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Old 04-09-2009, 12:09 PM   #1
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Default Noisy map signal under boost

I've just recently upgraded from an EMB to an EMU. During that time I also switched from a GM 3bar to a Honda MAP sensor to gain back some resolution since I'm only boosting 6 psi.

You can see my MAP output compared to my TP% (tapped into MAP). Does the EMU average out the TP% for logging? It's greatly affecting my timing and my injector adjustments.

I want to remove my AFM but my issues with the MAP readout is preventing me from doing it. I don't know if this is a result of using a Honda MAP sensor or because I teed the MAP input right next to the supercharger and I'm catching the pulses of the lobes. The comparison of the MAP and TP% suggests to me that the EMU calculates the values differently. I want to find out before I go out and try redoing grounds and vacuum/boost sources.

Otherwise the car drives like a dream, I just want to ditch the AFM. If I can't find a solution I may just have to go and buy a Greddy MAP.

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Old 04-10-2009, 11:52 PM   #2
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It's been a while since I played in EMUland, but I don't think you're seeing any kind of averaging in software, I believe it's just a matter of how the input circuits are physically configured. The TPS input in the EMU seems to be a tad more capacitive than the others, and thus it inherently smooths out the signal a bit. I'd suspect this was done intentionally, as potentiometers are known for being noisy, and one doesn't want to be falsely triggering accel fuel.

As to the MAP signal itself, one common trick for smoothing out the reading is to install a restriction in series with the line leading from the manifold to the MAP sensor. A simple and inexpensive restrictor is one of the cheap plastic inline fuel filters that you commonly find at auto parts stores, intended for small carbureted engines. This both restricts the signal and adds a bit of volume to the line, both of which will smooth out the pulses a bit, assuming that what you are seeing in the log is in fact consistent with reality at the inlet to the MAP sensor.
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Old 04-11-2009, 12:43 PM   #3
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Thanks Joe,

I've decided to leave the car as is for now. I've got a Greddy map sensor coming in.

After doing some research on the Honda and different MAP sensors, I don't think I would be able to remove my AFM without spending the money for the Greddy or an equivalent priced unit.

Majority of MAPs use a 0-5V sweep and the EMU is restricted to 0.5-4.5V for the usable range. In turn I lose alot of vital readings in vacuum and I will end up with a crap idle/cruise.
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Old 04-11-2009, 02:08 PM   #4
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For my AEM FIC on my BMW I used 2 pcs $2 plastic vacuum restrictors which I bought from my FLAPS. I placed one near the manifold, and the 2nd halfway down the vacuum hose.
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