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Old 10-23-2009, 01:48 PM   #1
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EGR Valve Operation

I have been dealing with a non working EGR valve for a while now and just realized something. When I remove the vacuum line from the EGR valve solenoid, the truck runs a lot better but it will miss a bit at idle and has definate detonation when pulling hills like everyone elses does with no EGR.

What I dont get, is that with the vacuum hose disconnected so the EGR valve is closed, it runs OK and seals perfectly shut. But if I put the vacuum line on the EGR solenoid, if i even CRACK the throttle a hair, the solenoid MUST be giving the egr a bit of vacuum and opening it because my engine will start to lean out horribly and not rev up past 1000rpm and sputter, choke, cough, and die out.

I thoguht the EGR was ONLY suposed to open at 45+ sustained cruise? Why on earth is my valve opening on part throttle idle? I have cleaned the hell out of the valve, new gasket, and bought a new EGR solenoid and hoses. It seems like the EGR vavle solenoid is pulsing my EGR at the wrong time or the vacuum port for the EGR solenoid is not working? I am puzzled how it can be opening on idle... When it should be shut tight until needed???
Old 10-23-2009, 03:35 PM   #2
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Lightbulb Re: EGR Valve Operation

Quote: Originally Posted by Shaddix
I have been dealing with a non working EGR valve for a while now and just realized something. When I remove the vacuum line from the EGR valve solenoid, the truck runs a lot better but it will miss a bit at idle and has definate detonation when pulling hills like everyone elses does with no EGR.

What I dont get, is that with the vacuum hose disconnected so the EGR valve is closed, it runs OK and seals perfectly shut. But if I put the vacuum line on the EGR solenoid, if i even CRACK the throttle a hair, the solenoid MUST be giving the egr a bit of vacuum and opening it because my engine will start to lean out horribly and not rev up past 1000rpm and sputter, choke, cough, and die out.

I thoguht the EGR was ONLY suposed to open at 45+ sustained cruise? Why on earth is my valve opening on part throttle idle? I have cleaned the hell out of the valve, new gasket, and bought a new EGR solenoid and hoses. It seems like the EGR vavle solenoid is pulsing my EGR at the wrong time or the vacuum port for the EGR solenoid is not working? I am puzzled how it can be opening on idle... When it should be shut tight until needed???
========================

shad---

The 40-45 sustained MPH thing is when the PCM "tests" the EGR system.

If the hold close spring gets tired or weak, and the exhaust has a bit of backpressure from the cat or the muffler, then that backpressure can nudge the EGR valve open.

Then, like on my own '89, it has a goofy idle (speed), up and down, up and down, as the O2 sensor "sees" the EGR valve being pushed open and compensates by rich-ing up the air/fuel mix.

When you bump up the idle speed, you increase exhaust gas flow (and backpresssure) and then the EGR valve opens even MORE..

Although it doesn't say in the GM Shop Manual, when the EGR valve works, I imagine it opens up anytime the O2 sensor detects an air fuel mixture richer than 14.7 to 1..such as during coast down and at other times...as it's smog reduction function is to lean it out.

It is a very bad smog reduction system, in so far as it has many run-ability issues built into it.

Your EGR solenoid valve must be leaking by some, at idle, putting a positive vacuum on the EGR valve.

Last edited by Steady Eddie; 10-23-2009 at 03:40 PM.
Old 10-23-2009, 03:48 PM   #3
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Re: EGR Valve Operation

And, the more you "fix" the "System", with new sensors, a tune-up, and etc..the more sensitive it becomes to things like backpressure and weak EGR valve springs. (a new O2 sensor may be more responsive than the old, although working, one you took out..)..

It took me a long time to realize this, and only after reading threads on here, where the "fixing" made the issues worse...I wondered why, and that must be it...
Old 10-24-2009, 01:32 AM   #4
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Re: EGR Valve Operation

Well I did check the vacuum diagram on the radiator shroud and it shows how to hook them up, and they are hooked up properly as the diagram says. I thought that the solenoid was the problem, maybe it was telling it to open at the wrong time. A new EGR solenoid didn't help at all.

I dont know how to check my cat to see if its colgged and having high backpressure, but the tailpipe after the muffler is gone and it has a definate exhaust leak somewhere near the collector? My guess is that your right and I just may have a bad EGR valve spring or something. I hope a NAPA replacement valve will work, because thats the only parts store on the Oregon coast!
Old 10-24-2009, 10:56 AM   #5
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Re: EGR Valve Operation

Exhaust gas dilutes the intake, since the fuel part of the intake is controlled by the computer it would actually tend to richen, less O2 in exhaust then fresh air. EGR should stay closed at idle. When rpm drops too low the computer opens Idle Air Control (IAC) to increase fresh air intake at idle, tend to lean it. Of course the amount of fuel being injected should be adjusted accordingly by the computer (when in closed loop). IAC is likely the slowest part to respond and miss fire, vac leak and floating EGR valve can make it hunt for idle.

When mine died out (still idled OK) it had a big loss of power at full throttle on the highway, and free revving it was weak. The exhaust was plugged a good bit. You can check that by replacing, temporarily bypassing, or disconnecting the exhaust. Often you get a rattle from inside exhaust (not heat shield, hanger, etc) when you bump it. Usually it's the cat but sometimes the cat's innards can get blown into the pipe or muffler.
Old 10-24-2009, 12:07 PM   #6
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Re: EGR Valve Operation

EGR solenoid is providing manifold vacuum at all times when its plugged in through the solenoid ports. No vacuum when solenoid unplugged. How is this possible when the EGR valve isnt being used at idle?!? It should have NO vacuum to EGR until the ECU calls for it, not vacuum all the time at the solenoid port! If my valve stayed shut until I was actually driving the thing, I bet mine would run perfect, but it gets opened at all times through the solenoid! [Solenoid is brand new]

When it goes back to idle and no manifold vacuum is present, the valve shuts all the way and stops the EGR leaking into intake, making it idle ok.

If the solenoid is open at all times, why would we need it. Why not just run a line from the vacuum port straight to the valve if it was suposed to work like this? Because something is not working right!!! This makes me think the EGR valve might be OK and I wonder if the ECU is malfunctioning now???
Old 10-24-2009, 10:52 PM   #7
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Re: EGR Valve Operation

That is how the Early 2.5l TBI works, it has a port on the TBI that supplies vacume when the throttle is open. The Later 2.5l TBI has the solenoid that is controlled by the ECM. Has anyone reset the ECM? Has anyone Reseated the PROM in the ECM? Used a NOID light on the connector for the solenoid (may be 5vdc operation, may be 12v IDK)?
Old 10-24-2009, 11:43 PM   #8
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Lightbulb Re: EGR Valve Operation

shad--

"Maybe" the solenoid valve is SUPPOSED to leak by..the function of that would be to keep its' little guts clean and why there is a foam filter on the one port..?? It can't leak by very much, though, because vacuum leaks tip over the Iron Duke, and make it idle too high. I really believe your EGR valve has a marginal spring in it, good enough to hold it closed, when the vacuum line is disconnected, but too weak to hold it closed, when the lines are hooked back up.

The whole, entire EGR valve system is a major PITA, and that is why, if you do not need it, to be able to pass a smog check, then it is best deleted entirely..In its' place you put a plate over the opening, and install a new Prom Chip, like the one from Sinister Chips, for $55...it has all of the EGR valve functions programmed out..
Old 10-24-2009, 11:53 PM   #9
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Lightbulb Re: EGR Valve Operation

shad--

IIRC, NAPA does have the AC-Delco/Delphi EGR valve..they list it as an OE replacement part.

But, as was posted before, it costs about 1/4 of what most old S10 trucks are worth.

For those of us that are cash strapped, like me, it is very hard to justify....
Old 10-25-2009, 12:57 PM   #10
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Re: EGR Valve Operation

Quote: Originally Posted by Steady Eddie
shad--

IIRC, NAPA does have the AC-Delco/Delphi EGR valve..they list it as an OE replacement part.

But, as was posted before, it costs about 1/4 of what most old S10 trucks are worth.

For those of us that are cash strapped, like me, it is very hard to justify....
Yeah, I bought my truck for $450 complete! Now I am wondering only 1 thing. Do I spend $75 for a new EGR valve or $50 for the Sisnister performance chip??? I personally NEVER want to deal with another EGR system again nor take that chance that I buy a new valve and it will get gummed up in a month. But its very unclear wether or not the chip does exactally what its suposed to....

I never thought about it suposed to leak slightly which makes sense because it always has a slight misfire from being lean always. I just want to get it taken care of so I DONT burn those exhaust valves. They sure dont sound happy without PREMIUM, and even then, their is definate tons of detonation!

Thanks a ton Eddie and lesterl! Ive read hundreds of posts from yah both about this Iron Duke, and both of yah are always sopt on! =) NAPA does definatly carry that Delphi valve as well just like you said!

Last edited by Shaddix; 10-25-2009 at 01:04 PM.
Old 10-25-2009, 06:35 PM   #11
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Lightbulb Re: EGR Valve Operation

shad--

Thanks for the kind words...

For me it is a no-brainer..the "performance" chip ain't a hot rod part..as Ryan (at Sinister), re-programs your stock Prom chip, and, simply removes all of the EGR valve stuff in it, then sends it back to you.

In the meantime you can check your timing to make sure it is right on 8*--the stock setting.

Even with a screwy EGR valve, I do not think it should ping or have any spark knock. Not unless there is so much carbon built up in the combustion chambers that it is causing hot spots to form. Even the sharp edges on the spark plug electrodes are knock and ping makers, and should be filed down, rounded a bit, with a set of jeweler's flat files. Real Men don't just take 'em out of the box, and stick 'em in there...

Our "beta" Sinister Chip Tester (Member Jason) is presently testing the results as we speak, and is rolling up the miles on his Sinister Chip..as posted, he reports over 1K miles of combined highway and city driving, and his Iron Duke has a warm idle that is smooth as silk...

Which is good enough for me...
Old 10-25-2009, 08:13 PM   #12
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Re: EGR Valve Operation

I think I know what way I am going too!

I do daily pizza delivery with my truck. I bet I am prone to carbon buildup, especially in our hilly town, but I do regular seafoaming every 6 months or so. I also have out of box plugs that I set the gap to .060 which is what the sticker says. I have never heard of this large of gap before but thats what I gapped them to.

PREMIUM fuel is my only option. I should check timing like yah mention but it must be somewhat close, as it drives well. I just read about that EGR valve dumping in inert gasses that take up combustion chamber space so the mixture isnt so lean and figured that would fix all of my drivability problems. I still manage about 20-25MPG all day city driving, so I cannot complain one bit!
Old 10-25-2009, 09:59 PM   #13
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Re: EGR Valve Operation

Might close that gap some, .045 would be good, just ask Eddie, that is what he runs. He found out that some of the racers found that the large gap causes high rpm issues on gas engines and the closer gap runs better, might produce a stronger spark to more fully burn the fuel too!
Old 10-26-2009, 01:29 AM   #14
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Re: EGR Valve Operation

shad---

The amount of inert, non-combustible gases injected into the average engine is fully 7% of the swept volume contained in each cylinder--NOT, as you said, in the combustion chamber, which is tiny by comparison.

The EGR valve does this as a function of smog reduction. by cooling down the burn.

It amounts to a whopping 7% reduction of air/fuel mixture, spread over all 4 of the Duke's cylinders.

As I have posted before, I will never get over the fact that our engines are being force fed their own dung. How in the world are they ever going to run right??

About the narrowing up of the plug gaps:

The OE HEI ignition will introduce a high speed misfire at or very near the peak torque RPMs.
The Pontiac Engineers did a very good job of designing an ignition system that would go for 100+K miles, but they did drop the ball with the 32K volt coil. The wide gap was designed to, once again, reduce smog production.

This problem is often blamed upon poor head flow, or valve float, but it is not.

The workaround is to simply narrow the gap, and I have found that 45 thou. works very well..

Last edited by Steady Eddie; 10-26-2009 at 01:34 AM.
Old 10-26-2009, 06:42 AM   #15
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Re: EGR Valve Operation

Diluting the intake reduces peak temp reducing NOx, but also slows the burn similar to using high octane fuel. Ignition is advanced is more to make up for slower burn which is why simply removing or disabling egr can increase pinging at part throttle. The advance curve should be recalibrated. Should normally be no egr at idle or full throttle and not really affect there, as far as I know. Just setting initial timing back kills idle and full throttle.

The book I have says that we have ported vacuum and non ecm controlled negative back pressure egr. Though it appears that egr solenoid is connected to ecm in wiring diagram. I guess the solenoid is switched when the engine warms up to temp, as it says to check that egr functions after warmed up to temp (idle to 2000 rpm in neutral).

Another test (not same book) for this type egr mentions that with hand vacuum pump and gauge connected directly to egr that the egr should hold a vacuum when engine is not running, but not when is running. The pulsing of exhaust opens a vacuum bleed inside the egr when exhaust valve closes (negative back pressure). Perhaps the internal bleed is plugged or partially plugged.

Did you check the exhaust?

Last edited by max1million; 10-26-2009 at 06:45 AM.
Old 10-26-2009, 11:40 AM   #16
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Re: EGR Valve Operation

Max--

Thank you for your thoughtful post.

It explains something I have wondered about for a very long time..the only reason that the EGR valve solenoid is wired to the ECU/PCM brainbox is for the "test" that occurs after "x" amount of time @ a sustained speed of 40-45 MPH...the rest of the time that the engine is running, it functions as a 100% mechanical devise, only being fully closed at idle and being non-functional at WOT. It sits in there, operated by negative backpressure, and chatters away, adding that 7% of non-combustibles ALL the time, with no input from the brainbox, other than at testing time, and to supply vacuum to it, after warm-up.

You mentioned "ported vacuum", and I want to add a bit of explanation to that. If you understand that the vacuum supply for the EGR solenoid comes from the TBI and goes to a little vacuum manifold at the base of the TBI, then if you shine a bright light down into the throat of said TBI, with the butterfly OPEN, you will see little "holes" in the TBI housing's wall, that become exposed as the butterfly tips open. These holes are the vacuum supply source. And explains why there should be no vacuum at idle, butterfly and EGR valve fully closed. These holes are called "ported" vacuum sources.

Last edited by Steady Eddie; 10-26-2009 at 11:45 AM.
Old 10-26-2009, 01:33 PM   #17
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Re: EGR Valve Operation

This is very informative. I bet you guys are 100% right and the valve does work mechanically as well as by the solenoid. When the paycheck gets in, I will definatly report back with a new EGR or chip.

I just was assuming that the solenoid does all the work opening and closing, but thats not the case apparently. Also, didnt want to spend $75 on a part of the truck that WONT fix it when I see some people replace every sensor on their duke, only to find it runs the same as when they bought it and still doesnt idle correct or run right! I wouldnt be happy
Old 10-26-2009, 01:37 PM   #18
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Re: EGR Valve Operation

Quote: Originally Posted by max1million
Diluting the intake reduces peak temp reducing NOx, but also slows the burn similar to using high octane fuel. Ignition is advanced is more to make up for slower burn which is why simply removing or disabling egr can increase pinging at part throttle. The advance curve should be recalibrated. Should normally be no egr at idle or full throttle and not really affect there, as far as I know. Just setting initial timing back kills idle and full throttle.

The book I have says that we have ported vacuum and non ecm controlled negative back pressure egr. Though it appears that egr solenoid is connected to ecm in wiring diagram. I guess the solenoid is switched when the engine warms up to temp, as it says to check that egr functions after warmed up to temp (idle to 2000 rpm in neutral).

Another test (not same book) for this type egr mentions that with hand vacuum pump and gauge connected directly to egr that the egr should hold a vacuum when engine is not running, but not when is running. The pulsing of exhaust opens a vacuum bleed inside the egr when exhaust valve closes (negative back pressure). Perhaps the internal bleed is plugged or partially plugged.

Did you check the exhaust?
No, I have not checked my exhaust system. I have the stock manifold, into stock downpipe. From the stock downpipe, I have a catalytic convertor that I dont know if its good or not, which goes into a short 12" pipe into a muffler then a turndown. Very simple, very unrestrictive exhaust, unless the catalytic convertor is plugged. I heard that you whack the bottom of the cat and if it rattles its broken, but mine doesnt rattle. I am rally not sure how to tell if its plugged other then to remove it, but I have no exhaust clamps to put it back together.
Old 10-27-2009, 05:11 AM   #19
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Re: EGR Valve Operation

I believe the only test on these (82-93 2.5L) may be if the solenoid is shorted (or open?), but not positive. This may be why some with S10 can simply disconnect and plug vacuum line without ses light. The 2.8L V6 has lot more in diagnostic chart and is supposed to be ecm controlled and monitored with egr temp switch to check it's working. This may cause confusion if you simply say S10 or such. From what Iv'e read and trying to decipher it (Haynes book mostly).

Ported vacuum, yes on the throttle body (or carburetor ), into near the throttle plate at closed position. Closed little vacuum if any, part throttle vacuum increases (book says to above 6 inches), then getting near full throttle vacuum drops again.

I understand reluctance to just throw money at it. Some say clean or replace egr valve and it's fixed, other say no difference. Some say only use the AC delco. There's no guarantee. If someone has worked on it they may have connected vacuum lines inadvertently to wrong ports, just a thought. Different ports can be close together and they're not all the same.

Catalytic convertor not rattling does not necessarily mean not bad or plugged but is good indication it may be. There is generally 2 types the honeycomb core (usually more rounded and tappered ) which can break into chunks, and pellet packed (usually flat top/bottom and plug in bottom used for filling) which likely wouldn't rattle inside. Either may be installed depending on year or replacement. I did not actually check the effect cat had on egr when it suddenly went (honeycomb core), though from what I've read I believe it can.

A short coupler and 2 clamps could be used to put cut pipe back together fairly quickly, and cheaper then having header/manifold bolts replaced if broken.

Original post here does appear to point to egr, be it wrong ported vacuum source, egr valve, cat or combination of them. That does not completely negate other possible problems. Should also check for stored trouble codes if any.
Old 10-27-2009, 08:35 AM   #20
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Lightbulb Re: EGR Valve Operation

Max--

Another great post from you!!

I never once thought that there may be 2.8L V-6 Guys lurking here, and mentally transposing the info on the 4-cylinder over to their V-6s, which are, as you say, completely different animals, with regard to how the EGR valve works.

The info about how some can "get away" with eliminating the EGR valve on the Iron Duke 2.5 is due to a shorted or open EGR solenoid valve is, however, incomplete...on the '88 up Code E and Code A engines (and especially my own '89) the ECU/PCM brainbox DOES look for a change in O2 content at the O2 sensor and WILL set a code, if the EGR solenoid is shorted or open..this happens during the pre-programmed in EGR test-at-sustained-speed. The only way these year models will NOT turn on the SES light (under these conditions) is if the SES light bulb (lamp) is burnt out to begin with.

The level of produced vacuum at WOT does fall way off, and explains why the EGR valve is supposed to be closed at full throttle. I did not know about the 6 inches of vacuum threshold.
This also explains why the EGR solenoid valve remains switched "on" at WOT, as there is simply not enough vacuum then to operate the EGR valve, pure physics in action.

The 6 inches of vacuum threshold of vacuum-for-operation also explains why a brand new EGR valve solenoid could "leak by" vacuum at idle and still be OK--*IF*--the hold close spring tension in the EGR valve is sufficient to actually hold the valve shut. An EGR valve that is as clean as a whistle, but lacking in spring tension, will leak by (or open), during this time, even at a supplied (leaking by) level BELOW the threshold of 6 inches of vacuum.

This whole issue is now becoming perfectly clear.

Last edited by Steady Eddie; 10-27-2009 at 08:41 AM.
Old 10-27-2009, 12:14 PM   #21
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Re: EGR Valve Operation

Thanks for the information guys. I too can clearly see what is going on with this EGR system. This information needs to stick around. So many people have EGR issues with these motors its incredible.

I will definatly check the exhaust system first. I wonder if running for 10,000 miles with no EGR valve has destroyed my cat?? I cant imagine the insides of the cat like all that fumes and detonation.
Old 10-28-2009, 09:39 PM   #22
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Re: EGR Valve Operation

If I remember correctly(IIRC), on my 92Duke disconnecting vacuum line from EGR valve and plugging it (didn't try all combinations) didn't code IIRC, may have missed it. I only did for short time to see what if any effect (more ping part throttle load).

****
Haynes - code 32 EGR - Vacuum switch shorted to ground on start-up, switch not closed after ECM has commanded the EGR for a period of time or the EGR solenoid circut is open for specified period of time . Raplace EGR valve. - The EGR system consists of a negative backpressure EGR valve, a ported manifold vacuum source, tube and, on the v6, a solenoid which controls this vacuum source. - Four Cylinder engine EGR valve check (non ECM controlled EGR) See accompning diagnostic chart - Haynes

Me - How ECM does know if EGR is bad if it's not ECM controlled? what vacuum switch? mine has EGR solenoid but if it's not ECM controlled how can ECM command it, or check that it is open? Do i ignore solenoid cause it's a v6 feature? The chart says to warm engine to temp before checking EGR system, why? you said the ECM control and solenoid was for v6 so theres only a EGR valve ported vacuum and tube, right? why would temp affect the EGR? what vacumm switch? why does it have a solenoid for v6? is the vacuum switch the v6 solenoid that switches the ported manifold vacuum source to the EGR on or off, it it was used on the 4? but not by the ECM, right? the chart makes of mention of this stuff either.
****
I need better reference source.

A far as I can tell ECM only check our (82-93 Duke) solenoid electric and allows non ECM controlled EGR vacuum at operating temp. V6 monitors EGR temp switch in EGR valve (I read that as exhaust temp) for actual EGR function and to control it via the solenoid(V6), once some other conditions are met. v6 EGR temp fluctuates in proper range EGR responding and less NOx, does't fluctuate or out of range not responding. Both ECM take care of O2 changes (which occur anyway, they're supposed to, within range) by calling for more/less fuel unless, so much EGR as to cause missfire that O2 (and fuel) in exhaust way out of range and throw code. O2 change likely just coincidence, not measure of NOx. Guess that it may cause a slight stumble/surge if the EGR valve suddenly unstuck, I haven't noticed any.

Guessing 6+ and sufficient exhaust flow to increase pressure pulse. Positive back-pressure pulse in exhaust when exhaust valve to helps to open EGR. Negative back-pressure (vacuum) pulse in exhaust when exhaust valve closes let EGR close, by dumping the ported vacuum from tbi. Tie rock to elastic, hold other end of elastic, throwing rock is positive, rock keeps going pulling elastic is negative, more or less.

When my cat went because it was sudden, the way it acted (idle ok, no power), and change in exhaust note (deep groan near engine with some high pressure hiss, wot), I checked exhaust and cat first. Don't remember what the code was before clearing it. SES light was brief while driving.

It can hard to find complete accurate easy to understand info and I take what I find with some skepticism. As I say this is my interpretation (right or wrong) and experience with the Duke.
Old 10-28-2009, 09:53 PM   #23
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Re: EGR Valve Operation

EGR Solenoid is commanded by PIN A3 of the ECM as per my schematic....... so.... I would ASSume that it is indeed controlled by the ECM (on the newer TBI 2.5l engines as the early 85/86 didnt have the solenoid)
Old 10-28-2009, 10:40 PM   #24
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Lightbulb Re: EGR Valve Operation

OK...

Here's how I see it.

The EGR Solenoid is "on" all the time that the Duke is warmed up and running...kinda...

BEFORE the motor gets to operating temperature (131* F. and into closed loop) the EGR solenoid is "off"..and at 131* F. it is commanded to come "on" and it stays on, for a time.

This supplies full available vacuum TO the EGR valve..

But the O2 sensor can "see" the rich or lean and when the exhaust reaches a certain "smog level", then the PCM brings the EGR solenoid back "on".

The results happen nearly instantaneously, smog is reduced far faster than the O2 sensor can react...(the O2 sensor being rather slow) and it (the O2 sensor) "catches' the perfect 14.7 to 1 air/fuel ratio on the way (up or down) and controls the fuel mix accordingly. This never sets a code or the SES light to on, UNLESS the mix ratio never comes back into spec. It all happens that fast.

It is a delicate balance...the EGR valve sits there, just on the balance point of opening, hold close spring fighting a constant battle with exhaust pressure, ready to be commanded to open with a vacuum pulse from the solenoid. And it happens right now. Boom, it is open and Boom, it is shut.

But, at a sustained speed of some 40 to 45 MPH everything related to excessive smog production
is at a zero point. The engine is at a steady throttle state, with the EGR valve commanded "off".

Input from the VSS is monitored by the PCM, and it looks for this steady state at speed...this is the time that the PCM "tests" the EGR system to "see" if the EGR is there and working.

The PCM commands the EGR solenoid valve to "on" and watches the mix ratio signal from the O2 sensor. It is looking for an immediate change, more exhaust, less oxygen. After a time period (remember that the O2 sensor is slow), the O2 sensor sees the change and the EGR solenoid is commanded "off".

The reason that the EGR valve is tested at a high(er) road speed is that the stumble induced by the opening EGR valve is not so driver noticeable at speed...
Old 10-28-2009, 10:49 PM   #25
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Re: EGR Valve Operation

88 and older dont have a VSS in the transmission like 89 later...
Old 10-28-2009, 11:00 PM   #26
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Lightbulb Re: EGR Valve Operation

One way to test the EGR solenoid valve, and resulting EGR valve operation, would be to electrical tape a "noid light" to the outside of the windshield, carefully routing the wires down into the engine bay, and landing them on the EGR solenoid valve's connector, so that when the solenoid was on, the light is on.

Then drive it around like that for a while....watching that little light like a hawk...
Old 10-28-2009, 11:08 PM   #27
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Re: EGR Valve Operation

A light wont always give you a pulse pattern that is being presented to a coil, but yeah, that would be a good way to "SEE" what is going on. If it comes on when it gets stupid, there ya go!
Old 10-28-2009, 11:10 PM   #28
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Question Re: EGR Valve Operation

Quote: Originally Posted by lesterl
88 and older dont have a VSS in the transmission like 89 later...
=======================
les-

You are correct...the VSS was a "refinement"---- something (a signal reading) that the PCM could monitor to "see" actual road speed.

I imagine (don't really know) that the PCMs in those Code E motored (with a TBI 700), earlier, rigs recognized steady state conditions from the O2 sensor and the ignition module only.

Last edited by Steady Eddie; 10-28-2009 at 11:12 PM.
Old 10-29-2009, 02:33 AM   #29
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Re: EGR Valve Operation

If EGR is supposed to control NOx at part throttle a.k.a. cruising speed or slow to medium acceleration, it makes no sense to stop it then.

Excess combustion temperature increases NOx and EGR reduces it by lowering combustion temperature. Most everything I read about EGR and NOx together says so. Say I accept that.

EGR lowers temps to lower NOx and, slight increase O2 freed from NOx is diluted by EGR. So the lean condition, if it exists, that would increase combustion temps, NOx, and knock/ping, actually occurs when temps and NOx are lower. That's 1 why it makes no sense to monitor for O2 to increase EGR. Less O2 (rich) lowers temp but with more unburnt fuel. That's 2 why. Add fuel to proper mix with O2 and it don't be lean/rich anyway. That's 3 why. While EGR dilutes the intake and causes less power having less knock/ping and proper mix works to increase power. That's a side note.

As for ECM monitoring/testing function of Duke's EGR valve, I haven't yet found an explanation I can accept.

Perhaps we can just agree to disagree, since it's been fairly well beaten.
Old 10-29-2009, 03:25 AM   #30
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Re: EGR Valve Operation

For O2 sensor I accept an explanation that basically says (from memory)

There is no steady state during normal operation of O2 sensor, as the O2 in the exhaust changes with varying operating conditions. Air fuel mix is constantly adjusted by ECM based in part on O2 sensor value to keep it at optimum without ever succeeding, at best it teeters at optimum. When cold at startup O2 sensor value is fixed out of range and sensor is is non-functioning. If the sensor's value is fixed for a period of time it is currently non-functioning and ECM will throw a code. If sensor value stays out of range, high or low, for a period of time ECM will throw a code.
Old 10-29-2009, 01:41 PM   #31
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Re: EGR Valve Operation

This is all done with EGR valve unhooked and not working.

When climbing hills in my Duke, for over half the hill the motor sounds like its running 100% normal. It is only at a certain part of the throttle range when you are going up a hill steady, it seems like it starts to load up a smidge and ping/detonate a bunch. The only way I can make it stop, is either let off the gas a smidge and bog, or mash the gas down farther and speed up the hill faster then the designated MPH. I usually just speed up the hills at 5MPH over or something, which is opening up the throttle and giving it more fuel down the TBI.

When it starts to knock, I have to be careful to make sure I dont let it knock knock away. I always have to feather the damn pedal. If I had no pinging or detonation, I would have not a single complaint, but even PREMIUM fuel knocks. Its not like its even losing power when it knocks; The noise is horrible that I feel like I will blow it up in a matter of a few revolutions.

Of course I get the infamous code that comes and goes. On the highways it must try to test the valve and it will show a SES light for a few seconds and then the light will shut off.

I have ran it with both EGR hooked up and the solenoid connector unplugged and it doesnt set a permanent code. I also have tried to unhook the EGR valve and leave the solenoid plugged in. It still will throw the code for a minute, and then the code goes away. It will always come and go everytime I drive it.

I guess I am just confused on why the valve works to stay shut IF the solenoid isnt connected to it. How can it stay shut? I thought we ruled that the EGR works mechanically and is only tested by the EGR solenoid. If thats the case, wouldnt the only way to keep the EGR shut is to remove the vacuum line? How is the EGR staying shut if the solenoid is disconnected to the ECU plug, but is still hooked up with vacuum lines to the manifold???
Old 10-31-2009, 12:38 PM   #32
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Re: EGR Valve Operation

As before:
Little or no vacuum to the egr valve and the spring inside the egr valve is supposed to shut it. When everything is hooked up and working the solenoid is supposed to allow the vacuum to reach the egr valve when engine warmed up (or ecm say so) and part throttle.
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