2020 Cummins IKE pull

Travlingman wrote:

Cummins12V98 wrote:
"The computer is applying the wheel brakes both truck and trailer."

How do you know if the brakes were coming on the trailer on this test? Maybe the engine was doing what it needed with the trans?

Right past the 2 minute mark they say that it is using the truck and trailer brakes and also making the lights come on both.

In my motorhome the engine brake activates the brake lights. Brakes lights alone is not good evidence that the mechanical brakes were applied. In truth, if you are holding back as much as they were the brake lights should be applied no matter what the source of the impediment is.

Travlingman wrote:

Cummins12V98 wrote:
"The computer is applying the wheel brakes both truck and trailer."

How do you know if the brakes were coming on the trailer on this test? Maybe the engine was doing what it needed with the trans?

Right past the 2 minute mark they say that it is using the truck and trailer brakes and also making the lights come on both.

Thank you!

Missed that part.

I personally would want to disable the trailer braking if I want to. From my weights and knowing I can hold 34k on 14% grade the test truck should have held without the trailer braking.

How about discussing what’s more important. One minute plus faster up a specific test or cold brakes with 25k pushing you down the hill like I have.

Travlingman wrote:

Cummins12V98 wrote:
"The computer is applying the wheel brakes both truck and trailer."

How do you know if the brakes were coming on the trailer on this test? Maybe the engine was doing what it needed with the trans?

Right past the 2 minute mark they say that it is using the truck and trailer brakes and also making the lights come on both.

The fact that they state the brakes are being controlled by the computer isn't enough evidence on ts own, as Mr Truck is full of $#!^ half the time but the way truck behaves while they are asking "will it downshift?" is more evidence. Based on their comments and on the video the truck is holding the load back prior to the downshift. If it could hold that kind of weight back prior to the downshift (at about 2000 rpm) strictly via exhaust brake then the downshift would have cause sudden over braking while the turbo adjusted. The fact that the speed before and after the shift is so precise is strong evidence of wheel brakes being utilized. Additionally, to hold 39000 lbs back on a 7% grade would require 377 lbft of torque on the crankshaft in second gear. There is no way an exhaust brake could generate enough back pressure to generate that kind of torque.... the exhaust valves would float before the required back pressure could be reached.

Cummins12V98 wrote:

Travlingman wrote:

Cummins12V98 wrote:
"The computer is applying the wheel brakes both truck and trailer."

How do you know if the brakes were coming on the trailer on this test? Maybe the engine was doing what it needed with the trans?

Right past the 2 minute mark they say that it is using the truck and trailer brakes and also making the lights come on both.

Thank you!

Missed that part.

I personally would want to disable the trailer braking if I want to. From my weights and knowing I can hold 34k on 14% grade the test truck should have held without the trailer braking.

On your Ram does the boost gauge read reverse HP while the exhaust brake is working? What is the highest value you've seen it display?

4x4ord wrote:

Cummins12V98 wrote:

Travlingman wrote:

Cummins12V98 wrote:
"The computer is applying the wheel brakes both truck and trailer."

How do you know if the brakes were coming on the trailer on this test? Maybe the engine was doing what it needed with the trans?

Right past the 2 minute mark they say that it is using the truck and trailer brakes and also making the lights come on both.

Thank you!

Missed that part.

I personally would want to disable the trailer braking if I want to. From my weights and knowing I can hold 34k on 14% grade the test truck should have held without the trailer braking.

On your Ram does the boost gauge read reverse HP while the exhaust brake is working? What is the highest value you've seen it display?

Yes it does, I will have to look at old pics to see.

Just looked the pic on the 14% grade the gauge is blinded by the sun!

4x4ord wrote:

Travlingman wrote:

Cummins12V98 wrote:
"The computer is applying the wheel brakes both truck and trailer."

How do you know if the brakes were coming on the trailer on this test? Maybe the engine was doing what it needed with the trans?

Right past the 2 minute mark they say that it is using the truck and trailer brakes and also making the lights come on both.

The fact that they state the brakes are being controlled by the computer isn't enough evidence on ts own, as Mr Truck is full of $#!^ half the time but the way truck behaves while they are asking "will it downshift?" is more evidence. Based on their comments and on the video the truck is holding the load back prior to the downshift. If it could hold that kind of weight back prior to the downshift (at about 2000 rpm) strictly via exhaust brake then the downshift would have cause sudden over braking while the turbo adjusted. The fact that the speed before and after the shift is so precise is strong evidence of wheel brakes being utilized. Additionally, to hold 39000 lbs back on a 7% grade would require 377 lbft of torque on the crankshaft in second gear. There is no way an exhaust brake could generate enough back pressure to generate that kind of torque.... the exhaust valves would float before the required back pressure could be reached.

The smooth engagement was probably from the TC unlocking and locking again between shifts. As for as turbo adjustment, there should not be one. Back when I had my stock turbo, I monitored the turbo vane position. When the exhaust brake was applied, it would close the vanes from 95% to 99% in auto depending on the braking needs. In full mode or at max braking in auto(like in the test) it would stay at 99% closed even between shifts. There was no turbo vane adjustment going into a lower gear and it was still a smooth engagement. It just got stronger the higher the rpm(i.e. downshifting).

^^^ Exactly so if the turbo was holding enough back pressure to hold the load back at 2000 rpm (which is impossible), the engine would have been generating 175 reverse HP. Now, if, the transmission downshifts from 3rd to 2nd, the rpm would increase from 2000 to 3000 rpm. So even if the back pressure remained unchanged (The only reason the back pressure would remain unchanged would be if the valves started floating otherwise the back pressure would increase dramatically because the engine would be trying to push 1.5 x as much air past the turbo) the reverse HP generated would go from 175 to 262 reverse HP. So if 175 reverse HP was holding back about right and now all of a sudden the engine is holding back 1.5 times as much the truck would quickly start over braking while the turbo adjusted to relieve back pressure.


(and because the increase in engine rpm would not only cause 1.5 x as much air to be compressed it would also be compressing that air to a higher value ( ie the back pressure would go up ) so the reverse HP would rise even more than 1.5x )

So based on the behavior of the truck, it is my opinion that the exhaust brake was not the only thing holding the truck back.

4x4ord wrote:
^^^ Exactly so if the turbo was holding enough back pressure to hold the load back at 2000 rpm (which is impossible), the engine would have been generating 175 reverse HP. Now, if, the transmission downshifts from 3rd to 2nd, the rpm would increase from 2000 to 3000 rpm. So even if the back pressure remained unchanged (The only reason the back pressure would remain unchanged would be if the valves started floating otherwise the back pressure would increase dramatically because the engine would be trying to push 1.5 x as much air past the turbo) the reverse HP generated would go from 175 to 262 reverse HP. So if 175 reverse HP was holding back about right and now all of a sudden the engine is holding back 1.5 times as much the truck would quickly start over braking while the turbo adjusted to relieve back pressure.


(and because the increase in engine rpm would not only cause 1.5 x as much air to be compressed it would also be compressing that air to a higher value ( ie the back pressure would go up ) so the reverse HP would rise even more than 1.5x )

So based on the behavior of the truck, it is my opinion that the exhaust brake was not the only thing holding the truck back.

But it wasn't hold the truck back at 2,000 rpm and was gaining speed which is why it downshifted to a higher that not only allowed it to hold speed, but also slowed it down. After it slowed it down to desired speed then the turbo vanes probably actuated between 95-99% to keep it there.

Also, the IKE is not 7% all the way down. There are sections that are as low as 3%. Especially the section coming right out of the tunnel. It is steep when you first come out and the decreases the grade for a short distance.

^^^ So, based on my observation I would say the wheel brakes were largely what was holding the truck back. The computer recognized the need for a downshift to produce more exhaust braking. After the downshift the back pressure and rpm increased to produce the maximum level of exhaust braking the engine was able to do .... the wheel brakes made up the difference.