Jump to content
  • Welcome To Mopar1973Man.Com

    We can see that your guest and been lurking about. When you register on the Mopar1973Man.Com site you'll be able to interact with all the other members. This is the most friendliest Cummins forum you'll ever join. Take the time right now and  REGISTER  on the Mopar1973Man.Com this will open up many more options and functions on the website. Everyone is very friendly and helpful just ask questions and everyone will help you out the best they can. 

Sign in to follow this  
Collinst15

Bucking at 40 to 50mph

Recommended Posts

Good afternoon everyone,

 

I did some searching on the site before posting, but would like some other insight.  My truck bucks between 40 and 50 mph and rpms are around 1100-1200 on level 2 and 3; I have not gone above level 3 as pump is not tapped.  I feel it may be timing related as it did not buck today when I had the Quad on level 0.  Current tune set up is below. Do you guys have any suggestions where to move timing to stop the bucking? 

 

Tune:  Mopar1973man Economy Tune

Max Load Timing Offset: 1 degree

Low PSI Timing Reduct: 3 degrees

Timing Reduct Scale: 40%

Light Throttle Timing Adv: 1 degree

Light Throttle Load Limit: 25%

 

RPM Timing Max
1500rpm: 14

2000rpm: 16.5

2500rpm: 19

3000rpm: 21.5

Max: 24

 

I attempted to data log today, but closed app before I could import data.  I will get data tonight when I leave work.

 

Thanks,

 

Tim

Share this post


Link to post
Share on other sites

Me78569 - You talking about the Canbus fuel sliders correct?  If so I have them set as follows:

 

0psi: 80 - goes up 1 until 4si
5psi: 86 - goes up 2 until 9 psi
10psi: 97 - goes up 3 until 20 psi
22psi: 125
24psi: 130

26psi: 135

28psi: 110

30+psi: 85

Edited by Collinst15
added values

Share this post


Link to post
Share on other sites

Perfect.  Thanks for your help.  Been reading like crazy to learn the Quadzilla better.  I am trying to get 18mpg in the city, but winter fuel has messed all my data up.  I dropped timing a few days ago and it seemed to pick up some power, shall see if mpgs improve.

 

Tim

Share this post


Link to post
Share on other sites

I was at 4.5 spread and the starting at 14*. Then now dropped to 4.0 spread and gained 2 MPG. Now dropped to 3.5 spread fine out if I get the MPG's up. The cetane means more than than intake air. The high cetane fuels this winter ignite super easy high timing is counter productive in the winter.

Share this post


Link to post
Share on other sites

I changed the fuel sliders to:

 

0psi: 84

1-3psi: 85

4-5psi: 86

Then rest are untouched.  The bucking seemed to not be as bad, but still bucked in O/D with low boost.  I am going to change the entire fuel map to start at 90 at 0spi and see what happens.  If it does not clear up, I may send box out as this is a recent issue.

 

Tim

Share this post


Link to post
Share on other sites

I tend to drive with a light foot.  I dont think I have ever gone WOT from a stop.   I do get a slight puff/haze of smoke when in O/D and I put foot into it, but nothing crazy.  I'll give it a go tonight after work.  

 

Tim

 

 

Share this post


Link to post
Share on other sites

Go wot from take off.  Mikes tune is made for 7 x.010's you are running a good bit less fuel than that.  I am guessing your offidle fueling is causing your issues.

 

Too little fuel will cause bucking low in the rpm band.

  • Thanks 1

Share this post


Link to post
Share on other sites

The adjustments I made in the fuel curve helped.  The bucking is still there, but not as bad, but truck has way more power off the line than it has before.  Thanks guys for your help.  Going to add a little more fuel down low and hopefully get bucking to go away for good.

 

I did some wot pulls but couldn't tell if it was smoke from exhaust or salt dust being kicked up from road.  I'll try some more wot pulls in coming days.

 

 

 

Tim

Share this post


Link to post
Share on other sites

Give a bit more time. I'm building a winter tune as well. Last tank netted 19.06 MPG with running temps of 20 to 30*F.

 

Current timing...

14.0, 17.5, 21.0, 24.5 

 

I've had a bucking issues between 1,200 to 1,400 RPM forever. Right at 30 MPH is a PITA going through Council, ID every trip. Bucking for the entire 2 miles. I'm pretty sure if I turn off the Quad it would go away.

Edited by Mopar1973Man

Share this post


Link to post
Share on other sites
On 12/8/2019 at 6:36 PM, Me78569 said:

Too little fuel will cause bucking low in the rpm band.

 

On 12/10/2019 at 9:03 AM, Me78569 said:

it would, its the ecm and quad fighting for control in a 5 speed.

 

Can you elaborate on these a little bit when you have a spare minute? If I allow my Torque converter to lock up too early, or allow the trans to shift into overdrive too early, I experience what I thought was TC shudder, but now I'm thinking might be this surging/bucking scenario. (35" tires and 3.54 gears, RPM can be fairly low in this situation).

 

If I give it more throttle, the problem disappears immediately. It's only a light throttle scenario, I'd estimate 15% or less throttle.

Edited by kzimmer
More Info

Share this post


Link to post
Share on other sites

I think because of the taller tires and 3.54 gears you might only need to adjust the TV cable, but should only be affecting the lower gears at low speeds. Mine will go in and out of 1st and 2nd, drive you crazy, but only happens when I'm just floating engine speed (neither accelerating nor slowing). It goes away the rest of the time or if I just click into second gear manually on the shifter.

 

If you have the trans hunting gears in the higher gears, in and out of 3rd and 4th then most likely too high of AC ripple thu the electrical system.

Edited by JAG1

Share this post


Link to post
Share on other sites

So how it works sub 1200 rpm

 

 

     if(RPMS > idle_limit && TPS > 2)// && RPM > 850)
     {
       idle_limit = 600;   // RPM low limit
       fuel_trigger = 1;  //Quad on of off?

     } 
     else if(RPM > 1200 && MPH > 30)
     {
       fuel_trigger = 1; //Quad on of off?
     }
     else
     {
       
       idle_limit = 1000;  // new RPM low limit
       fuel_trigger = 0;  / Quadzilla On of off.
      
     } 
      

 

 

So I set the rpm limit at 1000 if you go idle state.  Below 1000 the ecm is in charge, as soon as you increase tps above %2 and rpms increase above the limit of 1000 then the quad fueling messages are enabled.

 

at that point the idle low limit is set to 600 rpm, so the quad will try and stay in control unless rpms drop below 600 or throttle is below %2   if those conditions are met then the ecm is back in control

 

if rpms are greater than 1200 rpm and speed is greater than 30 mph hten the quad is in contorl.  This is to get around the fact that tps  = 0% on trucks with electric cruise control.  

 

 

 

So on top of it all the ecm has stuff in place to manage offidle fueling aka anti stall type stuff.   The ecm will boost or drop fuel EXTREMELY rapidly if it senses that rpms are not doing what it expects them to do.  It seems like this happens until ~1500 rpm.   

 

So if you are pulling a TON of fuel in your tune and you are sub 1500 rpm and you are at light throttle / low rpm you will see the ecm freak out a bit and send the quad spikes in fueling.   

  • Like 1

Share this post


Link to post
Share on other sites
1 hour ago, JAG1 said:

If you have the trans hunting gears in the higher gears, in and out of 3rd and 4th then most likely too high of AC ripple thu the electrical system.

 

No hunting gears for me. Just a small shudder that can be felt in low rpm low load situations when the TCC is locked. I haven't measured A/C with my new alternator from a 2001 Dodge Durango (160A Hairpin Stator), but it seems to be doing great.

 

58 minutes ago, Me78569 said:

So if you are pulling a TON of fuel in your tune and you are sub 1500 rpm and you are at light throttle / low rpm you will see the ecm freak out a bit and send the quad spikes in fueling.   

 

Thank you very much for the explanation. The specific scenario in the above quote can probably be viewed in a datalog for verification purposes I suppose. 

Share this post


Link to post
Share on other sites

When my truck bucked it would want to shake truck apart.  Spilled many coffees due to it.  Since I added fuel down low it is slightly noticeable now.  Although trans does not like wot pulls.  I noticed it doesnt always start in 1st.  I will be ordering updated sensors after Christmas. Hopefully dont need a trans rebuild bc truck would be put on back burner for while as funds wont allow a trans rebuild at moment.

 

Tim

Share this post


Link to post
Share on other sites
3 hours ago, Me78569 said:

violent bucking is typically too little fuel for the load

Mine definitely was because of this  it is now a slightly noticeable shutter.  Just hate that trans started to act up.  Always something

 

Tim

Edited by Collinst15
  • Like 1

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  



×
×
  • Create New...