Turbo / Exhaust Brake Problem...

[Bob4x4]

Not much help here

The VGT works in conjunction with the engine and the transmission to provide an integrated braking system used to help slow the vehicle. This is commonly called exhaust braking. This braking power is achieved by modulating the turbo sliding nozzle ring to restrict the flow of exhaust gases from the engine, which in turn creates a high back pressure on the engine. The high back pressure creates a high level of resistance to the motion of the pistons within the engine and this resistance is used to reduce engine speed and thus vehicle speed.



The exhaust brake feature will only function when the driver turns the exhaust brake switch to the on position. Once the switch is in the on position and the vehicle is moving faster than 8 k/h (5 MPH); the exhaust brake will automatically operate when the driver removes pressure from the throttle pedal allowing the engine to see 0% throttle and 0 fuel delivery.



Exhaust braking is most effective when the engine RPM is higher. The automatic transmission has been programmed to downshift more aggressively when the exhaust brake is enabled to increase brake performance. Use of automatic transmission Tow/Haul Mode improves interaction between the engine and transmission. Inputs to the exhaust brake feature include:



Coolant temperature

Ambient air temperature

Exhaust manifold pressure sensor

Throttle pedal position sensor

Fault codes with any of these sensors will cause the exhaust brake feature to be disabled.



The exhaust brake feature can also be used to reduce the engine warm up time. To use the exhaust brake as a warm-up device, the vehicle must be moving less than 8 k/h (5 MPH), the exhaust brake switch must be in the on position, and the coolant temperature must below 82°C (180° F) and ambient temperature below 15. 5°C (60° F).







Note: For optimum braking power it is recommended to use the exhaust brake while in TOW/HAUL mode.

 

[EdGarcia]

Bob... I appreciate the input... but not sure what you are trying to tell me. I am aware of what the manual says ... but I know what I know through driving experience... the exhaust brake is just not working the way it was, it's not slowing my truck going down hills... I hear it spool up, but all it's doing is making the noise and not slowing me going down the hills.

One thing the service tech I spoke said was that he checked with Chrysler and he was told that my tire size (285/75/R17's)would not affect my exhuast brake...

I have spoken with other Ram owners at other forums who are experiencing this same issue with their rigs.

 

[HBarlow]

Bob... I appreciate the input... but not sure what you are trying to tell me. I am aware of what the manual says ... but I know what I know through driving experience... the exhaust brake is just not working the way it was, it's not slowing my truck going down hills... I hear it spool up, but all it's doing is making the noise and not slowing me going down the hills.

One thing the service tech I spoke said was that he checked with Chrysler and he was told that my tire size (285/75/R17's)would not affect my exhuast brake...

I have spoken with other Ram owners at other forums who are experiencing this same issue with their rigs.

A service tech who tells you bigger tires won't affect your exhaust brake is uninformed. Larger tires change effective gear ratio which definitely reduces effectiveness of exhaust braking. The difference may be only very small but it can also be significant depending on the size of change.

What is the difference in rotations per mile between the two different sizes?

 

[mfurrh55]

When i had my 01, i went from 265-70-16 to 305-70-16s, and it never effected my exhaust brake, still slowed me down in the mountains, worked great, monte

 

[EdGarcia]

A service tech who tells you bigger tires won't affect your exhaust brake is uninformed. Larger tires change effective gear ratio which definitely reduces effectiveness of exhaust braking. The difference may be only very small but it can also be significant depending on the size of change.



What is the difference in rotations per mile between the two different sizes?

OK Harvey, so I found a tire calculator on line and this is what it gave me:







Dimensions Tire A: 265/70 R 17 Tire B: 285/75 R 17 Difference

(32 x 10. 43 x 17) (34 x 11. 22 x 17)

Width 10. 43" 11. 22" +0. 79"

Sidewall height 7. 30" 8. 42" +1. 11"

Overall height 31. 61" 33. 83" +2. 22"

Circumference 99. 29" 106. 28" +6. 99"







If your speedometer has been calibrated for 265/70 R 17 (32 x 10. 43 x 17) tires, replacing them with 285/75 R 17's (33 x 11. 22 x 17's) would result in the speedometer reading low by 6. 58%.





if your odometer has been calibrated for 265/70 R 17 (32 x 10. 43 x 17) tires, replacing them with 285/75 R 17's (34 x 11. 22 x 17's) would result in the odometer reading low by 6. 58%.





Effective Gear Ratio Change



Rearend ratio with 265/70 R 17's Rearend ratio with 285/75 R 17's

3. 75 3. 50





As far as gearing goes, if you have a 3. 75 rearend and 265/70 R 17 tires (32 x 10. 43 x 17), changing to 285/75 R 17's (34 x 11. 22 x 17's) would be the same as if you kept your current wheels and tires but changed your rearend gears to 3. 50's







RPM Change



RPM with 265/70 R 17's RPM with 285/75 R 17's

1600 1494



Replacing your 265/70 R 17 (32 x 10. 43 x 17) tires with 285/75 R 17's (34 x 11. 22 x 17's) would lower your finish line RPM by 106 RPMs.







Harvey, is this what you mean by effective tire change? And is this the reason my EB is working differently? Any Idea why Chrsysler would tell the service tech that my tire change would not effect my EB? I am asking because I'm wondering, If there is a problem that is covered under warranty... take care of it now, or if it's my truck's "new norm" because of my tire change, I will let things be and just live with it.



Ed

 

[EdGarcia]

Harvey,

Sorry. . the info I just posted didn't post/show the way I wanted. Here is the link to the tire calculator I referenced.

http://www.dakota-truck.net/tirecalc/tirecalc.html


Ed

 

[EdGarcia]

Harvey,



Sorry. . the info I just posted didn't post/show the way I wanted. Here is the link to the tire calculator I referenced.



http://www.dakota-truck.net/tirecalc/tirecalc.html





Ed

 

[JLeake]

My 2011 2500 with the exhaust brake does exhibit different behaviors at times Ed. Much of my driving is to and from work over a hilly route just less than 20 miles. The exhaust brake varies from very pronounced to much less aggressive behavior on the same roads and terrain. I am not sure what is the underlying difference, could be the miles since the truck had a long drive at steady load (over 500 miles) or my driving. Just before I get to work, the route goes down a steep hill that has two tight switch backs. Those turns are less than 30 mph turns for me, some days I have to touch the brakes, other days the exhaust brake slows the truck to the desired speed. I drive with the exhaust brake enabled and on those tight corners always engage the tow haul mode in advance since I would rather use the exhaust brake than the hydraulic brakes. I have just accepted the difference as due to factors I am not aware of. The truck is stock and has 24K miles on it, original tires, and the same driver since new.

 

[RonD]

Why don't you mount a pair of 265 tires on the rear, and go see how it is then?, that will give the story

 

[HBarlow]

OK Harvey, so I found a tire calculator on line and this is what it gave me:



Dimensions Tire A: 265/70 R 17 Tire B: 285/75 R 17 Difference
(32 x 10. 43 x 17) (34 x 11. 22 x 17)
Width 10. 43" 11. 22" +0. 79"
Sidewall height 7. 30" 8. 42" +1. 11"
Overall height 31. 61" 33. 83" +2. 22"
Circumference 99. 29" 106. 28" +6. 99"



If your speedometer has been calibrated for 265/70 R 17 (32 x 10. 43 x 17) tires, replacing them with 285/75 R 17's (33 x 11. 22 x 17's) would result in the speedometer reading low by 6. 58%.


if your odometer has been calibrated for 265/70 R 17 (32 x 10. 43 x 17) tires, replacing them with 285/75 R 17's (34 x 11. 22 x 17's) would result in the odometer reading low by 6. 58%.


Effective Gear Ratio Change

Rearend ratio with 265/70 R 17's Rearend ratio with 285/75 R 17's
3. 75 3. 50


As far as gearing goes, if you have a 3. 75 rearend and 265/70 R 17 tires (32 x 10. 43 x 17), changing to 285/75 R 17's (34 x 11. 22 x 17's) would be the same as if you kept your current wheels and tires but changed your rearend gears to 3. 50's



RPM Change

RPM with 265/70 R 17's RPM with 285/75 R 17's
1600 1494

Replacing your 265/70 R 17 (32 x 10. 43 x 17) tires with 285/75 R 17's (34 x 11. 22 x 17's) would lower your finish line RPM by 106 RPMs.



Harvey, is this what you mean by effective tire change? And is this the reason my EB is working differently? Any Idea why Chrsysler would tell the service tech that my tire change would not effect my EB? I am asking because I'm wondering, If there is a problem that is covered under warranty... take care of it now, or if it's my truck's "new norm" because of my tire change, I will let things be and just live with it.

Ed

Ed,

Yes, that's exactly what I was referring to. If I were the teacher and you the student I would assign a grade of A for that work. With mathematical calculations you demonstrated a classroom approach to explaining precisely how gearing effectively changes with larger tires and wheels.

The effective change in gearing caused by your larger tires and wheels is comparable to measuring the force generated by your exhaust brake in fifth gear at 50 mph then upshifting to sixth gear and measuring exhaust braking again. Braking effectiveness is reduced by higher effective gearing.

I often see members here quote something their "dealer" meaning their salesman, service writer, or tech has told them. Realize that very few Ram dealer salesmen, service writers, or techs actually own a Cummins-powered Ram truck. It is common to learn that they don't know as much as you do about your truck. Bob 4x4 and sag2 are exceptions to that statement. They do own them and do work on them. The ordiary tech may know how to diagnose problems by using the computer troubleshooting ladder and can usually replace parts but they seldom know much about operation. Their usual mode of operation is to stretch the truth a bit. I consider it very unlikely that a tech actually talked to anyone in the know at Chrysler. Even if he did he didn't know how to ask the proper question without bias and whoever he spoke with probably didn't understand the issue. Several years ago I knew better but put my normal cynicism aside and called the Chrysler help line to ask a complex question about long idle period and soot issues on my Ram truck. The help line hung up on me not once but several times. They are kids with an information sheet or booklet. They don't "know" anything. It's a waste of time to ask them.

Many TDR members know far more than anyone in most Dodge dealerships in the country. Collectively, TDR members know more than all Dodge dealerships combined.

 

[EdGarcia]

Harvey... thanks for the assist, I really appreciate it, if I could I'd buy u a beer!

 

[HBarlow]

Ed,

Thanks for the offer but not necessary. It's a pleasure to offer a little information or advice to someone like you who listens with an open mind then researches and proves the answer to himself. Many of our members ask a question but don't want to hear the answer. Some automatically reject it and chose to believe their opinion instead.