. Not totally sure what condition that works under, perhaps its just at a higher temperature than the diverter valve works on. I know the EEC controlled ones it basically runs to the back of the heads for a couple minutes, then to the cats for a little longer, and by the time you're at full operating temperature the thing is basically de-activated. If you have a hole in the pipe, it will definitely be leaking exhaust back into the engine bay. If you can get by without the emissions nonsense, just crimp that pipe shut and call it square.

[marquisman]

Looks like its a kanadian car so,it probably does not have a secondary set of air tubes going to the cats. The thermactor system for the carb'd 302 had a single pipe at the heads. Only seen the secondary tubes on the 351W, like my wagon. Both carb'd 302 engine cars I previously owned, did not have the tubes going to the cats. Like said, crimpit off and forget it, if you decide to remove the emissions parts.

[gadget73]

oh, so you guys got head injection only? yeah rip that shit out.

Ever seen the 351 setups with the spider on the exhaust manifold and the dual smog pumps? What a clusterfuck that is. I de-smogged an '87 F250 that had that. It was so jacked up you couldn't not blow fireballs out of the exhaust at idle. Ran like a watch with all that junk removed though.

[kishy]

Yes, head injection only on this car.

"Crimp it off" is not so simple, again this is a line/fitting barely bigger than a brake line and it seems to be sheared clean off on the manifold. I pretty much have to pull the manifold to get a screw extractor into it or tap it and stick a screw in to plug it.

And if I'm doing that I might as well put that set of 1990 Town Car manifolds to use that I've been hanging onto...but the cats and Y (!) pipe should go if I'm doing that and the tailpipe off the Y is pretty much made of dust. The exhaust rust (and an unused dual exhaust hanger) is one reason why I suspect the odometer did roll over, but the rest of the car doesn't really show it. Basically if I touch this manifold situation I have a list of "might as wells" that I was hoping to put off for a while. If I happen to find a good factory dual setup in a junkyard then I'm game to do it, but I can't really do the expense of new at this point. The '91 deserves new stainless duals from the cats back before the '83.

The car will be keeping its factory cats for the time being...my understanding is that removal of the air pump can cause premature cat failure. However, since this is head injection only, it seems to me the only time the pump is active is during warm up and after that it "should" be constantly bypassing/diverting to atmosphere and the cats don't know the difference. Does this sound right?

Also for completeness I'll get some more pics of this arrangement for the benefit of future people wandering in here. Difficult at the moment because the car's in storage away from home.

[slack]

You could also probably have a muffler shop just weld the line closed at the manifold and leave it in there. I had a shop do that for me before on an Olds 307 I did a smog delete for and I think they charged less than $20.

I'm also under the same impression that the smog/air pump is only active during the initial warm up of the car and then bypassed after that.

[85crownHPP]

The thin line going to the exhaust manifold flapper should not need to be plugged, it should not be letting exhaust out unless it's defective, I would think.
On my CFI car, that device was plumbed into a heat-switched vacuum device screwed into the water port in the driver's rear corner of the intake manifold.

[kishy]

There is no source of regulated, switched or otherwise controlled intake vacuum connected to that line, it goes from the exhaust manifold to the thermactor bypass valve (appears "diverter" is incorrect, a diverter only exists on cars with the cat injection too). Suggests either exhaust vacuum pulses (which are a thing and do exist) are used to influence control of the bypass somehow, or temperature is sampled via that hose.

Emissions book is on its way to the house where the car is parked...

[gadget73]

some of this is guesswork. You guys in Canuckistan got different emissions stuff than we did here so there probably isn't a huge lot of experience save for the handful of early box owners that live up yonder.

[marquisman]

What is pictured, is not a diverter valve. It simply opens and closes, to allow air flow to the heads. Diverter valve just controls(diverts) air to either cats, heads or neither. The pipes going to the cats was to meet california emission. So, canadia cars did not need.

[kishy]

Had my friend storing the car take a couple pics:



It isn't completely obvious where the metal line goes, or used to go. But again, that metal tube you see dangling is connected to the thermactor bypass. Looking at the pics (I had basically been poking around blindly by feel before) I'm not sure if that black dot is a hole or oil or what.

Will block it off and see what happens. But to satisfy my curiosity (I hate not knowing how something works) I'll still be hunting down more info.