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Discussion Starter #1
Just wired up my new msd 2 bar map and I'm not getting the right voltages.

I have 5V on pin A
i have 4.5V on pin B
i have 0V on pin C

Am I right in assuming A is power, B is signal, C is ground?

Pin B changes to 5V when I unplug it from the map sensor.

Why the hell is my signal so high? The wiring and crimps were done top notch.
 

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Discussion Starter #3
Thanks

well mine was wired just like the diagram.

I switched power and ground and now I get 1.3-1.5.
 

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Discussion Starter #5
key on, engine off.

getting about 1.3
 

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Discussion Starter #6
doesnt move up or down with rpms. Shit

Wierd that I'm running so rich. It's at 10.0 at idle, anything above it dips into the 9s and dies out.
 

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Discussion Starter #7
Looks like Delphi makes the MSD unit. Ordered a new one to try tmrw. Maybe I fried it hooking it up wrong
 

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ROFLcopter
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Your voltage is way off. If your reading isn't 2.1-2.4 at key on engine off, the truck won't run correctly. I went through a few sensors, and had some incorrectly labeled sensors shipped to me. MSD had a batch of 3 bar map sensors labeled as 2 bar sensors. Summit exchanged all of the wrong sensors, and the ones that went bad. Let us know how it turns out!
 

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I replaced the sensor and its right at 2.38. truck runs good now on the first blower tune from hemifever. now I can get to logging.
I'll return the msd to summit.
 

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I replaced the sensor and its right at 2.38. truck runs good now on the first blower tune from hemifever. now I can get to logging.
I'll return the msd to summit.
What did you replace it with? My truck did a similar thing. I hooked it up the way shown above, and it read 2.2, so far so good right. After I got the truck running, I noticed on the datalog that it was down to 1.3x, WTF. Now when I check it key on, engine off, I get around 1.5x.
 

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SideSkirt Central
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What did you replace it with? My truck did a similar thing. I hooked it up the way shown above, and it read 2.2, so far so good right. After I got the truck running, I noticed on the datalog that it was down to 1.3x, WTF. Now when I check it key on, engine off, I get around 1.5x.
Disconnect the vacuum line from the MAP sensor and then see what the voltage is with Key ON/Engine OFF.

What is your MAP sensor vacuum line feeding from? Are you sure it is from either your TB or Intake Manifold and NOT from your vacuum canister feed?

My understanding of MAP sensor voltage is like this:

All have a range of 0-5 volts although most if not all will EVER give you a reading of 5 volts so expect the max voltage to be closer to 4.8 or even a hair less than that. Key ON/Engine OFF reading is always that of 0 vacuum so depending on which MAP sensor you have, you simply divide 5 by the respective MAP sensor type to determine which one you actually have from your reading.

1BAR max voltage reading for 0 vacuum reading is that of 5 volts (5/1=5).
2BAR max voltage reading for 0 vacuum reading is that of 2.5 volts (5/2=2.5).
3BAR max voltage reading for 0 vacuum reading is that of 1.66 volts (5/3=1.66).

Again, the reading you get at 0 vacuum will be even less than these max values because of not being able to achieve a true 5 volt reading. Hence, on a 2BAR MAP reading at 0 vacuum it will most likely be between 2.1 - 2.4 instead of 2.5.

If your 0 vacuum reading isn't close to your MAP sensor type, then the sensor is either bad, wired incorrectly, or simply the wrong one.

With the engine running at idle, the voltage reading will be equivalent to your actual vacuum at idle. So someone with an aftermarket cam will most likely have less vacuum at idle than someone with a stock cam and will naturally have a higher MAP voltage reading at idle than someone with a stock cam given they both have the same type of MAP sensor.
 

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Disconnect the vacuum line from the MAP sensor and then see what the voltage is with Key ON/Engine OFF.

What is your MAP sensor vacuum line feeding from? Are you sure it is from either your TB or Intake Manifold and NOT from your vacuum canister feed?

My understanding of MAP sensor voltage is like this:

All have a range of 0-5 volts although most if not all will EVER give you a reading of 5 volts so expect the max voltage to be closer to 4.8 or even a hair less than that. Key ON/Engine OFF reading is always that of 0 vacuum so depending on which MAP sensor you have, you simply divide 5 by the respective MAP sensor type to determine which one you actually have from your reading.

1BAR max voltage reading for 0 vacuum reading is that of 5 volts (5/1=5).
2BAR max voltage reading for 0 vacuum reading is that of 2.5 volts (5/2=2.5).
3BAR max voltage reading for 0 vacuum reading is that of 1.66 volts (5/3=1.66).

Again, the reading you get at 0 vacuum will be even less than these max values because of not being able to achieve a true 5 volt reading. Hence, on a 2BAR MAP reading at 0 vacuum it will most likely be between 2.1 - 2.4 instead of 2.5.

If your 0 vacuum reading isn't close to your MAP sensor type, then the sensor is either bad, wired incorrectly, or simply the wrong one.

With the engine running at idle, the voltage reading will be equivalent to your actual vacuum at idle. So someone with an aftermarket cam will most likely have less vacuum at idle than someone with a stock cam and will naturally have a higher MAP voltage reading at idle than someone with a stock cam given they both have the same type of MAP sensor.
I disconnected the vacuum line from the MAP and the voltage was 1.54, the exact same as with the line hooked up.

The vacuum source is the intake.

Do you think that I might have a 3-bar, labeled as a 2-bar? I have seen a few post where people have gotten MSD MAP sensors that ended up being a 3-bar, but was labeled as a 2-bar. 1.54 x 3 = 4.62
 

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Discussion Starter #14
Glad you got the sensor issue solved!
me too, thanks man.

so in conclusion...
I installed a Delphi brand 2 bar map part# 12247571. (looks the same as MSD)
I have 5V power to Pin A, signal wire in Pin B, and ground to Pin C.
I get 2.38V on the signal wire with key on and engine off.

I do not know if my original MSD part from summit was defective, mismarked, or if i fried it by hooking up power and ground backwards.
 

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