Vortec EGR System?

[EagleMark]

Does anyone have a understanding of the mechanical end of the EGR system in a Vortec Engine? It's a 98 but I think mechanically 96-00 are all the same.

I'm wondering if there is a possibility of it feeding one bank more then the other? Or could something get plugged?

Why? Well I have my tune dialed in for fueling, did so with WB in Open Loop and EGR off. Back to Closed Loop fueling is still spot on. With EGR enabled Bank 1 STFT/LTFT is off by about 3.1% all the time EGR is on.

Side topic: I'm wondering if the EGR being on from 3 MPH is hurting my around town mileage? My understanding and testing shows EGR to give better mileage on highway for sure! But it does produce less HP, so why would I want it on when HP/Torque is most important? From a standstill it is on at 3 MPH with a varying % based on TPS, more TPS = higher EGR%. I'm thinking this would hurt mileage? Maybe turn it on at 25 after vehicle has made it up to speed and HP/torque requirements are much lower...

[1project2many]

I suppose the EGR could get plugged in a way that tends to direct exhaust gas one way but I wouldn't suspect that first. Are you using the stock TB with the diffuser plate on the bottom? Check to see if the plate highly carboned up.

Most of our GM buses are mainly around town, stop and go. My testing has shown improvements in mileage if EGR is disabled during these conditions. Unfortunately I can't leave them set that way.

My suburban is showing about 10-12% rich in closed loop. Initially I suspected across the board timing changes were needed for the 302 but those are not bringing O2 into line. I'm going to return to stock timing and see if the EGR is sticking open next.

[EagleMark]

Are you using the stock TB with the diffuser plate on the bottom? Check to see if the plate highly carboned up. It is stock. Can you see that with air cleaner off or have to remove TB?

I'm doubting it, the intake gaskets and spider were recently done, not by me, before I got it. Very nice work too along with everything else, I have maintenece records since new, no expense was ever spared on care of this truck... but you never know?

It is EGR related as I can turn off EGR and no more Bank 1 fuel trim changes?

[1project2many]

No, you can't see it without pulling the TB.

Are you also seeing O2 readings that are different between the banks? Does that cal have an option to turn off individual bank fuel trims?

[EagleMark]

O2 readings are same both banks... I even swapped the new O2 sensors awhile back. I know why your going there as I had the issue with post cat O2 sensor which was also same bank. Replaced it and went away... I thought, well the O2 swing of that post Cat sensor went away but this fuel trim issue came back. Post CAT 02 sensors are removed now for testing. Finally tracked it to EGR On/Off.

Wide Band is only in driver side bank which is bank 1 as well. Runs a steady .98-.99 on gauge and logs and no change when fuel trims go to 3.1%. That's well within boundaries of correction and well within goals of a good tune. Just very strange one bank sees correction only when EGR on?

[EagleMark]

There is a Two Bank Fuel Control flag in TunerCat! Just like everything else so much more usable parameters then EFI Live.

TunerCat is also where I found the EGR enable speed. EFI Live only has one parameter for EGR... Enable/Disable...

[gregs78cam]

So with that flag you can run in Batch fuel control, or Bank fuel control?

[EagleMark]

From what 1project2many says below it sounds like just trim, not a bank/batch change.



Does that cal have an option to turn off individual bank fuel trims?

[Lextech]

It's too bad we don't have any EGR related TPS and RPM parameters available to us. That way we could use the PCM's EGR circuit as a switching circuit.

Jeff

[gregs78cam]

From what 1project2many says below it sounds like just trim, not a bank/batch change.
That's what I meant, it can trim each bank, or both as one?

[EagleMark]

My suburban is showing about 10-12% rich in closed loop. Initially I suspected across the board timing changes were needed for the 302 but those are not bringing O2 into line. I'm going to return to stock timing and see if the EGR is sticking open next.That's about the same amount of change in cubic inches too? Have you done the VE tables? You still have the 98-00 Vortec PCM?

I've confirmed my issue once again as EGR. Turned it off yesterday and fuel trims were back to as close to 0 as possible all over but more importantly same bank to bank.

Going to try turning off the individual bank trims and see what happens, more curiosity. Seems like it would be a patch for a known EGR issue?

Also going to check MPG on this tank with EGR enable MPH raised to 25 MPH

[Fast355]

That's about the same amount of change in cubic inches too? Have you done the VE tables? You still have the 98-00 Vortec PCM?

I've confirmed my issue once again as EGR. Turned it off yesterday and fuel trims were back to as close to 0 as possible all over but more importantly same bank to bank.

Going to try turning off the individual bank trims and see what happens, more curiosity. Seems like it would be a patch for a known EGR issue?

Also going to check MPG on this tank with EGR enable MPH raised to 25 MPH

My MPG is better EVERYWHERE with the EGR turned off and always has been.

[1project2many]

Sorry, Mark. Didn't mean to leave you hanging. Had a road trip to visit family.

Change that bit and you should see fuel trims follow only bank 1. I have been told the selection for 1 or 2 O2 sensors will do the same thing but haven't played with it.

Spent time with my cal. Problem was solved with engine displacement per cylinder. The displacement step size is 10CC so I bumped it from 630 to 640CC.

Imported trans module from 99 Envoy for faster response to throttle changes. I need it due to reduced torque at lower rpm. Much more driveable now and less fuel wasted. Still need to work on a few things but better overall. Didn't realize TC can do that until this weekend. V. Cool.

The EGR helping / hurting mileage has been a back and forth issue for years. Claims on both sides by respected individuals lead me to believe there are more than simple variables involved. I look at cam overlap and exhaust configuration to decide how much is needed. Decent overlap and mufflers indicate EGR already present at part throttle without opening valve so why add more?

[EagleMark]

Hope your trip went well.

I tried the bank fueling bit and no change? Still had difference on 1 and 2... I'll give it a shot again tomorrow. Also asked John at TC to verify it's purpose.

As you found TunerCat will do the Import Calibration of Engine/trans or... which others call a segment swap. It will also do it table by table if the table is open. The more I use it the more I like it.


The EGR helping / hurting mileage has been a back and forth issue for years. Claims on both sides by respected individuals lead me to believe there are more than simple variables involved. I look at cam overlap and exhaust configuration to decide how much is needed. Decent overlap and mufflers indicate EGR already present at part throttle without opening valve so why add more?That is the first time I've ever heard a theory on why! Makes perfect sense as well.

I just can't pull the TB off right now to check EGR/diffuser issue you asked about, can't chance the vehicle being down. Have no idea when I may have to leave town and bring wife to OR for surgery... The Suburban just has to many issues for a trip...

[pmkls1]

Well Mark, I may be a little late chiming in here, but I just happen to be resealing the intake on my grandfather-in-law's '99 suburban. I snapped some pics of the bare intake to illustrate what I believe may possibly be the issue. The particular truck that I'm working on is a 1999 Chevy C2500 Suburban with an L31 5.7 (obviously) and a 4L80E. Mechanically, the '96-'02 L30 and L31 intakes are essentially identical AFAIK. Anyway, I've got a couple things to do and then I'll upload my pics to the computer and post them with a few notes showing the passages and such.

[Hog]

There are some small EVAP differnces between the 96-97 and 98+ intakes, but the 305 and 350 intakes are NOT differnt.

peace
Hog

[pmkls1]

Alright, the first pic is of an assembled manifold with a few things pointed out for anyone not familiar with the layout. http://i149.photobucket.com/albums/s71/pmkls1/L31%20egr/complete_1.jpg

[pmkls1]

The next pic is of a bare intake in the same orientation. http://i149.photobucket.com/albums/s71/pmkls1/L31%20egr/bare_1.jpg

[pmkls1]

Sorry for having to post one pic per post, but I'm having problems with posting. This next pic is a close-up with the EGR passages pointed out. http://i149.photobucket.com/albums/s71/pmkls1/L31%20egr/detailed_1.jpg

[pmkls1]

This next pic illustrates the difference in distance that the EGR gasses have to travel to reach the runners. The bank 1 ports in the pic are for cylinders 1 & 3 and the bank 2 ports are for cylinders 2 & 4. http://i149.photobucket.com/albums/s71/pmkls1/L31%20egr/31e36951-e2b1-44f8-a9c5-8dd2d18be4f5.jpg

[pmkls1]

The next few pics show the throttle body and the air diverter on the throttle blade as well as the underside of the upper plenum. http://i149.photobucket.com/albums/s71/pmkls1/L31%20egr/2013-05-30_10-07-03_782.jpg http://i149.photobucket.com/albums/s71/pmkls1/L31%20egr/2013-05-30_10-07-19_22.jpg http://i149.photobucket.com/albums/s71/pmkls1/L31%20egr/2013-05-30_10-07-54_820.jpg http://i149.photobucket.com/albums/s71/pmkls1/L31%20egr/2013-05-30_10-13-44_45.jpg

[pmkls1]

After looking at how the EGR gasses enter the plenum and everything else it still seems like the EGR gasses are going to feed cylinders # 1 & 3 more than any others. But, you would think that bank #1 would go rich and not lean since cylinders 1 & 3 are getting more exhaust gasses and less fresh air thus requiring less fuel. Either way, I can see how a bank imbalance could easily occur with this setup. On a side note, I am testing some different cleaning solutions for cleaning aluminum and I will be using this manifold as a test-bed. The above pics are of the manifold directly after being removed and will serve as "before" pics. You can see just how nasty it was in there and this is typical of these engines. This particular engine has 19x,xxx miles on it for reference. I'll post the "after" pics after using some different cleaners as well as the name of the cleaners used and what they contain. I'll post in a new thread so as to not interfere with the purpose of this thread.

[EagleMark]

Thanks pmkls1 ! :thumbsup:

That was quite an effort to document the EGR system.

Mans that is disgusting in there....

[Fast355]

Thanks pmkls1 ! :thumbsup:

That was quite an effort to document the EGR system.

Mans that is disgusting in there....

Aluminum Wheel cleaner works well

Oven cleaner works well

So does an Diesel EGR shaker bath. My TPI setup and runners were spotless after being dipped in that for 30 minutes.

Express runs like crap with the EGR turned on, especially in hot weather and after having cleaned that mess up myself once, I just disabled it.

[EagleMark]

Sure runs better with EGR coming on after 25 MPH instead of off idle. MPG around town is up as well. Have to do some more data but not much EGR activity at cruise speeds? Only showing some EGR after 25 MPH to 40 MPH and none at highway speeds? All light throttle... When I'm done with this tank I'm going to do a tank with no EGR at all and see what MPG does.

EFI Live only has 2 paremeters for EGR. On/Off and the spark advance table which only adds 3 degrees tops.

TunerCat has those and the EGR enable/disable speeds as well.

No EGR fueling tables in either.

Pulled the throttle body today and it's near spotless in there so looks like they did a good job when the intake gaskets and spider were replaced.

[pmkls1]

I actually snapped a few pics anyway for a visual reference so that I don't have any trouble during reassembly so it was no big deal really. This vehicle was a recent purchase for pulling a camper and it was used as a tow rig before so I assumed it would be pretty nasty in there. Regarding EGR functions I feel that 1project2many has the best theory about EGR and gas mileage. Every engine configuration reacts differently to changes so it would only make sense that EGR operation would be no different. If you take a moment to remember the theory of how EGR is supposed to work it helps to understand when it may be helpful and when not. The function of EGR is a crude way of reducing engine displacement and fuel consumption by pumping a metered amount of inert exhaust gasses into the cylinders under light engine loads when the demand for power is low. Still, different engines are going to respond to when the EGR is enabled and such differently. I personally have always disabled EGR functions on my vehicles for simplicity, but it can be useful. As for my cleaner testing, the cleaners that I am testing are eagle one chrome wheel cleaner and eagle one mag wheel cleaner. I have worked with oven cleaner before too and it is pretty decent too. It is not just the actual brand names that I am looking into rather it is the base chemicals and the combinations. Everybody knows that muriatic acid is excellent for stripping iron and steel, but it literally eats aluminum. Phosphoric acid works on both, but has limitations. Sulphuric acid also works in small quantities. Sodium hydroxide is an excellent cleaning agent and is the main ingredient in oven cleaners as well as aqueous parts washer solutions. All of these chemicals are readily available and they are also the main ingredients in many cleaners out there. The problem is that these over-the-counter cleaners are pretty expensive by volume. My testing is for the purpose of finding which cleaner I like and referencing the main ingredients and percentages listed on their MSDS sheets and then attempting to mix up my own concoction using readily available and inexpensive concentrated solutions of the chemicals.

[EagleMark]

If you take a moment to remember the theory of how EGR is supposed to work it helps to understand when it may be helpful and when not. The function of EGR is a crude way of reducing engine displacement and fuel consumption by pumping a metered amount of inert exhaust gasses into the cylinders under light engine loads when the demand for power is low. Still, different engines are going to respond to when the EGR is enabled and such differently. I personally have always disabled EGR functions on my vehicles for simplicity, but it can be useful. That is my understanding, but the purpose was only for emissions.

But off idle while accelerating from a stand still is not light load? And it's on?

At light cruise which is light load it is off?

I've never really studied EGR in data, but this is exactly the opposite of what I expected...

[gregs78cam]

I can tell you that on our '99 Grand Am with 3.4L, EGR not functioning reduces MPG by 10%.

[EagleMark]

That is my understanding, but the purpose was only for emissions.

But off idle while accelerating from a stand still is not light load? And it's on?

At light cruise which is light load it is off?

I've never really studied EGR in data, but this is exactly the opposite of what I expected...Rethinking this it's backwards, the EGR is enabled at higher loads for emissions.


I can tell you that on our '99 Grand Am with 3.4L, EGR not functioning reduces MPG by 10%.I've done this before, 3 times, all on stock factory cam engines and results were the same. 10-15% loss in mileage.

But never have I studied the data of what EGR was doing... :laugh: I'm an idiot... :rolleye:

[1project2many]

Mileage gains, if any, are secondary. EGR reduces combustion chamber temps to keep NOx levels lower. GM must have seen a need for more EGR under higher load on the L31 so that's when it's active.

Be careful not to strip protective coatings / platings from components during cleaning process. Acids and bases are both very capable of doing that. I wonder if the "electrolytic rust removal" process would be effective here. It does a great job removing paint on parts that aren't rusty. I wonder how it will work on carbon?

[Fast355]

I can tell you that on our '99 Grand Am with 3.4L, EGR not functioning reduces MPG by 10%.

Funny thing, my grandmothers '03 Alero 3.4 that is driven only in the city increased its MPG over 20% with a tune, running disabled EGR.

[Fast355]

Mileage gains, if any, are secondary. EGR reduces combustion chamber temps to keep NOx levels lower. GM must have seen a need for more EGR under higher load on the L31 so that's when it's active.

Be careful not to strip protective coatings / platings from components during cleaning process. Acids and bases are both very capable of doing that. I wonder if the "electrolytic rust removal" process would be effective here. It does a great job removing paint on parts that aren't rusty. I wonder how it will work on carbon?

Makes sense with the retardedly high gearing and tight torque converter they used that the engine would be prone to creating NOx emissions trying to accelerate.

[EagleMark]

Funny thing, my grandmothers '03 Alero 3.4 that is driven only in the city increased its MPG over 20% with a tune, running disabled EGR.

There's got to be some differences here we are not looking at like:
1. Elevation? Greg and I are at 2000 feet.
2. Tempreture? We rarely hit 90 in summer. Cooler all year then you.
3. Fuel? I think we've had this discussion before but is E fuel there's the same as here? Refiners are close to texas so is fuel fresher? It's old by the time it gets here? I really don't know where our fuel comes from.

Fuel: In Closed Loop my WB reads AFR of 13.8. E10 is supposed to be 14.1, do we have more E in out fuel? IIRC last summer I did some MPG data and the expense on Non Ethanol was well worth it.

[EagleMark]

Just found some strange differences in EGR operation from old TBI engines $42 to the 0411 PCM I'm using in this Vortec engine.

First there's SO MANY more parameters defined.

Second $42 looks like EGR is always on under 50% TPS and if above 1.95% TPS after enabling at 3.12% TPS, with complete fueling compensation tables and up to 5.98 degrees spark added.

Vortec with 0411 PCM = no parameters and data showing EGR on during acceleration and off at all light cruise. Got me curious so I'll be watching data to see what it's actually doing.

Maybe EGR is why I can get better fuel mileage from an old TBI truck then I can with a 1998 Vortec and 2002 PCM and OS?

[RobertISaar]

that would be a hilariously depressing explanation, considering what it costs to play with OBD1 compared to OBD2.

[pmkls1]

The EGR system does reduce combustion temps and thus reduces NOx emissions, but at the same time it is effectively reducing the displacement of each cylinder by partially filling it with inert exhaust gasses that will not burn. This is why when the EGR system is active the fuel system is designed to deliver less fuel. That is where the old and partially true "myth" that removing the EGR valve from an otherwise stock engine would "burn it up" because it would run too lean. Of course, that myth was started back in the carbureted days where the EGR was completely vacuum operated and the carburetor was jetted leaner and the enrichment systems took care of adding the proper fuel under load. Although I have never personally seen a carbureted vehicle actually experience some sort of engine damage by removing the EGR valve, I could see where it might be theoretically possible if the carburetor were left untouched. Throw in fuel injection, though, and all of that changes somewhat. But, like I said before, different engine configurations are going to react differently and you could also go a few steps further by figuring in ambient temperature, the fuel, elevation, vehicle weight, converter stall speed, and gearing etc.... Which would explain why different people experience either mileage losses or gains by disabling the EGR system. This is why on my personal vehicles I have always just disabled the EGR system. Not only is it one less variable to work around, but it is also fewer components that can fail and less crap cluttering the engine bay. About using strong cleaners and stripping protective coatings, I am looking at solutions for reconditioning parts where you would purposely want to remove those coatings. I will post some results on cleaning up the intake and what I used but I will definitely strongly warn of any dangers to both the parts and the person handling the cleaners. As far as any "home-brew" cleaners that I come up with I may eventually share the recipe if it seems to work well and be worth the effort of making, but I will definitely caution people to the dangers of them as well.

[pmkls1]

Well, even the TBI engines still used a vacuum operated EGR valve that they controlled with a solenoid, but it was still an ON/OFF type valve. Aren't the newer electronic EGR valves "variable" in that the pintle is opened in percentages ? That would explain some differences at least.

[RobertISaar]

i think GM gave everything the "linear" EGR setup in 96, a couple of applications got it before then. and before that, EVRV, positive backpressure, negative backpressure, digital, etc.... lot of different systems all occuring at the same time.

[EagleMark]

I hadn't even thought of coating on an intake? But I guess if I were in the cleaning process I would...

If you think about carburators they are coated. This I was taught in high school auto shop, we had one that someone had scratched the inside of a float bowl with a screwdriver in cleaning. Well without the coating it would sweat fuel!

[EagleMark]

that would be a hilariously depressing explanation, considering what it costs to play with OBD1 compared to OBD2.Just the limitations of what can be done is depressing. Locations are all hidden, you can add things in EFI Live by including them in a CAX file if you have locations. One CAX file I have for lean cruise works, but not nearly correct. newest update will not allow changes to their locations, there's no way to add, change or correct descriptions... the limitations are endless compared to TunerPRo RT...

TunerCat is much more forgiving for old software as you can add to and edit definitions with the TDF editor.

That said the xdf for 2002 OS is coming along with using dimented24-7 disassemble for 2001 OS but being careful as some locations have changed, many tables are identical in different place.

RoadRunner works with all three softwares...

But I think some of the missing items in EGR case is because of MAF compared to speed density? EGR gas takes place of some of VE so fueling needs to compensate. Wouldn't the MAF do this?

[EagleMark]

The EGR system does reduce combustion temps and thus reduces NOx emissions, but at the same time it is effectively reducing the displacement of each cylinder by partially filling it with inert exhaust gasses that will not burn. This is why when the EGR system is active the fuel system is designed to deliver less fuel. That is where the old and partially true "myth" that removing the EGR valve from an otherwise stock engine would "burn it up" because it would run too lean. Of course, that myth was started back in the carbureted days where the EGR was completely vacuum operated and the carburetor was jetted leaner and the enrichment systems took care of adding the proper fuel under load. Although I have never personally seen a carbureted vehicle actually experience some sort of engine damage by removing the EGR valve, I could see where it might be theoretically possible if the carburetor were left untouched. Throw in fuel injection, though, and all of that changes somewhat. But, like I said before, different engine configurations are going to react differently and you could also go a few steps further by figuring in ambient temperature, the fuel, elevation, vehicle weight, converter stall speed, and gearing etc.... Which would explain why different people experience either mileage losses or gains by disabling the EGR system. Take $42 for instance. If EGR is not disabled properly? And EGR removed? It still cuts fuel and adds spark when EGR is enabled!!!

Wonder why your running lean and pinging?