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

We have decided to just put a new fuel pressure regulator on it. We ordered it and it will be here tomorrow, we do not have the tools to check the pressure and have no way of getting the car to anyone who can scan it for us at the time. Thank you for replying, I will let you know if the regulator works.

We changed the fuel pump less then a month before this problem started. I do not know if we should have changed the fuel pressure regulator then. I know it is also the filter.

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.

__________________________________________________

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

Take care,
Joe

wife left the key in the on posistion for 6 hours. The car started after jumping but will not idle when in gear.

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.

Jeep was running fine last night. Never had an issue with it before, but have owned grand Cherokees before. I went to start the jeep this morning, would crank over, as if the battery was dead. I jumped the jeep with my wifes car, and after giving it a little gas, the jeep fired right up, however it would not stay running unless I was on the accelerator. I jumped it again from a friends truck, I kept on the accelerator for a minute or so at 1000RPM and had him disconnect the cables, and the jeep would stay running as long as I was on the accelerator, but if I let off it died. I have had alternator problems in the past with other vehicles, but never experienced this. I have been told that my battery may be junk which would make sense but would appreciate a second opinion. any ideas?

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.

Vehicle starts then immediately shuts down. I have cleaned and checked all throttle body sensors. Replaced fuel filter and regulator. Does this pretty much confirm a bad fuel pump?

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

Thanks for the get back. I'm on my way out to get started on the beast. Will let you know what worked.

You are welcome.

Always glad to help.

Roy

As it turned out my situation had nothing to do with security related issues.
I installed a new fuel pump and it still started up and run 2 seconds then quit. After pulling the rest of my hair out, l remembered removing the CPS along with the oil pump drive. I didn't know that little fella controlled the injector sequence. I did a reset on the timing and reinstalled everything. The engine turned 1/2 round, fired and runs like a champ.
I want to thank you men for everything you did to walk me through this. Y'all saved me my other leg. Now l know who to go to when l run into another auto problem.
Thank you

You are welcome.

Glad to help.

Roy

I was working in the steering column and unplugged the immobilizer. Since then my Vehicle will start and run about 2 seconds. What can l do about this issue without paying $300.00 for a locksmith?

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

My vehicle will start but then will shut off straight after. we changed the fuel pump, no engine check lights and the problem is still occurring. Would it be my mass airflow sensor?

Add to the post have done a full service including transmission.

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.

_____________________

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

Yes that was it all fixed thank you so much!

My jeep won't not idle unless you started it up with you foot on the gas I change the battery because it was always dead when you let it sit over night and now it won't start you hear it want to turn over but it doent all the way I don't know what to do.

Go out and drive it. The Engine Computer lost its memory and has to relearn "minimum throttle" before it will know when it must be in control of idle speed. It also might not give you the normal "idle flare-up" to 1500 rpm when you start the engine. To meet the conditions for the relearn to take place, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the brake or gas pedals.

I took a round trip of about 334 miles with a 15 hour break. in the middle stopped 3 times on return trip, on second stop noticed the check engine light was on though i could detect nothing wrong vehicle started and ran fine. This morning after vehicle sat for 7 hours went to start, it fired right up upon releasing the key RPM's immediately dropped and vehicle shut off, several attempts, same result, though i can keep my foot on accelerator pedal and keep motor running, also noticed check motor light now off. Also all fluid levels good. Any ideas? Any help greatly appreciated.

Good morning,

I would start by cleaning the throttle body as it controls your base idle.

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

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

Can you have codes read at a parts store? It is a free service. Those codes could be a clue as to the failure.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Roy

Someone said you can turn a Jeep's key forward and back 3 times and get a code on the odometer ?

Yes, if you cycle the key 3 times, it will put it in a diagnostic mode.

There will be 2 number codes based on the number of flashes for the light.

Roy

will not idle when engine is cold

You may have a bad IAC ( idle air control) but try cleaning the throttle body first. Remove the intake snorkel, have someone hold the throttle wide open for you and scrub the back side of the throttle plate and surrounding bore with an old tooth brush and some carb cleaner. Be sure to spray some into the small holes next to the throttle plate. That should help stabilize the idle. If it still has a problem, replace the IAC.