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Old 12-16-2004, 11:01 AM   #1
x99percent
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Default UTEC gurus! Question about MAP sensor + UTEC's FCD

Information:

When you plug a UTEC into your car, it is *always* screwing with the MAP sensor signal, even when the UTEC is in "stock" mode.

The UTEC's FCD switch has two settings.
From what I understand, this is how those settings work:
Enabled - Moves factory fuel cut from ~17psi to ~20psi by tweaking the MAP signal.
Disabled - Completely disables the factory fuel cut by clamping the MAP signal to ~13-14psi (you should be using the OLF fuel cut instead!).

If you are using a UTEC, this is why the Manifold Pressure readings you see in DeltaDash are incorrect.


My goal:
I would like the UTEC to pass the MAP sensor signal through, unmodified (don't ask why.. just run with it ).


Questions and possible solutions:
Running the MAP signal "around" the UTEC isn't the best solution, as the UTEC uses the MAP sensor signal for load in its fuel and timing maps.

Can I just "Y" MAP signal into both the stock ECU and the UTEC, and just not use the UTEC's MAP output?


Does anyone have any input?
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Old 12-16-2004, 11:09 AM   #2
RiftsWRX
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You know what though... I've never noticed a difference in my load references (charge/air grams) with the UTEC in line or not. For me, frankly, having the MAP pass through would be nice since I can then properly do a DeltaDash log, and not just rely on the UTEC logs for accurate MAP readings.

Hell, with the proper isolator and spliter you can physically hardwire the harness to pass the unmodified signal back to the ECU.

Jorge (RiftsWRX)
www.ProjectWRX.com
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Old 12-16-2004, 11:16 AM   #3
x99percent
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Quote:
Originally Posted by RiftsWRX
You know what though... I've never noticed a difference in my load references (charge/air grams) with the UTEC in line or not.
Agreed. I've always been 90% sure ( ) that the factory ECU didn't use MAP in its load calculations.


Quote:
Originally Posted by RiftsWRX
For me, frankly, having the MAP pass through would be nice since I can then properly do a DeltaDash log, and not just rely on the UTEC logs for accurate MAP readings.
Would be nice, wouldn't it?


Quote:
Originally Posted by RiftsWRX
Hell, with the proper isolator and spliter you can physically hardwire the harness to pass the unmodified signal back to the ECU.
This is part where I need some guidance...
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Old 12-16-2004, 11:21 AM   #4
mick_the_ginge
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The ECU uses the MAP sensor reading for 2 things, one is boost control and the other is to trigger overboost fuel cut. With a reflashed ecu these two things may not be an issue. If no reflash, do you really want to supply the correct MAP signal to the ECU?
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Old 12-16-2004, 11:27 AM   #5
RiftsWRX
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Quote:
Originally Posted by mick_the_ginge
If no reflash, do you really want to supply the correct MAP signal to the ECU?
Not at all, short of the aforementioned desire to log MAP in with other utilities besides the UTEC.

Jorge (RiftsWRX)
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Old 12-16-2004, 11:37 AM   #6
x99percent
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Quote:
Originally Posted by mick_the_ginge
The ECU uses the MAP sensor reading for 2 things, one is boost control and the other is to trigger overboost fuel cut. With a reflashed ecu these two things may not be an issue. If no reflash, do you really want to supply the correct MAP signal to the ECU?
Shhh!


For some reason, I don't think it will be as simple as T'ing off the harness.. does anyone know how to make/find a simple isolated splitter?
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Old 12-16-2004, 02:58 PM   #7
TurboXS (Pete)
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If you cut the MAP sensor harness wire (B135 Pin 8) on the UTEC and solder the wire going to the connector to the matching PCB connector pin this should give the ECU the unaltered MAP signal.

Just double check my thinking and pin number before trying.

regards
Pete
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Old 12-16-2004, 03:49 PM   #8
x99percent
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Quote:
Originally Posted by TurboXS (Pete)
If you cut the MAP sensor harness wire (B135 Pin 8) on the UTEC and solder the wire going to the connector to the matching PCB connector pin this should give the ECU the unaltered MAP signal.

Just double check my thinking and pin number before trying.
But will the UTEC still get the MAP signal, too? What I would like to end up with is both the UTEC and the ECU getting an unaltered MAP.

I also have a way to logically do the same thing you're suggesting, but without cutting any UTEC wires (I *really* don't want to do that!).


EDIT: Followup: Just tapping the signal worked without a hitch. Both the ECU and the UTEC get a good MAP signal.

Last edited by x99percent; 01-11-2005 at 11:40 AM.
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