EGR Valve Questions: 1987 2.5L Renix

[NickyV]

My MJ failed smog so now I'm troubleshooting. This is all new to me and I wish I'd taken a video when the smog tech was giving me advice, but here's what I remember of what he said:

 

1) Something about not seeing any pressure when connecting his vacuum tool to my EGR valve.

 

2) Something about too much NOx?

 

3) Suggesting I replace my EGR valve, my O2 sensor and replace my tailpipe which is full of holes (not sure where... I haven't identified all of them).

 

I have since replaced the EGR valve, with a Standard Motor Products EGV580 from Rock Auto. But before moving onto the O2 sensor and the exhaust, I wanted to make sure I did it right, so I tried to reverse engineer what he did and now I'm just getting confused and wondering if I picked up a bad EGR or if I'm just not doing these tests right.

 

I've tried various tests by hooking up my own vacuum pump to various connections under the hood and I've noticed a few things:

 

1) With the engine off, I hook up the vacuum pump directly to the newly installed EGR vacuum port. It does not hold pressure.

 

2) With the engine running and warm, I hook up the vacuum pump directly to the newly installed EGR vacuum port and I do not see it creating any pressure.

 

3) With the engine running and warm, I hook up the vacuum pump to the vacuum line that normally connects to the EGR vacuum port. I rev the engine and the needle on the gauge reacts, but only for a split second. I don't know enough about this to understand if this is a normal behavior or not.

 

I've been Googling around and getting more confused. At first I thought that the EGR valve should hold vacuum right out of the box. (Unfortunately, I did not test it out of the box and am only testing now that it is installed). But then I'm coming across information that with back pressure EGR valves, it will NOT hold vacuum out of the box, and maybe this is a back pressure EGR valve?

 

Any and all advice is appreciated. Thanks.

[eaglescout526]

EGR shouldn’t hold any vac at all which is what the engine vacuum is for. There’s a solenoid that controls when the EGR gets vacuum or not. 

 

Way to test a bad EGR is actually by blowing into it and seeing if any air comes out. If no air comes out, it’s good. If air does, it’s failing. So I was told by a mechanic who was familiar with 70’s and 80’s smog equipment. 
 

Another way to see if everything is working alright is to push up on the EGR diaphragm and see if the engine tries to cut out. 
 

Now i dont know how to test the solenoid to see if it’s good or bad but I can check some of my literature and see if there’s a way to test it. 
 

Usually NOx is an indicator of the O2 getting lazy. 

[NickyV]

This is my old EGR valve. In the bottom view I can see what appears to be a gasket that has shrunk. That’s what I’m pointing to with the toothpick.

 

In the top view there is the vacuum port. It’s wrapped in a little white electrical tape, which I used to make a seal for my vacuum pump when I was trying to test it.

 

You are saying I should not be able to pass any air through that tip when blowing into it?

 

I do think there are some models of older EGR that will hold vacuum if you attach a vacuum pump to them, even if they are cold. But I am now convinced that my MJ uses a back pressure EGR valve. And I don’t think they hold vacuum unless the engine is running and under load. Watched a ton of YouTubes today. Lol.

 

At any rate, I appreciate the insights, as always!