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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / July 2007EGR Valve Beginner Question
I was helping my brother in law with his '94 Saturn (failed smog for "EGR Function") when we came across this symptom that I don't understand. There are many things I don't understand, but cutting straight to the chase . . . When applying vacuum (sucking on the hose to the EGR valve, it holds vacuum nicely (sticks to the tongue) and moves the diaphram and piston in the EGR valve a good 1/2 inch or so. But only with the engine off. When the engine is running, no amount of sucking will build up a vacuum, and the diaphram barely moves. My first thought was that the exhaust pressure must somehow be leaking into the vacuum chamber of the EGR valve, but this idea doesn't make sense to me. There's only a mechanical linkage, so what gives? Well, intelectual curiousity aside, the real question is should we shell out the $80 for a new EGR valve? Is this a known symptom of a bad valve, or should we look elsewhere? TIA > I was helping my brother in law with his '94 Saturn (failed smog for "EGR > Function") when we came across this symptom that I don't understand. There [quoted text clipped - 15 lines] > > TIA ========= ========= Don't go spending your Red Lobster night out to dinner funds quite yet........... The computer is likely dumping the vacuum when you're testing it with the engine running......a design of the system. The computer controlls the vac apply on that model........ i think....... maybe........ should.............. mite........................ oughta............................. but.......i could be wrong...if so.....the sharks will be here soon to eat my carcass and spit out the bones. any whooooo.........i would suggest cleaning it....that will most likely pass the emission test for you if the pintel has a bit of carbon on it allowing it not to seat correctly.....which in turn should, mite, could, possibly......cause the NOx readings to be high on the test. or.......you could jest spend yer hard earned Red Lobster night out to dinner money......and git yerself another one if yer too lazy to take it off and clean it....after all.......some folks can afford to be lazy..oops..meant catered to. (my bust) The new one should have an extremely clean pintel and seat on it. ~~ oo L O ~:~ MarshMonster ~sips his homemade blackberry wine.....takes a toke....... mmmmmmm.........good stuff~ ~:~ > Don't go spending your Red Lobster night out to dinner > funds quite yet........... > > The computer is likely dumping the vacuum when you're > testing it with the engine running......a design of the system. >....... > any whooooo.........i would suggest cleaning it....that will > most likely pass the emission test for you if the pintel has > a bit of carbon on it allowing it not to seat correctly.....which > in turn should, mite, could, possibly......cause the NOx readings > to be high on the test. Thanks for the reply. I always appreciate suggestions that help me to think things out. In abbreviating my story, I may have left out too much. I did remove the EGR valve, clean it and verify its function on the bench. It works on the car too, as long as the engine's off. I'm reasonably sure that the computer's not involved, as the EGR valve was only "commanded" by mouth-vacuum in the tests I described. And I verified that the passages were clear (exhaust gas chugged out the exhaust port of the EGR mounting plate, and the engine rev'd way up when I lifted my finger allowing fresh air to leak into the vacuum port). I blew the passages out with compressed air for good measure, and got a bit of soot in the face. All for good measure. It surprised me (maybe that it was originally a non-California car) that the smog check didn't include NOx measurement. It was just "EGR Function", a tester observation rather than a measurement, that failed. While I don't really know, I assume that this means that the test technician pulled vacuum on the EGR valve and observed the change (or lack of change) in RPMs. > > Don't go spending your Red Lobster night out to dinner > > funds quite yet........... [quoted text clipped - 28 lines] > really know, I assume that this means that the test technician pulled vacuum > on the EGR valve and observed the change (or lack of change) in RPMs. ======== ======== The computer will dump vac through a solenoid.......if theres one attached to this particuler application...which...honestly i'm not sure on. Newer vehicles have programing that allows the computer to "tell" the EGR when and how much to open. I would be concerned that ANY one at a test center could possibly know ALL variations on EGR function that are out there today, and be able to test one without a NOx reading or by simply hook'n up a vac hose....... anywhooo......... I've got some sites for you..........lemme dig em out.... and i'll make another post. ~:~ marsh ~:~ ======= ======= > > Don't go spending your Red Lobster night out to dinner > > funds quite yet........... [quoted text clipped - 28 lines] > really know, I assume that this means that the test technician pulled vacuum > on the EGR valve and observed the change (or lack of change) in RPMs. =========== =========== a couple sites.............good info............. file it somewhere. http://www.asashop.org/autoinc/nov97/gas.htm http://www.asashop.org/autoinc/dec97/egr.htm Do a repost when you get this thing passed.....and let us know if it was the tester dude......or your vehicle. Out of curiousity.......what state are you try'n to pass the test in.....don't recall reading it? ~:~ marsh ~sips his crown'n'coke.......bills you $29.95 for tech support~ ~:~ > I was helping my brother in law with his '94 Saturn (failed smog for "EGR > Function") when we came across this symptom that I don't understand. There [quoted text clipped - 15 lines] > > TIA Is this a negative back pressure type egr valve? If so it's acting like it's supposed to. |
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