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Dan 84 CJ-7 02-24-2002 07:45 PM

Another EGR valve question...(more info)
I was attempting to "test" my EGR valve today before I go in for another emissions test.
How much vacuum should it need to pull the valve open? I could push the diaphram open by hand, but i couldn't get any ported vacuum to have enough force to open it. It did take a bit of pressure to push it open by hand too.
Is this a sign of a bad EGR valve?
I bypassed the CTO valve for the test and hooked a vacuum line directly to the EGR, and could feel that there was a vacuum present, it just didn't seem to have enough vacuum, to pull the valve open.
I don't have a vacuum guage, so i don't have any real numbers to post.


Dan 84 CJ-7,Weber,HEI. 95 ZJ,V8.

TiminMb 02-24-2002 08:51 PM

Re: Another EGR valve question...
Hope I'm not insulting you with this, but you know that at idle ported vacuum is nil, and it peaks when you open the throttle partly. So you will have to work the throttle to get it to open the egr. Or you could test it using manifoold vacuum, that should give you at least 25 HG of vacuum.

84 CJ7, 258, HEI, M/C 2100 carb, 5 inch lift, RS9000's, 33x12.5 BFG M/T's, 4.56's and Detroit softlocker, full cage & belts, Xenon flares, Dana 44 rear, GM dual diaphragm brake booster

Dan 84 CJ-7 02-24-2002 11:12 PM

Re: Another EGR valve question...
I should have said in my post that even when revving up to about 2500rpm (which is the RPM my emission test is done at) there wasn't enough vacuum to pull the EGR valve open.
I do know that there shouldn't be any vac at idle, but it also didn't pull open at higher RPM's either.
I was working the throttle at the carb and watching the EGR valve for movement.
maybe it's time to go out and get a vacuum gauge and make sure there is enough vacuum?


Dan 84 CJ-7,Weber,HEI. 95 ZJ,V8.

Dan 84 CJ-7 02-25-2002 11:36 PM

Re: Another EGR valve question...(More info)
I took my EGR vavlve off tonight to check it out and I need to see if anyone agrees with my diagnosis.

The diaphragm moves freely when pressed by hand. However, when I plugged the vacuum inlet of the EGR valve and pressed the diaphragm by hand again I noticed no difference. I think there should have been some noticeable resistance trying to push the diaphragm in with the vacuum inlet plugged. That leads me to believe that the seal around the diphragm or diaphragm istself is no longer good and is leaking. If I had a vacuum pump, i could test it for sure, but I don't have one.
I'd like to avoid buying the valve, but I need it to pass my emissions test. Does my diagnosis sound correct, or are there more (better) tests I should perform before I consider this EGR valve bad and buy another one?
Also, how bad would my idle test suffer if I was to block open the EGR valve just for the pourpose of passing the high RPM test (2500rpm) and then return the EGR valve back to it's closed non working condiditon emmidiately after the test?


Dan 84 CJ-7,Weber,HEI. 95 ZJ,V8.

JimmyZ 02-26-2002 07:26 AM

Re: Another EGR valve question...(More info)
EGR's are funny things. They have internal passages that will bleed off vacuum, to the point that you might think they won't work. Useing a little hand vac. pump sometimes won't supply enough of a constant flow to keep valve open. See if you can watch the valve move on the vehicle. Also there are two kinds of EGR valves, positive and negative back pressure. This deals with the exhaust pressure present at the valve during the period when it's supposed to open. This exhaust pressure also has to do with the vacuum bleeding off. Now finding out if you have the right kind of replacement valve can be hard. Tomco emission products have good tech support. Good Luck.


Dan 84 CJ-7 02-26-2002 11:11 AM

Re: Another EGR valve question...(More info) assumptions based upon my test mentioned above are not enough to consider the valve bad. I stopped by NAPA this morning and a brand new EGR valve had the same behaviour...holding a finger tightly over the vacuum inlet of the valve seemed to make no difference in the resistance of pushing the diaphragm.

I have watched for movement of the valve on the vehicle and there is none, that's why I originally thought the valve was bad. I picked up a hand vacuum pump today, so I will try applying some vacuum to it tonight and see if it moves.

I may just go in for the test with the EGR vavle as it is...might just pass with my recent re-jetting of the carb.

Thanks for all the help and suggestions.

Dan 84 CJ-7,Weber,HEI. 95 ZJ,V8.

**DONOTDELETE** 02-26-2002 12:45 PM

Re: Another EGR valve question...(More info)
Dan, when you say you recently re-jetting of the carb, what did you do? Did you install smaller jets? If so, what size? What prompted you to change the jet(s)?
As my 88YJ failed the emission standard for the 2500 RPM test I'm looking for easy fixes. When is your emission test?

Dan 84 CJ-7 02-26-2002 01:53 PM

Re: Another EGR valve question...(More info)
When I got tested, I passed with no problems at idle, but when I did the 2500rpm test, my CO (carbon Monoxide?) output was 3 times the allowed limit while my hydrocarbon readings were well under the allowed limit.
The most likely cause for that is running extremely rich.
When I examined my main and secondary jets, I noticed that they had the size ground off of them (I bought the Weber used). That is usually an indication that they have been modified (drilled out). So I decided to go to the local VW shop that carries Webers and start fresh with jets that I could be certain of the size. For my altitude (around 3000ft) the shop recommended a 135 main, 140 secondary and 170-180 air correction jets.
I need to be retested in the next week or so, so I'll be sure to post my results. I'm beginning to think that my EGR valve isn't going to have much effect on the results, and I'm hoping the jets were the problem and will allow me to pass.
I'd be happy to share any other info I've collected in my quest for passing the emissions test, if you have any other questions.
Also, if you do a search on my UserID, you will find multiple posts throughout my history on this board where I'm asking (begging and pleading) for help to pass my test.
Good luck.

Dan 84 CJ-7,Weber,HEI. 95 ZJ,V8.

dorfs 02-26-2002 06:58 PM

Re: Another EGR valve question...(More info)
They make positive and negative backpressure tranduced egr valves. Normally, an egr valve won't pull with vacuum unless you stuff the tailpipe with a rag to build backpressure. Your are on the right path. High CO at cruise is normally too a large a main jet in a Weber. A basic rule of thumb is one main jet size equals 3 air correction jets. Lowering your float lever will also effect how fast the main metering circuit comes in.

unhumen 02-26-2002 10:23 PM

Re: Another EGR valve question...(More info)
TR I think posted a while back about drilled jets and how bad an idea it is because they are drilled at a taper when they are made,So that may have been your problem.
DO NOT loose the gasket from your EGR because from what I have read it has a metering hole in it (Special size based on your engine )Even if you get a new one you may need to match it up to the new metering inserts they give you.

I don't know if they have an Autozone or another chain store by you but they loan tools out,you pay for them and when you bring them back you get your money back.A hand vacume pump is one of the tools they loan out.
EGR valves can be cleaned ,clean all the carbon build up out of it.Put it back on,let your engine idle and open it manually and the Idle should break up.

Learn to let go of what does not serve you ,but forces you to serve it
why does everyone ask if I am gonna paint it ?

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