It's Impossible 2

[Terry Martin]

Tuck wrote:
> 
> Switching out the fuel pump accomplished exactly zilch.  Same problem as
> before - stumbling at high rpm's (starting at, and randomly above 3800 rpm
> - which is where the secondary injectors switch on).
> 
> Engine temperature and atmospheric conditions have no effect whatsoever
> (perhaps slightly worse when cold, but it'll do it on a 100+ degree day).

Somebody way brighter than me said if you eliminate the impossible all
that remains is the fact. If you have eliminated everything that can
possibly produce this effect, you have an overall system fault, which
means the arrangement you have will always do what it does.

I can see a couple of assumptions right off:

a) Engine temperature and atmospheric conditions always have an effect,
noticeable or otherwise. I can produce condensation at room temperature
by simply breathing on a mirror.

b) You have changed out apparently everything, effectively replacing the
system. Don't assume the replacements work. If they come from the same
manufacturing batch, they may have the same problem. 

c) The indication that the problem starts when the secondary injectors
switch on suggests that if the problem is not with the injectors,
something else is coming on or going off line at the same time as the
2'nd injectors. Does it always do that, or is it intermittent? If it's
intermittent you're screwed, but I would start checking every single
electrical ground in the system. Put a digital ammeter directly between
the high side of the electrical block and watch the total electrical
demand. Check for "back-feeding" from injector circuits, induced
transients, and all things electrical. 

d) Have a terrible crash and burn. :-)

T