Question about 2000 Jeep Grand Cherokee
Current Freeze Frame Data on scanner, as follows:
Engine Load: 16 %
MAP KPA: 41
Coolent Temp: 114
ST FTRM1: 26.5
LT FTRM1: 32.04
LT FTRM3: -2.2
LT FTRM3: -52.2
Fuel System Closed
Have replaced fuel filter/regulator, 02 sensors, air Inlet sensor, removed & cleaned throtlle body, checked voltages on throttle position sensor, MAP sensor with VOM meter and checks out OK. Checked fuel pressure at rail schrader valve and OK. Pulled and cleaned spark plugs. Checked and found no apparent vacuum leaks
Previously, engine would idle fine for about 30 minutes than after it was up to temperature with load ( accelerate to 2000 rpm, with AC on ) engine would stumble.
I'm totally baffled. Do I focus on vacuum related issue or fuel relatd issue. Maybe waer in fuel ? Injectors ? Would appreciate your advice.
Check EGR valve. Also check all injector pulses with NOID light especially when vehicle is stumbling. It may be computer related. Get back to me if you need more help. Good Luck
Posted on Dec 28, 2008
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Posted on Jan 02, 2017
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Sep 30, 2016 | 1999 Pontiac Grand Am GT
The barometric pressure (BARO)
The manifold absolute pressure (MAP)
The intake air temperature (IAT)
The engine RPM
P0121 The predicted air flow and the predicted MAP combined are outside a calibrated range for more than 3 seconds.
Inspect thoroughly for any type of leak or restriction
Air leaks at throttle body mounting area and intake manifold sealing surfaces
Throttle body for dirt, debris, and coking--Refer to Throttle Body Cleaning.
Increase the engine speed slowly to 3,000 RPM, then back to idle.
Exit from the snapshot and review the data.
Observe the Mass Air Flow (MAF) Sensor parameter frame by frame with a scan tool. The MAF sensor g/s should change smoothly and gradually as the engine speed is increased and is returned to idle.
If the MAF sensor g/s does not change smoothly and gradually as the engine speed is increased and is returned to idle, refer to DTC P0101 or P1101.
Broken throttle shaft
Any throttle body damage
If any of these conditions exist, replace the throttle body assembly.
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Table 3: Using the Hi-Scan Pro in the Hyundai Diagnostic Menus Current Data Screen TPS (%) 0
MAF (kg/h) 9.5
Table 4: Using the Hi-Scan Pro in the OBD-II Menus Current Data Screen TPS (%) 0
MAF (g/h) 2.5
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Manifold Absolute Pressure/Barometric Pressure Circuit Malfunction
The MAP (Manifold Absolute Pressure) sensor is part of the fuel management system. It reacts to changes in engine manifold pressure. The PCM (Powertrain Control Module) monitors the MAP sensor continually to properly run the engine. Changes in engine load require changes in the amount of fuel injected, and timing of the ignition system, etc. An engine under load has more manifold pressure(or less vacuum) than an engine that is coasting. As the load changes, the MAP sensor voltage signal to the PCM changes accordingly. To check the MAP sensor operation, though, the PCM watches other sensors to verify that the MAP sensor is working properly.
For example, the PCM compares the TPS (Throttle Position Sensor) signal to the MAP signal to verify the MAP signal isn't "sticking". If the PCM doesn't see a MAP sensor change immediately follow a change in the throttle pedal sensor, it knows there is a problem with the MAP sensor and sets P0105. Or, if the PCM notices that the TPS indicates the engine is under load, but the MAP signal indicates that the engine is "coasting" it, again, knows there is a problem with the MAP sensor or TPS and sets P0105.
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Symptoms of a P0105 check engine light code may include:
A P0105 DTC could be caused by:
Using a scanner or code reader, turn the ignition on and engine OFF; what does the MAP sensor voltage read? It should be about 4 Volts for sea level. If you are at a higher altitude, it should decrease about half a volt or so for each 1,000 ft. of altitude (this will vary from model to model) Or if you have a separate MAF (Mass air flow) sensor on your vehicle, they are usually equipped with a Barometric pressure reading. If so, the Baro reading should match the MAP reading (they both measure ambient air pressure). If they're roughly equal, then, check for Freeze Frame data of the MAP sensor (if available).
NOTE: Freeze Frame data is the PCM recording a fault when it happens. It captures the readings of the various PIDS (parameter identifiers)available to troubleshoot what happened. It's like a recording of the problem as it happened. At idle a typical MAP sensor Voltage reading should be about a volt, and at WOT (wide open throttle) it should approach 4.5 to 5 Volts. As for the TPS, at idle, the voltage reading is about 1 Volt or less. As the throttle is opened the reading will increase to 4.5 Volts at WOT. Do the two readings make sense? For example, if the TPS reading on Freeze Frame data shows 2.5 Volts (indicating partial throttle) does the MAP sensor indicate a reading that isn't at either extreme? Using the Freeze Frame data (if available) compare the MAP reading to the TPS when the problem occurred. This can help you identify what happened
If you have no access to Freeze Frame data then check if the MAP sensor voltage changes when you apply vacuum to it. You can do this by mouth or a vacuum pump. The voltage should increase as you apply vacuum. If the reading doesn't change as you apply vacuum, make sure there are no obstructions in the hose to the sensor. If the hose is clear, the MAP sensor is usually bad, but it doesn't rule out the following from causing the problem: Does the MAP sensor appear to be stuck at less than .5 Volts? Then:
NOTE: This code shouldn't set if the MAP is stuck at extremely low voltage, however, I'm adding it in because there's no way to know for certain for which vehicles a low voltage condition may set a P0105.
Does the MAP sensor appear to be stuck at full 4.5 voltage? Then:
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