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500, 472, 425, 368 Discussion, what engine is in the 81 coupe deville in Cadillac Engine Technical Discussion; Stop it Kevin, you're makin' me blush... Another thing about the 81's that I forgot about that is really great. ...
  1. #16
    ssstealth's Avatar
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    Stop it Kevin, you're makin' me blush...

    Another thing about the 81's that I forgot about that is really great.

    The on-board diagnostics on these cars was actually VERY useful. Unllike the current Fleetwood systems which give information only, the system on the 81 would allow you to scan multiple systems and see values for things like temps, injector pulse widths, timing, etc. It also had ways of testing every underhood switch, selenoid, sensor, etc. from inside the car. It made working on the car a real dream.

    Of course to make use of these things, you will have to purchase a REAL GM service manual for it, but trust me, it is worth every penny.

  2. #17
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    Re: what engine is in the 81 coupe deville

    Yep, "Output Cycling" is a rather useful thing when you are trying to diagnose certain issues. The DFI system was the first of many OBD systems on Cadillacs. Unfortunately, only the RWD Fleetwoods strayed away from that type of system, all the FWD cars remained with that degree (and greater) of OBD. Viewing operating "parameters" is just the tip of the diagnostic iceburg which would become available to the customer (and would-be mechanic) on later FWD Cadillacs.
    A while ago, I posted some info about these systems and I will reiterate that you CAN gain a rather in-depth guide to their inner workings through a small "Quick Reference Guide" available through Helm. It cost $7 for each year, and covers every model available in that year.

  3. #18
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    Kevin,

    Is this available for the Fleetwood? The only "advanced" parameters and readings I have been able to find is the 05 and up codes, most of those dealing with AC readings.

    I do use 14 occasionally as yet another speedometer check

  4. #19
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    Night Wolf is offline Cadillac Owners 10000+ Posts
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    according to what I just read, the V8-6-4 feature seems real god and cool...... V8 power when ya need at, but cruise on the highway and get 32mpg....... why was there soo many problems with it?

    the 368 seems to be underpowered though, 160hp?

    seperate question, between the 425 and 500, which is better?

    say if you got a '77 CDV and you wanted to make a big sleeper, keep the 425 and build it up, or swap in a 500 and build it up?

  5. #20
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    Some people have had no problems with the 8/6/4, I dunno why it acts up some times.

    That hp measurement is probably nett, so it will seem lower than what they used to use (gross).

    I'd say go for the 500. If you're looking at nitrous, the 425 crankshaft might not take it. Plus Edelbrock makes an aluminum intake for the 500/472, though you can't use the stock AC compressor with it. And the 500 is bigger, therefore it's inherantly going to be more powerful.

  6. #21
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    The apparent "failure" of the V-864 was due to a few different things.

    First off, our federal government, in their infinate wisdom, would not allow the true mileage of this engine to be posted on the EPA sticker. EPA held that there was no eveidence to properly assertain how much time the engine was in each mode. So since this value could not be agreed on, they formulated the rating on the car being in 8 cylinder mode all of the time. This was not aided much by GM either. They pushed for a ruling on the "MPG Sentinel" as well stating that since the driver could VIEW the mileage while driving, that his driving habits would improve, thus getting BETTER mileage. EPA didn't buy into this argument either.

    With pressure from CAFE requirements, and NO help from EPA, the engine was dropped in 1982 for the puny underpowered HT4100. It was still silently placed into limos for a few more years.

    Now, since the engine was dropped after only a year, the general public immediately came to the conclusion that the engine was unreliable. Remember that this was an era where anything advanced that did not come from Japan was labelled junk. This was also a time when Quaker State was running ads stating how their oil was good for 15,000 miles between changes. The only mechanical complaint I could think of on this engine was that the 6 cylinder transition mode was a bit unbalanced.

    I guess my point is that the "general public" does very little thinking for themselves. They hear one person talk and that it repeated as gospel from that point forward. You need only to look around to prove this point. Is the McDonald's hamburger the best burger ever? Is a Taurus or a Camry the best car? If you buy a minivan to have more room, then why is all of your luggage on the roof?

    I guess I should not complain... If the entire world were populated with geniuses, who would be left to cook our fries?

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    jsulliva is offline Cadillac Owners Member
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    Thumbs up

    I had an 81 SDV with the V8-6-4 and loved it. I put over 125K miles on it, sometimes towing a 6000+ lb boat with it. I did not disable MD - it had lots of power and yet got great mileage on the freeway. As the other guy wrote, it had a little vibration in 6 cyl mode, which you rarely used (cruising up a slight hill would use teh 6 cyl mode). And the On-board diagnostics (OBD) were great as well. I would drive with the OBD turned on and push the buttons to turn off 6 cyl mode is I was going to be at it for a long time. The switch idea is a good one. I also had an 81 El Dorado with the MD V8. Loved it too. I developed an overheat problem which I never solved and finally sold.
    I still have the genuine GM shop manuals if someone wants to make me an offer. Write me. john_sullivan(at)BMC.COM.

  8. #23
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    my '93 DeVille has all that cool OBD stuff, I have a factory service manual and learning about it, it really makes working on the car nice.

    Just hearing about all this makes me want to get a V8-6-4 powered car, they seem really cool and interesting to run.

  9. #24
    Cadillac Pat is offline Cadillac Owners Member
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    Re: what engine is in the 81 coupe deville

    Lux Hauler,
    The blocks are different as the V8-6-4 block doesn't have the hole machined for a mechanical fuel pump. Everything else is the same on the block. The intake, valve covers and additional V8-6-4 components are different/added.


    Pat

    Quote Originally Posted by lux hauler
    Someone correct me if I'm wrong but.......don't the 368 and the 4-6-8 (8-6-4) use the same block? It was the electronics that made them different, right?

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    Re: what engine is in the 81 coupe deville

    Vanasia,
    Have you ever owned a V8-6-4? If not, please reframe from calling it "troublesome". If you want to call any engine troublesome, start with the 4100 followed by the Diesel. How many of either make it to 100,000 miles? I have two perfect working examples and love them both (192,000 and 139,000 miles). Besides having four bad 4100's, two of which just barely breaking 100,000 miles, one going through two engines by 100,000 miles, and the fourth going to 129,000 miles with proper maintenance (I bought the car at 66,000 miles), I have had one with the Buick 4.1 that threw a rod at just over 100,000 miles. Another Buick 4.1 powered car, my current summer daily driver, had it's engine replaced BEFORE the 78,555 miles I bought it at with a '72 500 already installed.

    Pat

    Quote Originally Posted by vanaisa
    ´81 De Ville had three engines
    - Buick´s V6 252cid, 125bhp
    - troublesome V8-6-4 368cid, 140bhp
    - and optional diesel engine - 350cid, 105bhp

  11. #26
    Cadillac Pat is offline Cadillac Owners Member
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    Re: what engine is in the 81 coupe deville

    Stoneage_Caddy,
    Of the engine options from 1980 to 1982, the best, believe it or not, was any of the 368's, including the '81 V8-6-4. Although the modulated displacement system might be unworking or disconnected, they are still running. The Buick V6 and Olds Diesel powered have long since either had their engines replaced, or been scrapped.

    Pat

    Quote Originally Posted by Stoneage_Caddy
    "The '81 should have a 368, I believe"

    and hopefully not the 8-6-4

  12. #27
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    Re: what engine is in the 81 coupe deville

    Lux Hauler,
    I am disappointed at you. As a member of the MTS board, and having an engine in the 368 family (368/425/472/500), you should know better. The 368 was the BEST engine available in any Cadillac from '80-'81 (through '84 in Limos). In 1982, the 4100 was the standard engine and the Olds Diesel was an option.
    How many Olds Diesels are on the road today? How many 4100's have been had their head gaskets replaced or engines replaced? What's the biggest problems with a V8-6-4? That the V8-6-4 system quits working? At least the car is still being driven.
    I have owned four 4100 powered cars, two Buick 4.1 powered cars, two V8-6-4 cars and one carbureted 368. Of them, the ONLY two still running with their original engines are the V8-6-4 cars. Additionally, I have replaced the bad 4100 in my '82 Coupe with the carbureted 368 out of a very rusty '80 Coupe. One of the 4.1 V6's threw a rod at 103,000 miles. The other V-6 was replaced BEFORE I bought the car at 78,555 miles, with a '72 500 installed. One of my V8-6-4's has 190,000 miles and the other 138,000 miles. The '80 368 has 132,000 miles and uses a quart of oil every 1000 miles or so (the engine is over 24 years old and has not been apart except for a water pump and timing chain which was changed as preventative maintenance). Two of the 4100 cars, which I have pulled the 4100's from, are getting 472/500's.

    Pat

    Quote Originally Posted by lux hauler
    It looks as though you are correct.
    http://100megsfree4.com/cadillac/cad1980/cad81d.htm

    I guess the 368 was never offered any way except in the V8-6-4 configuration.
    It looks like the Buick V6 was the best engine offered.

  13. #28
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    Re: what engine is in the 81 coupe deville

    Well I'm really getting an education on my V8-6-4 motor here!

    I too have been through too darn many of those piece of crap HT4100 4.1 Garbage motors. I getting sick just thinking about it.

    My 368 is still under 100,000 original miles and I'm very happy to hear that it's not so much of a TIME BOMB.

    Never had the diesel or the V6, probibly cause there all in the junk yard.

    PS: I've yet to see a 4.1 make it over 132,000 miles.
    if there's one out there, put it in a museum,
    It may be the only one worth saving!
    But I won't pay to see it!

  14. #29
    Cadillac Pat is offline Cadillac Owners Member
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    Re: what engine is in the 81 coupe deville

    Of all the cars I have owned, I bought the manual for my '81 V8-6-4's and no other cars. The V8-6-4 was the first car to offer on board diagnostics, and you are right about the scanning ability for things such as:
    Throttle position (in degrees; 0 to 31)
    ECT Engine Coolant Temperature (degrees Celcius-the sensor signal is also used for the amber "Coolant Temp Light"; because of this, the engine additionally has a "engine metal temperature switch" that gives a red "Stop Engine Temp" light when the back of the driver's side head gets to 380 degrees)
    MAT Manifold Air Temperature (both it and the ECT measure from -40 to 150 degrees Celcius)
    MAP Manifold Absolute Pressure (in kPa or kilopascals)
    BAP Barametric Absolute Pressure (atmospheric pressure; in kilopascals)
    Engine Timing (up to 52 degrees; not counting initial)
    Injector Pulse Width (from 0 to 99 milliseconds)
    O2 sensor voltage (0 to .99 volt)
    Electrical system voltage (0 to 19.9 volts)
    Open/Closed Indicator-0 for open loop and 1 for closed loop
    Number of key cycles since a fault occured; after 20 cycles with no malfunction, it is reset to 0 and all codes are cleared
    Additionally, the "switch test" function can be used to test the following:
    Cruise control brake switch
    throttle switch
    drive switch
    reverse switch
    cruise control dash switch
    cruise control "set/coast" button
    cruise control "resume/acceleration" switch
    "instant/average" button on the MPG display
    the ECM's ability to recognize the A/C clutch signal





    Pat

    Quote Originally Posted by ssstealth
    Stop it Kevin, you're makin' me blush...

    Another thing about the 81's that I forgot about that is really great.

    The on-board diagnostics on these cars was actually VERY useful. Unllike the current Fleetwood systems which give information only, the system on the 81 would allow you to scan multiple systems and see values for things like temps, injector pulse widths, timing, etc. It also had ways of testing every underhood switch, selenoid, sensor, etc. from inside the car. It made working on the car a real dream.

    Of course to make use of these things, you will have to purchase a REAL GM service manual for it, but trust me, it is worth every penny.

  15. #30
    Cadillac Pat is offline Cadillac Owners Member
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    Re: what engine is in the 81 coupe deville

    Night Wolf,
    Although only rated at 140 hp @3800 rpm, the engine is also rated at 275 ft.lbs. at a very low 1600 rpm. Additionally, these are "net" ratings. The "gross" ratings are about 25% more.

    Pat

    Quote Originally Posted by Night Wolf
    according to what I just read, the V8-6-4 feature seems real god and cool...... V8 power when ya need at, but cruise on the highway and get 32mpg....... why was there soo many problems with it?

    the 368 seems to be underpowered though, 160hp?

    seperate question, between the 425 and 500, which is better?

    say if you got a '77 CDV and you wanted to make a big sleeper, keep the 425 and build it up, or swap in a 500 and build it up?

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