Lazy Boost?

[tmcIlwain]

Towing towing on the level with my 13,000# 5th wheel with Speed control on and set set at 60 mph and in 6th gear. Boost in the range of 6-9.


A slight rise in elevation and the speed drops to 59 mph and boost stays at 8-9. Speed drops more to 58 and then to 57 and boost still at about 9. At about 56 mph the transmission downshifts to 5th gear, then boost jumps up to 20 or more, and speed now picks up.


This failure of the boost to try to maintain speed occur maybe 90% of the time. But occasionally it works normally and boost will jump up into double digits in 6th gear and work correctly. This also had been seen to occur in 5th​ gear but not as often. Scanning by Ram reveals no codes. Ram dealer checked and all updates/software up to date.



Any ideas as top the cause and repair of this problem?

 

[Cummins12V98]

Just manually downshift before the speed drops. Some will say don't tow in 6th, I agree with MUCH heavier loads but yours use 6th all you can.

 

[tmcIlwain]

I do downshift regularly at the bottom of a grade, but on mild grades I know from past driving that if the boost did what it is supposed to do on 6th (and sometimes in 5th) I can maintain speed without downshifting. Something has changed...

 

[Newsa]

I guess we would need to know what RPM's this is all occuring?

Could it be that the 68RFE "learned" something and is keeping your RPM's too low for ADEQUATE boost?

The definition of lugging on a diesel is that with added throttle the diesel can not increase speed. Maybe this is lugging? Or the cruise control is not throttling up enough?

I think testing it without cruise control might help see if it is lugging?

 

[tmcIlwain]

Hi Newsa,
Good questions. I'm not sure of rpm but somewhere near 1300 would be a guess. I cited the 60 mph example as that is most often what I run. But I have seen the same problem with speed control set at 65 mph. And there I know the rpm is 1500. Maximum torque rpm if I remember.

I'm not sure where the problem is... turbo? software? transmission? My observation of the about of boost and the speed mph is all I see. I'm not a mechanic and I don't know whet is the cause and what is the effect.

 

[Jim W]

Hi Newsa,
Good questions. I'm not sure of rpm but somewhere near 1300 would be a guess. I cited the 60 mph example as that is most often what I run. But I have seen the same problem with speed control set at 65 mph. And there I know the rpm is 1500. Maximum torque rpm if I remember.

I'm not sure where the problem is... turbo? software? transmission? My observation of the about of boost and the speed mph is all I see. I'm not a mechanic and I don't know whet is the cause and what is the effect.

I am towing a little heavier 5er than you with my 08, 6.7L, 68RFE. If my RPM's drop below 1,400 regardless of road incline, I will down shift to 5th gear. My truck just does not like to be below 1,500 RPMs when towing in any gear. My Boost pressure is usually above 10 PSI when towing, but the RPM's are always above 1,500.
I never ever let the RPM's drop below 1,500 without down shift to 5th gear.
just my $0.02

 

[Newsa]

I am towing a little heavier 5er than you with my 08, 6.7L, 68RFE. If my RPM's drop below 1,400 regardless of road incline, I will down shift to 5th gear. My truck just does not like to be below 1,500 RPMs when towing in any gear. My Boost pressure is usually above 10 PSI when towing, but the RPM's are always above 1,500.
I never ever let the RPM's drop below 1,500 without down shift to 5th gear.
just my $0.02

Yeah. I think the programming in these trucks doesn't give you double digit boost until 1650+ RPM's. Soumds like the 68RFE of the OP is not allowing the RPM's to get high enough for double digit boost. I wonder if Tow Haul has been activated?

 

[Hoefler]

With 3.42's, your RPMs is way too low. The sweet spot is 1800-2100. Also make sure you have the T/H engaged.

 

[tmcIlwain]

Yeah. I think the programming in these trucks doesn't give you double digit boost until 1650+ RPM's. Soumds like the 68RFE of the OP is not allowing the RPM's to get high enough for double digit boost. I wonder if Tow Haul has been activated?

Yes, T/H always activated. And Exhaust Brake too.
I will try to rpm above 1500 and in fact today I will drive only in 5th or lower and watch boost as I head west o I-90. Confusion here is what has changed...??? Been towing like this since 4/2014 and boost always (in 6th gear) would go above 10 and more and down shift when speed was 3-4 below set point. Now boost in 6th only to 8-9 until after shift. (I'm not trying to climb hill this way... only minor elevation changes).
I have heard of "stickey vanes" on turbo, but don't know if that can be a real problem or only imagined...???
Won't be able to replay after this message for about 11 days as I will be going into the boonies here in MT for a while.

 

[SnoKing]

Towing towing on the level with my 13,000# 5th wheel with Speed control on and set set at 60 mph and in 6th gear. Boost in the range of 6-9.


A slight rise in elevation and the speed drops to 59 mph and boost stays at 8-9. Speed drops more to 58 and then to 57 and boost still at about 9. At about 56 mph the transmission downshifts to 5th gear, then boost jumps up to 20 or more, and speed now picks up.


This failure of the boost to try to maintain speed occur maybe 90% of the time. But occasionally it works normally and boost will jump up into double digits in 6th gear and work correctly. This also had been seen to occur in 5th​ gear but not as often. Scanning by Ram reveals no codes. Ram dealer checked and all updates/software up to date.



Any ideas as top the cause and repair of this problem?

I have had it occur on to occasions. Both times were when above 6-6500 ft elevation on highway 93 in Nevada. Towing at 24500 combined in 5th gear at 1750 RPM and 60 miles per hour. Happen on the way South last full the first time and the way home this spring in the same area.

Another member here told me to watch the boost between the two trips. Sure enough boost did not go up when it occurred. So this spring I start trying different things. I sped up to 61 and it happen less, and at 62 it did not do it. Got back below 6000 foot and back at 60 MPH it was fine.

So, I ask were you at high elevations?

SnoKing

 

[EHoxie]

The ecm changes the boost program when in an active regen. This is more apparent at lower engine speeds. Maybe this is what you are noticing

 

[kthaxton]

Sounds like the exact same thing I have been dealing with....intermittently. While it doesn't contain any solutions, see this discussion here.
https://www.turbodieselregister.com/threads/252405-2015-down-on-power

I just got back from a towing trip to the Black Hills and noticed one curious thing. I had noticed that on stretches of the drive where the problem happened fairly consistently, after a stop (gas, etc) the next stretch it would work fine.
After realizing this, on one stretch when it was occurring, I pulled off to a parking area, shut the ignition off, restarted and got back on the highway. It then worked fine. However after an hour or two, it started again.
Weird.
Snoking noticed a correlation with elevation, however my issue is very intermittent. It sometimes happens on my daily commute, and sometimes it doesn't. Also, the issue is almost non-existent in the winter, but does not always change with temperature variations.

Wanted to add that this happens when towing or not, and it is definitely related to lack of boost (whatever the cause) because as the OP said, normally boost gets into the mid-to upper teens before a downshift. When the problem occurs, its as if boost gets stuck between 8 and 10-ish.

 

[TERRA]

So at this point it seems air density and/or temperature are, at least a few of the variables related to this problem. Given the complexity of the firmware of these machines, perhaps many 10s of thousand of line of code, it may be a glitch in the coding.

 

[kthaxton]

It's definitely odd, and really inconsistent. As I said before, I do the same drive every day, sometimes it does it sometimes it doesn't.....but it is very rare in the winter.....but on the flip side, it also doesn't always start doing it again in the summer. It may come in late summer.

 

[SnoKing]

It's definitely odd, and really inconsistent. As I said before, I do the same drive every day, sometimes it does it sometimes it doesn't.....but it is very rare in the winter.....but on the flip side, it also doesn't always start doing it again in the summer. It may come in late summer.

Warmer the air thinner it is.?

 

[Missouri Mule]

tmcIlwain, My Mule(5 spd manual) has less hp than your does but shifting down to low gear increase rpm and boost a little ( tested on the way home going 35 to 40 down shifted to 3rd naturally rpm went up but so did the boost but not as much as the rpm.)
It's not boost that keeps the speed it's the amount of fuel being supplied the cylinders! The more fuel means more exhaust and the hotter the exhaust is the faster the turbine /compressor wheel which = more boost.
I don't think your turbo is the problem I think you have a fuel problem. I have to agree your should be in tow /haul mode pulling that much weight. Since have gauges (boost/egt), when running up a hill in 5th at highway speed my boost will go from 6-8 to 10 to 12 lbs,egt will go from 750 to 850/900 (No trailer, bed very little to full bed.(The weight of the load on Mule doesn't matter much boost and temp always run about the same. And I have only to steep hills to climb and their miles apart.)
Also if you have a strong head wind that will increase boost and egt temp, tail wind will decrease them. I was making a run to the market one morning and my egt was up to 900 and boost was at 10. I whats going on Mule usually at 7 lbs and 750 temp. As i got to my exit in started to rain the wind was blowing it side wards right in to the front of Mule. I said oh that was the problem.Mule had a very strong head wind it had to deal with.

 

[SnoKing]

"The MAP sensor converts engine vacuum/manifold pressure to an electrical signal so the computer knows how much load the engine is under. This data is the basis for fuel delivery and timing control."

On my truck this has only occurred at over 6,000 foot elevation and 60 MPH. So when I come to a hill the cruise control should advance the throttle (electronically on a new setups) as the truck slows a bit. However it drops 3 or 4 mph and boost does NOT go up, until it finally shifts down and takes off again. My guess it is going to take a dealer or factory tech with their scan tool out on the road to catch an event to figure it out. In my case increasing speed to 62 caused the condition to quit occurring.

Then the trucks will be in the bone yard before new code comes to fix it.

Maybe TransEngineer will come along and see this and take up the cause to get it figured out. Or RAM could parachute him in as we head South the fall and ride along and capture some data.

I do not believe this is going to be an easy fix. SnoKing

 

[Newsa]

So when I come to a hill the cruise control should advance the throttle (electronically on a new setups)

My 12 valve friends get a real kick out of these "drive-by-wire" trucks.

One of them drove his truck to the shop with a "blown computer",

Wouldn't happen with these newer trucks.

Then again, they don't realize the torque increases realized in the 4th gens.

 

[SnoKing]

Then again, they don't realize the torque increases realized in the 4th gens.

I do not know, my 2001.5 mildly bombed was around 325/650 at the rear wheels! If you figure 14 % lost to the wheels, the 385/865 turns into 331/744. Does the new truck tow a lot better, you bet. transmission has a lot to do with it and the flat torque curve. SnoKing

 

[Cummins2014]

Towing towing on the level with my 13,000# 5th wheel with Speed control on and set set at 60 mph and in 6th gear. Boost in the range of 6-9.


A slight rise in elevation and the speed drops to 59 mph and boost stays at 8-9. Speed drops more to 58 and then to 57 and boost still at about 9. At about 56 mph the transmission downshifts to 5th gear, then boost jumps up to 20 or more, and speed now picks up.


This failure of the boost to try to maintain speed occur maybe 90% of the time. But occasionally it works normally and boost will jump up into double digits in 6th gear and work correctly. This also had been seen to occur in 5th​ gear but not as often. Scanning by Ram reveals no codes. Ram dealer checked and all updates/software up to date.



Any ideas as top the cause and repair of this problem?

Mine has the same symptoms , whether towing or not. I can set my cruise for say 65 unloaded it will lose speed on a slight grade that should have no problem pulling in 6th gear, until nearly 5 mph lower then set, then kicks down to fifth ,and goes back up to 65. Mine is pretty consistent.

I thought maybe it might be something like the cruise control calibration or whatever, but have never had cruise control do that on my previous truck, it would just maintain speed set on any grade without gearing down when unloaded. Naturally it would gear down towing when the power was needed.

Talked to my son about it, and on his 2016 3500, it does the same thing. Says it drives him crazy going up a long grade unloaded loses speed shifts down shifts back, keeps repeating itself. There is times unloaded with mine where it will do it just once on a long grade, shifts down, gets back to speed shifts back to 6th, and remains there like it learned. Crazy stuff.

Got to get my truck in for the T25, and T05 recalls, will ask them if this is a common problem or a fix for it.