Hello again, quick request/question for those of you with a known functional EGR valve. Can the EGR on our vintage (82 300) be simply tested with a vacuum pump? My old crusty valve wouldn't hold vacuum, so I ordered a NOS motorcraft replacement and it is nice and shiny but it also won't hold vacuum. I recall reading here somewhere that these valves rely on exhaust back pressure to function and a vacuum pump test doesn't yield results. So how exactly can one test the EGR valve on these trucks?

Much appreciated!

 

The EGR should hold vacuum. You are able to test it with a vacuum pump to see if it holds.

 

That's what I also assumed, seems silly to have a vacuum source feed to something that won't react to or hold vacuum. I have a hard time believing that this new valve is also bad. Anyone else confirm the correct way to test these valves and anyone that can replicate the process on their own working valve would be much appreciated.

 

You can grab a known fulltime vacuum source line and start the engine and let it idle. When you attach the known vacuum source (or vacuum pump) to the EGR the engine will stall. Then the EGR is good. It stalls because the EGR is operating properly and allowing too much exhaust gas into the cylinders which will not burn the fuel.

 

I also have the same question for my 1981 F-250 EGR Valve. Hopefully, we can check the function of our EGR valves in a fool-proof manner cuz the replacement is anywhere from 50 to about 85 smackers. My truck was running fine (as long as the accelerator was pressed), but wouldn't idle without stalling. After reading posts on FTE, I suspected a vacuum leak and found that the air check valve had rusted through. (I'll post a photo as soon as I'm allowed to do so.) I replaced the air check valve and now the truck idles GREAT...but as soon as I press the accelerator, it hesitates and bucks wildly. I'm suspecting the EGR, but don't want to replace it unnecessarily.


-PapaTruck

 

Parsedout, you have an '82 300, here's the EGR off my '81 300. Maybe this image will help someone answer your question, assuming the trucks have the same style EGR. (I'm new to the forums, I'm just trying to help if I can. I've heard pictures are preferred. Hope this helps you out.)


-PT

 

^^^^^ Exactly the same one. Searaging FTE has come up with a bunch of conflicting answers. Some say there is a built in vac leak and isn't supposed to hold vacuum. Others say definitively that "theirs holds vacuum". Others say they've checked countless new valves at the store and none hold vac. It's enough to drive a person mad. Tonight I'm going to rev the truck to 2k and see if the diaphragm moves at all. Hopefully that'll be enough load to activate it.

 

My EGR valve was caked in muck and rust when I bought the truck. Cleaned it up looking for a part number of some sort, but bout all I can make out is "Made in Canada." I feel your pain on search confusion, especially when searching by symptoms. My suspected EGR issue is only one of seven different possibilities I found when typing my truck's symptoms into the search bar. I do have an idea for how to test it...while waiting for a better answer from the FTE elite... The function of the EGR is simply to recirculate a small bit of exhaust gas after the engine has warmed up. If the EGR recirculates the gas too early, the engine might stall...or so I read online. With this in mind, simply disconnecting the vacuum hose and plugging it would yield (in my layman theory) one of two results: 1) no change, thus it's not an EGR malfunction; or 2) the truck runs better, meaning the EGR is allowing exhaust too much or too soon into the engine. NOTE: I'm a newbie, and this is just conjecture.

-Papa

 

Most of the EGR's on these trucks CANNOT be tested with a vacuum source. Take your EGR valve off and look underneath in the diaphragm area. If you see fuzzy looking felt all around the outside edge it cannot be tested.

It has a metal diaphragm inside that regulates the vacuum to the valve, Exhaust pressure operates this metal diaphragm, without exhaust pressure acting on this piece, the vacuum will leak through the felt filter around the inside edge.

 

That makes sense. So, basically one would have to replace the EGR valve altogether just to see if a new one makes any changes in performance. Gotcha.

 

Thank you, I do have the felt on the new motorcraft EGR installed so that helps a ton. I didn't have a chance to test if free revving up to 2k is enough to move the diaphragm but based on how the car runs at part throttle I'd say it's doing it's job. I did notice I have 2 plugs with some spark arcing from the plug wire to the valve cover, good thing I ordered a new set last week.

Getting this beast sorted out, only a few more mechanical things left on the list of to-dos.

 

Tested the EGR function on the truck last night, free revving it I could see the diaphragm moving as expected. So once and for all, based on Franklin's post and my direct observational experience. These EGRs cannot be tested with straight vacuum yet can still be 100% functional.

 

I didn't know either till I took one apart. I ground the metal down all the way around the edge till it separated, determined to figure out why it would not work. Once I looked at the guts and found out how it worked, I went back to the factory explanation and right there it is in black and white.