I was just curious as to what hiway spark does. Do the stock gm proms use it at all? What driving capabilities would it change? Was it enabled on later ecm's? (yea, i know,i'll shutup soon)
Just pondering while i'm awaiting my burner

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89 IROC-Z 350 TPI

-Flowmaster Catback
-Performance Resource Chip
-Rebuilt 700R4 Tranny
With the goodies to go

-K&N Airfilters
-Ported Plenum
-2.77 Gears (not much to brag about but eh, its there)

 

im pretty sure its not enabled on the ecm

from what I understand it was a parameter GM was planning on using to increase highway fuel mileage but apparently the epa didnt allow it im guessing because emissions were changed from where they tested the vehicle

 

Just got this from the GMECM mailing list...

Date: Sun, 08 Oct 2000 23:23:05 -0400
Subject: Fuel Econ and Hiway Mode
From: Bob Valentine <bob@tecmark.com>
Reply-to: gmecm@diy-efi.org
To: gmecm@diy-efi.org

With the seemingly renewed interest in fuel economy lately around here,
I've spent some time messing with Hiway Mode in the '730 / 8D / AUJP
calibration. Seen mention of it in the archives, but no details of the
settings. With 93 Octane pushing $1.90 around here, want to get as much
as I can for what I pay.

Here is what I found in the ANHT_HAC and what I've done. None of it would
have been possible without the ANHT_HAC, thanks (for the 10^6 time) to
whomever wrote it.

$81A7 Min coolant for Hiway Mode moved FFh to 76h (70deg. C)
$81A8 Max kpa for Hiway Mode moved 2Bh to 32h (50kpa)
$81A9 Min RPM for Hiway Mode moved FEh to 40h (1200 rpm)

$8482 Lockout time for Hiway Mode moved 0Ah to 01h (1 second)
$8484 Min speed for Hiway Mode moved FFh to 01h (1 mph)

Table at $8485 for A/F vs. Kpa
Table at $81AB for S/A vs Kpa

The results are pretty cool. As soon as all conditions are met, 02
sensor voltage drops to around 75-85 mv, and stays there until
acceleration. Integrator locks at 128, and no error codes set. Having
a WB02 would be nice here, since I already know my 02 doesn't read 14.7 A/F
correctly. Plugs do not show any detonation or burn signs. Transitions
to power are just fine, butt-o-meter indicates a slight improvement.

Keep in mind I run no cats; I'm not sure what extended lean A/F ratios
would do to a cat but I doubt it would be good. I haven't done enough
highway driving to make any definitive statement as to improved mileage,
but mixed driving is up a good amount, 150 miles and still 1/4 tank left,
usually refill time by now.

Initially I was planning on trying to add EGR back in, but I thought about
it and couldn't see how diluting the A/F mixture would help economy.
Also, turning on Hiway didn't require adding any wires and hoses - just
changing bits.

-> Bob Valentine
-> bob@tecmark.com

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.587 @ 107.97mph (1.710 60ftr) on the long runner setup.
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels. Stock Wheels. No Weight Reduction.
Gunning for NA 11's with the MiniRam II and Hooker LT Headers.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org