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HELP PLEASE! 1981 Fleetwood Coupe

Started by 80redcoupe, April 30, 2022, 10:56:17 PM

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80redcoupe

Team,
I could really use some advice/help.

Recently purchased a 1981 Coupe Deville. The car idles well when cold and idle will get higher as vehicle warms up. The major issue I have is that it backfires and bogs HEAVY on acceleration. Worse from a stop. Pops and backfires through intake. I have checked codes and come up with code 23. I replaced the ignition module. Currently no codes, but still same problem. I checked timing at 10* with green connector disconnected. Also checked fuel pressure. Right at just over 10 pounds at idle. Does not drop off on accel. Replaced plugs, fuel filter, caps, rotor.

VERY frustrated at this point. Can anyone offer some ideas please?
R Clerie

V63

#1
Could the fuel be  'stale'? ( older than 6 months) Typically causes valve stem sticking and then complete  seizure

TJ Hopland

Popping through the intake would be a timing issue of some sort.  It means you are getting some sort of burn going on when an intake valve is open.   Could be an ignition timing issue, perhaps not an actual timing adjustment but some sort of issue.  Could be a sticking or damaged valve.  Could be a cam timing issue. 

Like many engines of the era these had a plastic covered cam sprocket.  Age and or mileage isn't kind to these so if it hasn't been replaced its possible that it has come apart making the cam timing very sloppy.  Easiest way to get a hint if that is a possibility is to remove the distributor cap.  No need to remove the wires just twist it out of the way so you can see the rotor.  You then rotate the engine by hand in one direction so the rotor starts moving.   Either turn it so the timing mark aligns with the gauge or make a temp mark with some tape or chalk.   Now turn the crank the other direction till the rotor starts turning the other direction.  Note the distance of crank travel that took.

You can figure out how many degrees the distance is by getting the scale off the timing gauge.  There should only be a few degrees slop there.   If there was a lot you probably need to investigate further and likely replace the timing set.  luckily you have a RWD car which doesn't require the engine to be removed to do it.

If the cam timing is solid then I would check the regular ignition timing.  Note that to do this as well as base idle speed you have to go through some specific process to put the computer into the proper modes then set things to the setting in the book.   You can't just get make up settings or try and do them without the computer in the proper setting modes. I don't recall the process for an 81 but can go look for my 81 manual if you don't have one or someone else doesn't have one.   If you are going to work on one of these you do really need a factory service manual.   
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

80redcoupe

Thank you for the replies! Means a lot to know we can help support one another in our "addiction" to these old girls!

The fuel tank is new, so fuel is fresh. I like the idea of timing chain going bad. My 80 coupe had the timing chain disintegrate. COMPLETELY forgot about that.

TJ,
THANK YOU and I will be sure to keep us all updated.

R Clerie

The Tassie Devil(le)

G'day Roland,

You have an email from the Moderators that requires your attention.

Thanks,

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

Saturnin15

It happened to me on my 1981 Pontiac Parisienne.  The problem was a cam lobe that was eaten round.  I know it is a common issue for the chevy 305 like in my car.  I don't know if Cadillac engine may have this problem.
Sedan Deville 1956

V63

Some additional  thoughts.

Given the tank is new,  can it be assumed it's because the old tank had rancid fuel?
The typical symptom of engine damage from rancid fuel is sticking or stuck valves. The tank is new but Additional damage may remain?!

The 1981 models had V864 that deactivated cylinders.

Exhaust Catalyst damage was a problem, check for restricted exhaust.