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Hi all,

New to the group. I picked up an 02 998 last weekend. There's a photo in the Intros thread. Bike is running too lean. It has FBF slipons, BMC air filters, and an old serial Power Commander. The guy I bought it from bought it from a guy in Aspen. He told me the PC was mapped for Aspen's altitude and that's why it's too lean down here at 5000 ft.

Is the dude blowing smoke at me? I thought FI compensated for altitude. My GT runs just as good at 10,000 ft. as it does down here. I know I need to get the 998 remapped, but I'm just curious about this.

Debby
 

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Fuel injection can compensate to an extent but everything has it's limitations. The bike is going to run very differently at those different altitudes, so I don't think he is blowing smoke up your ass. Be thankful it came with a power commander, you should have little trouble richening up the mixture for your altitude :)
 

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Open-loop vs. Closed-loop?

Hello
I'm trying to figure all this stuff out myself, as I get my 996 motor and Nemesis ECU to play together well, but it may be a matter of the '02 bike running an "open-loop" FI system. The ST4S bikes of that era do (996 motors) and they do not employ any environmental sensors, and do not actually "feed back" to the ECU to adjust itself.
The newer "closed-loop" FI systems (CANbus, I believe) have O2, thermal, air density, etc. sensors that send info back to the ECU to help it regulate the proper mixture and stuff. That may be why your '07 adjusts itself for altitude, and your '02 may not.
From what I understand about the open-loop design, once they are adjusted to certain parameters (such as altitude) that's pretty much where they stay until they get manually reset.

Just a shot in the dark....
 

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The thing about Power Commanders is that they do skew with altitude.
The PC measures the amount of time the injector is grounded and takes control of the ground side. If you ask for 10% more, it holds the injector grounded 10% longer.
The problem is that the ECU knows that the injector does't open instantaneously when the ground is completed and adjusts only the full open part of the cycle.
This delay is called dead-time or latency and is adjusted for different battery voltage. There is a table in the calibration for that.

When the injector time is short (light load) the dead-time can be as much as 50% of the total pulse width. When the ECU corrects for altitude (air pressure compensation) changes 1/2 of the pulse width (the full open part) by let's say 10%, but the PC detects a difference of only 5%in total pulse width. That is 1/2 the intended compensation.

So, when I tuned a Harley in Minnesota with a PC and it went to the Black Hills (Sturgis), it got richer.

As to the earlier Magneti-Marelli systems; they all have air temp sensors and barometric pressure sensors, so they do compensate constantly.
But, a lot of the P7, P8, and 16M cals (chip stuff) have too little altitude compensation written into the tables.
I've been told that stems from some early (mid-late '80s) pressure sensor failures, the failure mode of which caused the vehicle to go lean.

Any calibration may have the wrong data in any table and they all have the wrong data in the fuel tables.

Doug
 
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