The "negative feedback" term is with the way the EGR valve operates
internally... this http://tinyurl.com/5ehap9
probably explains it better
than I can (with pictures added for clarity, no less 8^) ). The feedback I
am referring to isn't feedback on valve position to the PCM.
The OP didn't say ground electrode but did mention the "element"... I may
be wrong, but I am assuming that this is the centre electrode he is
referring to... At the same time, it is common for some erosion to occur
on
the ground electrode, especially on plugs at or beyond their expected
service life... And we must also consider what motors are fitted with a
wasted spark system... The "ground" electrode will suffer more erosion
than
the centre electrode on the negative side plugs. But here is where careful
inspection is required... Is the electrode eroded or is it melted away?
Erosion can occur from oxidation, corrosion, fuel quality (perhaps even
fuel
additives) or even the metallurgy of the plug itself. A spark plug with a
burned away electrode could be because of pre-ignition, detonation or
faulty
EGR operation. or any other circumstances that keep the spark plug hotter
than intended.
Remember, the spark event typically lasts for 1.5 milliseconds (most COP
systems are now "multi-striking" at idle)... during this time, the spark
plug is at it's hottest and, depending on the system, one electrode or the
other is being bombarded by a stream of electrons... and this can create
the
condition...
HTH.
"Happy Traveler" <happy_traveler@[EMAIL PROTECTED]
> wrote in message
news:4MmdnXrciJmYo4PVnZ2dnUVZ_gWdnZ2d@[EMAIL PROTECTED]
> Hi Jim,
>
> Thanks for the compliments!
>
> A couple comments:
> 1) I still have one of those mid-80 Fords (to be donated to a
> not-so-well-off friend, as soon as I can replace the worn control arm
> bu****ngs). The EGR is not a negative feedback type, but uses a position
> sensor - a potentiometer mounted on the top.
> 2) In my humble experience of repairing my own vehicles for the last 30+
> years, I have never seen a ground electrode that's totally burned - not
> even close. So what else would cause such thing?
>
>
=============================================================================================
>
> "Jim Warman" <mechanic@[EMAIL PROTECTED]
> wrote in message
> news:mb9Tj.251$Yp.126@[EMAIL PROTECTED]
>> HT, you have a very good grasp on the subject of pre-ignition... A gold
>> star for you 8^)
>>
>>
>> For the OP.... it is normal for spark plug electrodes to suffer from
>> erosion... Pre-ignition will tend to leave deposits on the ground
>> electrode if it is severe or has been left unattended for any length of
>> time...
>> If this vehicle is, indeed, a 1986.... IIRC, Ford used a "negative
>> feedback" type EGR valve... There is a small ****t inside the valve that
>> can carbon over and this would have the effect of having the car "nose
>> over" on light acceleration...>
>
>
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