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Old 03-04-2007, 01:49 AM   #1
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Default Spark knock, preignition, detonation? Causes?

I have been battling a problem for a long time with my driver. Engine has a great deal of spark knock upon acceleration or load while cruising.

1990 LE, used for daily long trips, example, friday was 300+ miles. Plugs are 15k miles old. Oil gets changed about every 5k.

A can of seafoam in the tank will greatly reduce, but not eliminate the condition.

Never a trouble code or SES light.

144k miles.

My gut feeling is carbon in the cylinders that refuses to burn off, or oil being introduced into the cylinders.

Cooling system seems to be working as advertised, recent thermostat change and radiator flush and repair.

Last compression test was 170ish on all 6 holes.

uses about a quart every 1000 miles.

Where else do I need to look?
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Old 03-04-2007, 02:27 AM   #2
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A quart every 1k miles? There'* a good source for KR.
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Old 03-04-2007, 02:27 AM   #3
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Old 03-04-2007, 01:07 PM   #4
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With my compression being high, where would be some good places to look for the excess oil consumption? I can't take the car off the road too long so if you think rings or something major, I might be better off picking up another engine to I can swap over a weekend.

Former owners were elderly folks who stopped driving it and it sat inactive for a few years. If that helps in suggesting where the problem is at

Its only gotta last in "road warrior" status for about 3 more months. After that I will either have a company provided vehicle or another job.
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Old 03-04-2007, 01:52 PM   #5
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High compression doesn't necessarily mean you don't have problems with the oil control rings, or stem seals for that matter. You will need to do a leakdown test to find out for sure the sealing conditions are in that engine. My educated guess is that if you are losing a quart ever 1k miles, and no visable leaks on the outside of the engine, you are burning it and your plugs are fouled.

Another scenerio which for some strange reason just popped in my head: winter gas blend. But that only explains the knock, not the oil consumption.
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Old 03-04-2007, 04:33 PM   #6
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Quote:
Originally Posted by sandrock
Another scenerio which for some strange reason just popped in my head: winter gas blend. But that only explains the knock, not the oil consumption.
maybe your right and he has some leaky gaskets on top of it all?

Edit to say - Is your engine oily? check around your oil pan for oil also...
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Old 03-04-2007, 05:04 PM   #7
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No leaks. Everything is snug and dry underneath. Since its leaning towards internal engine work, I will cross my fingers that it lasts another 3 months, then maybe the pressure will be off a little for me to deal properly with it.
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Old 03-05-2007, 12:05 PM   #8
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Default knock

Spark knock is frequently caused by timing or low octane fuel or the ethanol they are adding. could also be deposits on the intake valves.
In addition your TPS could be out of adjustment resulting in the timing being off.
You could try another brand of gas, an anti knock additive or rislone in the oil to clean up the valves. Also check the voltage at the TPS signal wire at idle position.
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Old 03-21-2007, 09:52 PM   #9
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Wierd thought hit me today. What if I have an intake gasket sucking oil from the lifter valley area? Is that a likely cause too? Knocking and oil usage hasnt gotten any worse. Hopefully soon enough I will be able to fix this properly. Its still getting 250-300 miles per day as my service vehicle.
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Old 03-21-2007, 10:08 PM   #10
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I'd pull all the plugs & inspect them. Keep track of which cylinder each one comes from.
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