backfire (?) problem question

[Mike C]

Hi:

the engine is 3.9 L ( how gay ) in a '90 van -- fuel injected of course

it may only happen when it gets too hot ( which is sometimes )
but on the highway when i get to cruisin', it will act like it backfires
if I syay on the gas or give it more - hard to tell if it's a backfire
without being able to stand outside and listen ( highway noise )

It will lose power for a split second like an engine would if
the fuel filter were going bad but it only jerks once rather than
a repeated jerking like you'd get with the filter prob.

The computer has been replaced within 1.5 yrs as well as the coil, pickup,
and converter.

I'm running a hot thermostat and
it may be causing the coolant level to become low despite the bars leak and
no obvious leaks. Last time I topped off the coolant and ran it ( not hard
but it should have missed / backfired ) the temp stayed down and
I had no probs.

Could this jerking / missing / pop sound be caused by over heating?
If so, is it due to early detonation / late detonation?

thanks in advance for your help,
mike
cm...@ptd.net