Question about 1992 Oldsmobile 88

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1999 olds 88. I have replaced the fuel pump, sending unit, filter, mass air flow senson, spark plugs and wires, fuel pressure regulator. The car idles fine but when you apply pressure to the gas pedal it bogs down. I also disconnected all of the lines and blew them out. I am at an end what else can I do

Posted by cbtoolio on


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Jeffrey Turcotte

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Recommend you check your MAP sensor. You will need a voltmeter.
If you don't have a vacuum gage, just use your mouth to pull a vacuum on the hose and see if the voltage drops when you do.
Let me know if you have questions.

OPERATION The Manifold Absolute Pressure (MAP) sensor, used on 1996-99 vehicles, measures the changes in intake manifold pressure which result from engine load/speed changes, and converts this information to a voltage output. The MAP sensor reading is the opposite of a vacuum gauge reading: when manifold pressure is high, MAP sensor value is high and vacuum is low. A MAP sensor will produce a low output on engine coast-down with a closed throttle while a wide open throttle will produce a high output. The high output is produced because the pressure inside the manifold is the same as outside the manifold, so 100 percent of the outside air pressure is measured.
The MAP sensor is also used to measure barometric pressure under certain conditions, which allows the PCM to automatically adjust for different altitudes.
The MAP sensor changes the 5 volt signal supplied by the PCM, which reads the change and uses the information to control fuel delivery and ignition timing.

TESTING See Figures 1 and 2

  1. Visually check the connector, making sure it is properly connected and that all of its terminals are straight, tight and free of corrosion.
  2. With the ignition ON , check the voltage between terminals A and B (probe the back of the connector to connect to these wires). It should be above 4 volts. Apply 15 in. Hg of vacuum at the MAP vacuum port and check the voltage again. The voltage should be 2 volts now.

1999 olds 88.  I - jturcotte_326.gif

Fig. Fig. 1: Manifold Absolute Pressure (MAP) sensor circuit
When pumping up and releasing the vacuum, check to make sure the voltage readings are smooth. When applying vacuum to the sensor, the change in voltage should happen instantly. A slow change in voltage could point to a faulty sensor.

Fig. Fig. 2: MAP sensor voltage specifications

  1. If the sensor voltage is not within specification, check for a 5 volt reference at terminal C. If the reference signal is found, the sensor is faulty.
  2. If the sensor and circuits are functional, the PCM may be faulty.


3.8L (VIN K) Engine
See Figure 4
On these engines, the MAP sensor is mounted to the PCV valve cover.

  1. Disconnect the negative battery cable.
  2. Detach the MAP sensor electrical connector.
  3. Carefully bend the locking tabs holding the MAP sensor to the PCV valve cover, just enough to remove the MAP sensor.
  4. Pull the MAP sensor straight out of the PCV valve cover.

Fig. Fig. 4: On the 3.8L (VIN K) engine, the MAP sensor (1) is mounted in the PCV valve cover (2)

To install:

  1. Make sure that the seal is installed on the MAP sensor and that it is not damaged.
  2. Position and install the MAP sensor to the PCV valve cover. Make sure the locking tabs engage to hold the sensor to the cover.
  3. Attach the sensor electrical connector.
  4. Connect the negative battery cable.

Posted on Nov 27, 2010

  • Andrea Lock
    Andrea Lock Nov 27, 2010

    Hello JT

    I would jut like to inform you that i have read a couple of your solutions, and i am really impressed by the great solutions you manage to post with such a great detail.

    Keep on the good work.

    Kind regards

  • Jeffrey Turcotte
    Jeffrey Turcotte Nov 27, 2010

    Thanks Lock!! I'll have to read some of yours...



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Priority Action Part Type Cause
1 Inspect Spark Plug Fouled, Damaged, or Broken Spark Plug(s).
2 Inspect Hose (PCV) Clogged or Collapsed PCV Hoses.
3 Inspect Wireset Worn, Damaged or Faulty Spark Plug Wire(s).
4 Inspect Distributor Worn, Damaged or Faulty Distributor.
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7 Inspect TimingSet Slipped TimingChain or Worn TimingGear(s).
8 Inspect Knock Sensor Improperly Connected or Faulty Knock Sensor.
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10 Inspect Throttle Position Sensor Faulty or Incorrectly Connected Throttle Position Sensor.
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