Hey guys, a few more questions here

My truck needs a new muffler which I’ll probably have replaced in a couple weeks, but at the same time I was thinking of removing the converter. Would doing that remove too much backpressure for my 81 300-6? I read in another post somewhere that a certain amount was required on some of these trucks for the EGR to function correctly. Also any recommendations on a muffler for that engine?

Second question is about the vacuum to the EGR. I hooked the line up to a vacuum gauge tonight but the needle barely moves at any RPM. I tried this with the truck parked in neutral. Does the engine maybe need to be under load to activate the EGR? The line to the EGR comes directly from the VCV valve on my truck with one line split to the WOT trigger. Maybe the VCV valve is not functioning correctly?

And lastly, I’ve noticed on some diagrams for the carter carb on my truck that there’s a ”heat shield” between the choke housing of the carb and the choke thermostat. Is this critical or needed in any way? I bought a new thermostat recently and I’d rather not damage it if the heat shield is there to protect it.

Thanks again for all the help.

 

Yes, a certain amount of back pressure is needed, but I've never heard of it (or lack of
it) affecting the EGR.

No, but it DOES need to be at full operating temperature.

Could be. Is your ported vacuum line hooked up to the carb correctly and are all your
vacuum hoses free of dry-rot, breaks, crumbling & leaks? Follow the diagram on your
radiator support.

What is a WOT trigger? Never heard that one before.

 

Hey Ctubutis, before I checked the vacuum to the EGR I did drive the truck for about 4-5 miles and pulled into a parking lot to check it. Im pretty sure it was warmed up by then, but ill try it again tommorow after I drive home to be sure its fully warmed up (its about a 10 mile drive).

You might recall my post from about a week ago here also.

https://www.ford-trucks.com/forums/9...questions.html

Ive replaced all of the vacuum lines in the truck (except for the one to the brake booster) and since that post ive also fixed the heat / vacuum pipes for the choke that run through the exhaust manifold.

Acording to the other poster in that thread it appears I have everything hooked up correctly. the WOT trigger I mentioned was explained to turn the EGR off at wide open throttle.

So to answer your question, yes everythings hooked up correctly and with new hoses. I did find what I think is the correct VCV valves on ebay for cheap, so I might buy a couple since im thinking that might be the problem.

 

WOT = Wide Open Throttle
But I don't know what RVF150 is referring to.

(EDIT) this is what you get for leaving 14 threads open in tabs...

Sorry.

 

I would expect that to be warm enough... With that being the case, I would then check
the vacuum *at the vacuum source.* From what I remember, the EGR is supplied by a
ported vacuum connector on the carb, that vacuum is then managed by at least one
VCV and maybe some other components (VRESER?) to accommodate various
changes in operational characteristics (lack of vacuum at WOT, for example).

So, study your vacuum diagram, or maybe just pull hoses off the carb at random (one
at a time) and find the one that doesn't supply much - if any - vacuum at idle but
supplies it at, say, 2,000 RPM while warmed up. Compare that reading to what
you're getting through the managed vacuum source (that which is managed by the
VCVs and other components - IOW at the EGR valve).

You can also remove those VCVs and put 'em in a pot of water on the stove; as the
water heats up, you should be able to blow through different passageways than what
you can blow through when cold. It helps if you put lengths of rubber hose on the
nipples before heating up the valve on the stove.

I still have no idea about that thing you're calling a WOT trigger, we need a 6-banger
expert for that.

 

Most of the VCV(Vacuum control valves) open up above 100 degrees water temperature. So once it's warmed up, rev the engine and you should have vacuum going in and out of the valve.

If your EGR valve has a little felt filter going around the bottom of the diaphragm area, then yes your EGR works on exhaust backpressure. This is how they metered the amount of EGR according to engine rpm. The felt filter is there to filter the air going into the vacuum lines, because when the EGR is partially open, the rest of the vacuum is "leaked" or sucks air through this filter.

That's why on these valves, you can pull a vacuum on them all day long on a test bench, and they will not open, which can make you think it's bad. It's not, there is a metal diaphgram that is closed by exhaust pressure, and that's what makes it work.

 

Franklin is spot on with his reply.

I would just like to add that the VCV valves should be replaced or checked at regular intervals, or every time the coolant thermostat is changed or checked. The VCV valves are color coded for the correct temp. Make sure that the replacement are the exact same color.

There is a WOT (Wide Open Throttle) valve on the carb that is indirectly hooked to the carb throttle linkage. When the throttle is moved to the WOT position the throttle pushes a "little button" on the WOT valve that releases the vacuum to atmosphere, thus disables the EGR valve at WOT conditions for increased performance at WOT.

 

I didn't know they had a WOT valve, though it does not surprise me either. I don't think all EGR systems on different engines had them? I think most of the time when you go to wide open throttle, you are going to naturally lose vacuum anyway and the egr will close by itself. It might be on the six the carb is so small, even at WOT you still have enough restriction through the carb to have enough vacuum to keep the EGR open some.

I think of the late 70's-80's as the dark ages for emissions. The added and cobbled up so much junk on these engines to make them pass emissions and still be driveable. It's like little bandaids all over a perfectly good sound engine design underneath. When fuel injection came out, it really cleaned up a lot of vacuum hoses(but replaced them with wires I guess).

 

Thanks for all the awesome help and info as usual everyone.

Yesterday I did test the vacuum to the EGR again, and it does actually work (it gradually pulled more vacuum as RPM increased). I think the truck was just not hot enough the first time I tested it is all.

I did order a new VCV valve from eBay that was listed as a replacement for my trucks year and engine just in case ill ever need it. Not sure if the link below works but the one on my truck is colored green, the eBay picture looks grey, but they had the same picture for all their valves, so I’ll see what it looks like when I receive it.

1981 81 Ford Pickup F150 1/2 Ton Ported Vacuum Switch: eBay Motors (item 260613602907 end time Jul-02-10 15:35:17 PDT)

As far as the EGR valve, I don’t believe it has any “felt” where the diaphragm is. The sticker on it listed the valve as EITE-9D448-H2A. I found that EGR on Autozones website listed for use on the 300-6 2wd with a manual transmission so it seems to match up.

Tomorrow I’m planning to block off the EGR ports with a solid brass shim stock gasket temporarily. I think the valve might be leaking and causing a bad idle so ill get a better look at it then to see if there was any "felt".

Chances are ill probably end up buying a new one (I recall the valve looking pretty charred up when I had it removed a couple months ago) So if there’s no felt present on the current valve, or the new one if I buy one, I should be safe to remove the converter?

I wouldn’t worry about it normally, but I think it’s the original converter, and id assume after 30 years its probably pretty clogged and not doing its job anyways.

I know some people would say to just remove the EGR, but reading about their benefits I’d prefer to keep it intact and working correctly.

 

Hmmm. i've learned all sorts of stuff about the early EGR in this thread. I've got an 85 and I cut off the cat and put a free flowing muffler on. Similar to a mellowtone. It was too loud for me and the truck started running terrible. Well, I guess it RAN okay, but I lost a LOT of low end. I went back and had a glasspack added in the spot of the old cat. MUCH better.

 

If you reduce the backpressure, this type of EGR will still work, but it will not pass as much exhaust gas into the intake that it's supposed to. What you will usually notice right away when you get the engine warmed up is pinging under a light load. The EGR has a cooling affect inside the combustion chamber, and keeps the engine from pre-detonation or "pinging".

I went through this whole senario, and I found going to a 180 degree thermostat helped the pinging a lot after I had modified the exhaust.

 

Thanks Franklinn the pinging is what I was worried the most about especialy since I dont think the truck has any sort of knock sensor.

Would you think something like kevin mentioned would work though, a glasspack + a muffler? Or would that just be a totaly random guess to get the right backpressure, and would it even sound decent?

When I have the exhaust worked on ill have the cat looked at. If it looks ok ill just leave it there, but having options is good incase its in bad shape.

 

Too much backpressure from a clogged cat will cause the EGR valve to open more than it should as well. Been there done that...

I've seen WOT valves on 300's and early 302's with EGR valves.

My 1973 F-100 with a 302 had one as an example, and so does my 1981 with the 300. The 1973's EGR valve did not use backpressure to activate the valve, but my 1981 does.

Be careful with the new VCV, if the color doesn't match, IE: Green, then don't use it because the temp of when the new VCV opens will be wrong and could cause drivability issues when the engine is cold.

 

No backpressure is required for an engine to run properly. This is a myth perpetuated by those who don't know any better. What you are looking for to get optimal performance is to maintain velocity as the exhaust cools. Open headers will hurt this, which is why guys that run open headers will often attach a short length of pipe to the collectors but not a full exhaust. Removing a cat and still running a full exhaust will not hurt anything.

 

Backpressure is required for the EGR and smog systems to function properly. Too much and/or too little backpressure will also mess with the stock timing curve on these engines. The correct backpressure is very important on stock running engines using factory smog and components. So I dissagree with the above statement concerning this topic.

Now on a performance engine that's not stock, well anything can be adjusted and modified to compensate, etc...