Re: help! hesitation again

[Scott Fisher <sefisher@cisco.com>]

Rocky Mullin mentions:
        
        i forgot to mention - before this hesitation problem
        recurred, i had pulled off the freeway to fill up 
        with gas.  i was literally running on fumes.

Ah.  Now, it's always touchy troubleshooting from one kind of vehicle to
another, but I had a similar experience with hesitation (so extreme as
to practically keep the car from running, though it would idle fine)
after running a gas tank down near empty.

The culprit in my case was sludge, crud, and slime from the bottom of
the gas tank.  It had been picked up and deposited neatly into the first
choke of my front Weber 40DCOE, effectively shutting down that
cylinder.  

What was especially maddening is that, Webers being known for
susceptibility to dirt, I'm pretty good at the usual drill: unscrew the
jet cover, pull out the jets, remove the idle circuit, spray some carb
cleaner in and blow it out backwards with compressed air (*do* wear face
protection).  Takes, oh, less than ten minutes to do this on all four
chokes.

No dice, in this case.  The crud was somewhere deep in the bowels of
carburetor #1; repeated cleaning did nothing, and dialing the #1
cylinder's idle circuit from one extreme to the other made no difference
in the car's performance.

I ran a high concentration (full bottle, half tank) of Techron through
the car, suffering and stumbling and driving carefully all the way, and
in a few miles it cleared up.  Of course, I replaced the fuel filter at
that time, too.  The stuff that poured out the intake end of the old
filter when I removed it looked like the last sips in a cup of Turkish
coffee.

So one suspicion (which I'd had when you described the symptoms, and
which is stronger now that you mention the running-on-fumes episode) is
that gunk plugged up some portion of your fuel injection system, either
an injector or two, or possibly the metering head -- that would explain
why it was running poorly till you floored it, because that would cause
the metering plate to raise the piston all the way up past the blockage
in the metering unit.  And the car would run at idle because enough gas
to keep it ticking over would trickle past the obstruction.  But in the
middle, where most of the time is spent driving (yes, even if you drive
like we all do, with what someone described as a "binary throttle"), the
blockage is enough to cause really ugly behavior.

Try swapping out the fuel filters, add some proper fuel system cleaner,
and drive gingerly for a day or so while the blockages get dissolved. 
You might also want to look at the injectors and see if they're badly
blocked; how difficult would it be to blow compressed air through them
backwards if you removed the opposite end from the metering head, or is
there then some unobtainable gasket set required to hold it in place?

Best of luck,

--Scott Fisher