"Scott C" <sns1820@[EMAIL PROTECTED]
> wrote in message
news:hY0Tj.13459$V14.5429@[EMAIL PROTECTED]
> A friend of mine has a 1986 Ford Explorer. It's runs very rough from 700
> (idle) to about 1500 RPM. He's found several things wrong and fixed
them,
> but the problem is still present. He took it to a mechanic who removed
the
> plugs and found the element (for lack of a better word - where you gap
the
> plugs), burned totally away - it was not there any more. The mechanic
> explained this as a pre-ignition problem, it's getting way to hot - and
he
> was not surprised the pistons did not have holes in them. The
compression
is
> good, but the mechanic seems to think the valves are being pushed into
the
> valve seats very hard. To me it seems like the valves are closed to long
> when the engine fires - but I don't know.
>
> Can someone explain pre-ignition in more detail than it fires early.
What
is
> the cause of pre-ignition? A timing belt problem? Seems the timing is
> off,but checks OK.
>
> Thanks
>
> Scott
>
>
Well, I can't explain pre-ignition but rough idle is often caused by a
dirty
IAC valve (located on the intake manifold on a 1996 4.0 V6). If you
really
have a 1986 Explorer I'm not sure what you have--a pickup, perhaps?
It sounds like this vehicle has been neglected so if it was me I'd replace
the air cleaner, serpentine belt, spark plugs, plug wires (Motorcraft or
at
least Bosch--don't get the cheap ones), fuel filter, check all the vacuum
hoses, check the vacuum cluster on the intake manifold for loose or
contaminated fittings (look for automatic transmission fluid on the
fittings), check the coolant level and determine if there is a head or
intake manifold gasket leak, and clean the throttle position, idle air
control (IAC), and mass air flow (MAF) sensors with some brake or carb
cleaner and then see what you have. Also check the battery cables and
make
sure they are solid.
If you have clouds of white smoke at startup it might be burning coolant.
If it's burning transmission fluid it'll probably run rough at low speeds
but your transmisison would probably be slipping due to low fluid level.
The good news is that if your compression is even it's probably not a head
leak.
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