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Old 04-19-2012, 11:30 AM   #1 (permalink)
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instant mpg mirrors speed? (video)

I'm still trying to get this cool device dialed in. It was giving me some weird readings, then I realized that the instant miles per gallon usage was mirroring my speed.
If I take my foot off the gas and the engine goes into injectors off, it goes to 999 mpg, but if I'm just going along no matter engine load, the instant mpg mirrors speed. If I put the car in neutral, it goes to 999mpg for a few seconds, then back to mirroring speed. If I cut the injectors (I put in a switch for engine off coasting) the instant mpg goes to 999

My MPH on the mpguino is the reading the same as the speedometer.
Please see the video I shot this morning-

Test1 - YouTube

I reattached the VSS and Injector wires to the mpguino to make sure a stray wire wasn't shorting to the other.

Any ideas? I'm about ready change my injector input to the injector itself - right now I'm attached by the ECU and am 100% certain I have an injector wire.

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Old 04-19-2012, 01:00 PM   #2 (permalink)
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A couple things. First, check your wiring a few more times. Make sure you have 50kohm resistors on the inputs for VSS and the injector as close to the board as possible. Second, make sure you used the right inputs for each one. VSS goes to digital pin 14, aka A0. Injector goes to both pins 2 and 3.

What kind of car are you driving? There could be some special injector or VSS signal or something that is causing the errors.
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Old 04-19-2012, 03:13 PM   #3 (permalink)
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Thanks for the quick reply - I'm using a prebuilt board (new) that others on ecomodder have had success with.

I am driving a 95 Saturn SL1.

I'll check the wiring again I'll probably change my injector input to be right by the injector at the engine. With the bad weather planned for the next 3 days, it may take awhile before I can do it.
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Old 04-19-2012, 07:50 PM   #4 (permalink)
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I think I didnt connect the injector correctly. I reread the wiki and it says to connect to the injector lead without power. I hooked to the lead from the ecu, but my multimeter tells me that has power when the engine and key are off. Once the rain stops, I'll see if all the injector ecu leads are powered.

Once again, looks like user error on my part.
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Old 04-19-2012, 09:07 PM   #5 (permalink)
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Quote:
If I take my foot off the gas and the engine goes into injectors off, it goes to 999 mpg
Correct behavior

Quote:
but if I'm just going along no matter engine load, the instant mpg mirrors speed.
Wrong behavior, and weird as fukk. I wonder what combination of wiring and config setting could produce this.

Quote:
If I put the car in neutral, it goes to 999mpg for a few seconds, then back to mirroring speed.
Wrong, and wrong. Neutral should only read 200-300 mpg, since you are idling 0.1 - 0.2 gph, and going 60mph. The only exception to this is during the first second (or less) of switching from load to idle, the ECU may cut off injectors to 0.00, giving you 999 mpg.

Quote:
If I cut the injectors (I put in a switch for engine off coasting) the instant mpg goes to 999
Correct. Seems that if you know where to install a cutoff switch, you should have a good handle on how to wire up the 'guino

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