GM 3.1 Piston Slap cylinder missing

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slacorte@yahoo.com - 21 Dec 2004 18:49 GMT

I noticed this weekend that my 1999 Buick Century is developing the
classic symptons of Piston Slapping (ticking noise when cold ... goes
away as engine warms up).

Last night when leaving the office park lot, the engine begun miss
firing, and after about five minutes set the service engine soon lamp.
I took the car to autozone, and they read it with a code scanner. They
said that cylinder 6 was missing. The techy said all the other
cylinders were OK, it was only 6 that was missing.

The plugs, wires and ignition coils are original. The car has about
60,000 miles on it. I pulled the spark plug from cylinder 6 this
morning and it looked fine (no fouling), but the gap was just below
.080. Cyclinder 4 looked similiar. I also did an oil and filter change.
Car seem to run well this morning, with minimal slapping. No new codes
and no missing.

Is the Piston Slap likely to be the cause of the cyclinder miss? Or, do
I have two problems?

Any suggestions on how I should proceed would be greatly appreciated.
Thanks,

Steve

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Steve W. - 21 Dec 2004 19:32 GMT

> I noticed this weekend that my 1999 Buick Century is developing the
> classic symptons of Piston Slapping (ticking noise when cold ... goes
[quoted text clipped - 20 lines]
>
> Steve

Change out the Plugs and wires they have outlived there useful lives.
What your hearing is probably not piston slap but a lifter that is
sticking or has a small piece of crud in it.

Signature

Steve

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Steve - 21 Dec 2004 23:07 GMT

> I noticed this weekend that my 1999 Buick Century is developing the
> classic symptons of Piston Slapping (ticking noise when cold ... goes
> away as engine warms up).

<snip>

> Is the Piston Slap likely to be the cause of the cyclinder miss? Or, do
> I have two problems?
[quoted text clipped - 3 lines]
>
> Steve

Piston slap doesn't cause a misfire, but a stuck valve or collapsed
hydraulic lifter certainly does. And it also makes a ticking sound that
goes away when the engine warms up.

Piston slap isn't a "tick", its a deeper sound- more of a muted "clank".
A single piston slapping can sound a little like a tick, but if all the
pistons have some slap what it really sounds like is a diesel engine idling.

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JazzMan - 22 Dec 2004 02:50 GMT

> > I noticed this weekend that my 1999 Buick Century is developing the
> > classic symptons of Piston Slapping (ticking noise when cold ... goes
[quoted text clipped - 17 lines]
> A single piston slapping can sound a little like a tick, but if all the
> pistons have some slap what it really sounds like is a diesel engine idling.

Will the knock sensor pick up piston slap and cause the ECM
to go into KR?

JazzMan

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Steve - 22 Dec 2004 18:15 GMT

>>>I noticed this weekend that my 1999 Buick Century is developing the
>>>classic symptons of Piston Slapping (ticking noise when cold ... goes
[quoted text clipped - 22 lines]
>
> JazzMan

Knock sensors pick up all SORTS of engine noises and trigger KR.
Wrist-pin noise is notorious for a false KR trigger on a lot of engines.
Both piston slap and wrist pin noise happen at the right time window
in the combustion cycle to trick the computer into thinking its knock.
Some other noises fall at the wrong time (valve or lifter noise, for
example).

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Shep - 23 Dec 2004 00:31 GMT

Good point, but by the time the cars goes into closed loop the noise has
dissipated.

>>>>I noticed this weekend that my 1999 Buick Century is developing the
>>>>classic symptons of Piston Slapping (ticking noise when cold ... goes
[quoted text clipped - 29 lines]
> cycle to trick the computer into thinking its knock. Some other noises
> fall at the wrong time (valve or lifter noise, for example).

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