General tuning question - fuel economy

[Marteney, Steven J.]

Unfortunately, the BLM is typically sitting around the maximum.  I've seen
it at 160, but it's typically around 145-150.  This says to me with the
bigger cam, it saw it was too lean (more airflow) and therefore it gave it
more fuel, hence less gas mileage.

Steve

-----Original Message-----
From: Squash [mailto:realsquash at yahoo.com]
Sent: Tuesday, June 13, 2000 5:04 PM
To: gmecm at diy-efi.org
Subject: Re: General tuning question - fuel economy


I'm not sure how that ecm works (165=C3?), but is it possible that the BLM
is sitting at the
minimum value?  That would mean it's trying to lean it out, but it stopped
because of the limit.  

Squash

--- "Marteney, Steven J." <smarteney at xlvision.com> wrote:
> Not having really any engine "tuning" experience I stumble on some of the
> basic concepts (such as when to add spark advance).  My rebuilt 350 TPI
> F-body gets about 20% less highway gas mileage with its bigger cam (GM
ZZ3)
> and stock computer.  I figure more air in at X rpm requires more fuel to
> appease the O2 sensor, hence gas mileage goes down.  How do I compensate,
or
> can I?  I noticed there are some Hiway mode parameters, such as Hiway
spark
> add (?), in the 165 ECM that I could take advantage of.  Or, is the only
way
> to get better mileage mean changing the target AFR?
> 
> However, I also thought that this engine cruises at about 2200 rpm on the
> highway at 75 mph.  I'm wondering if the different cam (and valve timing)
> has defeated the ram tuning effect of the runners and made the engine less
> efficient on the highway.  Any thoughts?  I'd appreciate a little basic
> help.  Since this car is my daily driver (70+ per day) I'd like to keep
fuel
> economy in mind when tuning.
> 
> Thanks,
> Steve Marteney
>
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=====
Trains, Trucks, and EFI at http://www.trailrunners4x4.org/users/realsquash

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