EGR question

M

macx

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Jan 27, 2011
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Actually, an EGR removal question.

81 which is stock but will be getting some mild mods.

Going to TBI, so will be losing ecu function, so will be going mechanical/vacuum HEI.

Going with a short duration efi & computer compatible cam with 0 overlap @ 050 on about a 9-1 comp ratio and a Performer type intake with Vortec style heads but no effective quench with the stock pistons.

I'm not in a smog test area, but I do know that if functioning properly an EGR does have some benefits, i.e. some help with avoiding detonation and sometimes a dab better mileage due to possibility of running a little more advance.

I haven't looked but don't remember seeing any external EGR on the basic Performer style intakes, and with no overlap there isn't any "internal" EGR-like function.

I know lots of C3 owners get rid of the ecu, and was wondering if anyone has ever worked thru getting a functional EGR when doing so.

Thx!
 
After doing quite a bit of research, I've come to the following conclusion.

On this particular vehicle, the ecu takes input from several sensors including temperature, rpm, and the hardest to plow into the formula if the carb is removed - a tps.

Earlier vehicles that had an EGR used a simple vacuum signal, with input also from a temp sensor, to either open or close it. This vehicle, according to what I read, has the ecu configured to the trans gear ratio and rear end ratio, also, and modulates the EGR opening rather than just switching it basically on or off. The ecu even regulates the air pump output and the fuel tank carbon filter system, and I'm sure that all those functions have overlapping effects, not to mention the signal the 02 sensor also sends to the ecu.

So, I think it would take more effort than it's worth to duplicate that.

Most guys change gears, as well as compression ratio, cam specs etc, all which have an impact on the ideal amount of EGR opening. So without a programmed ecu to determine that proper amount, I think it would be at best a crap shoot.

Some longer duration cams that have a fair amount of overlap, a good example is the Comp Cams popular XE268H flat tappet, create sort of an
"internal" EGR effect because of the amount of overlap.

From what I read, I also don't think the simple vacuum controlled EGR would do much good, either.

So - unless you're staying fairly stock and esp are leaving the electric carb, the oem HEI, the air pump etc, it seems to be useless to try to keep the EGR system functional.

Hope that makes some sense!
 
That article was one of many things I read while researching.

Seems the best stab a person could take at it would be an electric on/off
vacuum solenoid with vacuum (load) input somehow to keep the EGR closed
during heavy throttle (open loop), engine temp input so it stays off until the engine is warmed up, and closed during idle and slow speed light throttle.

Basically keeping it off except in closed loop highway driving.

And then it would be a guessing game on how much to let thru the valve.

A wide band might help to tune the efi for closed loop air / fuel mix, but sounds like getting all the inputs to work without having a known quantity for a result just wouldn't be worth it.

Well, at least now I've explored it, learned a lot more about the subject
than I knew before, and am satisfied with what the best approach is.

Now, for the next topic - - ;)

(Really!)

About the cat & the air pump -

I'm going to retain a cat, but will replace the oem one with a larger dia (true 3" in/out) hi flow cat.
Gotta have a cat to pass inspection, and am also replacing the single pipe portion of the exhaust
with a 3". Not going to be more than a mild build so don't need true duals with a crossover or anything,
and from what I've read on the Dynomax site, a large dia single is better for the low and mid range
torque I'm after anyway. Besides being a less expensive modification (incl no 2 cats).

Being I'm going to disconnect the ecu, which I understand has some control over the AIR system,
is it practical to retain the pump & related system back to the cat (that's the one smog thing
they do check where I have to get it inspected in rural MO - air pump & cat).

Is there such a thing as too much air from leaving it "on" all the time instead of having it controlled
by the ecu?

If, for any reason, it would be best to make that system non-functional (i.e. venting all the
pump output to the atmosphere instead of into the cat - I believe there's a provision in the system
'for that when the ecu doesn't direct all the pump air output to the cat?) then I suppose the only
reason to have a cat with an air tube would be for inspection.
 
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Quote: Seems the best stab a person could take at it would be an electric on/off
vacuum solenoid....

When they first appeared, the EGR valve control was sometimes via ported vacuum, acts like a switch. I think that unless you have a factory control system for it, that this would be a better option.

Quote: About the cat & the air pump -

I'm going to retain a cat, but will replace the oem one with a larger dia (true 3" in/out) hi flow cat.
Gotta have a cat to pass inspection (Earlier quote: "I'm not in a smog test area")

Don't know the specifics for your area. But from the above, I'll assume you just have visual inspection?

Being I'm going to disconnect the ecu, which I understand has some control over the AIR system, is it practical to retain the pump & related system back to the cat (that's the one smog thing they do check where I have to get it inspected in rural MO - air pump & cat).

If your Vette is to undergo verification, then it would make sense to leave the orig A.I.R. system intact?

Is there such a thing as too much air from leaving it "on" all the time instead of having it controlled by the ecu?

If, for any reason, it would be best to make that system non-functional (i.e. venting all the pump output to the atmosphere instead of into the cat - I believe there's a provision in the system 'for that when the ecu doesn't direct all the pump air output to the cat?) then I suppose the only reason to have a cat with an air tube would be for inspection.

If it were my car retaining the A.I.R. system, I would be careful messing with the controls of that system. It's a fairly simple system, in that it has a low pressure air pump injecting air into the exhaust. The fresh air provides sufficient oxygen causing more complete burning of the gases in the exhaust stream. This action consumes most of the objectionable emissions in the exhaust stream prior to entering the cat.
A check valve in each air manifold prevents exhaust gases from entering the air pump.
Also included is a pressure relief valve, which limits system pressure to prevent excessive exhaust temps during high-speed cruising.
It's possible that if this valve function fails, the exhaust stream could superheat or even melt some components! :evil::evil:
And there's a diverter valve, which shuts off injected air to exhaust port areas when triggered by high intake manifold vacuum during deceleration. This action prevents backfiring. The excess air is diverted to the atmosphere.
This action is also quite loud, but under controlled operation lasts a few seconds.
Hope this helps give a better understanding of your systems before you decide to enact any mods.
 
Not to get off topic, but if your switching to a TBI setup why not run computer controlled distributor instead of an old vacuum advanced unit?
 
Just a question about a ported vacuum for the EGR - that wouldn't disable the EGR during cold start warm up, tho, would it? And with the EGR running during warm up doesn't that make for a rough running engine till it warms up?

Correct on visual only.

I'd looked thru my oem service manual for the control layout of the AIR system so saw all those components.

But I also saw the system basically was controlled to some degree by the ecu, which will definitely be disconnected becuz of the swap to tb efi.

That was basically my question - any practical way to keep any functionality in the AIR system without ecu control?

Without any air input into the exhaust ahead of the cat, I don't imagine that's a particularly good situation either.

Just for the sake of "what if" - if a tps were rigged for ecu input and the ecu to carb signal just left unconnected - - ??

Re the ignition advance curve, I suppose the ecu curve has room for improvement - if the rpm input from the HEI to the ecu were retained and the advance signal from the ecu to the HEI disconnected, I wonder if the ecu would still function - i.e. for the AIR system. Leaving vacuum input, rpm input, speed sensor input (altho going to different rear gears) air & coolant temperature input, & tps input. Hmmm. I've heard of resistors being installed to fool an ecu into thinking output is still connected.

The trans will be replaced with a hydraulic controlled 200-4R, so the ecu input to the converter for lock up will already be disconnected.

I'll have to dig out the svc manual & study that some more.
 
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Fuelie74 said:
Not to get off topic, but if your switching to a TBI setup why not run computer controlled distributor instead of an old vacuum advanced unit?
Click to expand...

Quite alright - always open to input.

The TBI I'll be using doesn't not provide ignition control.

Or are you saying I could leave the ecu intact for the HEI?

But - how "effective" is the ecu's built in advance curve? Going to be running 91 octane.
I suppose the static timing could be advanced to provide more total, with the curve in
the ecu still functional.
 
macx said:
Fuelie74 said:
Not to get off topic, but if your switching to a TBI setup why not run computer controlled distributor instead of an old vacuum advanced unit?
Click to expand...

Quite alright - always open to input.

The TBI I'll be using doesn't not provide ignition control.

Or are you saying I could leave the ecu intact for the HEI?

But - how "effective" is the ecu's built in advance curve? Going to be running 91 octane.
I suppose the static timing could be advanced to provide more total, with the curve in
the ecu still functional.
Click to expand...
No I was asking about letting the ECU control the ignition timing.

What ECU are you using?
 
It's an 81 so it has an oem ecu that controls the electronic QJet, the
HEI, the converter lockup, the AIR system & the EGR.

Other than that, I have no ecu for it.
 
OK so what am I missing here. You say that you are converting to TBI. You have to have a computer to run the TBI setup. So are you switching to fuel injection or staying with a carburetor?
 
Yes, converting to TBI, it's Holley Pro Jection (a setup I already have and have used on another vehicle so am going to use it instead of spending $1k + for another system) and that system does have a control computer but it does not control anything with ignition. 'Fuel only.
 
I was trying to stay at near surface level and not go to deep with all this.

To answer your question further concerning the EGR control:
In many earlier Chevy app's, a thermo vacuum switch was employed to delay EGR function until the engine reached a predetermined temperature. This was typically seen atop of the thermostat housing, with a bunch of vacuum lines running to and fro. With the advent of the ECM, EGR control was integrated.

Quote: That was basically my question - any practical way to keep any functionality in the AIR system without ecu control?

I would have to see a diagram of your factory layout to give you any sort of accurate answer, as it's been years since I worked with this stuff daily.
But to satisfy for now, my guess would be no.
But one possible option would be to utilize components from an earlier (pre ECM) system. Just be aware that a lot of the earlier emission equipment was scrapped by owners in search of performance. It's rather hard to find. And if you do find it, you'll pay premium $$$!

Quote: Without any air input into the exhaust ahead of the cat, I don't imagine that's a particularly good situation either.

That's true.

Quote: Just for the sake of "what if" - if a tps were rigged for ecu input and the ecu to carb signal just left unconnected - - ??

You're slightly confusing in the above question. The TPS is a throttle position sensor, which tells the ECM where throttle position is at. The "electric Q-Jet" contains an M.C. (mixture control) solenoid which does just that.
The TPS is an input sensor, and the M.C. solenoid is an output devise, responding to ECM. The two are really at opposite ends of the stick (so-to-say).
I assume your asking about the "electric Q-Jet", and disconnecting the input to the carb M.C. solenoid.
My best answer to this is: I like to think of the ECM and the electric Q-Jet as married, or one unit.
I don't recommend running that E Q-Jet without the ECM.

I think I'm starting to get your drift and thought pattern here. So I'll give you some more school-for-thought.
Understand that these C.C.C. (computer command control) systems are 30+ yrs old, and crude by today's stds. These systems are designed to operate as a 'whole' networked system. When you start disconnecting/removing circuits to your custom needs, the system will detect this and kick into "limp mode".
Of course it is possible to rework/re-engineer anything, so you could substitute input feeds to generate desired results on the output feeds.
In my book, this amt of work with these systems just isn't worth it. I understand the stimulus in wanting to tinker with things to achieve better results, and to say "I did it"!
I say keep it whole, or dump it.

Since you state you want a 'mild build' result. I would research a few years ahead of the early 80's in search of a factory EFI with emissions incorporated. It's possible this could be a transfer swap with some tweaks.
Good Luck, as you sure have carved some interesting work out for yourself!
:mobeer:
 
Rod75 said:
Since you state you want a 'mild build' result. I would research a few years ahead of the early 80's in search of a factory EFI with emissions incorporated. It's possible this could be a transfer swap with some tweaks.
Good Luck, as you sure have carved some interesting work out for yourself!
:mobeer:
Click to expand...

That's basically my thought. If you want to run your Holley Pro Jection setup, then forget about EGR. If you want to keep your emissions equipment then go with a factory TBI set up.
 
It seems to be settling to the "dump it" scenario.

Figured I'd research it, however, in case there was a way to make it work.

If nothing else, I always seem to learn something in the process.

I've had a fair amount of experience working with Ford's eec-iv system, which
is very similar to the MassFlow systems. They're very adaptable and the stock program in the Mustang 5.0 ecu's is quite acceptable for a moderately built street engine. I swapped a moderately built 351 in place of the stock 5.0 HO and, using larger mass air meter, injectors, and throttle body, it worked extremely well. Very driveable for daily use, good power, great economy. I've got a TwEECer if I would need to modify anything in the programming.

I've found I could get my HEI modified to work with that system, but then I'd
have to get a different throttle body, ecu, harness, injectors, etc. Just not worth the expense and likely problems.

I could get one of those new stand alone TBI self adjusting systems as cheaply and with none of the hassle.

At least now I've explored the possibilities and can feel satisfied that what I'm going to do is the best way. Esp considering my budget constraints.

Thanks for all your thoughtful input.
 
Keep us up on the project there, I for one am very curious as to what you find and do......

:bounce::nuts:
 
I appreciate your interest as well as all your input, but I'm afraid it will be some time before I start to get my hands dirty.

I bought the car about 5 or 6 years ago, totally ignorant of the unique potential problems in the rear suspension as well as body mount, frame and brake issues. Of course when I got it home and started getting under it for a good look, and found several vette forums and begun educating myself, found numerous issues that I will have to address when I get to the point I have the time.

I work away from home on long term power plant construction projects so am seldom home for more than a short weekend and even that only on average once a month. I've been researching and re-familiarizing myself with it lately because I've been laid off for several months, but work is picking back up now so will not be around again till I retire. That, hopefully, will be in about 4 years, so - - .

At least now I have a fully developed and detailed plan of what needs to be done, and what I want to do. When I do finally figure out my retirement date, then I'll start ordering the parts I need. I've also got to take the body off to replace mounts, repair the badly rusted driver door pillar, and while I'm at it will blast and paint the frame. Will rebuild the rear suspension, hubs/brakes, and diff while the body is off, install (maybe home made) 6 link, replace brake and fuel lines, (probly) install a front monoleaf, and swap to (again, probly) a home made rack & pinion setup. And of course do the cam and efi swap, and the exhaust improvements before I reinstall the body.

So even after I retire and get started, it will be awhile. I'll also be freshening up the house and getting it on the market and preparing to move several states away. So hard telling just how much time I'll have to spend on the Vette or how soon I'll even get to it even after I retire.

I've become used to waiting to get at projects as I've worked like this for the past 15+ years. Don't like it, but the only way I can eventually get done what I want.

So, if the world is still standing, as they say - stay tuned -.
 
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macx said:
I appreciate your interest as well as all your input, but I'm afraid it will be some time before I start to get my hands dirty.

I bought the car about 5 or 6 years ago, totally ignorant of the unique potential problems in the rear suspension as well as body mount, frame and brake issues. Of course when I got it home and started getting under it for a good look, and found several vette forums and begun educating myself, found numerous issues that I will have to address when I get to the point I have the time.

I work away from home on long term power plant construction projects so am seldom home for more than a short weekend and even that only on average once a month. I've been researching and re-familiarizing myself with it lately because I've been laid off for several months, but work is picking back up now so will not be around again till I retire. That, hopefully, will be in about 4 years, so - - .

At least now I have a fully developed and detailed plan of what needs to be done, and what I want to do. When I do finally figure out my retirement date, then I'll start ordering the parts I need. I've also got to take the body off to replace mounts, repair the badly rusted driver door pillar, and while I'm at it will blast and paint the frame. Will rebuild the rear suspension, hubs/brakes, and diff while the body is off, install (maybe home made) 6 link, replace brake and fuel lines, (probly) install a front monoleaf, and swap to (again, probly) a home made rack & pinion setup. And of course do the cam and efi swap, and the exhaust improvements before I reinstall the body.

So even after I retire and get started, it will be awhile. I'll also be freshening up the house and getting it on the market and preparing to move several states away. So hard telling just how much time I'll have to spend on the Vette or how soon I'll even get to it even after I retire.

I've become used to waiting to get at projects as I've worked like this for the past 15+ years. Don't like it, but the only way I can eventually get done what I want.

So, if the world is still standing, as they say - stay tuned -.
Click to expand...

Do you work for Foster-Wheeler?? if so, or any related operation....have you run across a guy named Bill Higdon??

he is a very old friend from 30 years ago....married to the ex's best friend from elementary skool........talking late 70's we met up over a power plant in W. Va. he was company field engineer....tons of funny stories we laughed about....

:bounce::huh:
 
No, I don't work directly for any contractor or owner. I work contract basis.

Different project owner, different "headhunter" agency just about every job.

Have worked on a number of FW boilers on "shutdowns" (for repairs), and
on at least one new one for a combined cycle gas turbine plant. The last new
coal burner job I finished last summer might have been a FW, lots of them are.

Higdon just about rings a bell, but I've seldom, if ever, been on a job that
I can remember where he actually had any FW reps on site. Might have
been that one comb cycle one, don't remember. I usually remember faces,
but seldom names for very long. Of course, a different group of people every
job, too, altho I've seen some fitters & boilermakers on more than 1 job cuz of
course they travel from job to job, too. Incidentally, that was an Enron job and
I was on that job when Enron collapsed. Talk about luck!:clobbered:
Pretty much the story of my life :crap:
 
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