I found a YouTube video that excellently demonstrates how to test a MAP sensor(voltage-based)
via back-probing the wires & using a vacuum pump.
'Map Sensor Testing'
I finally got around to testing my MAP Sensor to see if it's voltage or frequency based.
I'd have to say, assuming I tested it correctly, it's 'Voltage Based' since I got variable voltages.
With the key turned to ON, but engine off:
Voltage changes were across MAP sensor wires #2 & #3:
At rest(no vacuum applied), the voltage was: 4.74v
The more vacuum applied, the lower the voltage reading. @~15in: ~1.5v ?(don't recall exactly)
The voltage across wires #1 & #2 remained a constant 4.94v no matter what the vacuum.
Note: I could only seem to hold about 15in of vacuum in the MAP sensor.
I don't know if that's normal or, perhaps the vacuum pump had issues sealing due to it's cheap plastic hose in FREEZING COLD TEMP. and a rather rigged setup.
The vacuum wouldn't hold. It'd leak within seconds after pumping it. With that said, I'm not totally convinced I did that test justice. But, it's the best I could do by myself outside in sub-freezing weather. Man is that getting annoying.
Also, I must note that the very 1st time I attempted this test,
I disconnected the wire plug from the MAP sensor(meaning the MAP was not in the circuit) in order to get to the wires for testing. I didn't fully understand what I was doing at the time. However, I soon realized that I likely wasn't doing something right since I wasn't getting any expected voltage variations with RPM changes.
The MAP sensor was also tested with the car idling, before I realized you could use a vacuum pump on it while engine is not running. Then I looked up the YouTube video mentioned above and learned the procedure.
OF COURSE NOW I HAVE A CHECK ENGINE LIGHT AS A RESULT of my 1st trial because the engine was idling without a MAP sensor! QUESTION: Is this now going to ruin my MPG even more?!
What should I do to safely clear the error code WITHOUT loosing
all the newly learned fuel trims?
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The following user(s) said Thank You: Tracy Gallaway
Not to worry. Just do another re-learn procedure w/ battery as Dan says. The whole Gadgetman gig is about learning, and I just learned from you, freind!
My vac. pump is a Mityvac just like in this vid, and it has clear vinyl tubing like this one, and that tubing does get stiff in the cold. So do a re-learn again, you WILL get better at all this, Trust Me! You'll know how to do the MAP test next time, maybe pick a warmer day or warm up the hose first!
Thanks Again for sharing this with everyone, this is great info!
Tracy G
Tracy Gallaway
Founder and Constant Aide to Gadgetman
Gadgetman Reno, NV
Cool, I'm glad you thought it was beneficial! I was excited when I saw it and had to share.
I suppose I shouldn't worry too much over my trials, specially when good can come from it.
Thanks for the support.
What I'm referring to is the following information regarding Honda vehicles
found in the document: 'vacuum systems and tweaks feb 2012.pdf' link to the document --->
Here's an excerpt from it:
"Most vehicles require only a few (20 or less) cycles to reprogram to a greatly enhanced level. Some
(like late model Honda's) require as many as three to FIVE tanks of fuel used during city driving to see
gains.
Honda's usually lose 1-2 MPG's on the first tank, gain 10%MPG's the second tank and then jump
SHARPLY by 40-60%! So, if your mod loses a mile or two initially, don't worry. It's the computer
being a stuborn little wench! She will come around in time. If after three tanks you still don't see a gain,
then go back and check the vacuum and clear the computer memory. That usually clears up what I
consider “locked” computers (those that neither increase nor decrease)."
My vac. pump is a Mityvac just like in this vid, and it has clear vinyl tubing like this one, and that tubing does get stiff in the cold..... maybe pick a warmer day or warm up the hose first!
Tracy G
Absolutely, it was the freezing cold weather that prevented me from getting a true reading that day.
I tried when it was 'relatively' warm out & the Map sensor held a vacuum no problem.
So I can rest now knowing the Map sensor is ok!