Tuning 7747

[David Cooley]

Poor mileage can result from too lean of a fuel curve as well as too 
rich...  You are getting alot less fuel than you need, so the throttles are 
open a lot more for said condition, but power is way down from what it 
could be...

O2's of 750mV to 850mV aren't necessarily safe... I had a 3800 V6 that 
below 900mV would buck, surge and detonate even on 93 octane.


At 05:08 PM 09/18/2000, you wrote:
>Tuning my first 7747 based system. I put a GM 5.7L TBI and GM 7747 on a Jeep
>360. Would hardly run at first until BLMs had done some major corrections by
>adding a lot of fuel. I have probably added over 40% to all values of the MAP
>vs. RPM VE table. At this point, all VE values above 50 KPa and 1200 RPM are
>over 61 when they were initially down around 40. I read in Bruce's Prog 101
>that the VE adder and the VE table values can't add up to more than 100%,
>otherwise the VE will be clipped at 100. Does this mean that any VE values I
>program over 61 are clipped at 61? I guess I don't understand the VE adder
>table. I zeroed this table out to see if it was PE mode only and the engine
>stalled so I guess its full time. Do I need to lower the VE adder table and
>compensate in the main fuel table? All my BLMs are still in the 150-160 range
>at all cruise loads and I reset the BLMs to 128 before each tuning run. It
>makes sense that I would have to add a lot of fuel since this truck only gets
>12 MPG compared to a Chevy 5.7L which gets 20+ MPG, but should I have to add
>this much? One comforting thing is that I do have 750 to 850 mV O2 at WOT so
>I am getting enough fuel. Just don't know where its coming from.

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David Cooley N5XMT Internet: N5XMT at triad.rr.com
Packet: N5XMT at KQ4LO.#INT.NC.USA.NA T.A.P.R. Member #7068
I am Pentium of Borg... Division is Futile!
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