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4-6-8 engine issues

Started by nick.stratta, August 17, 2009, 07:50:28 PM

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nick.stratta

Greetings!
I went to look at an 81 Fleet this evening that has been sat for some time. Has the 368ci fuel injected engine with the 4-6-8 feature. Guess what! Was parked up becuase the engine started running on all 8 full time and spewing black smoke out of the back - running very rich and using heaps of fuel. 2 computers later the owner has given up and intends to sell.
I've heard that the 4-6-8 feature on these engines is best disabled anyway but looking at the way the fuel injection system is done with all the early sensors and the troubles the owner has had with going through a number of computers I'm thinking the best way forward is a carburettor on a new inlet manifold.
What functions do the computers control and can the car be made to run without it?
Am I right inthinking the best thing is move to carburation or is it cheaper to fix the 4-6-8 FI?
Is the 368 the same block as the 425/ 472/500? If so can I just bolt on an inlet manifold and carb from a 425 a friend has spare?
What do you all think please?
Thanks! Nick :)
regards & thanks Nick
CLC 23023, CLCMRC Museum benefactor 113

nick.stratta

Bump!  27 views and no advice/ replies? Did I post it in the wrong place? Any help please people?
thanks, Nick
regards & thanks Nick
CLC 23023, CLCMRC Museum benefactor 113

The Tassie Devil(le)

G'day Nick,

I cannot assist, but hopefully, someone will soon.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

nick.stratta

regards & thanks Nick
CLC 23023, CLCMRC Museum benefactor 113

bill henry

the 368 had a composite intake for a quadrajet i would look on ebay if i were you . it is the same block as the 425/472/500
Bill Henry

nick.stratta

Bill,
Thanks - so junking the FI and the computer and going carburettor is the way to go? thanks,
regards, Nick
regards & thanks Nick
CLC 23023, CLCMRC Museum benefactor 113

bill henry

i like carbs myself but i am old skool
Bill Henry

TJ Hopland

#7
If it was mine and i could not get it running right I would be looking at swapping the factory ecu out for a more programmable one like Megasquirt.   That way you could get rid of the hard to find sensors as they died.  I like efi.  To disable the 8-6-4 there is a single wire on the transmission.  The system would only engage in 3rd gear so if it never sees 3rd it never tries.  Computers dont usually dont partially fail, its usually its other things and the computer gets replaced because people dont understand them and just start throwing parts.  I wonder if someone tried other ways to disable the system and thats what started the problem?  These early systems are fairly advanced yet simple at the same time.  Black smoke is usually more oil than fuel.  The other thing people often forget when working on cars with computers is the computer cant do anything about basic mechanical problems.  Remember this is almost a 30 year old car, lots of things could have happened to it over its lifetime.  A compression / leakdown test would be a good start to see if the basic mechanics are solid.  Leaky valve guide seals can build up all sorts of sludge on the intake valves and screw up the flow as well as make smoke.

The 472 500 425 intake should bolt up but I thought the 368 had smaller runners so I dont know how well it would work.  The 425's were single plane.  The earlier ones were dual.  
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

The Tassie Devil(le)

I thought Black Smoke would be running extremely rich in the fuel mixture department.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

Walter Youshock

Likewise, I don't know much about the 8-6-4 outside of the fact that a lot of people disabled the solenoids.  Being a one-year feature doesn't help matters.

A 92-year-old member of my church bought a Sedan deVille when he retired.  Both he and the car are still going strong!  He told me the only thing he ever did with it was to readjust the rockers.  The car has about 200,000 miles, the 8-6-4 still works and the car doesn't smoke or anything.

This sounds more like a fuel delivery problem than something related to the 8-6-4.  I don't think it would be computer related.  Has anyoe looked at the injectors for crud?  If the car sat for a long time, it could be the culprit.
CLC #11959 (Life)
1957 Coupe deVille
1991 Brougham

TJ Hopland

I imagine it would depend on the conditions, the engines that I have had running rich dont tend to smoke that much.  They do build up a black layer of carbon in the exhaust quick and also leave black deposits where the condensation drips so I suppose that would imply that there is a black component to the exhaust.  All my smoke problems have been oil related but that may just be me, your results may vary.  For me fuel problems tend to make more of a grey / whiteish  smoke like water does but the difference is if its water it disappears quickly but fuel tends to hang in the air like oil does.  Luckily its been a while since I have had a big issue so I may be remembering wrong. 

Depending on how long it has run with this issue the cat converter may be blocked now causing additional problems.   

At idle you should be able to easily see through the fuel stream coming out of the injectors.  It should also be a nice even sort of fan like pattern.   If there are open spots or fatter parts of the stream they are dirty.  Since the 80 and 81's had some different parts than the later models I wonder if perhaps at some point some of the wrong parts were installed at some point?  I would assume that the sensors could have looked the same and had the same connectors but the internals were different.  IIRC the service manual gave many of the specs for the sensors and many of them could be checked with a simple volt / ohm meter. 

I have never had a fuel pressure regulator fail on a tbi but I would imagine they have vacuum connection to the intake and like on the multiports and when they fail you get fuel direct into the manifold so the result is hard starts and running rich.  Usually this does not trip the check engine light. 
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

Tim Pawl CLC #4383

The 4-6-8 engines have a very neat feature..its self-diagnostic. With the engine running in PARK ,simultaneously press the "OFF" and "HOT' (Red higher temperature) buttons on the climate control until two dots appear, release the buttons and the display will cycle through the error codes. There is a supplement to the 1981 service manual that has a page with all the codes. Typically "33" is the "MAP to BARO"  check when the car is cold and this sets the fueling when cold (Think of it as a electronic choke) If this is a mismatch it goes to maximum rich and gives you the Black smoke you are seeing.  After it cycles through the code numbers twice, watch for the number "70" to appear. When 70 appears you must press "OFF" and "HIGH" buttons at the same time and hold until two dots appear, release the buttons, This clears the codes, watch for "70" to appear and then press any other lower button such as "OFF" or "VENT"   This will turn the "Check Engine" light off, the car should start running much better at this point, as it also monitors engine coolant temperature to adjust (lean out) the fueling rate.

Tim Pawl CLC#4383

Regarding swapping Carbs  in replacement of Fuel Injection, use the 1980 Intake manifold and Carb it is a direct substitution. One thing to remeber the Distributor on the 1981  4-6-8 engine uses electronic spark advance (i.e. computer control) so you may want to grab the distributor from the 1980 as well for the mechanical (vacuum) spark advance.

Otto Skorzeny

I love those OBD1 computer systems.

The only "new" car I've ever owned was a 1988 Dodge Dakota.

By cycling the ignition switch from off to on the requisite number of times, you could get all the error codes stored in the computer since the last time it was checked.

The engine light on the dash would flash while you counted (and wrote down) the number of flashes. It would pause and then flash a new sequence. All you had to do was look up what the number of flashes meant in the shop manual. It was simple and effective and the Do-it-yourself-er could diagnose his own car.

No need for a computer system and special jacks that cost hundreds of thousands of dollars.
fward

Ask not what your country can do for you, but what you can do for YOURSELF

HUGE VENDOR LIST CLICK HERE

nick.stratta

Gys, Especially Tim,
Many thanks! Tim, I think you may have hti the nail on the head. Sounds plausibly like what has happenned.  So the computers in the car may be OK, even after 12 years standing shut up.  The interior survived reasonably well. A bit musty from being closed but otherwise OK.
Maybe we'll see if we can get it going. It's probably dry seized though after 12 years standing. Time to pour something in the bores to soak in there.
regards, Nick
regards & thanks Nick
CLC 23023, CLCMRC Museum benefactor 113

Otto Skorzeny

The ol' Marvel Mystery Oil to the rescue once more!
fward

Ask not what your country can do for you, but what you can do for YOURSELF

HUGE VENDOR LIST CLICK HERE

Guidematic


To me it sounds like the owner just threw a couple of ECM's at it thinking that was the problem. Obviously he has not spent any time, nor has anyone else, really looking into the problem. Use the self diagnostic feature to its' advantage to scan for trouble codes. The black smoke is certainly caused by over fueling, but what is causing that?

Early 80's cars had problems with the connections on the temperature sensors, particularly the CTS and IAT sensors. The wiring could break at the sensor. There was an update to a proper weatherpack connector for these sensors. If the wiring breaks, then the ECM thinks the temperature is -45F, and fuels the engine accordingly.

This is no wa connected to the cylinder deactivation. That is only activated when the engine is up to operating temperature and is in top gear. If the ECM thinks the engine is cold, then it will not work.

These are really pretty simple systems compared to what we have today, and diagnosis should not be too difficult.

Mike
1970 Fleetwood Brougham 68169
1985 Eldorado Coupe 6EL57
1988 Eldorado Biarritz 6EL57
1990 Brougham d'Elegance 6DW69
1994 Fleetwood Brougham 6DW69

nick.stratta

Mike,
Think you are right - wil look into it in more detail.
regards, Nick
regards & thanks Nick
CLC 23023, CLCMRC Museum benefactor 113

TJ Hopland

It will be cool if thats all that is wrong.   Are those sensors hard to find?

I bought a chevy truck a few years ago that 'needed a new engine'.  It ran but very poorly.  It came with 4 computers, 4 map sensors, 6 o2 sensors, 3 tps, 2 egr, and a complete throttle body.   Base timing and idle were set wrong.  Put them back to factory spec with the computer in the proper mode and it ran great.

I have also bought several 307 equipped cars over the years that 'needed new motors'.  All of them just needed the choke fixed and the cat unplugged.

You just have to take the risk that its simple.  If the owners think the motors is shot it should be priced right so the risk should not be that great.
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

nick.stratta

TJ, thanks indeed - looks like it might be just in limp home mode, as Tim says, so may be a non parts required fix!
thanks, Nick
regards & thanks Nick
CLC 23023, CLCMRC Museum benefactor 113