Truck surges at about 40 MPG

[stephenrogers2000]

I’ve got a Dodge Ram 2500 with a V10 engine 8.0 liter. I’ve been having this problem where the RPMS starts to surge when the truck warms up and around 40-50 MPH. And on the highways it surges at any constant speed. It will surge every 5 seconds... the only time it doesn’t surge is when I’m accelerating fast or slowing down.

I’m very baffled by this! I’ve had the battery tested and it is at fully working capacity. I just changed the transmission oil myself last week. Any ideas on what this is?

Thanks!


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[dudeman2009]

In my experience, surging like that when light on the throttle is a trans going out. 40-55 is one of the places the Torque converter tries to lockup. If that is failing (as is common with these trucks) it will surge every time the TQ cuts out.

Try hitting the OD off button and see if that fixes it.

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[stephenrogers2000]

I tried pressing OD and the same thing happened. The interesting thing is, when I’m going 65 and the engine is warm, it surges very bad. It’s not just at 40-50mph. Any suggestions?


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[dapepper9]

Od off doesnt keep the converter unlocked, it just turns off od. Converter will still try to lockupbin 3rd gear regardless of the button.

Since it quits surging when you're giving it a more aggressive acceleration, I would definitely plan on replacing a torque converter. Not at all uncommon and luckily it doesnt require a full trans swap.

2 ways to do it: unbolt engine or unbolt trans. Trans can be removed or unbolted and slid back enough to work or engine can be removed or slid forward enough to work. At least on the 360 the engine can come forward enough. On that v10 i would probably slide the trans back instead

 

[dapepper9]

Also, going 65 it takes more engine tq to maintain speed than it does at 45-50. Converter still wants to lockup but the greater tq is going to cause it to shutter more than at lower speeds. And enough throttle input will keep it unlocked

 

[stephenrogers2000]

Thank you @dapepper9 !
Really appreciate the input. Are you saying that the cause of this is solely the TC or could I possibly be the TPS?


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[dapepper9]

Tps would likely cause erratic stumbling issues closer to idle at stops and stuff. Being as consistent as it is at the speeds it is would lead me to think its the TC. It's possible it could be the solenoid as well.

What may be worth your time is to change the solenoid first. At the least you'd be doing a fluid/filter service in the process

 

[Yeret]

Sorry, I can't resist, but if my truck got 40 MPG, it'd probably surge pretty bad too!