C3 Tech/Performance V8 Technical Info, Internal Engine, External Engine, Basic Tech and Maintenance for the C3 Corvette

1981 ECM/PROM Questions

 
Old 06-24-2018, 01:09 PM
  #41  
Antz81
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Originally Posted by Hamerdown View Post
*why run engine > > > I was under the impression once the battery is disconnected the computer resets and cods are gone (not true?) I've had the battery disconnected for several days and just though I'd start start 'fresh' with running the engine and jumping of the ALDL with a paper clip.
Yes all stored codes will be gone, but code 12 will still show.
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Old 06-26-2018, 08:40 PM
  #42  
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UPDATE...
first thing, I must thank everyone for their time, informative comments, suggestions etc...and I really mean that.
Many of you can eat a problem as I had/have for a snack, I'm envious!
Well, I can't say I found and fixed the problem because I did not. HOWEVER, I did remove the Computer and kicked the focker around my garage then reinstalled it along with the battery and the next day I started the Engine and it ran like there was never a problem > > > > > > WTF?

I did finally borrow the Snap~On brick Scanner and a SPECIAL thank you to AV81 as via phone (real time) step-by-step he walked me through the procedure from plugging it in, what to enter, what to look for, Key~0n, Start~engine, relaying to him what I was reading and if I could remember this correctly...EVERYTHING that Scanner could check was more/less in the middle of the parameters. (AV81 jump in anytime you want)

BTW, back in 2013 when I rebuilt (myself) the TH350c, the Diff, Trailing Arms, replaced the multi-leaf steel spring with camber bushings, and rebuilt rear spindles, bearing bla-bla-bla, all new rear hard brake lines, Y-Pipe, installed new Engine Mounts, new Water Pump, replaced AC components, replacement radiator (it's now leaking) and on and on...I removed the Air Pump, plugged the Heat Risers, removed the Catalytic Converter and the Engine ran good (until this mess happened) and never tossed a CEL.

So, I don't get it, the MCS still is not chattering (hasn't for years-but I recall it did)
Could a wire rubbed something and went to ground making the Engine act-up and I inadvertently move it?
Maybe the contacts at the two large plugs entering the ECM just needed to be removed-reinstalled and have better contact?
Could a solder joint in the ECM be bad, should I take a chance on a Cardone refurbished?
Do I just say 'F-it' and have a cold beer?
Thanks again, Ray

Last edited by Hamerdown; 06-26-2018 at 08:46 PM.
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Old 06-27-2018, 06:02 AM
  #43  
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Originally Posted by Hamerdown View Post
UPDATE...
first thing, I must thank everyone for their time, informative comments, suggestions etc...and I really mean that.
Many of you can eat a problem as I had/have for a snack, I'm envious!
Well, I can't say I found and fixed the problem because I did not. HOWEVER, I did remove the Computer and kicked the focker around my garage then reinstalled it along with the battery and the next day I started the Engine and it ran like there was never a problem > > > > > > WTF?

I did finally borrow the Snap~On brick Scanner and a SPECIAL thank you to AV81 as via phone (real time) step-by-step he walked me through the procedure from plugging it in, what to enter, what to look for, Key~0n, Start~engine, relaying to him what I was reading and if I could remember this correctly...EVERYTHING that Scanner could check was more/less in the middle of the parameters. (AV81 jump in anytime you want)

BTW, back in 2013 when I rebuilt (myself) the TH350c, the Diff, Trailing Arms, replaced the multi-leaf steel spring with camber bushings, and rebuilt rear spindles, bearing bla-bla-bla, all new rear hard brake lines, Y-Pipe, installed new Engine Mounts, new Water Pump, replaced AC components, replacement radiator (it's now leaking) and on and on...I removed the Air Pump, plugged the Heat Risers, removed the Catalytic Converter and the Engine ran good (until this mess happened) and never tossed a CEL.

So, I don't get it, the MCS still is not chattering (hasn't for years-but I recall it did)
Could a wire rubbed something and went to ground making the Engine act-up and I inadvertently move it?
Maybe the contacts at the two large plugs entering the ECM just needed to be removed-reinstalled and have better contact?
Could a solder joint in the ECM be bad, should I take a chance on a Cardone refurbished?
Do I just say 'F-it' and have a cold beer?
Thanks again, Ray
Kind of good news that it seems to be going properly again, but bad since you don't know why it came right. Have you checked to see if you get code 12 now?
Removing the smog stuff like you have wouldn't have had any effect on it as none of it is monitored by the ECU.
Most of the time i don't notice my MCS chattering unless i'm standing right over it. (I just assume its working)
Yes it could be a wire that has rubbed through, or a wire with a break internally that connects again if in the right position.
Could have been a bad contact on the plugs to the ECU.
Could be a bad solder joint.
Hard to say what could have been causing it. There will be other possibilities as well.
May as well have a beer for now. Unless you've solved the problem it will probably come back soon anyway.
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Hamerdown (06-27-2018)
Old 06-27-2018, 09:00 AM
  #44  
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I agree with the reply in POST #43.

I also do not hear the M/C solenoid making any noise when the engine is running. I only hear it clicking when I access the codes.

I am also glad you have it fixed and this has also happened to me on MANY occasions. I remove connectors and inspect them all and when I start it again it runs perfectly.

DUB
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Hamerdown (06-27-2018)
Old 06-27-2018, 11:32 AM
  #45  
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Originally Posted by Antz81 View Post
Kind of good news that it seems to be going properly again, but bad since you don't know why it came right. Have you checked to see if you get code 12 now?
Removing the smog stuff like you have wouldn't have had any effect on it as none of it is monitored by the ECU.
Most of the time i don't notice my MCS chattering unless i'm standing right over it. (I just assume its working)
Yes it could be a wire that has rubbed through, or a wire with a break internally that connects again if in the right position.
Could have been a bad contact on the plugs to the ECU.
Could be a bad solder joint.
Hard to say what could have been causing it. There will be other possibilities as well.
May as well have a beer for now. Unless you've solved the problem it will probably come back soon anyway.
Let me ask you this...(and I have not rechecked)...'if' the CEL does not flash '12' would the ECU and the Snap-on brick scanner be able to communicate with each other?
While the Scanner does give valuable feedback/values etc I had hoped that 'maybe' it also was able to diagnose the ECU for being faulty, but it doesn't. But being the scanner did 'work' that's telling me the ALDL terminals were good, I think.
BTW...I never knew the ECU & Vehicle Anti Theft Alarm share the same 10amp fuse at the fusebox. And I could slap the jackass that decided to mount the fuses panel where it is...either he was 2' tall or, had a Slinky for his neck and arms.

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Old 06-27-2018, 01:42 PM
  #46  
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'Generally'...when a scanner can communicate with the the ECM...it is fine...in regards to being able to communicate. In some scanners...which I doubt the Snap-On one can do for this or the ECM was not set -up for this 'diagnostic test'...which allows the person controlling the scanner to press a button and verify that the CEL flashes a CODE 12. I know my Tech 1 and Tech 2 can do this diagnostic test when requested to do so.

And IF you manually checked to see if you got a code 12...that would confirm that either by you kicking the ECM across the floor or moving some connections around...you 'repaired' the problem..

DUB
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Old 06-27-2018, 04:55 PM
  #47  
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Originally Posted by DUB View Post
'Generally'...when a scanner can communicate with the the ECM...it is fine...in regards to being able to communicate. In some scanners...which I doubt the Snap-On one can do for this or the ECM was not set -up for this 'diagnostic test'...which allows the person controlling the scanner to press a button and verify that the CEL flashes a CODE 12. I know my Tech 1 and Tech 2 can do this diagnostic test when requested to do so.

And IF you manually checked to see if you got a code 12...that would confirm that either by you kicking the ECM across the floor or moving some connections around...you 'repaired' the problem..

DUB
I definitely agree by just being able to read data and codes with a scanner that means the ecm is working , there are diagnostic tests he can do with the scanner I just walked him through reading the codes and data on the sensors I just don't remember off the top of my head to walk him through every test , I should have had my scanner on my vette so I could have him go through everything that I would normally look at but I did not have it ready . From the data parameters he read to me I did not see any issues related to the sensors or ecm , I believe he had a bad connection surface at the ecm that by unplugging it and plugging it back in it got a better connection or a cracked solder joint that the angle of the connector pulled it in.
either way the motor is running fine now so let's see what happens and if it starts to run rough let's not assume it's computer related he can plug in check for codes if none check basics , as far as the clicking Ray does not hear anymore I think he was hearing the air pump solenoid clicking that he removed awhile back.
Ray is a great guy BTW
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Old 06-27-2018, 05:07 PM
  #48  
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Unhooking the scanner probably scared it into thinking he was gonna go to the river and do the float-test thing. So it decided behaving was in it's best interest.
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Old 06-27-2018, 09:37 PM
  #49  
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Again, thanks for the comments and feedback, very much appreciated.
The fella that let me borrow this Snap~On Scanner told me to "keep it as long as u need it"...he hasn't used it in 20 years.
So, if anyone cares to dig deeper into what the Scanner can do and whatever else can be detected with my Engine and it's components it would be appreciated and it would be nice to take advantage of using the Scanner while I have it.
The live step-by-step phone call with AV81 was great, and I'm always willing to learn more.
Thanks, Ray
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Old 06-28-2018, 10:38 AM
  #50  
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Having that scanner is GREAT. It has been a while since I have had to scan a 1981. AND I know that the data that you can see is rather minimal at best due to this is the first year model ECM GM put in a Corvette. I have read somewhere that some 1980's had them but I have never worked on one.

Making sure the TPS is correctly set within the parameters nice to know. The activity on the O2 sensor also when it is in CLOSED LOOP. Making sure you VSS is working.

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Hamerdown (06-28-2018)
Old 09-16-2018, 03:55 PM
  #51  
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Update...
and just like that...BAM...the poor Idle problem is back.
Ran good since late last June
, last week I had a 2-year old battery go bad (voltage was at 2 volts) replaced it with a new fresh battery and never got to use the car because of bad weather.
Yesterday I start it up, idled low for a few moments then it snapped-out of it and was ok.

Today...start the Car, idle was low, rough and laboring but it never snapped-out of it...I though maybe the ECM was relearning so I drove for a while. Off-idle and above operation is fine, come to a red light and the RPM again drops and the engine is laboring, running rough.
Best way I can describe it...on my car (81) before using a Timing Light you must disconnect the flat plug at the Distributor, the engine labors down, you set Timing then re-plug the flat plug-in and it idles-up smooth again.
When driving the car no CEL came on.

I still have the borrowed Snap-On Scanner!
So...if someone, anyone (when time is good for you) that really knows the 1981 ECM operation and the Snap-On scanner could (via phone call) walk me through the scanners menu/modes to see 'if' it shows something I would be very appreciative, thanks Ray.
610-304-4729
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Old 09-19-2018, 11:22 AM
  #52  
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BUMP...please read post #51 (thank you)
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Old 02-04-2019, 10:52 PM
  #53  
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Did you ever get this sorted? I've never used a scanner or even seen one for mine so couldn't help there.
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Old 02-04-2019, 11:34 PM
  #54  
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Originally Posted by Antz81 View Post
Did you ever get this sorted? I've never used a scanner or even seen one for mine so couldn't help there.
OTC made them. I'll post you a picture tomorrow. I have two somewhere.
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Old 02-04-2019, 11:58 PM
  #55  
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Originally Posted by Antz81 View Post
Did you ever get this sorted? I've never used a scanner or even seen one for mine so couldn't help there.
Hey Ant, hope all's well...I had an old Rochester I bough decades ago bouncing around under my work bench just for this occasion. I had it rebuilt and bench tested on a running engine, by the carb numbers the rebuild shop told me I it came off a GM 454 truck.
I purchased a made in china HEI, installed both, unplugged that fuc*ing ECM, turned the key and vroooom...it instantly started and idled perfectly.
I did get to run it around locally and it runs very well and idles nicely...got a LOT of conflicting info as to whether the vacuum HEI should be pulling vacuum from ported or manifold vacuum source...the arguments are endless, and some down right nasty. However, if I ran manifold vacuum I have to recurve my HEI as it pulls waaaaay too much vacuum. So I've been running ported.
With my 90 year old father's health failing I have not had time to tinker with the engine or even to pull a spark plug to check color. But so far I wish I did the switch a loooooong time ago.
BTW...I returned the Snap-On scanner to the friend that let me borrow it.

Last edited by Hamerdown; 02-04-2019 at 11:59 PM.
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Old 02-05-2019, 07:39 AM
  #56  
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I tried the Snap On Red Box some time ago. Drove the ECM bonkers. CE light flashed randomly, and car ran like crap;. I gave up.
The OTC units work well, and are very informative. Usually about $85 on F Bay.
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Old 02-05-2019, 05:22 PM
  #57  
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Here ya go Antz. This is the deluxe model. It has to have the correct cartridge and cable.




I can, find my basic one right now. 3400??
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Old 02-05-2019, 07:26 PM
  #58  
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Found it. This one is great. You plug it in the ecm under ash tray, and power it from the lighter. Handy as can be. Reads egr function, oxy sensor values, tp sensor voltage, mc dwell, etc.
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Old 02-06-2019, 06:36 AM
  #59  
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37 year old ECM. Every one you buy is also 37 years old. A rebuilt ecm has the one bad part replaced. The rest are 37 years old. And then the carb it is trying to control is 37 years old and a one-year-only pool of parts out there.
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Old 02-07-2019, 01:54 PM
  #60  
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Originally Posted by DUB View Post
I have read somewhere that some 1980's had them but I have never worked on one.


DUB
I think the 1980 Corvettes sold new in California were the first Corvettes with the computer.
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