Intermittent stop - start jerking - JeepForum.com
 
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post #1 of 5 Old 09-21-2021, 02:29 AM Thread Starter
afnan
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Intermittent stop - start jerking

I have an eco diesel 2013 GC. I have a very strange problem which two dealerships are unable to diagnose and resolve. When car moves from stop to start it intermittently jerks around 1000-1300 RPM. So far I have spent 400$ in diagnosis without any outcome. The dealer was able to see the problem and said since there is no DTC they don't know where to start.

My findings are as follow:

1. If I disconnect the EGR Valve (attached to EGR Cooler) these symptoms do not happen
2. I have tried performing EGR Valve actuation test but fails
3. I purchased New Mopar EGR Valve and tried to perform the same EGR actuation test (without installing it on the cooler) it fails for that as well. This means that its not the EGR

What my thoughts are now
I noticed that at Idle and low speeds the EGR valve does open. If I disconnect the EGR valve it means that it does not open and the air to fuel mixture is perfect and as soon as the EGR valve opens the engine does not like it. This is seconded by the fact that when RPM goes to 1400 or so the EGR valve closes and the car comes back to life.

So, if its not EGR valve the problem is somewhere with EGR gasses mixing in and maybe O2 is lazy? What should be my next thing to do to find the problem?

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post #2 of 5 Old 09-26-2021, 07:28 PM
Bilko
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You may be better off looking for a good European forum, most WK2s sold in Europe are the 3.0 diesels, they are not so common in the US which means there is not much community support available, even many dealers are not really familiar with these engines. The US version has more stringent emission controls but the fundamental operations are very similar. That said many of the issues with the US versions are emission control related:-( The European version appears to be a very reliable option with great torque and good MPG considering the weight of the vehicle.
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post #3 of 5 Old 09-26-2021, 09:49 PM
ColdCase
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I notice you found the Australian Jeep Forum, where I think there are more diesels. What do you mean by disconnect the EGR valve, remove it or disconnect the electrical connector? I think it defaults to open when disconnected.

Sounds like the engine is stumbling at low RPM, intermittently, classified as a drivability problem. Dunno about the valve actuation tests, but anything that causes a marginal running condition may be causing this, its just that removing the EGR makes the engine run better.... Not much help, sorry. You may find some advice in the Diesel sticky thread here, most here tune the PCM to get rid of some of these drivability problems..

https://www.jeepforum.com/forum/f309...-info-2438921/ or perhaps check one of the RAM forums, there were many more diesels put in RAMs.

Just to be clear, on early US models there is the EGR valve on the cooler, an EGR Air Flow Control Valve on the manifold that adjusts the flow of fresh air into the engine during EGR operation, and a EGR bypass valve on the top of the EGR Cooler that is used to regulate the flow of exhaust gas through the EGR cooler.

The Exhaust Gas Recirculation (EGR) Air Flow Control Valve is an electrically operated throttle valve motor used to assist the EGR system function by creating a vacuum in the intake system to draw exhaust gas into the intake manifold. The valve is controlled by the Powertrain Control Module (PCM) through two control circuits. When the PCM closes the throttle valve creating a low pressure (vacuum) in the intake system. This low pressure effect helps draw exhaust gases from the EGR Valve into the intake system. The EGR Air Flow Control Valve has an internal position sensor. The PCM receives feedback from the sensor to indicate the position of the throttle blade. The position sensor operates as a typical three wire sensor. The PCM supplies 5VDC and the ground. The sensor varies the voltage on the sensor signal. The position at which the PCM will set the valve depends on the blended quantity of exhaust gas that needs to be recirculated into the engine in order for the exhaust gas to remain with the target emission level, which the PCM calculates based on input received from the oxygen sensors. When not actuated, the EGR throttle valve is in the open position.

So the relationships are complex. You may want to try a tuned PCM (also known as a ECU).

I just got lost in thought. It was unfamiliar territory;
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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post #4 of 5 Old 09-27-2021, 04:57 AM Thread Starter
afnan
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Thank you once again for a detailed reply. Yes, I have all three components that you have mentioned. I removed the MAP sensor and cleaned and the now it runs better but these symptoms do exist especially when cold or low rpm (1000-1300). When I disconnect the EGR Valve on the cooler it behaves well.

I would have deleted the EGR but its illegal here in Australia and penalty is just too much.

When the EGR connector is removed, there is no additional exhaust gasses introduced in the manifold and it works fine. When additional gasses are introduces it does not like it. This makes me think that there is something related to air - fuel mixture. Since I don't have check engine light or any codes I guess the sensors are fine. In my limited experience I think it leaves two options

1. Lazy lambda sensor
2. Leak in the exhaust system

I have checked the lambda sensor and the response time is approximately 500-600 ms slow than other sensors (Air Mass for example) I plotted graphs for it against various things and it seems that it does respond to overall air coming in the system but with bit delay. I am not sure what normal value is.

If there is exhaust leak then definitely AFR will be effected but why intermittent?

I can see why dealers (two) were not able to pin point this despite of seeing the driveability issues


Quote:
Originally Posted by ColdCase View Post
I notice you found the Australian Jeep Forum, where I think there are more diesels. What do you mean by disconnect the EGR valve, remove it or disconnect the electrical connector? I think it defaults to open when disconnected.

Sounds like the engine is stumbling at low RPM, intermittently, classified as a drivability problem. Dunno about the valve actuation tests, but anything that causes a marginal running condition may be causing this, its just that removing the EGR makes the engine run better.... Not much help, sorry. You may find some advice in the Diesel sticky thread here, most here tune the PCM to get rid of some of these drivability problems..

https://www.jeepforum.com/forum/f309...-info-2438921/ or perhaps check one of the RAM forums, there were many more diesels put in RAMs.

Just to be clear, on early US models there is the EGR valve on the cooler, an EGR Air Flow Control Valve on the manifold that adjusts the flow of fresh air into the engine during EGR operation, and a EGR bypass valve on the top of the EGR Cooler that is used to regulate the flow of exhaust gas through the EGR cooler.

The Exhaust Gas Recirculation (EGR) Air Flow Control Valve is an electrically operated throttle valve motor used to assist the EGR system function by creating a vacuum in the intake system to draw exhaust gas into the intake manifold. The valve is controlled by the Powertrain Control Module (PCM) through two control circuits. When the PCM closes the throttle valve creating a low pressure (vacuum) in the intake system. This low pressure effect helps draw exhaust gases from the EGR Valve into the intake system. The EGR Air Flow Control Valve has an internal position sensor. The PCM receives feedback from the sensor to indicate the position of the throttle blade. The position sensor operates as a typical three wire sensor. The PCM supplies 5VDC and the ground. The sensor varies the voltage on the sensor signal. The position at which the PCM will set the valve depends on the blended quantity of exhaust gas that needs to be recirculated into the engine in order for the exhaust gas to remain with the target emission level, which the PCM calculates based on input received from the oxygen sensors. When not actuated, the EGR throttle valve is in the open position.

So the relationships are complex. You may want to try a tuned PCM (also known as a ECU).
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post #5 of 5 Old 09-27-2021, 07:44 AM
ColdCase
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I think an intake leak or restriction could also be throwing the sensor data off causing marginal operation and then any upset sometimes causes the engine to stumble. Not sure if a dirty MAP gives higher or lower than actual volume/density. The PCM also used the intake manifold temperature sensor in its calculation.

Do you get any white smoke when stumbling? Its been awhile since I owned and dug into a diesel.

Good quality fuel? Water overflowing the fuel/water separator (fuel filter)

You seem to know what you are doing, just thinking of other possibilities.

I just got lost in thought. It was unfamiliar territory;
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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