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472 running on 7

Started by brian rachlin, December 11, 2006, 11:31:03 PM

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brian rachlin

Hi,

I have a 69 Eldo with a 472 in it.  It has a bad miss, and when I pull off the plug wires one at a time, the only cylinder that does not seem to make a difference is the rear cyl on the passenger side, (number 8?.

The plug wire will arc if I hold it next to the plug.

What should I check first?

I am thinking a compression check of that cyl will tell me if the valves are opening and closing...

Advice?

Thanks,

Brian

Bruce Reynolds # 18992

Gday Brian,

Yes, do a compression check, but as well as doing the standard one, do a wet one by squirting a few squirts of engine oil into the Cylinder with an oil can, and then note the difference.

If the pressures rise substancially, then the rings in the offending cylinder are at fault, but if the pressures arent that much different, then the valve seats ate a problem.

Your cranking pressures in all cylinders should be around 200 psi for a good 69 engine.

Plus, when doing the compression check, remove the coil lead from the coil, and wire the throttle fully open, and remove the air cleaner.   This way, all test procedures will be the same and you wont be flooding the engine with petrol each time the engine is turned over by the Starter.

Bruce,
The Tassie Devil(le),
60 CDV

Art Woody

Bruce has good advise AFTER you check the spark plug on the afore mentioned cylinder. You already said you have spark to the end of the wire, but how much? Also try swapping that wire temporarily with a wire from a known firing cylinder.

Jim Garner

Rear plugs often foul with oil when the valve guide seals are worn or cracked. I would suggest changing the plug for starters.
Jim

denise mccracken 20352


   Does it have air conditioning?  I used to do tuneups where I would find 7 plugs of one brand and the rear passenger side a different one, because it was too much trouble for somebody to reach that one spark plug behind the evaporator case.

   Start just by looking at the spark plug.  Is it white?  Dull black?  Oily?  Does it smell like gas?  Usually you can get your answer there.

-denise

brian rachlin

Thanks for the advice.  I think the plugs are all pretty easy to get to including the rear one.  I will pull the plug and see if it has been firing or not, and try new plugs, and swap the wire to see if the problem follows the wire.

Condition of the points/dwell/timing is also unknown, I just bought the car last Saturday.

Its a Black 69 Eldo, PERFECT interior, nice chrome, decent paint, BUT...mildly customized with a Gold and black two-tone, very nicely done, 4 wide whites (new Goodyears) And gold painted centers on the hubcaps.  Quite pimped.  I will post pics soon.  I think it would look much better with the OEM type whitewalls, and since the hubcaps are painted already, I may paint them black to match the sides of the car, which are black.  The gold is on the hood and trunk, with very tasteful pinstriping separating the two colors.

Neat car...

Thanks,

Brian

brian rachlin

The rear plug on the passenger side (number 8?) was fouled.  I know the car was sitting for a while.  I cleaned and gapped the plug, and it runs great!

I will put a new set of plugs and wires on it over the weekend.

Easy fix, thanks for the input.

Brian

Bob Dziewit

If the wet test does not increase the readings, it could be something more serious.  I once bought a used 69 that had a hole in the piston and yet it ran fairly well the 20 miles back to the motel parking lot where it went on my trailer.  This reminds me of the common used car ad line runs good.  Most large American cars of that era run good or not at all.

Dennis

You may have simply found a symptom of a larger problem.  Sure, you swuared away a fouled plug, but you have to ask yourself, why was it fouled?  Was it the only one?  You may have to periodically square away that same plug within a hundred miles or so--or longer--or shorter.

Chandes are you have a failing valve guide which is allowing an exorbitant amount of oil into that one cylinder and its whicking onto the plug.  

I had the same problem in an old 350 ci GM motor.  I knew I had the problem, but had to drive it about 150 miles round trip.  I squared away the plug before I left, thinking that itd be ok for the trip.  Shoot.  I got to my destination and had to go to Sears to buy a socket and ratchet and a wire brush to square away the offending plug. I had to stop once on the way home to square away the plug one more time just to make it home.

I later refreshed the heads: 3 angle grind, new guides and umbrella seals. ($215 for parts and machining) but I pulled and installed the heads myself.  Piece of cake.

Dennis

 

Geoff Newcombe #4719

Dont get in a sweat about the fouled plug until you see what happens next.  Could have just been a piece of carbon that got in between the electrodes and fouled the plug, might never happen again.

Back in the late 60s/early 70s we took a pretty 65 or so Chevy coupe with a 283 in trade for a new Pontiac.  The Chevy was a smoker and would regularly foul a rear plug; both the fellow trading it in and I figured there would be engine disassembly on some scale required to fix it.  Some diagnostic work, and the fact that it was using tranny fluid with no sign of a leak, soon proved the problem to be a bad transmission vacuum modulator that was sucking out transmission fluid.  Replacing the modulator fixed the problem and the car ran like new.  

brian rachlin

I just bought the car, and drove it home on 7 cylinders, hoping it was something simple like a fouled plug, or a bad wire.  Not knowing how old the plugs and wires are, I plan to replace everything.  GM top engine cleaner does wonders for these engines too.  I think I will give it the treatment before I put in the fresh plugs.

Back in the day, we used to tune these bears up about twice a year, plugs and points, new cap and rotor every other time, new wires about every 2 years.

The GM top engine cleaner and putting a little lubriplate on the back of the gas pedal, where it slides on the linkage, makes the car run like new.

This one is an 80,000 mile car, black 1969 Eldo, black cloth and vinyl interior, like new, perfect dash, everything works, even the AC!

Thanks for the advice.  I will do a full compression check, and look for other symptoms.

Thanks,

Brian

Jim Garner

I owned several Cadillacs from the fifties way back when I was a young man. One problem I encountered a couple of times was sludge plugged oil drain holes causing a buildup of oil inside the valve cover. This was evidenced by a big puff of blue smoke when the car was first started and when it had sat at a idle for a period of time. It also will cause the rear plugs to foul. Rodding the drain holes out helped the problem.
I am working on a 1962 Eldo now. It is my first Caddy since a 1959 Fleetwood which I wish I still owned.
Jim