My engine stalls at idle why?

Hi and thanks for using 2CarPros.

If you are seeing black smoke, chances are the engine is getting too much gas. Now, this can be caused by a few different things. First, a bad fuel pressure regulator can be bad. Next, a bad coolant temperature sensor can cause it.

With that, I need you to do the following. First, if the check engine light stays on when the engine is running, you need to scan the computer for diagnostic trouble codes. Here is a quick video of how that is done:

https://youtu.be/YV3TRZwer8k

I realize most people don't own a scanner. If that is the case, most parts stores will scan it for free. If you have that done, let me know the codes.

Next, I would recommend checking fuel pressure and the regulator to make sure it isn't too high. Here is a link that shows how it is done:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

The fuel pressure readings should be as following.

Fuel Pressure .................... 339 kPa ± 34 kPa (49.2 psi ± 5 psi)

If you find the pressure is high, the regulator has most likely failed. The regulator on this vehicle is located above the fuel tank and part of the filter. I attached a picture of it to help find it.

Check these things first and let me know what you find.

Joe

Hi again:

I hate changing things without being sure. Without checking pressure or knowing the fuel trims, I don't know for sure if that is the problem. It can be, but without testing, it becomes a guess. I hope you understand.

Regardless, here are the directions for replacing one. The attached pictures correlate with these directions.

The combination Fuel Filter/Fuel Pressure Regulator is remotely mounted to the vehicle body, above the rear axle and near the front of the fuel tank.

See Picture 1

1 Perform Fuel System Pressure Release Procedure.
2 Disconnect negative battery cable at battery.
3 Raise vehicle.
4 Clean area around 3 filter/regulator fittings.

Fuel Filter/Fuel Pressure Regulator Location

See Picture 2

5 Disconnect fuel supply fuel return and fuel pressure lines at filter/regulator. Refer to Quick-Connect Fittings.
6 Remove 2 mounting bolts and remove filter/regulator.

INSTALLATION
1 Before installing filter/regulator, be sure all fittings are cleaned of all dirt and contaminants.
2 Be sure O-ring is positioned into fuel return fitting in filter/regulator.
3 Apply a small amount of clean engine oil to O-rings.
4 Position filter/regulator to body and install 2 bolts. Tighten bolts. Refer to Torque Specifications.
5 Connect 3 fittings. Refer to Quick-Connect Fittings.
6 Connect negative battery cable to battery.
7 Start engine and check for leaks.

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Let me know if this helps or if you have other questions.

Take care,
Joe

This is common when you have a vacuum leak or the throttle bore needs to be serviced here are three guides to go over when fixing the problem.

https://www.2carpros.com/articles/throttle-actuator-service

and

https://www.2carpros.com/articles/stall-at-idle

and

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Please run down these guides and report back.

You need to know if the battery is fully charged, if the volts are too low, the computer will not operate correctly. Recharge or replace the battery.

This happens when the computer is trying to relearn this guide will help explain it better.

https://www.2carpros.com/articles/engine-stalls-idles-too-high-low-after-dead-or-replaced-battery

we have a new article that shows the throttle bore service step by step which can help as well.

https://www.2carpros.com/articles/throttle-actuator-service

Please run down these guides and report back.

Good morning,

I would check the pressure first before assuming the pump is bad. I attached the specs for you below. You can rent a tester to verify at a parts store.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

https://www.2carpros.com/articles/how-to-replace-an-electric-fuel-pump

Fuel system pressure 339 kPa +/- 34 kPa 49.2 psi +/- 5 psi

Check this first to verify.

Roy

You are welcome.

Always glad to help.

Roy

You are welcome.

Glad to help.

Roy

Good morning,

The locksmith is the best alternative. In order to do it yourself, you will need a DRB scan tool that is very expensive to reset the system.

https://www.2carpros.com/articles/how-to-reset-a-security-system

Roy

Welcome to 2CarPros.

The mass air flow sensor may cause it to run poorly, but what you described doesn't sound like it. Does the vehicle start right back up after it stalls only to do the same thing?

If that is what is happening and there is no check engine light, my first suspect is the crankshaft position sensor. If the vehicle won't start after it stalls, then you can take your scanner and check if there is an RPM signal when it won't start. If there is none, then the sensor is my first suspect.

Take a look through these links:

https://www.2carpros.com/articles/how-a-crank-shaft-angle-sensor-works

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

https://www.2carpros.com/articles/crankshaft-angle-sensor-replacement

Another way to test the sensor is by checking for ignition spark. If when the engine shuts off you note that spark stopped, the sensor is a suspect.

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Here are the directions specific to your vehicle for replacing the sensor. It is located right above the starter. However to access the retaining bolt, the starter needs removed. Make sure to disconnect the battery before you work on or around the starter. The attached pictures correlate with the directions.

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2001 Jeep Truck Grand Cherokee 4WD V8-4.7L VIN N
Procedures
Vehicle Powertrain Management Sensors and Switches - Powertrain Management Sensors and Switches - Computers and Control Systems Crankshaft Position Sensor Service and Repair Procedures
PROCEDURES
REMOVAL

Fig.22 CKP Sensor Location

Pic 1

The Crankshaft Position (CKP) sensor is bolted to the side of the engine cylinder block above the starter motor; It is positioned into a machined hole at the side of the engine block.
1. Remove starter motor. Refer to Starter Removal/Installation.
2. Disconnect CKP electrical connector at sensor.

Fig.23 CKP Sensor Removal/Installation

Pic 2

3. Remove CKP mounting bolt.
4. Carefully pry sensor from cylinder block in a rocking action with two small screwdrivers.
5. Remove sensor from vehicle.
6. Check condition of sensor O-ring.

INSTALLATION
1. Clean out machined hole in engine block.
2. Apply a small amount of engine oil to sensor O-ring.
3. Install sensor into engine block with a slight rocking action. Do not twist sensor into position as damage to O-ring may result.

CAUTION: Before tightening sensor mounting bolt, be sure sensor is completely flush to cylinder block. if sensor is not flush, damage to sensor mounting tang may result.

4. Install mounting bolt and tighten to 28 Nm (21 ft. Lbs.) torque.
5. Connect electrical connector to sensor.
6. Install starter motor. Refer to Starter Removal/Installation.

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Let me know if this helps or if you have other questions.

Take care,
Joe