Author Topic: 1981 Eldorado 368 v8-6-4 not working  (Read 363 times)

Offline Tonyv_73

  • Posts: 62
  • Name: Anthony Vanacore
1981 Eldorado 368 v8-6-4 not working
« on: June 13, 2017, 09:07:10 AM »
Anyone know how to get the v8-6-4 to work properly, (i know it never worked right in these cars and was poorly designed) but I found a few connections that were disconnected while working on my car, and I'm debating plugging them back in if it's for the 8-6-4
1973 cadillac eldorado convertible
1963 cadillac deville convertible
1966 cadillac Calais sedan
1970 buick wildcat

Offline TJ Hopland

  • Posts: 6712
Re: 1981 Eldorado 368 v8-6-4 not working
« Reply #1 on: June 13, 2017, 09:31:18 PM »
Over the years there were a lot of ways people tried to disable the 8-6-4 feature so you will just have to get a good manual and start following all the loose wires.   

The system was only allowed to work when the transmission was in 3rd (Hi) gear.   Simple way to keep the system in 8 was to disconnect that wire from the transmission.    Problem with just about every other way to disable the system was the computer still thought it was working so it would trim the fuel and timing to match the mode it thought it was in.   Result was usually a pretty terrible cruising because computer was fueling and timing for 4 cylinder when 8 were still running. 

I drove a few of these cars where someone put in a manual toggle switch in that 3rd gear circuit.  They would disconnect it 'around town' so it stayed in 8 then reconnect it if they were out on the highway.   If I ever get one of these cars I think that is what I would do.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
75 Eldo rusty but trusty
80 Eldo Diesel
And other assorted stuff I keep buying for some reason

Offline Tonyv_73

  • Posts: 62
  • Name: Anthony Vanacore
Re: 1981 Eldorado 368 v8-6-4 not working
« Reply #2 on: June 14, 2017, 01:48:59 AM »
I found the connection that goes to the transmission, (it's on the driver's side near firewall if I'm correct) I noticed the plug items has two holes whereas the sensor has only one prong, can anyone confirm this is correct or incorrect? And can someone send picture so I can compare?
1973 cadillac eldorado convertible
1963 cadillac deville convertible
1966 cadillac Calais sedan
1970 buick wildcat

Offline TJ Hopland

  • Posts: 6712
Re: 1981 Eldorado 368 v8-6-4 not working
« Reply #3 on: June 14, 2017, 09:25:49 AM »
That sounds correct for an Eldo.   The RWD cars had 2 pins in the connector, one pin was the 3rd gear switch and the other was the kickdown.   The Eldo trans didn't have the kickdown so it would make sense that it just used a single pin. 
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
75 Eldo rusty but trusty
80 Eldo Diesel
And other assorted stuff I keep buying for some reason

Offline Tonyv_73

  • Posts: 62
  • Name: Anthony Vanacore
Re: 1981 Eldorado 368 v8-6-4 not working
« Reply #4 on: June 15, 2017, 08:47:57 PM »
I plugged it in and I keep getting a code 18, which is an "open crank signal circuit" I'm not sure what that means though. And it still does not change to 6 or 4 mode at any speed
1973 cadillac eldorado convertible
1963 cadillac deville convertible
1966 cadillac Calais sedan
1970 buick wildcat

Offline g27g28

  • Posts: 141
    • CLC Member
      CLC Member #16120
  • Name: Greg Gottschalk
Re: 1981 Eldorado 368 v8-6-4 not working
« Reply #5 on: June 16, 2017, 07:53:49 PM »
I believe that as long as you have a code that is showing up that the engine will stay in 8 all the time  My question would be why do you want it be active?  I drove an 81 Sedan for 150k miles and it was active the whole time.  It was more a novelty than anything else, something I could live with but saw little benefit in mileage.  That said the car was one of the most trouble free Cads I have ever driven.
1941 Series 62
1954 Coupe DeVille
1978 Phaeton
1980 Fleetwood

Offline Tonyv_73

  • Posts: 62
  • Name: Anthony Vanacore
Re: 1981 Eldorado 368 v8-6-4 not working
« Reply #6 on: June 17, 2017, 12:42:30 AM »
I've had the car a little under a year, and I plan to drive it and enjoy it. That being said I like to understand my cars to the fullest of my ability and if something is not working (intentional or not) I would like to feel confident driving it. The roughness the car gets at idle and the code 18 is just frustrating to say the least when driving a cadillac
1973 cadillac eldorado convertible
1963 cadillac deville convertible
1966 cadillac Calais sedan
1970 buick wildcat

Offline r2law

  • Posts: 49
    • CLC Member
      CLC Member #26230
  • Name: L. Rehm; R. Lawrence
Re: 1981 Eldorado 368 v8-6-4 not working
« Reply #7 on: June 17, 2017, 07:09:57 AM »
I have an 81 Fleetwood with an operating V-8-6-4.  I never had a code 18 but I have the DFI/ECM Diagnostic Manual Supplement.  Attached are the pages relating to a hard DFI code 18.  According to the manual if the "check engine light" is not on with the engine running, the error code is an intermittent failure.  Attached are pages 1A and 2A of the manual that describe intermittent codes versus hard failures.

If you don't have the 1981 Service Information Manual, 1981 Electrical trouble shooting manual and the DFI/ECM Diagnostic Manual Supplement, I recommend you buy them.  I hope this information helps.