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Old 06-05-2008, 04:37 PM   #211 (permalink)
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MAP (air mass flow sensor, right?) sensors usually output a small voltage... the voltage range is probably different from car model to car model, but that only is easy to deal with. I don't know what other different sensor outputs are there.

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Old 06-05-2008, 04:53 PM   #212 (permalink)
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Quote:
Originally Posted by monroe74 View Post
So the system is designed to drop fuel pressure when manifold pressure drops. So the system keeps fuel pressure more-or-less constant relative to manifold pressure, not relative to atmosphere. (I say "more-or-less" because I don't know for sure that the relationship is purely proportional. Although I bet it is.)
Yap, that is it. As for proportionality yes, it's one-to-one except some response delay time that the valve might have... and maybe except if you installed one of these.

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Originally Posted by monroe74 View Post
Anyway, I have a feeling that my car is just like your car, in this regard. And I have a feeling that this is the prevailing design, for EFI. Which should mean that pulse width is a good proxy for true fuel flow, after all.
Yep, I'm very inclined to agree with it
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Old 06-05-2008, 05:14 PM   #213 (permalink)
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Quote:
Originally Posted by Njay View Post
MAP (air mass flow sensor, right?) sensors usually output a small voltage... the voltage range is probably different from car model to car model, but that only is easy to deal with. I don't know what other different sensor outputs are there.
MAP stands for Manifold Absolute Pressure - it's a different way of calculating the air intake than MAF, which is Mass Air Flow. MAF basically uses a heated element and allows the intake air to cool it off. I think the voltage that is read off the sensor is the voltage required to keep the element at a certain temp, but I'll have to look that up to be sure. MAP, on the other hand, is more complicated I believe, I'll get back to you on that one.
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Old 06-05-2008, 05:22 PM   #214 (permalink)
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Ok, real problem, the tank/current fuel consumption reading goes waaay up on the saturn after driving a bit. Any ideas? Anyone else noticed it? got to be some weird rounding thing. If tank and current are in synch, and both are on consumption runaway, I can reset the current and it goes back to normal and tank stays kablonkers. Need a bench test

For example, the tank was at 330 seconds injector time, the instant was idling at about 20microseconds/half second, and the tank was going up by a second every half second?!?
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Last edited by dcb; 06-05-2008 at 05:42 PM..
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Old 06-05-2008, 06:30 PM   #215 (permalink)
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Quote:
Originally Posted by cmags View Post
MAP, on the other hand, is more complicated I believe, I'll get back to you on that one.
MAP will vary between manufacturers, but most GM cars use the 1, 2, or 3 bar MAP sensors. These output between 0-5v based on vacuum (or boost) conditions.

http://shed51.com/gm_map.htm was the first one i found in google with a table showing an example of a 2 bar sensor.

If you could set up a fuel pressure gauge, and a dmm, you could create a quick table of fuel pressures seen at different vacuum readings. Or you could just take the manufacturers specs (say 30-35 at idle, 40-45 at wot) and scale it to fit 30-0 inches of vacuum.
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Old 06-05-2008, 06:40 PM   #216 (permalink)
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New thread for the map/sensor stuff please so this stuff doesn't get lost here.
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Old 06-06-2008, 08:07 AM   #217 (permalink)
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Can someone post the VSS parameter they use for a Honda. I want to flash this thing before i zip tie it into the car .
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Old 06-06-2008, 08:09 AM   #218 (permalink)
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Oooh, I don't think we are at the zip tie stage yet Velcro would be good. Or just a couple twist ties.
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Old 06-06-2008, 09:51 AM   #219 (permalink)
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If its not hooked to a VSS/INJ (IE sitting on my bench) is the tank.gallons() supposed to increment like a counter?


I've hooked it up in my car and I must have wired something up wrong.

I tapped the VSS properly I believe. As for the injecter, I tapped the brown lead of the farthest right injector ( standing in front of the car facing the engine).

Update
Ok fixed it. I tapped the VSS at the ECU. My MPH are half what they should be. I think i was using 8000 as the constant.

Last edited by MilesPerTank; 06-06-2008 at 07:03 PM.. Reason: problems
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Old 06-06-2008, 07:34 PM   #220 (permalink)
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Quote:
Originally Posted by Yoshi View Post
Prius, Honda and others, VSS specification is 637*4=2548 pulses per km, or 4100 pulses per mile.
I was scratching my head on this one till I saw this:
http://www.teamswift.net/viewtopic.php?p=147340#p147322
"My Denso speedometer has "1026 rev = 1 mile" printed on it." , earlier he says 4 pulses per revolution, which adds up to 4104 pulses per mile

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