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Thread: Disable EGR and engine runs better ???

  1. #1
    Member RobClark's Avatar
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    Default Disable EGR and engine runs better ???

    Team,

    My 86 Townie (302 Windsor) was
    • Idling smooth
    • Missing badly (running rough) under light acceleration
    • Running smooth under heaver acceleration


    Finally found if I disabled the EGR valve - ran very smooth all the time.

    I did this:
    • Removed vacuum tube going to the EGR valve
    • Plugged the vacuum tube. This means I did not add any new 'leak' into the vacuum system


    My questions are:
    • What could cause an EGR to make the car miss? I know an EGR adds exhaust gasses back into the intake.
    • Is there anything I should do to the EGR valve in the way of servicing it? Is it worth cleaning, or is that a waste of time?
    • Will replacing with a new EGR help? (Guess it won't if the computer system is telling it to open incorrectly?)
    • Do EGR valves only have two positions - 100% shut and 100% closed .. or do they progressivley open?
    • I know the EGR is just for pollution control. In Australia we have no smog checks ... so don't care if the exhaust gasses are wrong. But what if the EGR is disabled - is that bad in any other way for the engine?


    Thanks
    Rob the Aussie
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    Engine: 302 Windsor

  2. #2
    Rev up the Lincoln and let's get to drinkin' SVT98t's Avatar
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    Im not sure, but I've been running with no EGR or O2 sensors for over 4 years without an issue.
    And I still get amazing mileage.

    -ryan s.

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    Replace the egr valve. Clean the passages in the manifold it connects to as best you can. Removing egr is, at very very best, a bandaid solution.

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    Quote Originally Posted by RobClark View Post
    [*]Do EGR valves only have two positions - 100% shut and 100% closed .. or do they progressivley open?
    As I understand it, no. It's progressive. Someone please correct me if I'm wrong, but my understanding is that it has always been progressive, in the 70s when they were introduced, up until today.

    Quote Originally Posted by RobClark View Post
    [*]I know the EGR is just for pollution control. In Australia we have no smog checks ... so don't care if the exhaust gasses are wrong. But what if the EGR is disabled - is that bad in any other way for the engine?
    As I understand the theory (and I am NOT an expert!)

    EGR lowers the temperature in the combustion chamber, in an effort to reduce NOx production.

    The downside is that there's another part that can go bad.

    The upside is that, due to the introduction of extra volume of (inert) gases under part throttle conditions, there is less pumping losses - you can cruise at a certain speed/rpm/what-have-you with slightly less throttle opening - the engine's fighting slightly less against the almost-closed throttle plates. This supposedly improves light-throttle fuel economy.

    Additionally, the cooler temperatures allow for more aggressive timing without pinging.

    There is no loss of power, as at wide-open throttle, the EGR is closed.

    In a way, except for the fact that there's another part to go bad, EGR is almost a something-for-nothing emissions control device.
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    Theoretically, at least. Often times the fact that there should be less pumping losses and stuff like that doesn't pan out that well on a land yacht or truck. When I disabled EGR on my truck, my mpg never changed, but my intake stayed A LOT cleaner. That said, I've chosen to run one on the Crown Vic and so far, only 1 mpg better than when it was carbed.

    Depending on how the EEC reacts to the EGR not opening, you can end up running lean and knocking to death by not allowing it to open. Though most manufacturers have a method of determining when the EGR is/isn't open, they don't all respond appropriately at times and still pull fuel/add timing even with an EGR fault. That's likely what the OP was experiencing, the fuel and ignition changed in anticipation of where the EGR valve should have been but wasn't.
    Last edited by Crownvicman289; 04-12-2012 at 10:09 AM.
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  6. #6
    fuck no, not today, thank you kindly 1990LTD's Avatar
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    they're not just fully open or fully closed. pull the EGR valve off to clean it and when you do that put a hose on the vacuum port on the valve and suck on the other end, you'll see the pintle move in and out according to how much suction you put on it.

    the amount that the valve is open is dependent on the amount of vacuum that it is being given by the egr vacuum regulator (the hose that you removed connected them) which is given manifold vacuum and based on that regulates the amount sent to the valve itself to retract/extend the pintle.
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  7. #7
    I'm an air-conditioned gypsy gadget73's Avatar
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    Its possibly not the valve, but the solenoid that controls the valve. On US cars, its on the right side fender in a group with 2 other things, but knowing how things are moved around on your car, I'm not sure. Follow the hose and you'll find it. There is a cap on that solenoid you can pry off, and you should find a little foam filter in there. What you're probably going to find is a puff of dust. Clean that out, and shoot some penetrating lube down the tube that sticks into the ball of dust to clear it out. See if that doesn't make the EGR valve work normally again. When the solenoid gets sticky, instead of giving some amount of EGR action, you get 100% or 0%. 100% is too much at lower speeds, so you get the chugging and all that crap. If you want to see if the passages in the intake are blocked up, simply pull vacuum on the EGR valve. If the engine runs horribly, the passages are fine. If nothing changes, the passages are blocked solid.
    Last edited by gadget73; 04-12-2012 at 10:04 PM.

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    gadget73, what "passages in the intake" are you referring to? I pulled the vacuum to my EGR on my '91 Grand Marquis and there was no change in how my engine ran other than it did not produce the shudder/miss that it does when that vacuum hose is connected? I thought by disconnecting that vacuum hose the idle speed would drop? Mine did not drop and I attributed that to the throttle plate screw that has been adjusted to compensate for a bad IAC valve.

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    the passages in the intake are literally the holes in the intake where the EGR valve mounts.

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    I'll have to check those passages too I guess. The carbon build up was really bad inside the intake behind the throttle body. I can imagine these smaller passages behind the EGR bad too. I didn't pull the EGR off. I'll have to do that next time.

  11. #11
    I'm an air-conditioned gypsy gadget73's Avatar
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    Quote Originally Posted by MattDoscher View Post
    gadget73, what "passages in the intake" are you referring to? I pulled the vacuum to my EGR on my '91 Grand Marquis and there was no change in how my engine ran other than it did not produce the shudder/miss that it does when that vacuum hose is connected? I thought by disconnecting that vacuum hose the idle speed would drop? Mine did not drop and I attributed that to the throttle plate screw that has been adjusted to compensate for a bad IAC valve.
    when I said pull vacuum on it, I meant apply vacuum to the valve using a vacuum pump to force it to open. Its shut at idle, or at least it ought to be. If opening the valve causes the motor to run like crap, then the passages are OK. There is actually a lot more than just where it mounts. There is a passage from each head to the center of the lower intake manifold, and it passes from there through the upper manifold out around the air intake area where it finally comes out to the valve itself. On carb motors, the ports in the head were used as a heat channel to prevent carb icing. They tie to the exhaust side and actually carry exhaust gas. Over time, those can carbon shut to the point where no gas can get through, so the EGR does jack squat even if it does open. If they are packed solid, you'd need to remove the upper and lower intakes, clean the crap out of the ports in the heads themselves and then clean out the rest of the passages until it all flows clear again. Or just leave it alone because it doesn't matter *that* much.

    86 Lincoln Town Car (Galactica).
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    ok, I see now. Thanks Gadget73 for the clarification.

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    Member 84merc951's Avatar
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    i remeber with my egr disconnected it ran better at idle but got worse mpgs and it pinged way more.
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  14. #14
    Member RobClark's Avatar
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    Default I give up!

    So far done all this:
    • Opened and cleaned the EGR valve. It was not that dirty. Pintle moved freely. Checked by putting on a vacuum hose and sucking. Not sticky - went from fully closed to fully open.
    • Checked the EGR position sensor. Connected ohm-meter to the appropriate pins. As I sucked on the vacuum hose, reading progressively changed through full range. No 'dead' spots. (Anyway - changed that out about 3 yrs ago so it is not that old)
    • Checked the solenoid valve that controls the vacuum. Opened and cleaned. Was not dirty. Connected oscilloscope across the input signal. Saw the computer giving it everything from 100% (max vacuum) to 0% (min vacuum) duty cycle signal as I moved the EGR by sucking on the hose (which slowly opened the EGR). With everything connected and running engine above idle .. duty cycle was a fairly steady 30%.



    So as far as I can see
    • Computer is reading the position sensor OK
    • Computer is opening and closing valve OK
    • Too much exhaust gas is getting into the intake as the car still misses on light cruise



    All I can think of is:
    The pressure in my exhaust system is too high, and when the EGR valve is open to where the computer wants ... the higher Exhaust pressure is forcing in too much exhaust gas ???

    The exhaust system was changed out about 2 years ago, and as the 4 cats were gone - the shop replaced with 2 cats. I wonder if they changed the exhaust piping in such a way that my exhaust pressures are too high?

    Anyway, with EGR disabled, car runs very smooth, and does not ping.

    Decided to live with what I have.
    Rob the Aussie
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    Car: '86 Lincoln Town Car
    Engine: 302 Windsor

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    I'm an air-conditioned gypsy gadget73's Avatar
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    Just out of curiosity, does a vacuum gauge plumbed into the line with the EGR match up to the duty cycle you're seeing on the scope? In my case it did not. The ECM was feeding the regulator the proper signal, but I had either no vacuum or 100% vacuum to the valve. A snort of WD40 down the regulator got it working again but I did replace the regulator solenoid just because I didn't feel like dealing with it again.

    86 Lincoln Town Car (Galactica).
    Drivetrain: 5.0 HO, Explorer cam, FMS 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley, SuperCoupe stall converter

    Suspension: Bridgestone Protenza G019 225/60/16 on LSC turbines, 1 3/16" wagon front bar, 1" PI rear bar, cargo coils, KYB GR-2 front shocks, F150 rear air shocks, big front brakes, ES poly front suspension bushings, 00 CVPI steering box, ES poly body mounts, rear disc brakes

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    Member RobClark's Avatar
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    Gadget73:

    I don't have a vacuum gauge but I can tell the duty cycle of the solenoid valve does cuase more and less vacuum.

    Poor man's test #1
    -------------------
    Engine running at revs (EGR part open).
    Pulled vacuum tube off the EGR valve and quickly stuck my finger on the end of the vacuum tube. Could feel the (fast) pulses of the solenoid valve getting stronger and stronger while watching the pulse widths grow longer and longer as the computer tried to get the EGR valve to re-open.

    Poor man's test #2
    -------------------
    Engine running at revs (EGR part open).
    Pulled vacuum tube off EGR valve.
    See pulses get wider - eventually going to 100%
    Put tube back on EGR.
    See pulses quickly wind back to 0% (as valve opens , then overshoots a bit I guess as vacuum was at 'max')
    See pulses widen out again to around 30% duty cycle.
    So - this says the vacuum was indeed changing on command from the computer - and the computer could get the EGR valve into the position it wanted.
    Rob the Aussie
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  17. #17
    I'm an air-conditioned gypsy gadget73's Avatar
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    Sounds valid enough. If you can verify that the vacuum that gets to the valve is in fact variable, then I'd say the regulator passes. I didn't have the scope on mine, just a voltmeter set to AC but it did show some change in average voltage as the pulse width increased so I had some ability to monitor what was going on. My scope runs on 120v and its a clunky CRT model, so its not especially practical to take with me in the car on a test run. A voltmeter with long leads and a vacuum gauge is about as much as I can deal with while driving. I'd like to get a nice small digital LCD scope, but thats years out when they get nearly free

    86 Lincoln Town Car (Galactica).
    Drivetrain: 5.0 HO, Explorer cam, FMS 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley, SuperCoupe stall converter

    Suspension: Bridgestone Protenza G019 225/60/16 on LSC turbines, 1 3/16" wagon front bar, 1" PI rear bar, cargo coils, KYB GR-2 front shocks, F150 rear air shocks, big front brakes, ES poly front suspension bushings, 00 CVPI steering box, ES poly body mounts, rear disc brakes

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks.

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