Bucking in 4th and steady state 40 mph

[martinique78]

If i drive with my Quad set to stock I don't notice it.  Once i'm on level 3 and higher is get progressively worse with each jump up in level.  Sometimes its enough to make the trans downshift and upshift over and over till i get out of that area it's bucking.

 

Engine is completely stock and I'm running the daily tune created by the calibration creator tool on this site.

 

Trans was just rebuilt, pump pressure was turned up to 65 PSI.  Stock converter. 

Issue was happening before trans was rebuilt also.  Trans was rebuilt due to forward band failure. 

 

Edited January 3, 2018 by martinique78

[Me78569]

sure sounds like TC unlocking and locking issues to me.  does this happen if you lock OD off by pusing hte OD button the end of the shifter?  

 

40 mph is awful low rpm for 4th as well.  what rpm is this happening?  

also please post up the tune so we can look at it.

 

Edited January 3, 2018 by Me78569

[martinique78]

It goes away if I hit the o/d off button.  This is a Fummins swap into a 2004 Excursion.  I’m using the 47RE trans and the Dodge PCM to control it.  The truck has 4.30 gears in it which I think is the reason it shifts into 4th so soon.  I plan to swap them out to 3.73 when I get the extra money...have to do both front and rear.  Thinking the gearing might be the problem but figured I’d check here first.

It’s almost like I’m feeling the combustion cycles of the engine.  Once I accelerate to a higher rpm and speed it goes away.  At 70mph I’m turning about 25-2600 rpm.

[Me78569]

What is the timing doing when this happens?  what rpm when this happens?  It may be too much timing, 

[martinique78]

Here is the tune i'm running

Kevin Daily.json

[Me78569]

what rpm are you at?

[martinique78]

I'd have to look again but somewhere around 1100-1500

[Me78569]

Drop your 1500: timing setting from 17* to 15*

[Mopar1973Man]

I agree with too much timing I would even consider dropping that to 14* being winterized fuel and high cetane playing a role too.

[Quadzilla Power]

You can also check your alternator for A/C noise. It can cause the converter to lock and unlock at about that speed. 

[Mopar1973Man]

We even have the solution for the AC noise here on the site...

 

 

[Me78569]

heres the gearing spreadsheet

[martinique78]

Well I dropped the timing to 15.  That combined with installing the jumper inside the box needed for setting the map sensor for a 2002 fixed everything.  My map was reading 13 psi at idle. I’m guessing I was overfueling and it was causing a pulsing effect.

[Me78569]

glad it is fixed.  should be worlds smoother now

[martinique78]

Holy crap yes it’s smoother, night and day difference driving now.  Pretty sure I’ll get better fuel economy as well.

[Quadzilla Power]

I'm glad you got that figured out. There are so many things that can cause a "bucking" issue but it looks like you've got it figured out now so that is fantastic. 

 

[CSG]

I am having same bucking issue as martinique but lowering the timing didn't help much. My truck is manual so it's definitely not t/c. It typically happens when tps is 14-20% and engine load 20-35%. I've lowered timing to 14 at 1500 rpm and 17 at 2000 rpm. I did some data logging with power level set to zero and with IAT low 55 - 70 degrees truck was running 19 degrees of timing with no bucking not sure what to try next.

[Mopar1973Man]

Ok, so you even tried timing as low as I'm running now. I would suggest looking into doing valve lash. It really can have a impact on performance of the engine. 

 

My current timing settings are 14, 17,20, 23, Max 25

 

Max Load Timing 1.5*

Low PSI Reduct 4*

Timing scaling 100%

Light Throttle 2*

Light throttle limit 25%

 

Excessive advancement typically will get the bucking going in the low end of the RPM. But like I've learned even valve lash that is excessive tight or loose can do it too. It can get so bad that it will cause the engine to stall depending on the valve lash and Quadzilla settings.

 

[CSG]

I have springs and pushrods on the way so guess we'll see if proper lash fixes it. It has been a few years since I've checked them. I'll let you know if it fixes it. Thank you

[Me78569]

Bucking might also be related to your fueling curve being to lazy.