Possibly OT, ??s about a GM feedback Q-jet

[ae2598 at wayne.edu]

This makes sense too, as the wiring from the plug on the carb seems to be
in series with a coolant temp. sensor.  It looks like the jumpering job
has already been attempted, albeit poorly.  As you correctly guessed, it
is a 305, and it MAY have had "ESC" badges but all the sheetmetal has been
since replaced.

Maybe I should just turn my attention to the carb.. It looks like it has
been rebuilt (well, its cleaner than the rest of the engine!) and maybe
they screwed something up.


 On Fri, 9 Mar 2001, Shannen Durphey wrote:

> That's not a computer controlled carburetor.  The connector you're seeing is an
> auxilliary accelerator pump enrichment device.  The carbs are designed to run
> relatively lean mixtures.  This introduces the problem of lean stumble during cold
> engine operation.  To remove the stumble, the temp controlled accelerator pump
> enrichment allows an "extra" shot of fuel.
> 
> You haven't mentioned it, but I'll bet your blazer was originally equipped with a
> 305.  The "ecm" you're seeing is only a spark retard box, designed to sense knock
> and back off timing if it's present.
> 
> You're engine's not computer controlled.  You can remove the spark control box, and
> a simple jumper between 2 wires to the spark control box will allow the engine to
> run without replacing the module.  I've seen many of the spark control units (BTW,
> does your fender have an ESC badge on it?) fail intermittently, stranding a vehicle
> beside the road for a couple of hours each time.  The budget fix is to jumper the
> two wires.  It's been a couple of years since I've done this, so I won't try to
> remember which two.
> 
> Disconnecting the extra fuel circuit can cause some severe cold weather
> hesitation.  Sometimes retuning can make up for this.  Sometimes not, as some of
> these carbs had a hesitation from the factory.  Best bet if you don't want to work
> with it is to get an older Q jet.
> 
> If the carburetor is truly dumping too much fuel you might try disassembling it and
> looking around the metering well plugs for signs of fuel leakage.  It's very
> common.  A good job with epoxy can repair this condition for many years.  
> 
> Shannen
> 
> ae2598 at wayne.edu wrote:
> > 
> > I'm kinda at a loss to figure out exactly what I have here, so I'm turning
> > to you guys for advice.  The vehicle is an '85 K5-Blazer, with a
> > computer-controlled (somewhat) Q-jet.  I got it for cheap because the gas
> > stations that worked on this thing in the past apparently couldn't figure
> > out what to do with it (other than replace everything underhood!) and it
> > still runs lousy.
> > 
> > The first thing that I find odd is the HEI distributor.  It has advance
> > weights and a vacuum can.. In fact, the only way in which it differs from
> > the "standard" HEI is the use of a 5-pin module, and an extra harness
> > hanging out the back.  The pickup coil apparently feeds a signal to the
> > ECM as well as the module.. probably a timing reference signal.  This
> > harness has been butchered by previous repair attempts, and probably isn't
> > giving much data to the ECM anyway.
> > 
> > The next thing that's not exactly right (IMHO) is the carb itself.  It has
> > a M/C solenoid, but no TPS or IAC.  Every description I read about the C3
> > Q-jets shows at least the M/C and TPS, and usually an idle air control,
> > too.
> > 
> > The ECM seems a bit un-sophisticated.. It is in a very small package, and
> > has a single connector with only 7 wires connected!  No ALDL that I could
> > find, and no provisions for a PROM.  The service number is 16042121.
> > 
> > Anyway, what I would like to do is make this a non-computerized motor.
> > The distributor seems easy enough, I'll just plug in a 4-terminal module
> > and all it a day.  As far as the carb, what will be the result of not
> > connecting the M/C solenoid?  Are these carbs capable of metering fuel
> > without the help of the ECM, or should I just find another Q-jet?
> > 
> > Anyone with ideas to share on this would be appreciated..  the carb seems
> > to be dumping way too much fuel into the motor at this point, and I'd like
> > to solve this as cheaply as possible!
> > 
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