EGR valve won't hold vacuum

[Jeepdawg]

I ordered a standard motor products EGR valve, and it does not hold a vacuum.

Either the diaphragm has a hole in it, or that's the way they are.

Anybody ever come across this?

Its a standard motor products part no EGV533 that is supposed to interchange with Jeep part J3239372.

[Tripwire]

they wont hold a vac whilst testing in the traditional way of a mity vac or some other tester

you have to install it,( be sure your vac source is functioning correctly first)

start the engine, let it get warm and rev the motor while feeling the diaphragm from underneath - it should move

its a back pressure kind of thing I was told and I learned this after pzzing away 65.00 on a new one

second test is to let the engine idle and squeeze the diaphragm closed with both hands - the engine should start to die.... if not the intake passages are probably plugged up - that's what I was told

[Jeepdawg]

OK, it's definitely different than the one on my '75 J20. That EGR valve holds a vacuum.

This one has a slow leak. It would take a long steady vacuum to overcome the slow leak.

Any idea which washer is supposed to work with it? None of the EGR valves listed on the interchange sheet match the OEM jeep part number; J3239372.

[Jeepdawg]

OK, here is the answer I found, it's supposed to leak unless exhaust back pressure is present:

There are 2 common types of EGR valves: Ported vacuum EGR valves and backpressure EGR valves.

The most common type is the positive back pressure valve, the other one is the negative backpressure valve.

It is important to know the difference between positive and negative backpressure valves because they work differently and they are tested differently also.

Positive backpressure EGR valve:

This type of valve is used largely on domestic models. It uses exhaust pressure to regulate the EGR flow through a vacuum control valve. The stem of the EGR valve is hollow and allows backpressure to enter at the bottom of the diaphragm. When sufficient exhaust backpressure is present, the diaphragm moves up and closes off the control valve, allowing the full vacuum signal to be applied to the upper portion of the EGR diaphragm. This opens the valve and allows recirculation to occur during heavy loads.

Be careful not to incorrectly diagnose this type of EGR valve. Because backpressure must be present to close the bleed hole, it is not possible to operate the EGR valve with a vacuum pump at idle or with the engine off.

The valve is acting correctly when it refuses to move when vacuum is applied or it refuses to hold vacuum. Remember that anything that changes the pressure in the exhaust stream will disturb the calibration of the backpressure system including aftermarket exhaust systems, headers and even clogged catalytic converters.

[vacaisle]

Just get rid of the EGR and you won't have a problem.

[Jeepdawg]

My wag is subject to smog testing, needs to have it.

[vacaisle]

Oh. Gotcha.

I went through this too and it drove me nuts. I bought what was supposed to be a negative back pressure valve but it was positive. The effect is essentially the same. Positive opens when it receives back pressure and negative closes when it doesn't. So, the same end result.

Here's the link to my struggle which ended in removal all together.

http://www.ifsja.org/forums/vb/showthread.php?t=166664

[Jeepdawg]

Good thread. Setting up my timing is next.

I have Howell FI, so it's a bit more complicated to reset the idle after my timing is adjusted.

I am using the EGR valve that was the subject of that TSB; Jeep part J3239372 which is Standard Motor Products EGV533.

It does not use washers.

[letank]

EGV533 questions

Good thread. Setting up my timing is next.

I am using the EGR valve that was the subject of that TSB; Jeep part J3239372 which is Standard Motor Products EGV533.

It does not use washers.

The EGV533 package has washers, depending on the parts number it should be #58 or #64 , but of course it does not list J3239372, except on the rockauto site

The 85 the EGR is acting up... may be too much back pressure makes it open up at idle... and the idle does not hold up.... another day another challenge...



fixed... found that the boot on #5 cracked -so much for fancy taylor wire and silicone boot that are total crap -swaped some old MSD boot, perfect. There was enough misfiring that the only way to temporarily be able to drive, was to increase the idle speed, until I could do the correct fix, too much throttle opening cleared the ported vacuum port which activated the EGR circuit