General tuning question - fuel economy

[Marteney, Steven J.]

I have read tuning.doc (a couple of times even) which has got me to the
point of at least being able to understand the talk and ask (somewhat)
intelligent questions.  I have ZERO tuning experience but a good working
knowledge of engines.  And I have found that the cards are stacked against
me with the 165 ECM.  I've read the OEM PROM, burned my own PROM with NO
mods, and it works, so I've got the mechanism down.  I'd love to switch to
the 730 but... long boring stupid story.

I do now feel at least pointed in a good direction with a swift kick in the
butt.  I'll do the testing you recommended, thanks.

Steve

-----Original Message-----
From: Bruce Plecan [mailto:nacelp at bright.net]
Sent: Tuesday, June 13, 2000 6:39 PM
To: gmecm at diy-efi.org
Subject: Re: General tuning question - fuel economy



>  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?

Depends on your tuning ability.  For openers have you read Tuning.doc.?.
How much actual tuning experience do you have?.
  I'd say a 20% lose is excessive.

  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?

Target AFR is a correction for fuel.  As in Brazil, Mexico where alky
content is wildly higher then here in the states.

> However, I also thought that this engine cruises at about 2200 rpm on the
> highway at 75 mph.

75 is getting to where aero is raising it's ugly head.

>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?

Defeated, no.  Lessened the effectiveness, yes.
BUT, you now have the ability to tune to optimize your comination, so I
would imagine being able to match or exceed the oem's performance.

Try driving some and see where your TPS voltage is, and BL.  Try adding 2-3d
of advance at what would be cruise parameters.  Compare the TPS, and BLs.
Less TPSv means your able to run at a lower level of air consumption, should
use less fuel.  There is noone that can tell you what will work for your
car, you have to do the testing.
   Try reading tuning.doc at the ftp.
Ya know going to a 730 might be a real nice option, and not that big of deal
to change to.  For a beginner, the MAP is much easier to tune.  Also, is
more self explainatory.
Grumpy
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