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Discussion Starter #1
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???
 

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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???
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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.
 

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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...
 

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Discussion Starter #4
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!
 

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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.
 

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Discussion Starter #6
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???
 

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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)?
 

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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..:D
 

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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....
 

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Discussion Starter #10 (Edited)
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.... :rant:

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!
 

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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...:rotf:

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...
 

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Discussion Starter #12
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!
 

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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!
 

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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..
 

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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?
 

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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.
 

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Discussion Starter #17
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 :rant:
 

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Discussion Starter #18
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.
 

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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.
http://www.s10forum.com/forum/members/shaddix/
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.
 

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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.
 
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