2018 5.7 Tach fluctuating

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

SouthernBubba

Junior Member
Joined
May 3, 2021
Posts
7
Reaction score
1
Location
Florida
Ram Year
2018
Engine
5.7
2018 2500
5.7 Engine
6 speed auto
38K on the clock
No check engine lights or any other warnings indicated

I noticed the issue a couple of months back on a return trip from Tn not towing or any load in the vehicle . Driving on an incline 70-75 mps pushing on the accelerator and putting load on the engine it had a slight vibration but wasn't consistent . Figured maybe it was something on the road causing the vibration and didnt think much of it .
Flash forward to today , Past few weeks I have been paying attention to the tach . Ive noticed while accelerating lightly as the tach approaches 2K needle with fluctuate (bouncing maybe 200 rpms up and down) and I can feel that slight vibration again . Oddly enough if I give put more throttle into it , the vibration and the needle fluctuations will disappear and will accelerate normally with no issues . If I take off medium or full throttle acceleration no issues . Truck pulls strong and doesnt hesitate or anything that would indicate any issues . Tires recently balanced and rotated serviced regularly . Any thoughts or ideas ?
 

csuder99

Senior Member
Joined
May 28, 2014
Posts
557
Reaction score
428
Ram Year
2013
Engine
Hemi 5.7
Hard to say without seeing/hearing it. I'd venture torque converter clutch slipping/unlocking which can also be caused by TPS issues. Does it behave differently in tow/haul mode ?
 
OP
OP
S

SouthernBubba

Junior Member
Joined
May 3, 2021
Posts
7
Reaction score
1
Location
Florida
Ram Year
2018
Engine
5.7
Hard to say without seeing/hearing it. I'd venture torque converter clutch slipping/unlocking which can also be caused by TPS issues. Does it behave differently in tow/haul mode ?

I thought the same thing but will also do the same behavior in tow haul mode . I cleaned the throttle body recently hoping it would correct this issue . TB was pretty dirty , maybe clean it again?
 

Richard Kim

Senior Member
Joined
Jan 23, 2018
Posts
183
Reaction score
260
Location
Houston, Texas
Ram Year
2016
Engine
5.7 hemi
Had the same thing happen on my 2016 2500 5.7 except it was the speedometer fluttering when I did 70 -75mph. I wonder if this is related.
 
OP
OP
S

SouthernBubba

Junior Member
Joined
May 3, 2021
Posts
7
Reaction score
1
Location
Florida
Ram Year
2018
Engine
5.7
Had the same thing happen on my 2016 2500 5.7 except it was the speedometer fluttering when I did 70 -75mph. I wonder if this is related.

I did a Throttle position sensor calibration (Supposedly) Turn the key to on and hold the pedal to the floor for 15 seconds ,blah blah blah . It seems to have cleared it up some or reduced it . I will know more when I take the truck to work in the morning . As mentioned earlier its more of an annoyance then it is an issue . Hell I might try cleaning the throttle body one more time . Hell Im even wondering if the tach's behavior has been there the entire time and never noticed it . I want to plug into it and check to see if any codes floating around in the system . Probably wont be able to get around to it till this weekend .
 

SouthTexan

Senior Member
Joined
Jan 24, 2015
Posts
2,149
Reaction score
1,303
Ram Year
2014
Engine
408 CTD
Might be a faulty engine crank position sensor. That is a common issue on 5.7L Hemi's in other vehicles.
 
OP
OP
S

SouthernBubba

Junior Member
Joined
May 3, 2021
Posts
7
Reaction score
1
Location
Florida
Ram Year
2018
Engine
5.7
Might be a faulty engine crank position sensor. That is a common issue on 5.7L Hemi's in other vehicles.

That had crossed my mind as well . I had started googling it's location as well as places to get it from
 
OP
OP
S

SouthernBubba

Junior Member
Joined
May 3, 2021
Posts
7
Reaction score
1
Location
Florida
Ram Year
2018
Engine
5.7
Still doing it . As I said before if I keep steady pressure on the throttle while going up an incline doing 50 or so and the tach is around 2k will wobble / flutter . Same at higher speeds in upper gears. But romping on it no hesitation or anything. Would a bad crank sensor only screw up at a certain load and rpm ? Or do they just flat out fail ? Speedo is unaffected

Sidenote: I know tachs aren't the most accurate. Just never seen one wave before at certain rpms and speeds is all. I don't remember my 1500 doing it and had the same engine and 6speed auto in it.
 
Last edited:
Top