Re: overfiring

[Daniel Youngquist <dany@domain.elided>]

On Sat, 6 Dec 1997, J MICHAEL SHAW II wrote:

> Okay, I know you guys are sick of hearing about this problem, but I
> have a new question.  I thought it was going to be a few weeks before
> I had any new input, but I just found out, from the guys that fixed a
> leak in my exhaust manifold, that I have some leak in my intake
> manifold.  Could this cause misfiring and "bucking" once the engine is
> warmed up and travelling under load.  My thinking is, once the engine
> is good and warm, and some minor level of "expansion" takes place from
> the heat, this leak could be increased by the increased vacuum created
> under load, causing a very faulty air to fuel ratio going into the
> cylinders.  Does this make any sense to anyone, or am I reaching here? 

Vacuum _decreases_ as load increases, so the higher the load, the less
effect a vacuum leak will have.  Also, a vacuum leak only leans out the
mixture, so the affected cylinders would fire normally but with less
power, or maybe not fire at all if they're too lean.

I don't remember if anyone's mentioned this yet, but it occurs to me
that your problem might be a buildup of carbon in one or more cylinders.
When the engine warms up the carbon gets hot enough to ignite the fuel
before the spark does -- maybe way before, depending on how much heat,
carbon, and fuel is present.  The warmer the engine and the more fuel is
present, the greater the effect.

Regards,
Daniel Youngquist | INTERNET MEMORY EXCHANGE |     HOMESTEAD PRODUCTS
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