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76 Eldo (54k), 76 Eldo (52k), 78 Eldo (9k), 85 Deville (43k)
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668 Posts
Discussion Starter #1
Hi all--

So I've been driving my 1985 FWD Deville around for some time now, fussing around and playing with some things, and I found another HUGE cause of my power loss: sticky valves.

Before I bought my car, the previous owner had a new intake gasket fitted since the old one blew. The antifreeze seeped into the engine oil and the car overheated.

Ever since I bought the car, I've experienced "leisurely" acceleration. Acceleration seemed strong up to 1/3 throttle, then was somewhat spongy. My car also seemed to accelerate better when cold. Many little things, like a new crankcase breather and coil, have served to abate my problem, but over the past few days I found another culprit: sticky valves.

If you car has a lumpy idle in drive, backfires under heavy acceleration, or just doesn't seem to have a lot of get up and go, I HIGHLY recommend the following procedure, which has served to give my car a big power boost.

Remove both valve covers from the engine, and start the car. Warm it up to operating temperature. Some oil will drip/squirt, but not too much. Don't worry though, this procedure is worth the small mess. Take a can of carburetor cleaner and douse the valves with it while the engine runs. Rev it a bit while doing this. Then, shut the car off and change the oil. If you use enough carb. cleaner, it should trickle down the valves and help dissolve gummy anti-freeze residue on the valves caused by leaky gaskets.

For those of you who've blown a head or intake gasket, this procedure can only help. You'll be amazed by how much quieter your 4.x engine's valvetrain will be. Left uncured, this gummy antifreeze residue can cause valve float and even create bent pushrods.

For a quick, 5-minute fix on 3 or 4 of your 8 cylinders, remove the oil fill cap and spray the nearest valves with the engine running. Then, remove the crankcase vent tube from the other rocker and do the same thing. If this helps, you should really remove your valve covers and spray all valves.

As the engine warms, the gummy antifreeze deposits get progressively more sticky, causing acceleration troubles. If your car just doesn't seem to have the power it once had before you changed your gasket, try this procedure. It has helped my engine immensely.
 

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93 Sedan Deville 4.9L
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1,005 Posts
Do you think 1/2 can of seafoam in the oil a few mins before a change would accomplish the same? I just did that, didnt notice much change though. Mine has not blown any gaskets afaik and is not up to 100k miles yet so maybe mine just were not too bad to begin with
 

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76 Eldo (54k), 76 Eldo (52k), 78 Eldo (9k), 85 Deville (43k)
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668 Posts
Discussion Starter #3
I doubt yours were bad at all if you didn't have any blown gaskets. 4.9 engines usually are very clean under the rockers. They also had "scraper" valves that cleaned the seats and the guides. These were also outfitted on the 4.5 engines.

This tip is very pertinent for those who own HT4100's.
 
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