3.9 MAF voltage - Defender Source
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Old January 13th, 2006, 04:08 PM
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Tim Riccardi
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3.9 MAF voltage

Does anybody know what the transfer function is for a 3.9 D-90? Tim
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Old January 13th, 2006, 04:18 PM
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Hans Haase
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Between the black and blue/red wires should read 1.8 volts for a cat setting or between 1.0 and 1.5 for a non-cat system. According to RPI.

I wish I knew more about Mass Air sensors to figure out how they work, and to see if we have any other options that cost less than $600 to replace.

-Hans
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Old January 14th, 2006, 01:50 AM
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Tim Riccardi
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Hans What I meant was when the MAF voltage is 4.22 the cfm's are ______. Does anybody have a spare working MAF sensor and injector. I know the injector is around 22lb/hr, but that is not the exact number. I think I can get them flow tested. When does the 14cux go into closed loop( voltage of TPS). If we find the transfer function of the factory MAF, then we could use a different make. I just downloaded my first session from my LM-1. My stock 3.9 in 3rd gear WOT AFR 12.16, MAF 4.22, TPS 4.70, and RPM'S 4500(if you believe the tach. I'm having a very hard time getting the LM-1 to recognize the factory tach. I tried at the alt, at the tach, at the - coil, and white/black(pin 39) at the ECU. The factory ingition is very noisy. The best is a fuel injector wire, except when coasting. I have the 3900 tune resistor installed. I would like to get the AFR around 13 at WOT. I'll try the different resistors and log my sessions. Tim
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Old January 14th, 2006, 11:03 AM
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I know other people in the megasquirt world were having issues with noisy electronics and tach feeds.

http://www.megasquirt.info/
Can't get a direct link, but at this website click on the 'sensors and wiring' on the left side, then on the page that comes up click on 'ignition triggering'. They have a few methods to cure dirty tach signals.

But the ignition noise is starting to make me think.... if the ECU is seeing the same garbage, will that screw with the engine performance? And where the heck is it coming from?

-Hans
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Old January 14th, 2006, 12:56 PM
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Tim Riccardi
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Land Rover "made" the dizzy work with Fuel Injection. They can filter out the garbage, they made,but aftermarket companies need to work with everything. The coil(-) "times" the ECU on the 3.9, it is one step above points, and is very noisy. Most if not all other OEM companies use a cam, crank or HAL sensor. The LR does not use a HAL. I jus found 2 resistors and I'm going to play. Tikm
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Old January 14th, 2006, 05:37 PM
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Yeah, but isn't it a Variable Reluctance sensor? I know some folks swap GM HEI modules in place of the Lucas igntion module. That ones does have a tach feed, but is also a bit on the noisy side sometimes.

-Hans
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Old January 15th, 2006, 02:08 AM
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Tim Riccardi
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I just downloaded my 180ohm tune resistor log. By just changing the 3.9k for 180ohm, my WOT AFR when from 12.17 to 12.70. It definitely has response and a little more power. I didn't think it would change anything. The interesting thing is the MAF voltage is up by .10 volts. That doesn't sound like much, but .10 volts in a 55mmMAF/19lb-hr Ford is about 40cfm's. This was check multiple times on the same test road. It was not a difference in battery voltage, either. The TPS voltage was within .02 volts. I also did a 60MPH 5th gear cruise test. My AFR when from 14.6 to 14.75. I will try this for about a week and log info again. When in closed loop you can see the difference in mapping is major, but when open (O2's working) not much differnece. I'm going on long trip so I can check MPG. Tim
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