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    I have an '89 Cherokee Laredo 4.0. I had it inspected the other day and it failed emissions - hydrocarbons too high. The mechanic doing the inspection disabled the EGR system by unplugging the vacuum supply to the vacuum solenoid and ran it on the dyno again and it passed - HC came down to almost nothing and CO and NOx were still well below limits. After seeing these readings I decided to leave the EGR disabled and see if it runs any differently. It runs better than it ever did with more power. Prior to this I was having to keep the idle speed at 1000 RPM just to keep the engine from stuttering and stalling on take off and I was only getting about 13 miles to a gallon of gas. With the EGR disabled I turned the idle back down to normal ( 600 RPM ) and have no problems at all, like I said it runs better than it ever did. I still have to wait and see what the gas mileage is now. What I need to know is, should I leave the EGR disabled, is it safe to do so, and if not then what is the solution?
    Last edited by rsohm2001; 11-30-2005, 12:16 AM.

  • #2
    Personally, I'd leave it alone if you passed emissions. The EGR is not easy to replace and if I remember was a bit pricey.

    Here is a link that will explain what it is and what it does; http://www.misterfixit.com/egrvalve.htm

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    • #3
      Even a properly functioning EGR valve will hinder the performance of an engine at least a little. All it really does is recirculate exhaust gas back into the combustion chambers at higher RPMs to break down nitrous oxide. It's needed in the sense that it cuts back greatly on smog formation which, if you've ever been to a major city in 80's, you'll know it's pretty nasty stuff.

      From what you describe I'd guess that yours is probably stuck open, letting too much inert exhaust in, thus ruining the oxygen/fuel mix. Try squeezing the little diaphragm on the front of the valve to see if it moves freely. If it's stuck you should be able to tell. Also, if it were stuck closed, the emissions test should have been the same or worse after disabling it. It's a strange little device.....

      In conclusion, if you can afford to replace it, do it. If not, you're Jeep won't blow up without it.

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      • #4
        That is exactly what I was thinking when I thought that if my combustion chamber temperature did get too high I would here a ping. But then I realized that this engine has a knock sensor which would signal the computer to manipulate the timing so that there wouldn't be a ping. I don't know if manipulating the timing would have any effect on the combustion chamber temperature. Am I running the risk of melting a hole in a piston like actually happened on an old '73 Chevy Nova I once had?
        Last edited by rsohm2001; 11-29-2005, 07:16 PM.

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        • #5
          Hmmmm....the combustion temperatures will probably increase, not because of the adjust in timing but because of the disabled EGR valve. The knock sensor should detect any detonation caused by the increased temperature and adjust the timing accordingly. So the engine will likely be running with less advance and shouldn't cause damage to the pistonhead. Of course, I could be wrong.

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          • #6
            See, that is what I am wondering. If the knock sensor did detect detonation and the timing advance was decreased, would that decrease in timing advance actually lower the combustion chamber temperature and prevent heat damage? And then there is the probability that even if all that were so, due to the decrease in timing advance I would probably be looking at either no change or an increase in fuel consumption.

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            • #7
              $118 for a new one through Autozone. Id bet if you get a new gasket and a can of carb clean you can get it cleaned up and working. i would NOT run around without it working properly. Your engine is designed to run with it so it should be on there. Its not like the days of old where you can install a 3 dollar blockoff plate onto the manifold of a SBC and get away with it.

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              • #8
                I'm not so sure the problem is the EGR valve itself. The EGR valve does work, I checked that out and if it was stuck open then removing the vacuum source wouldn't change that, it would still be stuck open and it isn't. The problem is it opens when it isn't supposed to, like at take off from a dead stop, even when the engine is cold. The EGR isn't supposed to come into play at all until after the engine reaches normal operating temperature. My temperature guage works fine and the electric radiator fan only comes on when needed like its supposed to. I checked the routing and connections of all the vacuum hoses and vacuum components under the hood with a vacuum diagram for that year and engine and its all hooked up correctly. Any suggestions as to where to look for the culprit? I'm stumped on this one.
                Last edited by rsohm2001; 11-29-2005, 11:04 PM.

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                • #9
                  does it have a solenoid that the vac line to the egr hooks up to? usually it will look like a small junction with a wire plug to it. im not sure if yours has that or not but many engines do, if so, that could be the problem.

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                  • #10
                    Brian is exactly right follow the vac. line from the EGR valve to the EGR vac.solenoid. Make sure it is plugged in first, second make sure it has battery voltage on one side, if all this is good it most likely is bad. There are still a few other things that can cause it but very unlikely, ECM, shorted wiring etc.

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