MAP readings on Actron scanner
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Senior User
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MAP readings on Actron scanner
Hopefully someone else with an Actron scanner can help me. I have a CP9690 reader that is showing my MAP reading 15.8" Hg with the key on engine off when I would expect it to read closer to 30". I've probed the wire harness at the MAP and ECU connector with a Fluke multimeter and verified 158 Hz (about 30" Hg). I've replaced the MAP with a new Motorcraft part and no change. Also replaced ECU for an unrelated issue and no change. No codes are present indicating a MAP issue.
At this point I'm thinking that the Actron scanner has something wrong in its parameters and is reading the 158 Hz as 15.8" Hg. Can anyone else who has a similar scanner and EEC-IV verify this for me? Thanks for the help.
At this point I'm thinking that the Actron scanner has something wrong in its parameters and is reading the 158 Hz as 15.8" Hg. Can anyone else who has a similar scanner and EEC-IV verify this for me? Thanks for the help.
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Senior User
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Yes, OBD-I EEC-IV, and the CP9690 reads live sensor data from it. I recommend adding it to your Christmas wish list.
Fleet Owner
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From: Easton,Ks
I get 15.6 with my Actron Scanner CP9190-9185 on my 1994 460 and the engine not running.
The readout:
CANST PURGE On
ECT(V) 2.8
ECT(øF) 78
ENGINE SPD 0
EVP(V) 0.4
EVR(%) 0
FUELPW1(mS) 0.0
IAC(%) 0
IAT(V) 2.9
IAT(øF) 78
LOOP STATUS Open
MAP("HG) 15.6
O2SEN 1(V) 0.01
SPARK(ø) 0
ST FTRM1(%) 0
TOT(V) 2.8
TOT(øF) 79
TP MODE C/T
TPS(V) 1.1
VPWR(V) 12.1
VREF(V) 5.0
VSS(MPH) 0
The readout:
CANST PURGE On
ECT(V) 2.8
ECT(øF) 78
ENGINE SPD 0
EVP(V) 0.4
EVR(%) 0
FUELPW1(mS) 0.0
IAC(%) 0
IAT(V) 2.9
IAT(øF) 78
LOOP STATUS Open
MAP("HG) 15.6
O2SEN 1(V) 0.01
SPARK(ø) 0
ST FTRM1(%) 0
TOT(V) 2.8
TOT(øF) 79
TP MODE C/T
TPS(V) 1.1
VPWR(V) 12.1
VREF(V) 5.0
VSS(MPH) 0
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Also, for what it's worth when I read the data from my OBD-II '99 Buick with the engine off it correctly reads 30" Hg, so I think the issue may be isolated to the way the scanner interfaces with the EEC-IV.
Thanks, but your chart supports exactly what I am saying. 30" Hg absolute pressure is the same as 0" Hg manifold vacuum. That's why it says on the top of your graph "manifold vacuum data is based on 30.0 in-Hg barometric pressure." Doesn't really matter though, because either way it shouldn't read 15.8" Hg.
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From: Rhode Island
Read the chart again, it's saying 30" hG is 80 or so Hz, you're saying 30 inHg is 160hz. Yes it's esentially the same as what you're saying, but almost every scan tool I've used reports the pressure in terms of vacuum.
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The MAP reads absolute pressure, because with the engine off at sea level it would see atmospheric pressure of 30" but in a place like Denver it would see closer to 25" and adjust fuel accordingly. As such, it would output different Hz in the two different locations to account for the elevation change (your chart is "simplified" for sea level and doesn't account for this). What you are saying is that your scanner somehow reads this as 0" vacuum in both places, but that is not what I'm looking at and it isn't how the ECU interprets it.
Lead Driver
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From: Rhode Island
Yes, I'm acutely aware of the differences between gauge pressure, absolute pressure and what a MAP sensor does, how it works, and how the computer uses the information it gives it.
What I'm saying, is that almost every single scan tool I've ever used reports manifold vacuum as gauge pressure, as it's far more relevant to a technician working on the engine, who is going to have a mechanical vacuum gauge.
What I'm saying, is that almost every single scan tool I've ever used reports manifold vacuum as gauge pressure, as it's far more relevant to a technician working on the engine, who is going to have a mechanical vacuum gauge.
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I'm talking about using the MAP to measure absolute pressure with the engine off (i.e. BARO). From Ford TSB 98-23-10 "At sea level, BARO should read about 159 Hz (29.91 in. Hg). As a reference, Denver, Colorado at 1524 meters (5000 ft.) altitude should be about 144 Hz (24.88 in. Hg.)"
That may be true for a math-challenged technician that doesn't know how to subtract the MAP reading from atmospheric pressure to get manifold vacuum, but knowing that the MAP is accurately reporting atmospheric pressure at KOEO so the ECU knows the correct fuel requirements for the elevation is pretty "relevant" to me.
Fleet Owner
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From: Easton,Ks
All references to MAP in the Actron users manual.
MAP (0 – 255 kPa) or (Hg)
Intake Manifold Absolute Pressure displays
manifold pressure.
MAP:
Manifold Absolute Pressure (sensor). Measures intake manifold vacuum or
pressure and sends a frequency or voltage signal (depending on sensor type)
to the PCM. This gives the PCM information on engine load for control of fuel
delivery, spark advance, and EGR flow.
MAP GAUGE ("HG) Manifold Absolute Pressure Gauge Reading
BARO(V)/("HG)/(KPA) Barometric Pressure
MAP GAUGE ("HG) Manifold Absolute Pressure Gauge Reading
MAP (0 – 255 kPa) or (Hg)
Intake Manifold Absolute Pressure displays
manifold pressure.
MAP:
Manifold Absolute Pressure (sensor). Measures intake manifold vacuum or
pressure and sends a frequency or voltage signal (depending on sensor type)
to the PCM. This gives the PCM information on engine load for control of fuel
delivery, spark advance, and EGR flow.
MAP GAUGE ("HG) Manifold Absolute Pressure Gauge Reading
BARO(V)/("HG)/(KPA) Barometric Pressure
MAP GAUGE ("HG) Manifold Absolute Pressure Gauge Reading
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