Re: pinging on 4.7

From: Bob Tom (tigers@bserv.com)
Date: Fri May 31 2002 - 19:25:26 EDT


Hi, Ray.

At 10:48 PM 5/30/02 -0400, you wrote:
>I'm really curious about this pinging in 4.7s. I see a lot of posts about
>this with colder plugs, higher octane and 180 thermostats as the solution.
>
>My 4.7L '00 Grand Cherokee 4x4 has 24,000 miles, original plugs and
>thermostat and a steady diet of 87 octane. No pinging whatsoever!? It's
>run a best of 15.58 in the 1/4 with 15.80s common place in hot weather.

Do you have any slow cars or drivers in your family :-P

>Is this pinging issue only with newer 4.7s? Anyone have a theory why so
>many people have this problem and my '00 doesn't? Is it just a Dakota
>problem? If DC got mine right, why didn't they get all of them right?
>(oh yeah, I forgot, if it ain't broke, pay an engineer to fix it!) :-)

There have been a lot of posts in the past about pinging on the magnums
3.9/5.2/5.9. A major reason for the problem was the barrel intake and
a belly pan gasket prone to leaking.

I've only recently become aware of some pinging complaints on the 4.7 .

Two of the most common sources of pinging is excessive carbon buildup
and excessive cylinder temps. The leaking belly pan gasket leads to
an oil consumption problem which, in turns, leads to excessive carbon.
Other excessive carbon causes something causing the engine to run
way too rich. Excessive cylinder temps results in the sharp edges
of the piston to ignite the mixture. One case would be the result of
some problem in the cooling system. Hence the use of a 180 tstat
combined with reduced antifreeze/water ratio and use of something
like water wetter, or cooler temp. range plugs to dissipate the heat
away from the cylinders more quickly.

Here's something that I've come across that is controversial ... a properly
tuned engine pinging. Yes, they should ping, a little under certain
conditions.
Engineering is a field of compromise. You want the most power, the best
fuel economy, the cleanest emissions (by some, anyway), and the longest
longevity out of any engine. But each of these conditions requires different
tuning, generally opposite from each other. An engine needs to be tuned
to operate at a sweet spot that is the compromise of all requirements.

Pinging can be the result of high combustion temps, and this is the type you
would expect to occur. High temps are caused by a combination of lean fuel
and advanced timing. Lean fuel produces higher combustion temps and hence
more power. It also produces higher emissions and potential engine damage.

When the engine is under severe load and a low RPM (like climbing a steep hill
in top gear) then engine temperatures rise and will begin to ping. That is
normal.
That is desired. Yes, you are damaging the engine and melting the piston.
That means that you have crossed the line and are no longer is that compromise
zone. That is good because engines are not meant to be operated in that
fashion.
Pinging, in this case, means it is time to downshift.

Why pinging happens on some engines and not on others of the same type
is a mystery to me.

I am pinging MYSELF(temp. rising) now that I have just found out that
the Cayuga track won't be open in June (arrgggghhhh) :-)

Bob



This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 12:04:37 EDT