Should an EGR valve still operate off of a 20 in. Hg vacuum source? If so should I be able to see it moving when vacuum is applied and removed? My original source is dead, and I'm trying to figure out whether or not the valve works.

 

Yes. It should operate. 20 in is alot of vacuum.

The source for EGR vacuum is ported IIRC... it's not going to have anything on it at idle. The original source rarely "dies".

 

Well I bought a new EGR valve and it said that to check it I should hold the engine at 2500-3000 RPM and plug and unplug the vacuum line, which is routed straight to the valve from the carburetor. When I did that from the original EGR port, nothing happened, and I'm pretty sure there wasn't any vacuum coming from the line. Since I took off my THERMAC, I took off the plug and hooked the EGR vacuum line into that port (20 in.) and still nothing happened on either the new valve or the old valve.

Is there a better way to test or are they both broken?

 

Any possibility there's a BB or something jammed into the piece of line you're using?

 

I wish it were that easy, but I've tried the original line, and another one that I made from brand new hose©

 

If I hook up a hand-held vacuum pump to the valves I should be able to see the diaphragm move up and down, right?

 

There are also valves that require exhaust pressure to open, I can't recall the terminology though... the vacuum merely removes their restraint from opening then the exhaust pressure can do its thing... I don't think these cars are supposed to use those but I could be wrong, some might...

 

Well, in the instructions it says: "Do not attempt to perform an off the car bench test using a hand-held vacuum pump. Due to its design, the procedure described above is the only way to test its function." They pretty much killed that idea.

Maybe my intake manifold is clogged...

 

RB is correct. Your LG4 may have a positive backpressure EGR valve. (Incidentally, most TPIs used a negative backpressure valve.) In any case, these valves require a change in exhaust system pressure to operate. All valve require a clean intake manifold exhaust passage, so if you haven't removed the valve, it might be a good idea if only to clean the passages and the pintle of the valve. Remember - DON'T use any solvent on the EGR valve itseld, since they can destroy the pilot valve disc in the backpressure valve assembly in the valve.

 

Thanks a lot for those diagrams and the info. The valve does say POS on it, I was kind of wondering whether it stood for positive or something else...

I think I'm going to assume that at least the new valve works. My intake manifold is warped and needs to be replaced anyways. I'll probably just put this project on hold since my car will run without it. Last night my ball joint exploded on the highway so I've got bigger problems to dump my money into.

 

Fly,

Well, most of us would probably interpret that as a POSitive backpressure type valve, but it IS remotely possible that the manufacturer had the foresight to identify the valve for the next person who would inspect it that closely as a P.O.S. - Piece Of S...(excrement).

Just thought I'd cover most of the likely possibilities...

 

Well I got a new intake manifold, Performer 3706, and now everything has vacuum. I put a gauge on the vacuum line coming out of the solenoid and going into the new valve, and it reads about 7" or so every time I hit the throttle (while driving). The fact that I have vacuum now doesn't seem to change anything, it still pings and I'm running 93 octane and 6 degrees base timing. The engine didn't change speeds when I performed the same test as above. Any ideas?