I made a little stupid observation this week. My girlfriends house is 31miles away. I used to barely make it there on a quarter tank when I was 100% stock. Now I have a 10lb blower, 24# injectors, 3:73s and a custom prom where my friend invoked highway mode. Would you believe my mileage actually slightly improved. Even with the addition of the blower and 24# injectors!

Last night I had enough gas to make it home, and go cruising!

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91 Formula
305 TPI 5speed
1LE/G92/WS6

Paxton SN92 polished kit, SLP airfoil, ported/polished plenum, March pulleys, Crane AFPR(43psi),Crane Gold 1.6rrs,MSD coil,MSD6AL,MSD boost-master,Holley 9mm wires,Ac delco R43ts plugs,custom chip,Ford SVO 24# injectors,Bosch O2sensor, Bosch in-line pump(w/stock pump), SLP 1 5/8" headers,SLP catback,short shifter,3:73s w/Auburn posi,170* t-stat,JET 195* fan switch, Macewen white face gauges, Autometer gauges, Zoom hi-performance clutch.

[This message has been edited by theformula (edited February 27, 2001).]

 

Sweet! Must be efficient system! Closed-loop is great, ain't it?

 

sounds like a soon to be hot topic to me with all the new comers to the DIY world and the riseing gas prices...

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89 IROC-Z 350 TPI

-Flowmaster Catback
-Performance Resource Chip
-700R4 (Rebuilt) Too much done to actually list
-K&N Airfilters
-Ported Plenum
-2.77 Gears (not much to brag about but eh, its there)
-MSD 8.5 mm plug wires
-Problems every other day with the car (probably not a mod, but to me it sure makes a difference)

 

Would ya beleive I'm running a 17.2:1 AFR in cruise mode. Now if I could just keeep my foot out of it to do a mileage test. At 14.7 got 25.6 MPG.........

 

I'm upto 17.6:1 with spark advance of 46.9*. I REALLY found the Highway Mode Spark Advance necessary to keep the responsivness from dropping off and a "smooth feel" to the engine.

I found the GM HMSA code within the 8D eprom did not work and I had to alter the code to get it to work the way I liked. Also, I engage Higway Mode at 45 Km/h (28 mph) and Highway Mode Spark Advance at 64 Km/h (42 mph). Not only did my highway gas mileage dramatically increase (20% on my preliminary tests) but my city mileage even more so. I am even looking at leaning the engine in "normal" operation from 14.7:1 to high 15s.

The beauty is, this is all seamless. You never feel it go into/from highway mode from "normal" or "power enrichment". Very smooth when you get it working right.

For HMSA, I changed the code to engage at a certain vehicle speed (new code)while RPM is below certain levels (altered from the stock requirement of being over a certain rpm). Works far better than the stock parameters. I still check the coolant level and MAP (I disengage it at 73 kpa).

I can climb a 6% grade and remain in both Highway Mode and HMSA with no knock or loss of power.

I think 17.6:1 is the "outer limits" for Highway Mode. I found above that (tested 18:1) that the O2 sensor dropped to single digits and the injector pulse width actually increased from 17.6:1 on a stretch of highway I have been using to test all of this.

When testing all this, I discovered that "octane code" pulled out timing for "long term" and I had to "fiddle" with that to get it to "return" quicker and easier. But this is another problem with the 8D code, in that it will pull 4* of timing out of your maximum spark advance if you encounter more than 6* of knock at 70 kpa of MAP (or higher). Unfortunately, the code only adds back about .3* IF you do not encounter any knock the next time you go over 70 kpa. I have since modified these parameters and I now recover all my timing back very quickly. Now I can use my knock sensor as a "safety" without penalizing myself for a long time.

 

I should add, that this "octane" spark retard is in addition to the regular knock retard's attack/decay rates. It's amazing how much advance you can end up loosing.

 

Glenn,
what is that "octane" spark retard thing? Does it have to do with the fuel octane rating?
Rick