81 ELDO WITH 8-6-4

[81 Biarritz]

I know i have read a lot about prople disconnecting the 8-6-4 option, but i have a car that was disconnected, and I have since reconnected the 8-6-4 system, however, the system wont engage.  I would love to have an in-line switch that would allow me to run on all 8, and then switch into 8-6-4 mode, but i have a check engine light on ( error codes are 80, 30 , 28 i think ( i will double check tonight) and i think that is preventing the system from engaging.  Otherwise the car runs like a freight train, bulletproof and totally reliable.  All i read online about this is such a shame because the cars really have performed well over the years, except for the computer issues and sensor issues, which i attribute to Automotive Electronics and computer management in its infancy.

Cadillac was really ahead of its time, and its sad because their demographic wasnt patient enough with the technology to embrace it.  Its similar to the Edsel Story... I imagine a 50-something in 1981 who was used to big Cadillacs with big block power, and they were not having an engine that would shift into 6 or 4 when they wanted 8 cylinders.

any help?  THANKS!!

[Dave Shepherd]

Excellent engine basically an 80 368, with DEFI, the issue was a very slow computer, so the transition was erratic and annoying. The most common way to override the the computer was to disconnect the 3rd gear sensor connector on the side of the trans. this prevented any modulation.  Find out what the exact codes are and post back.

[TJ Hopland]

80 AC clutch circuit
30 idle speed control circuit
and there is no code 28 so you will have to confirm that one. 

The 3rd gear switch is the correct way to disable the system but over the years people did all sorts of things to try and disable it which mostly confused the computer and made it run worse which they then did other things to try and compensate for.    How did yours appear to be disabled? 

[r2law]

I have 1981 Fleetwood.  Attached is the 1980 press release for the Digital Fuel Injection.  The computer is monitoring the engine and controlling the timing, fuel delivery rate and idle speed.  If you’re going to try to work on the engine yourself you should get the 1981 Cadillac Digital Fuel Injection and computer Command Control Diagnosis Manual Supplement.  It tells you how to run the diagnostics through the car’s climate control. You should also have a back-up mechanic and a lot of patience. 

[Dave Shepherd]

Ha ha, agreed on all points, during my tenure with GM I spent mucho time trying to satisfy customers with all the issues pertaining to performance..  The isc ( code30) was a common failure.  As TJ stated there is no 28, could be 23 though.

[TJ Hopland]

I suppose 23 and 28 could be easy to interchange.
   
23 is EST / Bypass circuit shorted or open.

Est is the electronic spark timing.   It appears to be a starting aid active only during cranking.  Its part of the ignition module.


The regular 81 service manual has a large section on the DEFI system.  Each code has a written description and then a flow chart for trouble shooting.  Im too lazy to look for my 80 one but maybe there was a supplement for the DEFI in the 80 because only some of the cars got the DEFI?   I know 80 was a year with a separate electrical manual. Not sure what other years had that option.  Its way more detailed than the regular manuals.  That manual did not go into detail about the DEFI other than details of wiring and connectors. 

I worked on one of these cars where someone had disconnected the rocker solenoids.  They even put big resistors in their place to simulate the load.   Problem was computer thinks it should be running on 4 or 6 and cuts the fuel back.  When you try to run 8 cylinders with only enough fuel for 4 you have problems.

I know one guy that hooked a relay into the 3rd gear circuit that tied into the cruise control.   That way it would only drop cylinders when the cruise was engaged.  I never looked close at how exactly he did it.  I assume the relay tied to something like the cruise light.   

[r2law]

Regardless of all its flaws, our 81 Fleetwood has been in the family for over 30 years with no engine problems.  Right now the car is in the body shop being restored. Attached are the diagnostic manual supplements instructions for code 23 and 80.

[r2law]

Also attached are the instructions for code 30.