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1981 Eldorado V8-6-4 ECM smoking/fried

Started by Tonyv_73, October 14, 2019, 03:28:04 PM

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Tonyv_73

Okay recently I went to start my 1981 eldorado Biarritz and smoke started coming from under the glove box. I took apart the under dash cover and found the ECM was the issue. I removed it and purchased a replacement.  Installed the PROM chips to the new unit and the new unit started to sizzle as well so I quickly shut the key. The issue happens when the car is in the “run” position.  Can someone guide me through this issue? I cannot start the car without the ECM. The car has 70k miles and was running perfect with no issues before hand.
1963 Series 62 Convertible
1965 Eldorado
1966 Calais Sedan
1970 Fleetwood Brougham
1970 Wildcat
1970 Coupe Deville
1973 Eldorado Convertible
1974 Coupe Deville
1976 Coupe Deville
1981 Eldorado Biarritz
1985 Eldorado Commemorative Edition
1991 Brougham
1993 Eldorado 4.9
1996 Fleetwood Brougham
2006 XLR
2006 DTS
2014 XTS

TJ Hopland

Hopefully the prom has not been damaged.  If it is that may be difficult to replace these days.     For 2 ECM's to have smoked you must have a really badly failed device or damaged wiring.   Something that isn't protected is being overloaded or some external fault is sending voltage somewhere its not supposed to be. 

I have the tool to start troubleshooting that issue.  I will have to go out and find it and see what the model number is.  I do remember its from OTC.   Basically this tool is a box with some switches and readouts on it that plugs into a model specific ECM substitute board.    You look at the model number of the ECM then find the corresponding note card and circuit board.   You plug the board in in place of the ECU then follow the tests outlined on the note card.   The card says which tests to run and what is a pass/fail for each test.   It does basic tests of all the wiring and sensors.   Its not the end all be all test for anything but I bet would narrow down where to look for your issue.   

Without that or a similar tool you will either have to get the service manual and starting testing each circuit with a volt ohm meter or carefully inspect all the devices and harnesses till you find the problem one.   It would be nice if you had a clue where to start looking.  Maybe opening up the ECU's and looking for the damage you could get lucky and follow the traces to a connector and pins so you know which system to be looking at.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Dave Shepherd


81 BENY Biarritz

Hello, first post to this Forum.  I have a 1981 triple red Biarittz with the V864 engine that will run in this mode if I turn it on from a small switch installed under the dash.  I have been collecting information on the V864 system gradually for future reference on mine if ever the time comes.  Came across this thread from another Cadillac Forum so I hope that it is OK to post here.  It has some links to several Serviceman Bulletins about the ECM, PROMS and a troubleshooting ladder diagram for diagnosing repeated ECM failures.  Hope it helps.  Dave
https://www.cadillacforums.com/threads/cadillac-v864-proms-sharing.1017849/#post-17093257

TJ Hopland

Your dash switch most likely disconnects the 3d gear sensor from the transmission which is the 'right' way to disable the system.   The system was only allowed to go into 6 or 4 mode when the transmission was in 3rd gear so if it never thinks its in 3rd it just stays in V8 mode.   Most of the other methods would cause other issues because the computer didn't understand what was going on. 

I don't think we have heard from the original poster for a while.   His issue has to be external to the ECU since it happened to 2 different units.  Newer stuff is better protected from external issues but this early in the game they were still learning.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

bcroe

I have also read of 8/6/4 cars smoking multiple ECMs, but not a
resolution of the problem.  Yes it must be external to the ECM.

I suggest noting the area smoking on the original ECM.  To cause
this damage I would expect some kind of power input/output
circuit.  That could be the power supply.  But more likely its drive
to outside components such as valve activators or solenoids,
which may have shorted out and now draw too much current. 

Do not just keep burning up more ECMs, determine the fault.  If
a power driver is the only failure, the ECM might be repairable. 
The early proms were 2732A parts, which were very cheap for
many micro processors of that era, and we easily made duplicates
of them back then.  good luck, Bruce Roe

Tonyv_73

Hello All,

I’m finally getting back to resolving this issue (car has been sitting since I originally posted this, I would like to send my original ECM to someone to test out which circuit fried does anyone know of someone that can test ECMs?

-Anthony
1963 Series 62 Convertible
1965 Eldorado
1966 Calais Sedan
1970 Fleetwood Brougham
1970 Wildcat
1970 Coupe Deville
1973 Eldorado Convertible
1974 Coupe Deville
1976 Coupe Deville
1981 Eldorado Biarritz
1985 Eldorado Commemorative Edition
1991 Brougham
1993 Eldorado 4.9
1996 Fleetwood Brougham
2006 XLR
2006 DTS
2014 XTS

35-709

1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

Tonyv_73

1963 Series 62 Convertible
1965 Eldorado
1966 Calais Sedan
1970 Fleetwood Brougham
1970 Wildcat
1970 Coupe Deville
1973 Eldorado Convertible
1974 Coupe Deville
1976 Coupe Deville
1981 Eldorado Biarritz
1985 Eldorado Commemorative Edition
1991 Brougham
1993 Eldorado 4.9
1996 Fleetwood Brougham
2006 XLR
2006 DTS
2014 XTS

Dave Shepherd

Coming in late here, but sounds like a quad driver in the ecu. These controlled high load solenoids, so a shorted component could fry the driver.   As far as I know the ecu is not repairable.

Tonyv_73

Quote from: Dave Shepherd on February 18, 2020, 09:33:57 AM
Coming in late here, but sounds like a quad driver in the ecu. These controlled high load solenoids, so a shorted component could fry the driver.   As far as I know the ecu is not repairable.

does anyone know the part numbers for the solenoids? and where they are located?
1963 Series 62 Convertible
1965 Eldorado
1966 Calais Sedan
1970 Fleetwood Brougham
1970 Wildcat
1970 Coupe Deville
1973 Eldorado Convertible
1974 Coupe Deville
1976 Coupe Deville
1981 Eldorado Biarritz
1985 Eldorado Commemorative Edition
1991 Brougham
1993 Eldorado 4.9
1996 Fleetwood Brougham
2006 XLR
2006 DTS
2014 XTS

35-709

Quote from: Tonyv_73 on February 18, 2020, 09:13:43 AM
who is that?
See reply #5 in this thread.  Send him a PM if he doesn't respond here again.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

Tonyv_73

Quote from: 35-709 on February 18, 2020, 09:50:32 PM
See reply #5 in this thread.  Send him a PM if he doesn't respond here again.

Thanks, Hopefully this forum can help resolve the issue before spring!
1963 Series 62 Convertible
1965 Eldorado
1966 Calais Sedan
1970 Fleetwood Brougham
1970 Wildcat
1970 Coupe Deville
1973 Eldorado Convertible
1974 Coupe Deville
1976 Coupe Deville
1981 Eldorado Biarritz
1985 Eldorado Commemorative Edition
1991 Brougham
1993 Eldorado 4.9
1996 Fleetwood Brougham
2006 XLR
2006 DTS
2014 XTS

Tonyv_73

UPDATE: 

Replaced the Air Diverter Valve Solenoids (there was a short in one of them) Plugged in replacement computer and the car starts up,  however I am getting nothing on the display for the Fuel Economy readout, the check engine light is on, and I cannot check codes in climate control display.  Does anyone know if the ECMs are different between years?  (yes I used original PROMS)  Im wondering if I have a HT-4100 ECM instead of a V-8-6-4 ECM.  If that is the case does anyone have the correct ECM for sale?
1963 Series 62 Convertible
1965 Eldorado
1966 Calais Sedan
1970 Fleetwood Brougham
1970 Wildcat
1970 Coupe Deville
1973 Eldorado Convertible
1974 Coupe Deville
1976 Coupe Deville
1981 Eldorado Biarritz
1985 Eldorado Commemorative Edition
1991 Brougham
1993 Eldorado 4.9
1996 Fleetwood Brougham
2006 XLR
2006 DTS
2014 XTS

Tonyv_73

Original ECM "KD" 1225120? anyone know which other part numbers will fit?
1963 Series 62 Convertible
1965 Eldorado
1966 Calais Sedan
1970 Fleetwood Brougham
1970 Wildcat
1970 Coupe Deville
1973 Eldorado Convertible
1974 Coupe Deville
1976 Coupe Deville
1981 Eldorado Biarritz
1985 Eldorado Commemorative Edition
1991 Brougham
1993 Eldorado 4.9
1996 Fleetwood Brougham
2006 XLR
2006 DTS
2014 XTS

chevy350

I'm have a problem to start my '80(368 engine),I need to checkfollowing the service manual if the Ecm is gone,Is really difficult to find and replace the prom un the Ecm?

Thank you.
Best regards from Sicily,Giuseppe

Cadman-iac

If you get a remanufactured ECM for it, they used to include a small tool to remove and install the E-prom with. I don't know if it's still included, or even if the ECM is still available anymore. The last time I had to replace one was many years ago.
CLC# 32373
1956 Coupe Deville A/C car "Norma Jean"

Tonyv_73

My question is, is the remanufactured ECM the correct one for 1981? or is it a "one size fits all" for 1979-1985.  Ive heard that the ECM needs to be an 81 ECM because of the "Fuel Econonmy" display
1963 Series 62 Convertible
1965 Eldorado
1966 Calais Sedan
1970 Fleetwood Brougham
1970 Wildcat
1970 Coupe Deville
1973 Eldorado Convertible
1974 Coupe Deville
1976 Coupe Deville
1981 Eldorado Biarritz
1985 Eldorado Commemorative Edition
1991 Brougham
1993 Eldorado 4.9
1996 Fleetwood Brougham
2006 XLR
2006 DTS
2014 XTS

TJ Hopland

Any listing that says 79-85 is for sure wrong.  79 was a completely different animal.   No idea what else was the same.   Its possible that 80 and 81 were the same but its also possible that 82 could be the same.  The prom would tell it what sensors and outputs are needed and which are not.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Tonyv_73

So what ECM would you recommend if the original part number is “KD” “1225120”
1963 Series 62 Convertible
1965 Eldorado
1966 Calais Sedan
1970 Fleetwood Brougham
1970 Wildcat
1970 Coupe Deville
1973 Eldorado Convertible
1974 Coupe Deville
1976 Coupe Deville
1981 Eldorado Biarritz
1985 Eldorado Commemorative Edition
1991 Brougham
1993 Eldorado 4.9
1996 Fleetwood Brougham
2006 XLR
2006 DTS
2014 XTS