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From a 81 ecm to a (non corvette) 88 ecm.

Peer81

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Joined
May 21, 2003
Messages
2,497
Location
Netherlands
Corvette
'81 Black
Hello everybody,

A new thread about something I'm trying to do. I don't say it will work but it is also fun figuring things out.

What is the case. I have a all original L81 computer system with the original E4ME Qjet carb. I don't want to change to a easier carb but I want to change the old ecm for a better (later) one. Other cars featured the E4ME carb more years then the vette so I found out the last car with a E4ME carb was a 88 Monte Carlo (SS).

So I bought a 1228079 ecm (from a 88 Monte Carlo) which also can be found in 87 camaro's and caprices (with the E4ME carb engines). I also have the bin files for the ZZ4 upgrade that ones could be bought for the camaros. This ZZ4 bin file can be burned on a prom that works perfect in the 1228079 ecm.
Some complications... The new ecm has some extra functions (it controls the 700R4 I have so that is great) but it also need a electronic spark control with knock sensor and some other stuff.
Right now I'm comparing the ecm terminal in and outputs to see what the difference is between the 81 and 88 wiring harness. Some wires changes place and others went and new ones came in. I also have the full 88 ecm wiring diagram and the 81 ecm wiring diagram to compare them. Next time I'll show some pictures what I found.

But first a simple question to start with..
After digging into the shop manual many times I found the 88 has a baro sensor but I can't find it in our 81 wiring diagram. Does anybody know if an 81 has one? In the 81 shop manual code 32 is a "baro sensor circuit low" but I can't find it..
On page 6E1-44 all sensors can be found. I see the vacuum sensor (against the firewall) but no baro sensor. If somebody knows please let me know :)

Groeten Peter
 
Joined
Apr 29, 2001
Messages
2,141
Location
Rio Rancho, NM
Corvette
1981 HD Suspension; ZN1 Option
Hello everybody,

A new thread about something I'm trying to do. I don't say it will work but it is also fun figuring things out.

What is the case. I have a all original L81 computer system with the original E4ME Qjet carb. I don't want to change to a easier carb but I want to change the old ecm for a better (later) one. Other cars featured the E4ME carb more years then the vette so I found out the last car with a E4ME carb was a 88 Monte Carlo (SS).

So I bought a 1228079 ecm (from a 88 Monte Carlo) which also can be found in 87 camaro's and caprices (with the E4ME carb engines). I also have the bin files for the ZZ4 upgrade that ones could be bought for the camaros. This ZZ4 bin file can be burned on a prom that works perfect in the 1228079 ecm.
Some complications... The new ecm has some extra functions (it controls the 700R4 I have so that is great) but it also need a electronic spark control with knock sensor and some other stuff.
Right now I'm comparing the ecm terminal in and outputs to see what the difference is between the 81 and 88 wiring harness. Some wires changes place and others went and new ones came in. I also have the full 88 ecm wiring diagram and the 81 ecm wiring diagram to compare them. Next time I'll show some pictures what I found.

But first a simple question to start with..
After digging into the shop manual many times I found the 88 has a baro sensor but I can't find it in our 81 wiring diagram. Does anybody know if an 81 has one? In the 81 shop manual code 32 is a "baro sensor circuit low" but I can't find it..
On page 6E1-44 all sensors can be found. I see the vacuum sensor (against the firewall) but no baro sensor. If somebody knows please let me know :)

Groeten Peter

Peter,

Interesting work and project. I also made a preliminary search, but I could not find where exactly the barometric pressure is sensed. On page 6E1-35, The "Electronic Spark Sensor [EST]" General information says that the EST controller receives engine manifold pressure signal, barometric pressure, and engine RPM. So I am suspecting that it is also taken at the vacuum sensor, for if it was not there, and no other baro sensor is provided, then the computer would not have another reference signal to which compare the manifold vacuum signal. Maybe? ;shrug :confused
 

Peer81

Well-known member
Joined
May 21, 2003
Messages
2,497
Location
Netherlands
Corvette
'81 Black
Well, this is some what weird...

After looking at the page Gerry gave I looked at page 6E1-31. The Trouble code 32.. Halfway the page it says
ecm 7 or 22 - (baro sensor) A low (sensor ground)
ecm 1 - (baro sensor) B output
ecm 21 - (baro sensor) C volt. ref. (5 volt)

Not so strange but when you look at the wiring diagram, the baro sensor output on is ecm input number 1. But number 1 on the ecm wiring harnes is unused.. :ugh
Tomorrow more on this, I'm going to bed its 1am overhere.

Groeten Peter
 

Peer81

Well-known member
Joined
May 21, 2003
Messages
2,497
Location
Netherlands
Corvette
'81 Black
Well a new day so time for some pictures with an explanation. :)

I compared the 81 ecm terminal identification page to 88 terminal page.
Everything marked yellow didn't change.
Everything marked orange or red has changed.
The numbers (16), (17) in front are the new terminal numbers and the function (in black) behind a function (baro sens. etc) are the new functions.

81ECM2.jpg


As we can see, very much remains the same. Only a few functions switched places and moved a little. The new functions like the ESC and 4th gear lockup are put in not used terminal connections so that is easy. The question remains, terminal number 1 on a 81 should be (on this page) not used but other pages say it has the baro sensor output (like the 88 terminal). My vette is still at the painter right now (100 miles away) so I don't have the change to check this for a while.

Now we continue to the schematic wiring diagrams from the 81 and the 88.
Again in yellow is the same in both diagrams.
In orange is the same idea but connected in a different way.
In red are the new functions.

81WIRING2.jpg
88WIRING2.jpg

On the left the 81 wiring diagram and on the right the 88.

To begin with the 81 diagram.
There are a few bleed relais that the 81 has and the 88 doesn't (marked orange).
They doesn't seem to be a big problem, all the solenoids are connected in somewhat the same way to the ecm and the ecm doesn't have any extra connections for these bleed relais.
Weird thing to see is that the air switch solenoid and the air control solenoid switched places. Not a big problem but the ALDL terminal on the 88 connects to the air switch and on the 81 to the air control... Also some other functions on the ALDL terminal are connected to different sources.

The 88 diagram.
The biggest differences (red) are the 4th gear lockup, the esc with knock sensor. These are not a very big problem because they can simple be integrated into the system.
The 88 has a baro sensor and the 81 doesn't show it, and the 88 has a throttle solenoid which the 81 doesn't have (little ad-on on the carb).

Continue to orange..
In the diagram the O2 sensor is drawn in a different way (ground circuit) but it remains the same in reality. Because the bleed off relais aren't there any more the air control solenoid and air switch solenoid are alot easier.
I still need to look at the canister purge solenoid, don't know if an 81 has one.. The 88 has a lamp driver build into the system which controlles the SES light and the TCC solenoid looks somewhat different but shouldn't be a problem. On the ALDL terminal the ground wire switched a place.
The biggest thing in the changes is the VSS sensor. On a 81 the VSS sensor gets an 8volt feed from the ecm (has an extra 8v terminal) on the 88 that terminal is gone and the VSS works on 12 volts and is connected to a 12 v ignition source.

What I need to do know is find out what these changes mean and what this would mean for my 81. Is it easier to adapt the extra functions into my 81 wiringharness of put an 88 wiring harness into my vette and alter it so it would look original and the ecm would still be behind the driver seat and not under the dash (like an monte carlo etc).

Well, that's it for now. All ideas, options comments etc etc are welcome. I still need to find the right 88 wiringharness so time is on my side :)

Groeten Peter
 
Joined
Apr 29, 2001
Messages
2,141
Location
Rio Rancho, NM
Corvette
1981 HD Suspension; ZN1 Option
Peter,

Very intuitive. You're probably better-off figuring these out while your Vette is at the painter, for once you get it back, You'll want to drive it. :L

If I recall correctly, the throttle solenoid ( the idle solenoid?) is used by the computer to obtain the proper idle for the applicable conditions. The solenoid receives signals from the computer, and it moves to achieve the calculated idle setting. No idle adjustments can be made on these E4ME's that have this feature.

As far as the cannister purge....I believe that the current L81 configuration lets one of the TVS's at the thermostat intake housing purge the cannister when the water temperature rises between (approximately) 140 - 160 degrees F.

So it looks like the 88 system has a solenoid performing the same task. Good work!
 

KANE

Moderator
Joined
Mar 2, 2002
Messages
3,244
Location
KY
Corvette
Dark Blue 1982 Trans Am(s): Polo Green 1995 MN6
What is the case. I have a all original L81 computer system with the original E4ME Qjet carb. I don't want to change to a easier carb but I want to change the old ecm for a better (later) one. Other cars featured the E4ME carb more years then the vette so I found out the last car with a E4ME carb was a 88 Monte Carlo (SS).

So I bought a 1228079 ecm (from a 88 Monte Carlo) which also can be found in 87 camaro's and caprices (with the E4ME carb engines). I also have the bin files for the ZZ4 upgrade that ones could be bought for the camaros. This ZZ4 bin file can be burned on a prom that works perfect in the 1228079 ecm.
Some complications... The new ecm has some extra functions (it controls the 700R4 I have so that is great) but it also need a electronic spark control with knock sensor and some other stuff.
Right now I'm comparing the ecm terminal in and outputs to see what the difference is between the 81 and 88 wiring harness. Some wires changes place and others went and new ones came in. I also have the full 88 ecm wiring diagram and the 81 ecm wiring diagram to compare them. Next time I'll show some pictures what I found.

But first a simple question to start with..
After digging into the shop manual many times I found the 88 has a baro sensor but I can't find it in our 81 wiring diagram. Does anybody know if an 81 has one? In the 81 shop manual code 32 is a "baro sensor circuit low" but I can't find it..
On page 6E1-44 all sensors can be found. I see the vacuum sensor (against the firewall) but no baro sensor. If somebody knows please let me know :)

Groeten Peter

I think this is the ECM tied to a CCC carb that uses a MAP sensor. So, no- L81s don't use MAP sensors. Instead, they use a carb air fuel solenoid and a TPS.

You've picked a good ECM for modifying since you want to retain your CCC carb.

Maybe this will help-
http://www.autozone.com/az/cds/en_us/0900823d/80/11/cc/b2/0900823d8011ccb2/repairInfoPages.htm

This is a link that will take you Autozone's web page with GM mid-size harness diagrams. They are crude at best, but it is a start.

FYI- you'll need the harness connector in order to get the new ECM integrated. Not sure who sells the one required for that ECM though.
 

big2bird

Well-known member
Joined
Aug 26, 2007
Messages
178
Location
Anaheim,Ca.
Corvette
1981 Black Coupe
Well a new day so time for some pictures with an explanation. :)

I compared the 81 ecm terminal identification page to 88 terminal page.
Everything marked yellow didn't change.
Everything marked orange or red has changed.
The numbers (16), (17) in front are the new terminal numbers and the function (in black) behind a function (baro sens. etc) are the new functions.

81ECM2.jpg


As we can see, very much remains the same. Only a few functions switched places and moved a little. The new functions like the ESC and 4th gear lockup are put in not used terminal connections so that is easy. The question remains, terminal number 1 on a 81 should be (on this page) not used but other pages say it has the baro sensor output (like the 88 terminal). My vette is still at the painter right now (100 miles away) so I don't have the change to check this for a while.

Now we continue to the schematic wiring diagrams from the 81 and the 88.
Again in yellow is the same in both diagrams.
In orange is the same idea but connected in a different way.
In red are the new functions.

81WIRING2.jpg
88WIRING2.jpg

On the left the 81 wiring diagram and on the right the 88.

To begin with the 81 diagram.
There are a few bleed relais that the 81 has and the 88 doesn't (marked orange).
They doesn't seem to be a big problem, all the solenoids are connected in somewhat the same way to the ecm and the ecm doesn't have any extra connections for these bleed relais.
Weird thing to see is that the air switch solenoid and the air control solenoid switched places. Not a big problem but the ALDL terminal on the 88 connects to the air switch and on the 81 to the air control... Also some other functions on the ALDL terminal are connected to different sources.

The 88 diagram.
The biggest differences (red) are the 4th gear lockup, the esc with knock sensor. These are not a very big problem because they can simple be integrated into the system.
The 88 has a baro sensor and the 81 doesn't show it, and the 88 has a throttle solenoid which the 81 doesn't have (little ad-on on the carb).

Continue to orange..
In the diagram the O2 sensor is drawn in a different way (ground circuit) but it remains the same in reality. Because the bleed off relais aren't there any more the air control solenoid and air switch solenoid are alot easier.
I still need to look at the canister purge solenoid, don't know if an 81 has one.. The 88 has a lamp driver build into the system which controlles the SES light and the TCC solenoid looks somewhat different but shouldn't be a problem. On the ALDL terminal the ground wire switched a place.
The biggest thing in the changes is the VSS sensor. On a 81 the VSS sensor gets an 8volt feed from the ecm (has an extra 8v terminal) on the 88 that terminal is gone and the VSS works on 12 volts and is connected to a 12 v ignition source.

What I need to do know is find out what these changes mean and what this would mean for my 81. Is it easier to adapt the extra functions into my 81 wiringharness of put an 88 wiring harness into my vette and alter it so it would look original and the ecm would still be behind the driver seat and not under the dash (like an monte carlo etc).

Well, that's it for now. All ideas, options comments etc etc are welcome. I still need to find the right 88 wiringharness so time is on my side :)

Groeten Peter
An ambitious project. Would like an update. Although, I do not understand the why at all.
 

Peer81

Well-known member
Joined
May 21, 2003
Messages
2,497
Location
Netherlands
Corvette
'81 Black
Not much of an update right now. I already have two 88 ecm's at home but the vette is waiting for a new paint job and my money went into 4 weeks China :D So this project will take longer then i thought. :)

The why is a good one. Trying to optimize the E4ME carb with the newest ecm it can handle. And for the major part, just for fun and to see if it's possible :)

Groeten Peter
 

SIXFOOTER

Well-known member
Joined
Jul 15, 2007
Messages
117
Location
Boca Raton Fl
Corvette
1981 L81 Tan Coupe
Keep posting your progress. I ain't likely to do this change but it is interesting.
Ever thought of going to a Megasquirt type ecm?
 
Joined
Apr 29, 2001
Messages
2,141
Location
Rio Rancho, NM
Corvette
1981 HD Suspension; ZN1 Option
... my money went into 4 weeks China :D So this project will take longer then i thought. :)
Groeten Peter

Welcome back, Peter! I guess that if you're going that far, you might as well stay 4 weeks. ;)
 

Peer81

Well-known member
Joined
May 21, 2003
Messages
2,497
Location
Netherlands
Corvette
'81 Black
It has been a while but I'm going to continue with this project (but on a slow pace, as everything I do...)

First things I came across when looking again at the 81 and 88 diagrams (and ecm connectors) are the following.

As said, I looked everywhere but our '81s don't have a Baro sensor! So no wire at terminal 1 at the ECM.
Terminals 8 to 11 have a typo. Terminal 8 is not used and Oxygen Sensor-Hi is #9 etc etc and Ign. Module By-pass at #11. (so each function one step lower then shown)
Terminal 16 shows unused that is wrong, its the VSS input!
Terminal E shows a Canister Purge solenoid sorry we don't have that either.

But now the mystery. Terminal M has unused BUT it has a thick white wire in it (thickest wire at that connector). I have no idea where it's for and no idea where it goes to.
The ECM wiring diagram on page 8C-41 10 of 11 it shows Idle speed mtr lo output but that doesn't make sensor? Somebody?

Also the connector functions on this page are all correct!

Greetings Peter
 

Peer81

Well-known member
Joined
May 21, 2003
Messages
2,497
Location
Netherlands
Corvette
'81 Black
I looked at the wiring again (this time at the '88 wiringdiagram) to see what I have to change. But it isn't as much as I thought it would be.

Yellow remains the same.
Oranges wiring is the same but moved to a different ECM terminal
Red isn't present in a '81 vette
Grey are the parts that are blocked on my vette but are just there for show.

88ECM2.jpg


88WIRING3.jpg


I want to use the ZZ4 prom as a base setting and go from there. I already have the .bin file both with and without ESC. As I currently don't have ESC I'll go with the "without ESC" prom.

On the biggest connector I need to change the EGR wire from terminal T to #19 (it's disabled in the prom so no real need for it)
On #1 I need to find an Baro sensor as my ECM is only using an vacuum sensor right now (not to difficult I think)
As my AIR system is still in place but I don't needed it I don't really need terminal #4 and B but as they are in the right place already I'll just leave them there. Is this ECM going to throw a code if the AIR system isn't working (but still connected)?

Then the small connector.
Terminal E, my engine now has a idle control solenoid only to compensate for the airco kickin in (not ecm controlled). Would it be a problem if I leave terminal E unused?
Terminal L as I'm using the non ESC prom no need to connect it. So that problem is solved!
Terminal M has some black ?? in front of it as my current wiring harness has a white wire in there that isn't in the diagrams (already solved!)
Terminal N is high gear input I need to move that from terminal 17 in my harness.
And the last Terminal T, the canister purge solenoid. I also have the canister in my car but isn't ecm controlled. Would this give a code or ses if it wasn't hooked up?

The wiring diagram.
I need to hook up the Baro sensor, as the vacuumsensor is close by not a big problem.
My current VSS gets 8v from the ECM and I need to change that to 12v from ignition also no problem.
Throttle solenoid?
Canister purge solenoid?
I also have the SES light but not the lamp driver module. On my '81 the SES light ground is directly controlled by the ECM. Do I really need the lamp driver module to get it to work? As I see it in the wiring diagram there is an extra 12v source going in. One exits to the ECM ground the second one is a dead end at the ALDL terminal D and the third exits also to ALDL terminal A (ground)

I also checked the ECM trouble codes and could only find a code for the Canister purge solenoid. So I have to switch if off in the Prom or find another way to fool the ECM.
I also read that I can fool the ECM by placing an resistor in the connector to simulate the solenoid but I have to find the right ohm and watt's for the cannister resistor. Keep you updated! :)

Greetings Peter
 

KANE

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Mar 2, 2002
Messages
3,244
Location
KY
Corvette
Dark Blue 1982 Trans Am(s): Polo Green 1995 MN6
Peter... I think it is safe to say that you are entering a place where few Vette owners dare to tread: massive PCM configuration & customization. :chuckle :thumb :D



Back to what you are doing- HOW COOL!!! Wish I could be more helpful, but I think you are really deep into what you need to do and have it well under control. I've worked a lot more with TPI/EFI... so, aside from re-pinning and some basics... I'm not sure how best to offer help to you.

Closed loop vs open loop: unless you have the emissions stuff removed from the PROM, chances are the ECM will look for EGR and canister functionality when it enters closed loop.

Baro sensor: The MAP... yeah, I think your ECM will look for this one too. That also informs a speed/density system on how to trim the fuel and what the demand is relative to the air around it (in addition to the TPS). It's likely a three wire deal... not sure off the top of my head if the '81 uses the three wire MAP sensor.


Hope that helps!:thumb
 

Peer81

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Joined
May 21, 2003
Messages
2,497
Location
Netherlands
Corvette
'81 Black
Thanks Kane! :)

I'm not looking for somebody who did this before but for people who look at this from another direction. Maybe they see problems that I've overlooked. But so far so good!

I found somebody on the thirdgen forum that is going to burn the ZZ4 prom for me. He is also going to delete all the stuff that I'm not using (if that is possible).
I know I need the MAP sensor but I'm in doubt if I need the driver lamp module. As I see it in only controlled if the SES light is working and if there is power going to the SES light. At this moment my SES light is working well without it so I'll first try without it :)

Greetings Peter
 

Kevo

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Joined
Sep 10, 2013
Messages
46
Location
Hampton Va
Corvette
1993 torch red stripped automatic coupe
81 had Baro sensor it went away in 83 I think. Baro reading is from MAP or Vacuum sensor at key on engine off prior to starting. MAP and VAC sensors are different in the voltage reading they send so you what to be sure you have the correct type.

White wire problaly added by tech for some reason because it is so much bigger than other wires. Auto shops don't normally stock small wire spools.

Not sure where you are with your quest, normally easier to transfer complete 88 harness and related solenoids and switches to update engine emission to 88 vs trying to blend the two together.
 

Peer81

Well-known member
Joined
May 21, 2003
Messages
2,497
Location
Netherlands
Corvette
'81 Black
Hello Kevo,

Thanks for the information! As the vacuum and Baro sensor look exactly the same it is good to know they differ in output voltage range. I'm going to order one at rockauto this week.

As for the white wire, my friends 81 has the exact same wire at the same terminal so it is added before it left the factory.

I have a ebay search for a camaro -tpi wiring harness up for 5 years now but no real luck in finding a good one. Besides that our vettes have the ecm behind the seat as later cars have it under the dash. So then i need to relocate the ecm (if possible) or need to extend all the wires. As the changes in the wiring harness aren't that big I'm going to take my chances with the OEM wiring harness. :)

Greetings Peter
 

KANE

Moderator
Joined
Mar 2, 2002
Messages
3,244
Location
KY
Corvette
Dark Blue 1982 Trans Am(s): Polo Green 1995 MN6
Hello Kevo,

Thanks for the information! As the vacuum and Baro sensor look exactly the same it is good to know they differ in output voltage range. I'm going to order one at rockauto this week.

As for the white wire, my friends 81 has the exact same wire at the same terminal so it is added before it left the factory.

I have a ebay search for a camaro -tpi wiring harness up for 5 years now but no real luck in finding a good one. Besides that our vettes have the ecm behind the seat as later cars have it under the dash. So then i need to relocate the ecm (if possible) or need to extend all the wires. As the changes in the wiring harness aren't that big I'm going to take my chances with the OEM wiring harness. :)

Greetings Peter

Peter- have you looked into a Painless Wiring harness? If you haven't had luck with Ebay... I can tell you from personal experience that Painless is pretty good.
 

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