EGR Valve Questions: 1987 2.5L Renix

[NickyV]

EDIT: I've done a bunch of tests and am more familiar with this system now. A few updates here.

 

I only failed smog on one portion of the test -- NO (PPM) at 25 MPH. When on the dynamometer at 15 MPH, the truck was well within the permitted NO (PPM) numbers. It failed at 25 MPH when the NO (PPM) spiked significantly. From my reading, this could be due to the cat starting to fail (ugh...) or perhaps the EGR wasn't working properly.

 

--- --- ---

 

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.

Edited August 17 by NickyV
Added more information.

[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!

 

 

[NickyV]

Got some updates on this project. I am planning to do a video or more comprehensive write-up on this once all is said and done. But for now, I am now quite certain that @eaglescout526 is correct about the EGR Valves in 2.5L Renix MJs. Thanks!

 

The EGR valves for this model have a "bleed" feature and they cannot be tested using the traditional hand-pump vacuum test. Due to some science that I understand in the abstract but can't really explain using words, the truck needs to be warm and under load (not in neutral) for the EGR valve to actually open up. I guess it uses a combination of vacuum suction from the EGR nipple and pressure coming directly from the engine.

 

Anyway... I'm going to put it in bold, in case anyone comes across this later: The vacuum pump test that works on many older EGR valves DOES NOT work for the 2.5L 1987 MJ.

 

Testing your EGR valve this way will not help you diagnose it. What you can do, is get a pen or pencil or something like that, and push up on the diaphragm from the underside of the EGR while the engine is running. That will at least give you the sputtering idle test. And it will tell you that, at the very least, your EGR valve is doing what it is supposed to when it is shut. I hope to eventually make a video about all of this.

 

But now I've got another conundrum!

 

The vacuum diagram under the hood of my truck does not match the actual vacuum routing under the hood. So far, I've only discovered this discrepancy for the vacuum hoses routed to my EGR, but I'm wondering if there are other peculiarities. I'm going to do a little digging on the forum to see if anyone else has encountered this, and I may start another thread.

 

 

[eaglescout526]

I never saw the other response after my comment. But I am glad you got it sorted out!

As for the vac diagram, its very...well unapologetic to say the least. Its kinda wacky and can be tough to interpret at first. But its also straight forward once you follow where all the lines go, given a PO hadnt messed it up before your ownership. 

[NickyV]

Hey hey, @eaglescout526! I can always count on a quick response from you. I was thinking about making a new thread about this, but since you just replied to me, I'll post this here for now:

 

The emissions diagram sticker on the driver's side firewall of my truck matches what I've found online for the 1987 2.5L. But it seems like the EGR may actually be routed like a 1986. On the 1986 diagram, there is a T valve right before the inlet of the EGR solenoid. On the 1987 diagram, it appears that there is not a T valve.

 

The orange rectangle is the diagram I have under my hood. The red circle shows the T valve that my truck seems to have.

 

Maybe I'm reading my diagram wrong and it shows a T valve. But if not, I'm wondering if that could be a problem? Could it indicate other issues? Or is this just a common peculiarity?

 

[eaglescout526]

6 minutes ago, NickyV said:

Hey hey, @eaglescout526! I can always count on a quick response from you. I was thinking about making a new thread about this, but since you just replied to me, I'll post this here for now:

 

The emissions diagram sticker on the driver's side firewall of my truck matches what I've found online for the 1987 2.5L. But it seems like the EGR may actually be routed like a 1986. On the 1986 diagram, there is a T valve right before the inlet of the EGR solenoid. On the 1987 diagram, it appears that there is not a T valve.

 

The orange rectangle is the diagram I have under my hood. The red circle shows the T valve that my truck seems to have.

 

Maybe I'm reading my diagram wrong and it shows a T valve. But if not, I'm wondering if that could be a problem? Could it indicate other issues? Or is this just a common peculiarity?

 

 

I do my best!!

 

This image has always bugged the hell out of me and its really aggravating cause it doesnt match. Period. Might on the YJ but I have my doubts since the YJ used the 86 set up until 90.

If you flip the valve cover orifices to line up with the front, youll have the MJ and XJ set up. The 87 one is the way you want. But!! What year was your MJ built? 86 or 87? If its late 86, I can see them just using what was left at the factory and calling it good. If its 87 then maybe the PO found the wrong diagram and did it wrong.

[NickyV]

To your question about when my MJ was built: I'm not sure. I don't know if I have ever taken a deep dive into that. I just checked my VIN on Jeepz.com and all it said was that it was a 1987 model year.

 

What I can tell you is that there is definitely a T valve right next to the EGR solenoid. One end of the T valve traces to the hookups near the TBI. The other end is on a thicker vacuum line that goes to a plastic bottle under the passenger side headlight. The third end goes into the solenoid itself.

 

By the way, I've never had a terribly rough idle. It could be better. But it's good, all things considered. Also, I haven't ever encountered much to suggest PO tomfoolery (at least not under the hood... inside the cab... that's a different story). Then again, I'm still very much a novice under the hood, so who knows?

[eaglescout526]

1 minute ago, NickyV said:

To your question about when my MJ was built: I'm not sure. I don't know if I have ever taken a deep dive into that. I just checked my VIN on Jeepz.com and all it said was that it was a 1987 model year.

 

Have you not posted your VIN in here to get more accurate info?

 

2 minutes ago, NickyV said:

What I can tell you is that there is definitely a T valve right next to the EGR solenoid. One end of the T valve traces to the hookups near the TBI. The other end is on a thicker vacuum line that goes to a plastic bottle under the passenger side headlight. The third end goes into the solenoid itself.

Let me go look at my 88 and get back with ya.

 

2 minutes ago, NickyV said:

By the way, I've never had a terribly rough idle. It could be better. But it's good, all things considered. Also, I haven't ever encountered much to suggest PO tomfoolery (at least not under the hood... inside the cab... that's a different story). Then again, I'm still very much a novice under the hood, so who knows?

 

Rough idle could be anything. Grounds, sensors, dirty connections, bad O2, bad headgasket.

Well wiring is pretty easy to fix.

[eaglescout526]

Ok so that T is correct. Should be main vacuum supply to the EGR, Vac reservoir and 4wd if equipped. The from the reservoir would go to your HVAC and cruise control if cruise is equipped. Fun fact, with cruise control, the football shaped reservoir can only be installed 1 way.

[NickyV]

Thanks! I honestly don't remember if I've posted my VIN on CC. But I'm thinking that I haven't. Where should I do that?

[eaglescout526]

In our registry. Should be an 87 sub section. 

[NickyV]

Found it! Posted it! I had definitely been meaning to do that. So do I eventually get a report from @jdog? Hope so. Can't wait!