My car is 97 auto , all stock.

I put a scanner(handheld Acton CP9575) on it and the MAP Sensor reads as follows:

1. With the key on and car NOT started = 53 kpa
2. With the car idling = 27 kpa
3. on full throttle = 53 kpa

This looks incorrect to me, should the readings for items 1 and 3 be around 97kpa - 100kpa ?

Has anyone else seen something like this ?

Vic

 

I absolutely agree with you that your 1 and 3 readings should be in the general range that you listed.

 

Ya, should go up close to 100kpa with no vacuum. Almost sounds like a 2-bar MAF sensor.

 

Map kpa should read 60-74 at idle. That equates to 18-22" vacuum. Key on engine off it should read .3-3 kpa. Wide open throttle it should drop to between 1-10 kpa. If there was a problem with the sensor or circuit, the PCM should set either a p0107 or p0108.
Some scanners seam to read map values backward. Kpa is not mentioned in these flow charts, just signal voltage.
The values referred to above came from a conversion calculator.

 

Your values are backwards. A 1-bar MAP sensor reads up to one atmosphere of pressure or about 100kpa. Full vacuum is 0kpa and no vacuum or full atmosphere pressure is 100kpa.

 

Values came from alldata conversion calculator. Maybe they got it wrong, it happens. Does a stock 97 vette have a 1 or 2 bar map sensor? I thought only boosted gm engines used 2 bar map's.

 

http://www.engineeringtoolbox.com/va...ter-d_460.html

 

I am troubleshooting a minor issue and that is why I used the scanner, the only thing that looked incorrect via the scanner was the MAP sensor output.

As I am driving, the car bogs/jerks for less than 1 second, sometimes when it does this it throws code P0101.

Vic

 

Any type of bog or hiccup will show up on map output. The p0101 is a MAF code. Check for air or vacuum leaks. Pcv plumbing is troublesome. Clean the MAF and TB. Here is some info that should help.

CIRCUIT DESCRIPTION

The Mass Air Flow (MAF) sensor measures the amount of air ingested by the engine. The direct measurement of the air entering the engine is more accurate than calculating the airflow from the MAP, the IAT and the engine speed (speed/density). The MAF sensor has a battery feed, ground, and a signal circuit.

The MAF sensor used on this engine is a hot wire type. This engine uses the MAF sensor to measure air flow rate. The MAF output frequency is a function of the power required to keep the air flow sensing elements (hot wires) at a fixed temperature above the ambient temperature. Air flowing through the sensor cools the sensing elements. The amount of cooling is proportional to the amount of air flow. As the air flow increases, the MAF sensor requires a greater amount of current in order to maintain the hot wires at a constant temperature. The MAF sensor converts the changes in current draw to a frequency signal read by the PCM. The PCM calculates the air flow (grams per second) based on this signal.

The PCM monitors the MAF sensor frequency. The PCM can determine if the sensor is stuck low, stuck high, not providing the airflow value expected for a given operating condition, or that the signal appears to be stuck based on a lack of signal variation expected during the normal operation. This diagnostic checks the range/performance of the MAF sensor. The MAF system performance or rationality diagnostic uses the MAP, the IAT, and the engine speed to calculate an expected airflow rate. The PCM then compares the rate to the actual measured airflow from the MAF sensor. The PCM only compares the actual MAF value and the calculated value during conditions where the values are likely to match. If the actual MAF reading is not within a predetermined range of the calculated reading, this DTC will set.

CONDITIONS FOR SETTING THE DTC

DTCs P0102, P0103, P0107, P0108, P1120, P1220, P1221 not set
Engine running
Engine speed greater than 50 RPM but less than 2800 RPM
TP sensor angle less than 50% when engine vacuum (BARO-MAP) is greater than 65 kPa
Ignition voltage greater than 10 volts, but less than 16
MAF frequency 50% different from the speed density calculation
All above conditions stable for 2 seconds
All conditions met for 5.0 seconds
ACTION TAKEN WHEN THE DTC SETS

The PCM illuminates the Malfunction Indicator Lamp on the second consecutive drive trip that the diagnostic runs and fails.
The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive drive trip, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure records.
The PCM utilizes speed density (RPM, MAP, IAT) for fuel management.
CONDITIONS FOR CLEARING THE MIL/DTC

The PCM turns the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.
A last test failed (current DTC) clears when the diagnostic runs and does not fail.
A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
The PCM battery voltage is interrupted.
Use a scan tool in order to clear the MIL/DTC.
DIAGNOSTIC AIDS

If you cannot find any problems with the ignition feed circuit to the component, inspect the IGN mini relay for proper operation. Probe both sides of the ENG IGN1 fuse with a test lamp connected to ground in order to determine if the IGN mini relay is suppling the power. Refer to Body and Accessories for further diagnosis of the IGN mini relay.

The following may cause an intermittent:
Mis-routed harness
Rubbed through wire insulation
Broken wire inside the insulation For an intermittent, refer to Symptoms. See: Powertrain Management\Computers and Control Systems\Testing and Inspection
Any un-metered air may cause this DTC to set. Check for the following:
An engine vacuum leak
The PCV system for vacuum leaks
An incorrect PCV valve
The engine oil dip stick not fully seated
TEST DESCRIPTION

The numbers below refer to the step numbers on the diagnostic table.

The MAF system performance or rationality diagnostic uses the MAP sensor signal along with other inputs in order to calculate an expected airflow rate. The PCM then compares the expected flow rate to the actual measured airflow from the MAF sensor. The first few steps of this table verify that the MAP sensor is working properly. Correct any MAP sensor DTCs first. The value shown for the MAP sensor varies with altitude. The value decreases by approximately 3.0 kPa for every 1000 feet of altitude. 100 kPa is the approximate value displayed at or near the sea level.
Twist the sensor towards the front of the vehicle and lift upwards in order to remove the MAP sensor.
Using the Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This will isolate when the DTC failed. For any test that requires probing the PCM or component harness connectors, use the Connector Test Adapter Kit J 35616-A. Using this kit prevents any damage to the harness connector terminals.
Any un-metered air causes this DTC to set. Check the PCV system for vacuum leaks. Also inspect the dip stick for being pulled out. Check the oil fill cap for being loose.
This step verifies the signal circuit from the MAF sensor electrical connector to the PCM.
This step verifies whether a ground and B+ circuit is available.
This step checks the signal circuit for an open.
This step checks the signal circuit for a short to B+.

 

I just scanned another car and this is what the map sensor output shows:

1. With the key on and car NOT started = 103 kpa

The only way to get to the MAP sensor is to pull the intake , correct ?

Vic

 

I pulled the Intake to test the MAP sensor.

It showed 4 volts on the middle wire with the key in the ON position.

The new MAP sensor showed 4.90 volts on the middle wire.

I buttoned it back up and took it on a 50 mile drive.
No codes so far.

Vic

 

lionelhutz is correct - your values are backwards.

Your conversions are correct, except you are incorrectly equating manifold pressure with manifold vacuum. Vacuum is measured relative to ambient atmospheric pressure. Pressure is measured relative to perfect vacuum.