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96 sedan deville
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55 Posts
Discussion Starter #1
hi everyone.i hope someone can help me with this.a friend of mine has a 88 fleetwood brougham that he says it only has 30,000 miles on it.the guy he bought it from got it from an elderly couple and was supposedly used just to and from church and to the store and back.the other guy sold it to my friend.it had sit for 2 years prior.he is wanting to trade me the caddie for a ford aerostar van that i have.he drove the car to the store so i could hear it run and drive it.well he called me and told me it had a knock that he thought it was a pushrod.when i got there and started it up there was no smoke or anything there was no knock at idle.when i revved it a little the motor knocked pretty bad.i told him i thought it was a rod knocking.is there anything else that can make the motor knock that bad besides a rod knocking?someone told me a knock sensor could make one knock like that.someone had told me since the car sit for 2 years it could possibly be something with the plugs or wires to make it knock like it was.{never heard of that}i would like to trade for this car but not if i have to put a new motor in it.it has the 5.0 engine in it.i have never heard of a knock sensor to make one knock that bad but anything is possible i guess.i hope one of you guys can give me some answers.thanks.
 

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1989 Sedan DeVille is now just a fond memory ....
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10,429 Posts
You might want to try a can of EOS (engine oil suppliment) from GM, it adds lots of good slippery lubricant to the engine. Since it has been stored it may have "dried out" and needs a little extra help. If that doesn't quiet things down then I would suspect a little more serious problem. Give the EOS a try first, that'll only set you back a few bucks.
 

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'86 Brougham
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54 Posts
30k in almost twenty years! You could be looking at the holy grail! If he'll let you drive the car to a shop, have the compression checked, pay for the inspection, and make your decision. My suspicion is the knock comes from internal engine parts not being oiled. He may have changed oil every 3000 miles, unfortunately equalling two years of time for the oxidation procedures to do their thing on each oil change! Build up, more, build up,more....
If the price was right, and sludge was the knock cause, I'd buy it in a heartbeat and go to auto-Rx.com, spend a hundred bucks, and be the proud operator. You'll probably have to include a carb rebuild and replacement of every rubber hose and belt into the $ equation. That's a lot - brake hoses, vacuum hoses, fuel hoses, coolant hoses, drive belts, etc.
I find this the best way to buy a used car that you want to keep for a long time though.
I did this with an 86 that came my way in 1995. Still running today.
 

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94 FWB, 93 SDV, 94 FWB (sold), 90 Brougham (sold)
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3,730 Posts
I'm guessing ChiTDI has it right. With only 30,000 miles and having sat for 2 years, the engine probably should have been oil primed before it was started the first time. Let's hope it's just something simple like buildup. However, if it is the knock sensor, it's an easy fix.
 

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Actually, the prolonged sitting would be far harder on the transmission than the engine, but "IF" you are sure it's a heavy knock and (sounds like a bearing knock), and not just a top-end noise like a weak lifter might make, then it is either a bearing knock or a "carbon-knock". The two sound virtually identical because the carbon knock causes the same parts to make the noise. It's actually more likely to be a carbon-knock IMO unless the engine was seriously abused or run without oil for a time. It's also possible that the oil is diluted and causing a problem. First thing I'd do is verify the oil is good and then apply a can of top-engine cleaner to the engine to clear any carbon. Chances are this will get the engine running quietly again.
Hell, either way, chances are the car is well worth getting even if the engine is in need of a bearing or two. With that low mileage, I'd pop a bearing in that puppy and go driving!
 

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That's generally a CRACKED flex-plate that can make a noise like that. And you're right it CAN be mistaken for an engine tap or knock. It's usually a more intermittent one though. Not a rythmic one like a rod-knock or lifter tap. At least the ones I've heard over the years.
 

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96 sedan deville
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55 Posts
Discussion Starter #8
thanks guys.this info is greatly appreciated.i will look into it and let everyone know whats going on with it.i have a 96 deville with the northstar with 159,000 miles that im completely satisfied with.i just thought it would be nice to have an old caddie.there is a 66 caddie sitting up the road from me.the guy want sell it though.just sitting wasting away.just makes me sick to see a classic like that just sitting.
 
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