Mechanics

STUMBLES UNDER HEAVEY ACCELERATION WHEN RPM

2000 Ford Focus

Engine Performance problem
2000 Ford Focus 4 cyl Two Wheel Drive Manual 207000 miles

Car stumbles and won't go when under heavy acceleration. When starting from a stop car stumbles but once the RPMs climb above about 2200 it gets better but still persists. Car has no problem at highway speeds until you mash the pedal to pass then it bogs down. I pulled the catalytic converter to make sure it wasn't plugged and problem continued. The hose from the PCV valve to the intake manifold sucks itself closed. I've replaced the PCV valve and the hose with a thicker hose but still sucks closed. My repair manual talks of a secondary inlet that opens under heavy acceleration to allow more air to the engine but I didn't find anything of the sort when I pulled the intake manifold. Any help would be appreciated.
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Mattfrazier
December 6, 2009.




Oxygen sensor
Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)

Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include: Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires
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Tiny
Rasmataz
Dec 6, 2009.
Thanks for the quick response. I should have included more info. Both 02 sensors have been replaced. Fuel injectors are clean and look good. MAF has been replaced. Vacuum leaks are not an issue all hoses are new and many clamps added.
Ignition wires, plugs, coil have been replaced.
I will run a chemical that will get the possible water and alcohol.
The part the intrigues me is the TPS which hasn't been replaced but more so the MAP sensor. What exactly does it do and would it being defective cause the hose from the PCV valve to the manifold to suck itself closed? Both those parts are new so I now it isn't a stuck PCV valve and when it is disconnected smelly air does come out of it. Almost as if the manifold is sucking too hard on it. Any thoughts on this secondary inlet that opens that can accessed during heavy accelaration. Any help is great.

Tiny
Mattfrazier
Dec 6, 2009.
A throttle position sensor (TPS) is a sensor used to monitor the position of the throttle in an internal combustion engine. The sensor is usually located on the butterfly spindle so that it can directly monitor the position of the throttle valve butterfly.

The sensor is usually a potentiometer, and therefore provides a variable resistance dependent upon the position of the valve (and hence throttle position).

The sensor signal is used by the engine control unit (ECU) as an input to its control system. The ignition timing and fuel injection timing (and potentially other parameters) are altered depending upon the position of the throttle, and also depending on the rate of change of that position. For example, in fuel injected engines, in order to avoid stalling, extra fuel may be injected if the throttle is opened rapidly (mimicking the accelerator pump of carburetor systems).

More advanced forms of the sensor are also used, for example an extra closed throttle position sensor (CTPS) may be employed to indicate that the throttle is completely closed.

Some ECUs also control the throttle position and if that is done the position sensor is utilised in a feedback loop to enable that control.

Related to the TPS are accelerator pedal sensors, which often include a wide open throttle (WOT) sensor. The accelerator pedal sensors are used in " drive by wire" systems, and the most common use of a wide open throttle sensor is for the kickdown function on automatic transmissions.

It senses Manifold Absolute Pressure (MAP). The vehicle computer calculates how much fuel to deliver to the engine based on the amount of load being applied to the engine. The computer uses manifold pressure, barometric pressure, engine RPM and throttle angle to determine engine load. Fuel ratio and spark timing are then fine tuned by the computer using additional sensors, this also helps to control fuel economy and emissions. Some vehicles use a Mass Air Flow sensor to measure the amount of air entering the engine, this also is used to determine engine load, in some cases there may be a MAP sensor and a MAF sensor. In that configuration the MAP is used for Barometric pressure and is a back up should the MAF fail, the computer will illuminate the Service Engine Soon lamp and use a calculated air fuel mixture to allow the driver to get to a repair shop without damaging the catalytic converter.
The MAP sensor doubles as a barometric sensor. The computer will read barometric pressure when the key is turned on prior to engine cranking and then every time the computer senses wide open throttle it will check Baro pressure again.

Nspect and test the crankcase ventilation system, When was the last tune-up-Having the wrong PCV valve can dilute and lean out the A/F mix-

Tiny
Rasmataz
Dec 6, 2009.

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