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2012 ram 4.7 engine surging at cruising speed

3K views 9 replies 5 participants last post by  Thor1488 
#1 ·
Hi guys, hope someone can help me out. I have a 2012 ram with the 4.7 crew cab, 19K miles, k&n air filter and magnaflow exhuast. I have noticed within the past few weeks that at cruising speed, 30-50 mph, around 1100-1400 rpm, when you apply very little throttle, the rpm/engine is surging or hunting a little, about 75 rpms. i disconnected the battery for 5 hours and when i reconnected it did it again right away. I think it doesnt do it as noticeable if I have the tow/haul mode on, but then it just feels like its jerking a little. no MIL, no other problems. Some have mentioned Torque converter, PCM, just wondering if there is an update on this issue before I take it to the dealer. I got the lifetime warranty on it. Any help will be greatly appreciated.
 
#2 ·
Strange because the first thing I thought was to say unplug your battery to reset the system, but you did that, It takes a huge 15 min to swap the OEM CAI to the K&N CAI, I would try to swap back in the OEM CAI and see what happens, also by Having the OEM CAI back on the truck if it still does it, the Dealer can't start pointing the finger at the K&N. JMO
 
#5 ·
I have the same exhaust,and i have a part throttle lean surge too.
I think the exhaust flows enough to put the motors on the outer edge of the stock computors parameters.
My exhaust went on along with a ported throttle body the day i drove in home from the dealership,had a 120 miles on it,and has had the lean surge ever since
 
#6 ·
I'll check everything I can, im gonna start tonight with putting in the stock air filter which is brand new and seeing if that helps. if it does, maybe the k and n is just dirty enough to create a problem. this problem didnt occur until 3 weeks ago, The cat back magna flow was a bolt on, dual out the passenger side before the tire. I cant see it being an o2 sensor without tripping a DTC. im gonna put it on the scanner tomorrow and see if anything is there. If I can't find anything, im just gonna leave it i guess until something finally gives. its just really annoying, and i dont really see it if its in tow haul mode, so im thinking maybe if i get the PCM reflashed it might fix it, any thoughts?
 
#7 · (Edited)
I'd be more suspicious of the fuel then anything,especially if you haven't changed anything lately.
Winter blend gas can create havoc especially if you're on the ragged edge of the stock computors parameters.
Try throwing a can of octane boost in and see if it makes any differance.

My exhaust is differant,but only in the fact mine goes out the back,with a few more ft of pipe,probably the same muffler,5X22 SI/DO
 
#9 ·
I just found this.

The most likely cause for this would be a worn throttle [COLOR=green !important][COLOR=green !important]position sensor[/COLOR][/COLOR]. When the sensor gets worn inside it will start to create small voltage spikes in it's signal. The engine controller sees these spikes as you opening the throttle when you aren't, so the idle goes up along with the voltage.

You may also notice some RPM fluctuation going down the road. When the [COLOR=green !important][COLOR=green !important]TCM[/COLOR][/COLOR] sees these voltage spikes when you are at a steady speed it will think you are [COLOR=green !important][COLOR=green !important]accelerating[/COLOR][/COLOR] so it unlocks the [COLOR=green !important][COLOR=green !important]torque converter[/COLOR][/COLOR] clutch. After a brief period it will relock the converter. This gives a 2-300 RPM fluctuation in the tach.

This is best seen with a labscope, but sometimes can be seen with a fast voltmeter if you set up to backprobe on the center pin of the sensor. If the voltage is fluctuating with the throttle closed the sensor is bad.

You can also try tapping on the sensor when it acts up. If the idle is fluctuating and tapping on the sensor brings it back, replace the sensor. Unplugging it while acting up should give you some definite results also.

The TPS is mounted to the left side of the throttle body with two Torx screws, easy to replace
 
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