EGR valve stem seal.

Clone TIE Pilot

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Recently I smoked my Chevy 305 engine looking for vacuum leaks. I found a little smoke coming out of the stem seal in the base of the EGR valve. The diaphragm is ok and holds vacuum. I searched online and did not find much info about it. Only thing I found was that some Turbo Buick guy had trouble with boost leaking out of the stem seal on his EGR valve. Not sure how well the stem seal is supposed to seal for EGR valves?
 

oldsmobile joe

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Nov 12, 2015
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Should be a 100% seal. If not your introducing exhaust back into your intake when it shouldn't be there. This could be the cause of your rough idle. I don't know we didn't catch that info in your rough idle thread. You said it and it went right over our heads. Its a vacuum leak, but a vacuum leak of inert gas. You can't test for it the tradional way of adding fuel or propane, it won't re-act.
 

69hurstolds

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Jan 2, 2006
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The only stem seal I'm familiar with on an EGR valve is the one for the top of the EGR valve base which is above the main valve on the "vacuum" side. It shouldn't leak. If it does, you will find one of two things. Either an air vacuum leak if the EGR main valve is shut, or an exhaust leak when the main valve opens. Depending how big the leak is, and if the car has computer controlled carb, it may be able to compensate for the air leak, or it may not. Usually not since they're so darn finicky most of the time. Only sure-fire way to take it out of the equation is to replace the EGR valve with new. To my knowledge, there is no DIY stem seal changeout parts/methods available. If there is, I haven't seen it.
 
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Clone TIE Pilot

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The only stem seal I'm familiar with on an EGR valve is the one for the top of the EGR valve base which is above the main valve on the "vacuum" side. It shouldn't leak. If it does, you will find one of two things. Either an air vacuum leak if the EGR main valve is shut, or an exhaust leak when the main valve opens. Depending how big the leak is, and if the car has computer controlled carb, it may be able to compensate for the air leak, or it may not. Usually not since they're so darn finicky most of the time. Only sure-fire way to take it out of the equation is to replace the EGR valve with new. To my knowledge, there is no DIY stem seal changeout parts/methods available. If there is, I haven't seen it.

Yes that is the seal I am talking about. The valve isn't that old. The valve was closed when I pumped smoke into the intake manifold to find vacuum leaks. So it would have been leaking smoke from the intake side of the EGR valve. I can see that the stem seal is staked into place similar to the accel pump and TPS plunger seals in the airhorn, just no way to access it.
 
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Kra5379

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Apr 30, 2019
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I believe the “proper” name for it is the EGR “pintle needle”, if you’re seeing smoke coming out it it’s likely that you have a chunk of carbon causing it to hang up in the half open position, pull the valve off and clean it up, another thing I have found helpful, when you have the valve off, start the car up just for a second or 2 to blow all of that loose carbon out of the intake port so you don’t end up with another one stuck in there
 

Kra5379

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Apr 30, 2019
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The only stem seal I'm familiar with on an EGR valve is the one for the top of the EGR valve base which is above the main valve on the "vacuum" side. It shouldn't leak. If it does, you will find one of two things. Either an air vacuum leak if the EGR main valve is shut, or an exhaust leak when the main valve opens. Depending how big the leak is, and if the car has computer controlled carb, it may be able to compensate for the air leak, or it may not. Usually not since they're so darn finicky most of the time. Only sure-fire way to take it out of the equation is to replace the EGR valve with new. To my knowledge, there is no DIY stem seal changeout parts/methods available. If there is, I haven't seen it.
Kind of a petty detail but could make a big difference depending who you’re explaining it to, but when the engine is off, at idle, or decelerating the EGR is open, when you build vacuum to the EGR and the valve/diaphragm come up, that’s actually the closed position
 

oldsmobile joe

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Nov 12, 2015
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Kind of a petty detail but could make a big difference depending who you’re explaining it to, but when the engine is off, at idle, or decelerating the EGR is open, when you build vacuum to the EGR and the valve/diaphragm come up, that’s actually the closed position
No, this is wrong. An egr valve is normally closed, no flow. Vacuum application moves the valve to open, causing exhaust to flow through it.
 
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Kra5379

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oldsmobile joe

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Lacks context. Not sure where this came from but its not from a factory g-body service manual.
If an egr is open to flow, the engine will not start or starts hard and runs rough because your drawing in exhaust. Exhaust is inert air. Meaning it lacks enough oxygen to promote combustion.
 
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69hurstolds

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I can see that the stem seal is staked into place similar to the accel pump and TPS plunger seals in the airhorn, just no way to access it.
The valve was closed, so the stem seal would see whatever was in the intake. There's likely a way to access it, but it may require special tools, and even if you could, who makes/sells just an EGR stem seal? I'm sure it's likely made of something that can take the heat, so maybe some sort of graphite rope packing-ring-like substance similar to the junk we used repacking steam valves on the submarine. Never had one apart so I don't actually know.

Unfortunately, I don't know if any other way to re-seal the one you have without replacing it. If possible, get an ACDelco unit. I've always had the best luck with those. And I can't say that's your only issue causing the rough idle. It's a factor to be sure, but how much of one??

Is the original stamped 17084375 on the top hat?? If it is, then it's GM p/n 17110475 from the parts information.

Here's a slightly used one it appears. $42 and change plus tax. But it has no P or N on it, making it a Ported type. Meaning a simple vacuum pull test will make it open.


Or a brandy new one for 51 and change plus tax.


GM predominately used 3 types of EGR operations on G-bodies. Note: A vacuum check will NOT work on a Positive backpressure EGR valve. It will on the other 2 types, Negative backpressure and Ported. They all have a spring on the top of the actuating diaphragm so it fails to close.

So if it's moving when you apply a vacuum, it's either Negative backpressure (breaks vacuum when negative backpressure is felt or closes when vacuum source cuts off) or a Ported. On the ported, vacuum opens it, if vacuum cuts off it closes. Simple. Negative and Positive backpressure styles have the hole in the pintle (main valve disc) and actuating stem, but work with opposite pressure sensing.

Do a search on here for more info if necessary (this is just a call out for everyone if you're really wondering how one of these POS's work). Keep the pintle tips clean and hopefully you'll have many miles of smiles.

 

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