gm ecm/Carb Question

[David & Cheryl Haggard]

   On the feedback carburetors, the ECM can not turn OFF the fuel. The
mixture control solenoid is used by the ECM to control the fuel mixture by
cycling it between two positions. In one position, the mixture would be too
lean. In the other position, the mixture would be too rich. The ECM cycles
the solenoid back and forth between them up to 10 times per second (as I
recall), and that produces the correct fuel mixture.
   I also seem to recall that when the system fails, it defaults to the rich
side, so the engine will at least run. This could be the reason the 350 runs
way too rich. The solenoid could be stuck, disconnected from the ECM, or the
ECM isn't operating it. Emphasis on COULD.
   If there is NO fuel at all getting to the carburetor's venturii, then you
have a plugged jet or fuel gallery, or the float valve is stuck closed.
   You could be getting fuel TO the carb, but not INTO the carb. Does fuel
squirt when you pump the throttle? Is there fuel in the carb bowl when you
take the top off?
   You say you have had this one apart? Did you put the fuel filter in
backwards?

   Lots of variables to deal with, with a carb, that will be solved when you
convert to TBI. But that has its own problems. I recommend you go to
http://www.helminc.com, and order a shop manual for your car. This will help
you considerably to learn more about how it all goes together, how it works,
and how to fix it.
   Also, if you upgrade to TBI with salvage parts, be sure you get ALL the
parts, including the ECM. Then get a shop manual for the car that the TBI
system cam from.

   You're on the right track. Don't let it discourage you. I've always
believed that the best way to learn is to get your hands in it.

Dave Haggard

> -----Original Message-----
> From: owner-gmecm at diy-efi.org
> [mailto:owner-gmecm at diy-efi.org]On Behalf
> Of James Melton
> Sent: Thursday, May 10, 2001 4:00 PM
> To: gmecm at diy-efi.org
> Subject: gm ecm/Carb Question
>
>
>
> I have a 85 or so firebird  305 quadro jet that i have been
> having trouble
> starting and a Camaro 350 with the same carb which is way to
> rich (not
> caused by the choke). The firebird is getting good fuel at
> the carb, and the
> engine has good spark. I am not getting fuel into the carb throat.
> My question:  Can the enrichment solenoid  stop the flow of
> fuel from the
> float? Can the ECM turn off the fuel? I took one of these
> carbs apart ONCE.
> I dont learn easy, but wouldnt do that again. :-)  I am
> going to convert
> this firebird to TBI and have already received a lot of help
> from the list
> on that.  I dont want to spend much on getting the car to run and my
> daughter would like to use it until i can get to the
> conversion later this
> summer.
> I dont know much about cars yet, but like to work on them as
> a hobby.  Well,
> a hobby that has been taking more and more of my time.
> I am glad to see some of the new members of the list ask
> their questions
> although we probably try the patience of you older vets of
> the list.  I
> found the archive very hard to use, but have been searching
> it when i have
> the time.
>
> Thanks in advance
>
> oldmadog
>
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