5.7 TBI GMT400 EGR Question

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08-03-2019
daveosx

5.7 TBI GMT400 EGR Question

I currently have a project underway should be finished in two weeks.
I have a 1995 GMT400 SBC 5.7 TBI A couple of years ago I put a set of try-Y headers on the truck and began occasionally getting the code 32 EGR didn't bother me as it was the silly test not the actual EGR circuit.
So now I am overhauling the engine and adding a bunch of stuff.
I have ground off the air horn of the TBI unblocked the pressure adjuster and added the 1/4 inch spacer.
The intake is a matched Procomp four square dual plenum with a mid mount transadapt plate.
The Heads are pro comp 220cc 202 intake 1.65 exhaust.
The cam is a stock LT-4 roller with 1.5 rockers.
Bottom end just stock with fresh rings and bearings.
Headers are Long tube 1.75-2.5-3 single chamber race muffler 3 inch axle dump.
So absolutely no back pressure and no provision in the head or intake for EGR.

I am currently building a prototype BeagleBone Black based Fuel and trans management system so spending money on the stock computer and old style proms is not desirable.
I am an electronics engineer of sorts and have built many jettronic style ANALOG fuel injection systems in the past.

The question I have is actually pretty simple.
I know that the EGR test in the 1995 TBI vehicles takes place when coolant MPH and throttle is within parameters.
What I am looking for is the amount of MAP sensor voltage change the ECM expects.

So the TEST I understand opens the EGR looks for map change closes the EGR looks for MAP change and then reopens it.
The change in MAP voltage is what I am looking for.
Does anyone know the expected change in map voltage?
If anyone can check for me or knows off hand from prom bit banging I will make a small circuit that satisfies the ECM test and post the schematic here.
My current thought is that the solenoid signal can be used to trigger a Map sensor voltage change.
08-03-2019
dave w

3 Attachment(s)

Perhaps the attached TunerPro .xdf file and .bin file will be helpful. The .xdf includes conversion factors for the EGR parameters.

TunerPro is freeware: https://www.tunerpro.net/downloadApp.htm

dave w

Attachment 14449
08-03-2019
daveosx

Thanks Dave W
Thats the runtime variable isn't it ?
I am looking for the MAP change window for code 32 during the test.
I have used tuner pro and Cats bought full versions of both.
I have not taken the time to look closely through the bins and find the test pass fail thresholds.
I know most guys disable EGR test by raising the temp or map turn on but alas I do not have and old style prom burner.
I was hot on the GM66ECu that was used in a bunch of cars through out the 90s but never bothered to buy an old style bruner.
I threw out about 50 or more PROMs blue top long ones I had left over when I worked for GM I always used the old Tech 100 system not the tech 1000 handheld but the Podium sized roll around for making old style PROMs. When I retired from GM in 1993 I threw out crap loads of ECMs custom Proms ETC.
For a couple of years in the late 2000s I BINned a lot of the cast aluminum cased 66ECU. Even made a Crossfire corvette adapter for a MicroSquirt module.
I got seriously ill a few years ago and am now just starting to recover so I may get back into the Electronics on vehicles.
08-04-2019
dave w

Post #9 in this thread http://www.gearhead-efi.com/Fuel-Inj...Information-0D has the $OD HAC.zip file. I'm not sure the HAC has the EGR information you need, but likely it does.

dave w
08-04-2019
1project2many

Quote:

code 32 EGR didn't bother me as it was the silly test not the actual EGR circuit.

With the perspective of time it would seem the EGR "silly test" is not the best method. Code 32 in stock vehicles was always frustrating. EG richens mixture. Why not blip valve and watch for O2 spike, not MAP? Or, EG slows combustion rate so perform EGR test subsequent to passing the knock sensor test by advancing spark with EGR open and watching for knock. Valves have capacity to circulate more EG than required yet no "EGR Learn" function included to account for plugging of passage over time or stock replacement aftermarket parts that don't create same restriction to flow so "silly test" fails.
Ugh!

Quote:

I always used the old Tech 100 system not the tech 1000 handheld but the Podium sized roll around for making old style PROMs.

Hmm... I don't remember any tools for prom burning included with the T100. Between using that old 286 based tank at the dealership and then having my own personal machine, I'm pretty sure flash programming was possible from the Techline CD but the proms still needed to be purchased.

For entertainment value only: I'm still using the CAMS mechine in a matter of speaking. After playing around with trying to upgrade the hardware (can you remember thinking 18 minutes to boot was an acceptable time?) I finally stripped the machine and used the steel. The 1" thick weights from the base of the cabinet are currently in the counterweight box for my bucket tractor. The "power strip" was a cool part that switched all outlets on when current flow was detected at the primary outlet. I use one to power my router/cable modem/linux box in my office.

https://www.corvetteforum.com/forums...s-machine.html
08-04-2019
daveosx

Quote:

With the perspective of time it would seem the EGR "silly test" is not the best method. Code 32 in stock vehicles was always frustrating. EG richens mixture. Why not blip valve and watch for O2 spike, not MAP? Or, EG slows combustion rate so perform EGR test subsequent to passing the knock sensor test by advancing spark with EGR open and watching for knock. Valves have capacity to circulate more EG than required yet no "EGR Learn" function included to account for plugging of passage over time or stock replacement aftermarket parts that don't create same restriction to flow so "silly test" fails.
Ugh!

I played with trying all sorts of diagnostics on the EGR when I first replaced the broken manifolds thinking that the EGR wasn't working it was but occasionally set code 32 anyway the silly part is that the parameters for the test are to satisfy the NOX emission belief and the whole EGR belief system. The concept of EGR makes sense if you want to lean out fuel mixture or you have a lot of concern about the theoretical source of smog. So I consider any device or method that can cause engine damage for the benefit of a theory "silly". Back in the day our Busch series 348 CI V6 was 14.1 to 1 and we leaned it out on some tracks to save fuel till the last few laps. We never used EGR and had no problems with the engines longevity.

Quote:

Hmm... I don't remember any tools for prom burning included with the T100. Between using that old 286 based tank at the dealership and then having my own personal machine, I'm pretty sure flash programming was possible from the Techline CD but the proms still needed to be purchased.

I worked for Corvette action center from 1987 to 1993 Authored many of the Tech bulletins. I was the South East DCS rep and did forensic and PRO modification. The prom burner was attached to a VESA card and had a box with a ZIF socket burner the T100 was used along with a HUB attached Dyno and a Gas analyser I would set up new proms on rolling chassis and PRO vehicles. The crossfire corvettes had a lot of factory released issues that I solved. The S10 rolling chassis, Corvette rolling Chassis, and the P60 motorhome chassis all required after third party build prom determination. Once a new prom was confirmed it was duplicated and available to the SPIF system through GM parts. I do not know how many of us had burners but we badged all of the custom tuned Corvettes with Red and Black valve cover badges if you look around you may find some of them.

Quote:

For entertainment value only: I'm still using the CAMS mechine in a matter of speaking. After playing around with trying to upgrade the hardware (can you remember thinking 18 minutes to boot was an acceptable time?) I finally stripped the machine and used the steel.

Shame I still get nostalgic.

Quote:

The 1" thick weights from the base of the cabinet are currently in the counterweight box for my bucket tractor.

This was a a great idea to put the weights in the bottom when the machines first started being used at the dealers guys would forget to disconnect the ALDL and flip them over when they moved the car.
The added weight helped to keep the unit upright long enough for the tech to realize and disconnect before it flipped.

Quote:

The "power strip" was a cool part that switched all outlets on when current flow was detected at the primary outlet. I use one to power my router/cable modem/linux box in my office.

Yep it was kind of a fad back in the eighties that everyone had Managed PDU even for home computers. I think mine had a EATON one may still be available.
https://www.eaton.com/us/en-us/catal...du.models.html

The old T100 had many models depending on the dealer standing.
Lou Backrodt in Pompano for instance had one with just the bulletins and code reader.
Steve Moore in Green Acres had one with the breakout box code reader and flight recorder.
Roger Dean was a Corvette specialty dealer and theirs had the prom burner dyno and gas analyser add ons.

The Mosler Intruder was one of the cars I burned proms for in 1991 the drive train was scavenged from a Corvette Rolling Chassis so the dash and engine and VIN# were GM to finish the build we tuned one car and Lingfelter Racing tuned the rest.

https://www.gtplanet.net/forum/threa...s-1994.349102/

Calloway, Lingfelter, Gulstrand, Penske, and others had a good two way street with DCS and Corvette Action center prior to 1996. GM liked the idea of outside and racing engineering being brought in house to improve the products. Another example of this was Jim Costa's ZR-1 corvette He paid for someone to design and fabricate Headers for the ZR-1 I installed them and retuned the car although it had a 66ECU. These Headers were carried by all the dealers through GMPP and PRO along with the modified tune. We also removed the static chain followers and reinstalled the Lotus hydraulic followers to allow Syncopated cam timing. Another Mod done on Jim's car was the manually operated Secondary throttle valve all tuned at Roger Dean.
There was a native American guy I forget his name who I worked with Dick Gulstrand on making a Factory authorized Lowering kit for his ZR-1 that is still available through GMPP.
Rick Mears had his ZR-1 tuned but I forget what we did to it.
I remember a racing team that I supported that Calloway was involved with we would get their test bed in for a tune from time to time.

There was also a Lumina V6 with Factory Turbo that we did a lot of post factory tuning on.

I am old now so memory is wanky.
But my original "silly" statement is drawn from an experience at the time that the change at GM was made.
Prior to 1996 the electronics in cars were conceived to be somewhat failsafe.
The loss of any emission control system would still allow the vehicle to be operated until repair could be made.
The change came with OBDII that sensor failure should prevent operation and would allow damage to the car.
The entire emission control argument is in my view wrong.
I was driving when 104 octane Sunoco 360 was available at the pump.
Any car running it would never ping so why EGR and Hardened Valve Seats and lower compression?
To use inferior fuel.
So at a NASCAR event stadium stands full of people how many people are harmed buy the smog generated during the race ? 0
Where there is a problem is when people choose to run crap fuel in false economy assumptions with anemic cars that sit in traffic jams idling the majority of time.
Why the hell are these people mandating the laws that are forced upon all others?
Sillyness.
08-04-2019
daveosx

Back to my original question
I know that O2 varies during the test but the change threshold for the EGR test is the manifold Vacuum.
The question still is does anyone know the threshold values that the test is looking for the change in?
If someone has a working EGR system and a TBI, a flight record would show the change on MAP during the test and I could figure out the expected value.
There should be two values the lower limit and the upper limit could be in the look up table or could be in the test routine itself.
The code32 test watches MAP voltage as it opens and closes EGR valve this checks the operation and the flow function of the valve and passages.
It is very quick probably less than 70ms when it tests. Typical O2 delay can be as long as 90ms so not really a good check on the OLD ECU newer hardware can be using O2 voltage for a similar test IDK.
So the quest stands anyone know the expected MAP change ?

Referring back to my notes from 87 there are a couple of ways that Code32 is set.
1. Immediate all conditions is voltage at the ECM pin of the Solenoid is below 8.7V when EGR inactive.
2. Immediate all conditions is voltage at the ECM pin of the Solenoid does not go to 0 when active.
3. Warmed Up > 50MPH RPM > 1200 no Knock signal Map change when active.
4. Warmed Up > 50MPH RPM > 1200 no Knock signal Active Map Change when inactive for period.<<< this is the EGR restriction test I am looking for the threshold of.

Even guys still using EGR will fail this test if the MAP does not change because of LOW back pressure or even scavenging vacuum if using tuned exhaust.
The positive negative aspects of EGR valves are because of the possibility of sucking intake air fuel backwards down the EGR port to the exhaust on WOT
A perfectly tuned exhaust does have the potential to generate a lower pressure pulse than the intake this is called scavenging.
Flat Plane Crank SBCs do this regularly and there are some exotic exhaust systems that time pulses to create scavenge pressure at the exhaust valves in the power band.
Ed Iskenderian, Cord and a couple of early Indy racers made use of this effect.
BTW EGR on a Turbo motor is a good way to turn your engine into a thermo jet.
08-04-2019
daveosx

1 Attachment(s)

So my thought process shifted a bit
If I cannot find the voltage shift online I can always test for it In VIVO
I will change this circuit as I think about it more and post it here.
If I can not find those threshold values I will build the circuit and test try it in the truck after I complete the build.
Later I will post the fritzing file so anyone can make one.

Attached is a rough Schematic
The LM358 Op Amp stage 1 Configured Unity Gain for isolation
Stage 2 configured with a variable gain
The POT R2 lowers the gain when ECU solenoid signal brought to ground R8 sets the Low gain R8 and R2 sets High Gain
The Mosfet Q2 provides isolation from 12v and shorts across R2 when Solenoid active lowering Map voltage.
Attachment 14450
08-04-2019
daveosx

Quote:

Originally Posted by dave w

Post #9 in this thread http://www.gearhead-efi.com/Fuel-Inj...Information-0D has the $OD HAC.zip file. I'm not sure the HAC has the EGR information you need, but likely it does.

dave w

Thanks again Dave W
I am looking through the hack src
I see the EGR position info I was wondering if this bin is from a much later ODBII vehicle with the EGR sensor on the vacuum diaphragm ?
I don't recall when they started with that type of valve I know my 2002 Cadillac and My 98 Ws6 have the sensor the 95truck does not.
looking at the routines the code 32 tests are centered around the EGR pintle position I think that this code is much newer or from vehicle with pintle position sensors.
08-05-2019
daveosx

So I tried to register on the Corvette forum so I could add info to your post about the T100

The captcha did not show up so I could not register,
I'll post here you can copy over if you like.

There are several models of the T100 depending on Dealer class.
Corvette specialty dealers had the most equipment
Fleet dealers had additional components but not all
Regional third party support dealers had everything to tune a vehicle.

Some T100 had the gas spectrometer and a rear wheel hub dyno.
Some had a metal keyboard no touch screen
Some had an incar button board like a remote
Most had breakout boards
Some had an incar recorder that could play back a test drive

If I remember correctly you had to have a tech line account to login to the terminal.
Often dealer service managers would set tech terminals to login under their account.
I know I would do my weekly reports and my campaign solutions and tech bulletin submittals from the terminal.
For the ZR-1 and GM66ECU courses I would login and use remote learning through the terminal.
The terminal itself had very little storage most of the tech bulletins where on the dial up server.
I remember being pissed of in 86 because Florida had a fire that cut our phone lines and I was unable to work for 3 weeks because the thing would not boot without the phone home.
This is probably what prevented yours from starting up.
AT one dealer the phone lines were so bad that I rigged a POTS Station box to my Nokia 9100 so I could use the terminal.

I distinctly remember bitching because every time I came to Roger Dean I had to recal the gas analyzer wasting 1.5 hours of non billable time.
Techs at the dealer would run cars for weeks without recalibrating the unit.
Customers would fail emissions tests and I would get called to lemon law the cars only to find that they hadn't calibrated before tuning.

Roger Dean had a complete setup with the master programmer the chip blanks where socketed to the Blue carriers and the PROM burner was a small 4x6x3/4 inch metal slab box with a green ZIF socket on top.
The blanks billed warranty at 90 USD and i bought quite a few while working. I remember there being two parts to the Blue carriers one section was the Prom the other I think was called a memcal.
What sucked really hard was the proms where burn once and not erasable.
Once a new prom was created the BIN was uploaded to TechLine if approved for bulletin it was available pretty quick through the dealer SPIF or GM Parts.

One that I did was the 84 85 caprice with the New HyperUtetic Pistons in florida after 20K miles or so the pistons would clatter in the bore sounding like a ping but lower in the engine.
I remember swapping in an older part number as an attempt at fixing the problem. The ultimate solve was just riching the mixture as the engine got warm.

I spent 26 weeks of every year for 6 years in front of these terminals 26 weeks at tracks sleeping on nitrogen tanks and eating crappy food.
I was never a racing fan it was just as far up the ladder as a automotive engineer that anyone could go.
The fame and fortune of being a Nascar crew chief, Indy cart crew, NHRA Top Fuel Crew and GTP race Crew was not that great 500K in tools and three degrees to make 160K and sleep on tanks kinda sucked.
I retired from GM in 1993 with 22 years of union Gain time got the gold watch and all the arm badges.

I do get nostalgic about some of the stuff anyway.

Today I look at the tech laden cars and think blue tooth adapters.

All of my cars still have a throttle cable and E Brake all the rest is wonky.
08-05-2019
1project2many

Quote:

So I tried to register on the Corvette forum so I could add info to your post about the T100

Thank you, but that was not my post. It contained pictures and some information for anyone who was curious.

Quote:

This is probably what prevented yours from starting up.

My home unit started and operated. Without the phone I could not access electronic calibration information, i.e. flash calibrations, and I could only run the Techline CD's, but the machine was quite useful for a few years.

Quote:

Often dealer service managers would set tech terminals to login under their account.

Small dealerships often had one account. If you had a dealership # chances are you could log in. GM's security model was based on trust.

Quote:

Roger Dean had a complete setup with the master programmer the chip blanks where socketed to the Blue carriers and the PROM burner was a small 4x6x3/4 inch metal slab box with a green ZIF socket on top.
The blanks billed warranty at 90 USD and i bought quite a few while working. I remember there being two parts to the Blue carriers one section was the Prom the other I think was called a memcal.
What sucked really hard was the proms where burn once and not erasable.
Once a new prom was created the BIN was uploaded to TechLine if approved for bulletin it was available pretty quick through the dealer SPIF or GM Parts.

Very cool. I have never heard this before. It could explain some of the proms that I have with one-off calibrations in factory-style memcals in cars that were not substntially modified.

Quote:

I was never a racing fan it was just as far up the ladder as a automotive engineer that anyone could go.
The fame and fortune of being a Nascar crew chief, Indy cart crew, NHRA Top Fuel Crew and GTP race Crew was not that great 500K in tools and three degrees to make 160K and sleep on tanks kinda sucked.

NASCAR racing thrives while the people that make it happen rarely do as well. It was very frustrating for me to watch guys get injured then forgotten by the same sport that called them heroes when the $$ was good. I loved working on cars and spending time at the track but I was not interested in helping make small fortunes out of large ones.
08-08-2019
1project2many

Quote:

The question still is does anyone know the threshold values that the test is looking for the change in?
If someone has a working EGR system and a TBI, a flight record would show the change on MAP during the test and I could figure out the expected value.

I have looked through the '95 truck pcm calibration for the EGR related error conditions. The '87 C3's used MAP change for EGR detection but the later P4's appear to use different test criteria. Since the type of EGR is configurable (electronic or vacuum) the tables and tests that run are dependent on the configuration but one test definitely includes checking integrator values to determine whether or not ECM is making corrections while EGR is commanded open. MY 94 and 95 trucks with manual transmissions were equipped with C3 ECM's so it's possible to find MAP values from those cals but they won't help if you're using a P4.

Quote:

I see the EGR position info I was wondering if this bin is from a much later ODBII vehicle with the EGR sensor on the vacuum diaphragm ?
I don't recall when they started with that type of valve I know my 2002 Cadillac and My 98 Ws6 have the sensor the 95truck does not.
looking at the routines the code 32 tests are centered around the EGR pintle position I think that this code is much newer or from vehicle with pintle position sensors.

V8 TBI Trucks came with a vacuum EGR. IIRC the S10 with 2.2 which used the same codebase used digital EGR. The code was written so it could accomodate either type.

Quote:

The Mosler Intruder was one of the cars I burned proms for in 1991 the drive train was scavenged from a Corvette Rolling Chassis so the dash and engine and VIN# were GM to finish the build we tuned one car and Lingfelter Racing tuned the rest.

https://www.gtplanet.net/forum/threa...s-1994.349102/

Calloway, Lingfelter, Gulstrand, Penske, and others had a good two way street with DCS and Corvette Action center prior to 1996. GM liked the idea of outside and racing engineering being brought in house to improve the products. Another example of this was Jim Costa's ZR-1 corvette He paid for someone to design and fabricate Headers for the ZR-1 I installed them and retuned the car although it had a 66ECU. These Headers were carried by all the dealers through GMPP and PRO along with the modified tune. We also removed the static chain followers and reinstalled the Lotus hydraulic followers to allow Syncopated cam timing. Another Mod done on Jim's car was the manually operated Secondary throttle valve all tuned at Roger Dean.
There was a native American guy I forget his name who I worked with Dick Gulstrand on making a Factory authorized Lowering kit for his ZR-1 that is still available through GMPP.
Rick Mears had his ZR-1 tuned but I forget what we did to it.
I remember a racing team that I supported that Calloway was involved with we would get their test bed in for a tune from time to time.

There was also a Lumina V6 with Factory Turbo that we did a lot of post factory tuning on.

When I first started trying to learn about tuning I would "read" a cal to try and teach myself how the "big guys" were solving problems. I could sometimes pick out similar approaches to calibrating across different cals, and in some cases I would group cals as being done by the same engineer/lab/division based on particular tweaks. Whenever a cal from one of the unique vehicles you mentioned came my way I would read that as well and at first I was very surprised that there wasn't anything amazing in them. But over time I realized that it was just as you said... someone had to get a calibration built that made the car work well in a minimum amount of time. So that explained why I would see general changes vs many specific tweaks, codes turned off instead of test parameters changed, and an overall "get er done" approach. It was a good learning experience for me as it helped me decide when to stop making changes.
09-05-2019
daveosx

1 Attachment(s)

SOLVED

So this is the circuit I created
I works great I added the knock sensor to this before I built the EST in my other post today.
My headers and valve train are triggering the Knock retard at idle with the knock signal attenuated it stops but the idle timing is MAP triggered so it is crazy not related to this circuit solved with the EST module in other post.
The circuit watches for the EGR valve signal and changes the gain on the MAP and O2 about 6% while providing the expected resistance and current of the solenoid.
Attachment 14571