Author Topic: 1981 Eldorado 368 8-6-4 code 18  (Read 765 times)

Offline Tonyv_73

  • Posts: 66
  • Name: Anthony Vanacore
1981 Eldorado 368 8-6-4 code 18
« on: June 13, 2017, 09:02:23 AM »
Just had a lot of work done on my 81 Eldorado Biarritz. (New radiator, plugs, wires, cap, oil change, new filters, pcv, exhaust, front axles, front shocks)  And now it's having a rough idle.  The computer is showing a code 18 which means an "open crank signal circuit" could anyone tell me what that means?
1973 cadillac eldorado convertible
1963 cadillac deville convertible
1966 cadillac Calais sedan
1970 buick wildcat

Offline Tonyv_73

  • Posts: 66
  • Name: Anthony Vanacore
Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #1 on: June 15, 2017, 08:48:15 PM »
Does anyone know what this means?
1973 cadillac eldorado convertible
1963 cadillac deville convertible
1966 cadillac Calais sedan
1970 buick wildcat

Offline Glen

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Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #2 on: June 16, 2017, 01:27:07 AM »
I googled ďopen crank signal circuitĒ and got this:
Ö code for the engine control module (ECM) detecting an open or short circuit in the crank position sensor signal wire or sensor to the ECM.

It is from this page:
https://www.yourmechanic.com/article/p2617-obd-ii-trouble-code-crank-position-signal-output-circuit-open-by-jay-safford
While that is an OBD II page I think the meaning is the same.  You need to check the crank sensor to see that it is connected and the wiring is intact and not shorted.  If the wireing is good, then the sensor is bad and should be changed. 
Glen Houlton CLC #727 
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Offline Tonyv_73

  • Posts: 66
  • Name: Anthony Vanacore
Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #3 on: February 02, 2018, 06:22:33 PM »
Where is the crank signal sensor located??
1973 cadillac eldorado convertible
1963 cadillac deville convertible
1966 cadillac Calais sedan
1970 buick wildcat

Offline Dave Shepherd

  • Posts: 1977
Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #4 on: February 02, 2018, 08:26:40 PM »
No shop manual?  Anyway early Tbi systems used the pick up coil in the distributor as a crank sensor..

Offline Bobby B

  • Posts: 1828
  • Mendham, New Jersey
  • Name: Bob Bender
Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #5 on: February 02, 2018, 08:40:56 PM »
Though the mechanical components of the L62 V-8-6-4 may have been sound, the systemís electronics were not. Despite Cadillacís claims that the Computer Command Module could process some 300,000 commands per second, it lacked the programming sophistication and overall speed necessary to direct the system across all driving conditions. Cadillac released some 13 updates, all via EPROM chip, for the Command Control Module, but none managed to overcome the systemís insurmountable obstacles. Seems it could also point to a Bad ECM. If you have a wiring diagram you need to check the wires from the ECM to the sensor for continuity, and/or corrosion. I didn't know that these years had a crank sensor, thought only a throttle position sensor. You can disable the 8-6-4 feature by cutting the single black wire coming out of the trans on the side, just above the pan. It senses 3rd gear, and that's when it disables the cylinders. A friend of mine installed a dash switch to disable this feature unless he was going on a long trip and wanted better fuel mileage. Tough to get a lot of answers on a one year only engine. Good Luck!
      Bobby
1947 Cadillac Series 62 Convertible Coupe
1968 Mustang Convertible
1973 Mustang Convertible
1969 Jaguar E-Type Roadster
1971 Datsun 240Z
1979 H-D FLH

Offline Dave Shepherd

  • Posts: 1977
Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #6 on: February 02, 2018, 09:21:29 PM »
Excellent post, summed up the issues back then.  I was in the middle of it during this time as a field trouble shooter for Cadillac. Then we really added to fire with the inexusable 4100.

Offline jsanford

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  • Name: Jeremy Sanford
Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #7 on: February 02, 2018, 09:47:52 PM »
Tony,

The shop manual is cheap and invaluable, you can find an electronic copy on eBay.

"Open Crank Sensor" has nothing to do with the crankshaft, it has to do with cranking the engine over, i.e. what the starter motor does when you turn the ignition switch to the start position.

You did not mention if the "Check Engine" light is on.

Page 8D-22 of the shop manual says for code 18 "IMPORTANT: If "CHECK ENGINE" light IS NOT on with engine running (other than diagnostic display) - Do Not Use The Following Diagnostic Procedure/Trouble Tree - This is an intermittent failure and cannot be diagnosed using the procedure/trouble tree. Check all connectors in the appropriate circuit. Reset diagnostics and road test."

Jeremy
« Last Edit: February 02, 2018, 09:55:56 PM by jsanford »
Jeremy
Sacramento, CA
1981 Eldorado
2016 ELR

Online Eric DeVirgilis CLC# 8621

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Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #8 on: February 03, 2018, 09:06:13 AM »
If 8 cyl-only operation is desired, simply unplug the trans switch under the car. There is no need to cut wiring.
A Cadillac Motorcar is a Possession for Which There is no Acceptable Substitute

Offline Bobby B

  • Posts: 1828
  • Mendham, New Jersey
  • Name: Bob Bender
Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #9 on: February 03, 2018, 10:49:39 AM »
If 8 cyl-only operation is desired, simply unplug the trans switch under the car. There is no need to cut wiring.

To install an in-line switch there is.....
                            Bobby
1947 Cadillac Series 62 Convertible Coupe
1968 Mustang Convertible
1973 Mustang Convertible
1969 Jaguar E-Type Roadster
1971 Datsun 240Z
1979 H-D FLH

Offline cadillacmike68

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  • Name: M Santos
Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #10 on: February 03, 2018, 01:18:50 PM »
Though the mechanical components of the L62 V-8-6-4 may have been sound, the systemís electronics were not. Despite Cadillacís claims that the Computer Command Module could process some 300,000 commands per second, it lacked the programming sophistication and overall speed necessary to direct the system across all driving conditions. Cadillac released some 13 updates, all via EPROM chip, for the Command Control Module, but none managed to overcome the systemís insurmountable obstacles. Seems it could also point to a Bad ECM. If you have a wiring diagram you need to check the wires from the ECM to the sensor for continuity, and/or corrosion. I didn't know that these years had a crank sensor, thought only a throttle position sensor. You can disable the 8-6-4 feature by cutting the single black wire coming out of the trans on the side, just above the pan. It senses 3rd gear, and that's when it disables the cylinders. A friend of mine installed a dash switch to disable this feature unless he was going on a long trip and wanted better fuel mileage. Tough to get a lot of answers on a one year only engine. Good Luck!
      Bobby


Didn't the Series 75 run the V8-6-4 for a few years?
Regards,
"Cadillac" Mike
Current:
1968 DeVille Convertible
1996 Fleetwood Brougham
2009 STS NorthStar Platinum ed RWD
2011 CTS PRemiun ed Sedan RWD
Past:
2008 CTS Premium ed Sedan AWD
2005 CTS Hi-Feature Sedan RWD
2000 ElDorado ESC Hard Boot Convertible
1995 Fleetwood Brougham
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Offline Bobby B

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  • Mendham, New Jersey
  • Name: Bob Bender
Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #11 on: February 03, 2018, 01:30:18 PM »
Didn't the Series 75 run the V8-6-4 for a few years?

From an article in Hemmings Magazine April 2008:
                                                    Bobby

It wasn't until 1981, and Cadillac's notorious V-8-6-4 engine (dubbed L62), that the idea was heard from again. The system, standard on all 1981 Cadillacs, was developed by the division and Eaton Corporation, and was installed on the Cadillac's new-for-1980 throttle-body fuel-injected six-liter (368-cu.in.) V-8--essentially a destroked, debored 472/500.
The V-8-6-4 system was designed to shut off either two or four cylinders to increase fuel mileage; this was determined by Cadillac's on-board Computer Command Module, which used sensors to monitor engine speed, EGR, idle speed, intake manifold air pressure, coolant temp, air pump operation and exhaust, and adjusted the air-fuel mixture accordingly. If the computer sensed a sustained cruise, a microprocessor (said to be capable of 300,000 decisions per second) would then signal a solenoid-activated blocker plate that physically moved the rocker arm, preventing the camshaft from opening the valve. Your six-liter V-8 would become a 4.5-liter V-6 or a three-liter V-4 at cruise, and a digital "MPG Sentinel" gauge on the dash would reveal how many cylinders were in operation. With only four cylinders doing the work, intake-manifold vacuum and pumping losses are both decreased. Fuel economy gains of 15 percent or more were realized when (or should we say, if) it worked.
That "if" is a biggie. Disaster doesn't quite cover the scope of what happened. Throttle-body injection issues paled in comparison to the valve switchgear: While the bottom end of the engine remained strong, the software needed to run the system wasn't nearly fast or powerful enough to manage the job at hand. Also, while press reports mentioned smooth transitions between four, six and eight-cylinder modes, buyers reported noticeable hesitations while the computer and hardware got their act together. To a Cadillac owner, this was an unacceptable driveability concern. Most V-8-6-4s saw the cylinder deactivation deactivated, leaving them in V-8 mode.
1947 Cadillac Series 62 Convertible Coupe
1968 Mustang Convertible
1973 Mustang Convertible
1969 Jaguar E-Type Roadster
1971 Datsun 240Z
1979 H-D FLH

Online Eric DeVirgilis CLC# 8621

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Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #12 on: February 03, 2018, 01:50:00 PM »
I hope Hemmings realizes all those issues were dealt with decades ago when all 1981 V8-6-4 cars were recalled and received a better brains and connectors.

As far as the mechanical aspects of the V8-6-4 are concerned, the local Cadillac dealers told me they never saw any problems with any components related to the valve actuation system.

V8-6-4 was used in the Limousine models from 1981 - 1984. The Limousine models did not get the Fuel Data display dash panel readout of the standard models.
A Cadillac Motorcar is a Possession for Which There is no Acceptable Substitute

Online Eric DeVirgilis CLC# 8621

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Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #13 on: February 03, 2018, 01:51:34 PM »
To install an in-line switch there is.....
                            Bobby

For that, yes.
A Cadillac Motorcar is a Possession for Which There is no Acceptable Substitute

Online Eric DeVirgilis CLC# 8621

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Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #14 on: February 03, 2018, 01:54:24 PM »
I've owned two dozen [post recall] V8-6-4s, and never had a problem with one.

That Hemmings article makes it sounds worse than the HT4100 and a diesel combined.
A Cadillac Motorcar is a Possession for Which There is no Acceptable Substitute

Offline Dave Shepherd

  • Posts: 1977
Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #15 on: February 03, 2018, 03:51:09 PM »
True, from a basic mechanical point of view the 8-6-4 was basically bullet proof. The ecu was very slow to transition the valve deactivation, so stumbling and hesitation was common,. Traditional Cadillac owners were understandably intoletsnt of this issue.  Lot of customer dissatisfaction existed from 81 forward,  general quality began to fall of even more. Very fresh in my mind as I was in the middle of all this.

Offline Bobby B

  • Posts: 1828
  • Mendham, New Jersey
  • Name: Bob Bender
Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #16 on: February 03, 2018, 04:52:45 PM »
That Hemmings article makes it sounds worse than the HT4100 and a diesel combined.

I have Zero experience regarding the infamous HT4100, so I can't feel anyone's Pain  ;D....
                                                                                     Bobby
1947 Cadillac Series 62 Convertible Coupe
1968 Mustang Convertible
1973 Mustang Convertible
1969 Jaguar E-Type Roadster
1971 Datsun 240Z
1979 H-D FLH

Offline e.mason

  • Posts: 185
  • Name: Eric Mason
Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #17 on: February 03, 2018, 05:03:08 PM »
I seem to remember there was a class action suit vs GM because of the  V8-6-4 engine.  I believe a few fires occurred with these engines.  The basic problem is that, while the technology was a good idea, it really wasn't perfected, as it is today.  The reason for the engine was to avoid a sur charge for not coming with in CAFE requirements.  Cadillac rather then add a few hundred dollars to the cost of the cars, went for these engines.  Like man posted.  Its really a good engine if the computer wire is disconnected and the car runs as a basic V8.
Eric Mason

Online Eric DeVirgilis CLC# 8621

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Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #18 on: February 03, 2018, 07:22:24 PM »
Still needs the computer to run regardless of whether or not cylinder activation is disabled. Disabling did not affect the reliability of the engine either in any I've encountered. Again, all 1981s that I owned were long after the recall campaign updates had been performed.

I don't recall any lawsuit in connection with the V8-6-4 but I do know that Cadillac ultimately issued a supplemental 5 year/50,000 mile driveline warranty on all cars with the engine which would apply to any car and any subsequent owner. 
« Last Edit: February 03, 2018, 08:25:34 PM by Eric DeVirgilis CLC# 8621 »
A Cadillac Motorcar is a Possession for Which There is no Acceptable Substitute

Offline e.mason

  • Posts: 185
  • Name: Eric Mason
Re: 1981 Eldorado 368 8-6-4 code 18
« Reply #19 on: February 03, 2018, 09:13:36 PM »


I don't recall any lawsuit in connection with the V8-6-4 but I do know that Cadillac ultimately issued a supplemental 5 year/50,000 mile driveline warranty on all cars with the engine which would apply to any car and any subsequent owner.

https://www.leagle.com/decision/198350593nj412184

http://caselaw.findlaw.com/ca-court-of-appeal/1770877.html

https://www.newspapers.com/newspage/6380730/



Eric Mason

 

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