6.4 towing hold back trouble

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Coltws

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So I haven't found any good information on why my 6.4 doesn't hold back while towing. It seems to be something to do with programming. While going down a steep hill especially in 1st gear it acts like the throttle plate opens up. It will do it without a load also. Rev up to 3k or more and then start holding back until it's down to about 2k and then zoom it revs up again. With a load it will never get the rpms back down so you have to use the brake constantly. It's a 2021 tradesman with the 6.4. any advice or help would be appreciated. Dodge told me the egr was opening but I unhooked it and it acts exactly the same witch tells me it's letting air in somewhere else like the throttle.
 

Travelin Ram

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I don’t know the specifics but this is something I have seen in multiple trucks and not just Ram. My PW does it. A rental Rebel 1500 I had did it. My 2020 Chevy does it too.

Some idiots on the software side have decided something else is more important than our safety. Probably something to do with emissions.
 

Neil E

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I'm not sure exactly what you mean, but I assume you mean the engine is holding higher RPM's to keep the truck from coasting down a hill. Mine does this as has my last 3 vehicles. It lets the engine do the braking so you don't overheat your brakes. It's actually for safety, if this is what you mean.
 

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I'm not sure exactly what you mean, but I assume you mean the engine is holding higher RPM's to keep the truck from coasting down a hill. Mine does this as has my last 3 vehicles. It lets the engine do the braking so you don't overheat your brakes. It's actually for safety, if this is what you mean.
No, it’s the opposite of engine braking. The computer is opening the throttle, egr, or doing something with the VVT that causes the truck to accelerate downhill.
 

sandawilliams

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No, it’s the opposite of engine braking. The computer is opening the throttle, egr, or doing something with the VVT that causes the truck to accelerate downhill.
You will get that sensation going down a hill. I tow over the mountains often and have the same issue. It's the same way with all gas trucks. I suggest using lowest gear possible for the road and only use the brakes when rpm's exceed 4k. Don't ride the brakes. Bring the speed down a few mph lower than the speed limit. You don't see any loaded trucks running the speed limit down a mountain for a reason and you will seldom see trucks smoking the brakes. Let faster vehicles pass when possible.
 

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You will get that sensation going down a hill. I tow over the mountains often and have the same issue. It's the same way with all gas trucks. I suggest using lowest gear possible for the road and only use the brakes when rpm's exceed 4k. Don't ride the brakes. Bring the speed down a few mph lower than the speed limit. You don't see any loaded trucks running the speed limit down a mountain for a reason and you will seldom see trucks smoking the brakes. Let faster vehicles pass when possible.
Respectfully, I’ve been towing with gas and diesel trucks for decades, so stop assuming I don’t know what I’m talking about. And I also off road a lot where compression braking in 4L is essential. This is not something that happens with “all gas trucks”. Downhill with compression braking and a closed throttle is one thing. What some of these drive by wire engines are doing is something else entirely.

I don’t really care to argue, I just commented on this thread to confirm for the OP that his is not an isolated case. I won’t be adding more to this topic.
 

392DevilDog

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Respectfully, I’ve been towing with gas and diesel trucks for decades, so stop assuming I don’t know what I’m talking about. And I also off road a lot where compression braking in 4L is essential. This is not something that happens with “all gas trucks”. Downhill with compression braking and a closed throttle is one thing. What some of these drive by wire engines are doing is something else entirely.

I don’t really care to argue, I just commented on this thread to confirm for the OP that his is not an isolated case. I won’t be adding more to this topic.
It is rough. I feel your pain.
 

crash68

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The ECM/TCM doesn't know how fast you want to go, try setting the cruise control to give the modules a speed to achieve. Try dropping the speed 5-10 mph lower than what you crest the hill at.
 

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Do you have the "trailer" button to push when pulling a trailer. If you do does activating it do anything to your problem.
 

62Blazer

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Without experiencing the situation first hand it's hard to know exactly what is going on, or how unusual or non-typical the situation is compared to other vehicles. But in general the engine itself can only provide so much "hold bacK" force. If you are expecting the truck to always be able to keep the speed low regardless of the downward grade or load it's not going to happen unless either yourself or the ECM applies the brakes.

In any case I doubt the engine is truly accelerating as in the throttle is being applied, but rather just the weight of the truck and load is pushing it down the hill and the engine doesn't have enough compression braking to completely counteract the downward force, and hence it increases speed. The perceived change in speed, or hold back force, is probably related to the transmission and torque converter unlocking. If you are driving down the road and let off the gas pedal you just start coasting and don't get any major engine braking at all, even if you let it coast all the way to a stop. The ECM at some point will also unlock the trans and converter to keep the engine from over-revving. Yes, you can blow up an engine by over-revving it while going downhill even at no throttle....I've personally seen it on a manual transmission pickup where the person meant to downshift from 5th to 4th going down a steep grade, but went from 5th to 2nd instead. At 70 mph that caused the engine to hit over 7,000 rpm and spit a rod out of the block.....again this happened with their foot completely off the gas pedal.
 

sandawilliams

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So why do posts disappear from this thread? There is nothing I posted that was against the rules.
Respectfully, I’ve been towing with gas and diesel trucks for decades, so stop assuming I don’t know what I’m talking about. And I also off road a lot where compression braking in 4L is essential. This is not something that happens with “all gas trucks”. Downhill with compression braking and a closed throttle is one thing. What some of these drive by wire engines are doing is something else entirely.

I don’t really care to argue, I just commented on this thread to confirm for the OP that his is not an isolated case. I won’t be adding more to this topic.
So why do posts disappear from this thread? Are you a moderator that did not like my kind response to the OP? He asked for advice and I gave it to him from my personal experience towing for years now.
 

Bearcatrp

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My 2017 6.4 has a button by the tow haul to shut hill descent off. Is yours off? Mine will kick in only if I depress the brake going down a hill. Then it drops into a lower gear to help but its high RPM's. Scared me the 1st time it did this.
 
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Coltws

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Ok so I didn't even go through all the comments yet. I'm not asking for someone to explain to me how to drive down hill no disrespect meant by that. I am looking for someone who knows the problem I'm talking about and has possibly come up with a fix. Gas engines hold back because of vacuum instead of compression. If the vacuum is lost by say opening the throttle plate it will not hold back. This is a newer dodge problem maybe back to 2014 but I'm not sure. I will explain it again maybe better. Say I'm going down a steep hill no load behind the truck,( tow haul on or of doesn't matter) shift the truck to first gear and let my foot all the way of the gas. When the rpms hit about 2200 it speeds up like I stepped on the gas but I am still not touching the gas. When the rps hit somewhere between 3 and 4000 it will start holding back and slowing down until the rpms get to about 2200 and then do it all over again. I have had lots of pickups and this is the first one to do this. Again I'm not trying to be rude but I live in the Rockies I drive in and out of hell's canyon all the time. I'm a mountain driver so this is a mechanical question not a driving question thanks
 
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Coltws

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sandawilliams I'm not sure why your post are disappearing. I just logged on for the first time in a few days.
So why do posts disappear from this thread? There is nothing I posted that was against the rules.

So why do posts disappear from this thread? Are you a moderator that did not like my kind response to the OP? He asked for advice and I gave it to him from my personal experience towing for years now.
 
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Coltws

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Without experiencing the situation first hand it's hard to know exactly what is going on, or how unusual or non-typical the situation is compared to other vehicles. But in general the engine itself can only provide so much "hold bacK" force. If you are expecting the truck to always be able to keep the speed low regardless of the downward grade or load it's not going to happen unless either yourself or the ECM applies the brakes.

In any case I doubt the engine is truly accelerating as in the throttle is being applied, but rather just the weight of the truck and load is pushing it down the hill and the engine doesn't have enough compression braking to completely counteract the downward force, and hence it increases speed. The perceived change in speed, or hold back force, is probably related to the transmission and torque converter unlocking. If you are driving down the road and let off the gas pedal you just start coasting and don't get any major engine braking at all, even if you let it coast all the way to a stop. The ECM at some point will also unlock the trans and converter to keep the engine from over-revving. Yes, you can blow up an engine by over-revving it while going downhill even at no throttle....I've personally seen it on a manual transmission pickup where the person meant to downshift from 5th to 4th going down a steep grade, but went from 5th to 2nd instead. At 70 mph that caused the engine to hit over 7,000 rpm and spit a rod out of the block.....again this happened with their foot completely off the gas pedal.
I can see your not familiar with this problem and that's ok. I might take a video of it and post it. I would like to mount a camera inside the intake and watch what's going on. It's a loss of - vacuum pressure that causes the motor to accelerate. Dodge agrees but they have no fix. They claim it's the egr but I think they are wrong about that. I will continue to find out exactly what it is as I can get time. Just really hoping someone else has already done the work and found a solution I will sell this truck over this issue but I like it other than that one thing. I can't tow what I tow and the places I tow with it like this.
 

hemihustlin

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I went out and tried this today with my 5.7 8 speed and exactly like he said when going downhill in 1 gear when you hit a certain rpm point it stops engine braking and its like the pcm opened the throttle a little bit and it accelerates then you have to get on the brakes to maintain your slow decent.
 

Pttrader

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My truck when towing my 5th wheel will hold back within a 10mph range. Recently I was on a trip going down a 7% grade and wanted to go 55 max speed so I bumped the cruise down to 45. The tach jumps up and down as the gears change and it has consistently held me to 10mph over set cruise speed. I have never been down to 1st, usually 3rd, once in a blue moon 2nd. I have the 6 speed and I run in Tow Haul Mode.

I don't like the engine revving to 5k, but I am okay with it as long as it is holding the speed within the 10mph range and I believe I need it to be safe as I descend down the hill.

What is quirky is when I know I no longer need/want the engine at high rpms (5k) I tap the brake or cancel the cruise it will not always stop the high revving the truck was doing. When going up hills and the engine starts revving high I sometimes hit the brake and it stops the high rpms right away.
My truck is a gasser and I don't always need it to maintain speed up hills at the cost of revving the **** out of it! I can go slower and let it shift down to where it doesn't have to rev so high!
My truck is an Off Road and has the hill descent (HDC), but I never use it while towing because my understanding it only works in low range and speeds under 40mph. My towing is on the highway and not off road.

The 10mph over set cruise speed hold back is consistent for me as I have made quite a few trips and it always repeats within the 10mph window.
Hope that helps!
Just want to add that I use the Heavy Electric trailer setting on the trailer brake and the gain is on a very high setting 8 or more. I haven't checked it in some time since my set up serves me well.
 
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crash68

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My truck when towing my 5th wheel will hold back within a 10mph range. Recently I was on a trip going down a 7% grade and wanted to go 55 max speed so I bumped the cruise down to 45. The tach jumps up and down as the gears change and it has consistently held me to 10mph over set cruise speed. I have never been down to 1st, usually 3rd, once in a blue moon 2nd. I have the 6 speed and I run in Tow Haul Mode.
^^^ this
Setting the cruise control will give the ECM/TCM a speed that your looking to maintain. Without the cruise the transmission is likely to unlock allowing the truck to coast.
 
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Coltws

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I know pttrader is speaking about the 6 speed and I haven't had that transmission. The 8 speed does not unlock and coast. I'm mostly concerned about keeping my throttle plate closed so it can hold back to it's fullest capabilities.
 
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