MIL on, surge/buck at slow speeds

Leon Owner/Technician Berryville, Arkansas Posted   Latest   Edited  
Question
Driveability
2014 Ram 2500 Laramie 6.4L (J ESA) 6-spd (66RFE)—3C6UR5FJ8EG295816
P0171 - System Too Lean Bank 1
P0174 - System Too Lean Bank 2
P0740 - Torque Converter Clutch Circuit/Open
Harsh Buck

Hello all, my first time posting here so bear with me:) We have this Ram 2500 6.4L with 144,000 miles on it that came to us after stumping 2 dealers, and stumping me:/ but maybe with the help of like minded, smart peers out there collaborating, maybe we can get to the bottom of this. Customer concern: when driving slowly, 15mph or less, (like driving thru a parking lot) it will develop a severe lunge/surge, it will only do it with no throttle input. If it starts doing it, and you give it any throttle at all, the symptom goes away immediately. Driving otherwise (cruising, idling etc) absolutely no problems at all. 

The only codes stored are the ones listed above. LTFT will go to +27% when coasting if you coast for an extended distance (200 or 300 yards) but otherwise they will remain within 10-12% of zero at all times. While looking thru data I noticed that the EGR desired position moves around some but the actual does not. (Is this/could this be my problem??) This problem just started when the Chrysler dealer installed a reman engine for him. Fuel pressure is 58psi at idle with 16oz. of volume in 15 seconds vacuum is 18" @ idle smoke tested the intake system with no leaks found at the customer's request we flushed the transmission about 1,000 miles ago with no change. 

Thanks in advance for any help y'all can give me!!

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Dave Mobile Technician
Ironton, Ohio
Dave
 

If EGR desired and actual do not match I would go for this problem first. Fix what you know is bad before going any further.

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Mario Diagnostician
Weston, Florida
Mario
 

So symptom does not occur at parked idle? What are your ft at idle and when you lightly snap throttle what does it do? Get better or worse? Are you able to actuate egr?

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Leon Owner/Technician
Berryville, Arkansas
Leon
 

no, symptom does not occur at idle.. I don't recall what my fuel trims do @ idle and I mostly didn't pay a lot of attention to them @ idle because the problem doesn't occur at idle. I cannot actuate my EGR valve thru my scanner, however I jumper wired it up to manually actuate it and it moves and the sensor seems to be working properly. Also I scoped my wires at the valve and ecm is in fact

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Leon Owner/Technician
Berryville, Arkansas
Leon
 

OK I rechecked just now and the total trim is ~12-14% (TOTAL TRIM) not just long term

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Greg Technician
Colorado Springs, Colorado
Greg
 

Sounds like the Chrysler dealer owns this...

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Glenn Owner/Technician
New Sharon, Maine
Glenn
 

Does this engine have cylinder shut down?

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Leon Owner/Technician
Berryville, Arkansas
Leon
 

yes it does, but according to my scanner it is not activating when the symptom occurs

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Richard Technician
Virginia Beach, Virginia
Richard
 

The first thing is you have a fuel trim problem if your swing is -14 to +27 . Secondly, you should be graphing Pids as a correlation should stand out. I don’t work on these but I don’t know of any strategy to be using egr under a slow coast condition.

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Joel Diagnostician
Soquel, California
Joel
 

sound like maf sensor contaminated , fuel trim rich at dle and lean off idle is that even on both banks ? execive egr ar low rpm normally act like vacuum leak the simtopm but the engine runs rich , because the inert gas that do not contain 02 molecules to be re burn .

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Leon Owner/Technician
Berryville, Arkansas
Leon
 

Sorry Richard, I should have used a different symbol on that. the fuel trim swing is not negative 14 to positive 27%.. it is positive 14 to positive 27%

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Bentley Manager
San Diego, California
Bentley
 

Disconnect EGR and test for symptom. If LT FT is +27 both banks but ST FT is OK the system is in fuel control and should not severely surge. The P0740 can cause severe surge, was there wire harness damage during the engine swap?

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Allan Instructor
Winnipeg, Manitoba
Allan
 

Your vacuum is low. Have you checked the EGR to see if it’s stuck partially open?

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Leon Owner/Technician
Berryville, Arkansas
Leon
 

I blocked it off with a pop can... with some improvements on my fuel trims, but not a whole lot

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Eric Owner/Technician
Edgerton, Wisconsin
Eric
 

It sounds like the engine/computer management system is bouncing in and out of fuel cut/deceleration mode. Verify the throttle is closing all the way and the throttle position sensor is reading correctly. If the computer sees the throttle closed and cuts the fuel for deceleration but the TPS is not reading steady or moving a few tenths of a volt up or down it could be causing the EGR issue, the

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Brandon Diagnostician
Cleveland, Georgia
Brandon
 

Have you done a relative compression test? These engines like to eat lifters. I‘m not saying that is your problem but it does warrant the need to check the mechanical ability of the engine. Also, pay close attention to the cadence of the engine while cranking for roughly 10 seconds. Have you graphed all 4 sensors to see if one is lazy/lagging? This is a long shot but we have had a serious issue

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Leon Owner/Technician
Berryville, Arkansas
Leon
 

sorry about the delay in responding here Brandon, I was working on other vehicles and just getting back to it this morning. I didn't do a compression test due to the fact that it runs great other than while puttering thru a parking lot, my thoughts were if we had a mechanical issue, it would run rough otherwise?? also it has a fresh reman engine in it. Yes a couple of 02sensors seem somewhat

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