Can an EGR valve be rebuilt? (1 Viewer)

[fyton2v]

I bought a smoke machine to check for an exhaust leak, but while I was under the hood I also connected it to the brake booster hose. I noticed smoke coming from under the saucer-like top part of the EGR valve. This is bad, correct? It's not a big leak. The motor pulls about 19 Hg at idle. If I spray water or carb cleaner all around that valve nothing happens. Sucking on the vacuum hose does move the diaphragm and it seems to hold. The smoke would have traveled from the intake manifold through the EGR block under the carb to the EGR valve. With that path I'm not sure it's the diaphragm, or even if it's supposed to be air tight in that union between the orange hose and where the EGR heads down the plumbing towards the exhaust manifold.

Is the entire valve supposed to be air tight? If the diaphragm isn't leaking I'm not quite sure what could actually leak.

 

[mattressking]

If you separate the rolled edge cleanly and can reseal it then yes.

Short answer otherwise is no. If you want to learn, look into 911 gauge rebuilding, they use the same concept and north Hollywood speedometer rebuilds them. They have a tool that opens and closes the rolled edges on steel cleanly. Figure that out and you can apply that to the egr and vacuum advance canisters.

 

[fyton2v]

I took it apart and I think the EGR valve is functioning normally. Now that I see how the thing is built, I pretty certain the smoke is finding it's way through the hole that the valve shaft passes through on it's way up to the diaphragm. There can't be much of a leak there.

I read in a post from @Fast Eddy that you can apply vacuum to the EGR diaphragm when the engine is running and it should cause the motor to stall. That's not happening in my case. Vacuum creates a bubbling noise from the sound of exhaust gas passing through but no stalling. Exhaust is there. Should it really be stalling?

 

[mattressking]

Think of the egr as a controlled vacuum leak. The engine should stall and die because when the valve opens it creates a large vacuum leak. The engine vacuum pulls exhaust gases into the manifold.

The vacuum modulator controls how much exhaust goes in via the valve based on engine vacuum.

If you apply a lot of vacuum to the valve directly at idle, the more vacuum you add will cause it to stumble and ultimately stall and die. So if you apply 20inHg at idle, the truck will stall if the valve is opening/clear of soot. The egr also causes the opposite, if the valve is stuck open at all, it’s a vacuum leak (not your issue).

 

[fyton2v]

That makes sense. I took the EGR valve off and inspected it. The valve seems to be working fine. I cleaned it up anyway. I started the truck with the EGR valve off just to see if exhaust is making it all the way up that not very flexible pipe. It is. But when it was idling, and the pipe to the EGR block was wide open ... I was expecting a big vacuum leak. It wasn't a big leak. Applying throttle increased the suction from the EGR block and then the motor would stumble. In a 78 is that block only working off the carb vacuum when throttle is applied? Seems so. I need to do some more forum searching.

 

[Malleus]

Just idle curiosity: how did you get the top off? I assume it's salvageable?

 

[wimberosa]

If you wouldn't mind taking a picture of the inside and posting here...that would be interesting also.

 

[fyton2v]

The top just contains the diaphragm. It's not leaking so I didn't need to take it off. All of the important stuff is happening in the bottom. And after more searching, the EGR plate is above the throttle plate (on my truck ... it's different on others) and an open EGR system will not cause the truck to stall at idle. PinHead mentions this way back in time.

 

[fyton2v]

If you wouldn't mind taking a picture of the inside and posting here...that would be interesting also.

Already put it back on the truck. It's less complicated than I thought, however. Here's a picture of how it works. I think people would have a blockage where the EGR valve connects to the flexy pipe towards the exhaust manifold. Or the valve itself could be gunked up. And gunk at the valve port could further restrict the EGR from doing EGR stuff or even hold the valve open, which would create the vacuum leak that Nate (mattressking) described above.

I think the important takeaway is that you test these things differently depending on model year and whether or not it's a CA truck (mine is not).

 

[Fast Eddy]

I took it apart and I think the EGR valve is functioning normally. Now that I see how the thing is built, I pretty certain the smoke is finding it's way through the hole that the valve shaft passes through on it's way up to the diaphragm. There can't be much of a leak there.

I read in a post from @Fast Eddy that you can apply vacuum to the EGR diaphragm when the engine is running and it should cause the motor to stall. That's not happening in my case. Vacuum creates a bubbling noise from the sound of exhaust gas passing through but no stalling. Exhaust is there. Should it really be stalling?

Not sure which post that was. I have heard that later 2f motors would almost stall, but the 2 I have experience with, a '76 and '78, didn't change much when applying vacuum there. With the valve disconnected and cold you can tell if it's working by pulling vacuum and seeing if it flows or not.

 

[Brian/99uzj100]

@fyton2v Here's some info from the Emissions FSM for my 76.
My rig doesn't stall when manifold vacuum is connected to the egr at idle. The air intake just changes sound at the carb (with the air cleaner removed) per the FSM.
I've had smog stations connect manifold vacuum to the egr valve, and when the engine didn't stumble or stall they said it wouldn't pass the complete test, even when I showed them the FSM.
I had an older mechanic at another smog station test it correctly without me showing him the FSM, and he said they used to call these egr valve/ carb combination "gurglers", because of the sound change at the carb during the test.
It's more of a hollow sound to my ears.
The smog station I go to now doesn't test the egr at all, so I just smile and say "thank you" when It passes.

 

[fyton2v]

Thanks! I've yet to have a smog station in CA test the EGR, or any smog hardware. I did have one fail me for not having that vent hose that brings hot air around the manifold to the air cleaner. Oh, they always check the gas cap though.