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09-05-2021, 07:20 PM
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#1
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Senior Member
Join Date: Sep 2020
Posts: 1,482
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Any difference for you at 1/2 throttle and full throttle?
Cat 3126, Allison 3060, 30,000lb class A.
Accelerating from a stop, 1/2-3/4 throttle and full throttle feel about the same…
Acceleration to 65mph is reasonable, no issues…
(Tach goes to 3500… but manual says redline is 2500 max?)
I don’t get there any faster if I slam on the accelerator…
How about you?
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09-05-2021, 07:31 PM
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#2
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Senior Member
Join Date: Nov 2015
Posts: 26,846
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Full throttle from a stop just causes excess raw fuel washing down the cylinders
From a stop 1/2 throttle gets you rolling and then up to speed
It isn't a sports car
Pickup/trailer acts the same way so why waste the fuel
__________________
I took my Medication today. HAVE YOU?
Dodge 3500 w/Tractor Motor
US NAVY---USS Decatur DDG-31
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09-05-2021, 07:41 PM
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#3
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Senior Member
Join Date: Sep 2020
Posts: 1,482
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I figured the shift point might be different at full throttle…. But not really. Still shifts around 1300-1600 rpm…
At what p pint does full throttle come into play? On hills it doesn’t make a difference either. Thought it would downshift to higher rpm..
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09-05-2021, 08:11 PM
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#4
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Senior Member
Join Date: Apr 2018
Posts: 3,441
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Get your tach fixed. Over reving a diesel is certain death. The rotating mass is huge in large engines.
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09-05-2021, 09:16 PM
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#5
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Senior Member
Join Date: Sep 2020
Posts: 1,482
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Quote:
Originally Posted by shootist
Get your tach fixed. Over reving a diesel is certain death. The rotating mass is huge in large engines.
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It isn’t broken… spans from 0 to 3500 rpm on its face… motor spins up to about 2200 or so…
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09-05-2021, 09:26 PM
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#6
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Senior Member
Join Date: Oct 2014
Posts: 7,882
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NO, your tach is NOT correct if it ever shows engine RPM of 3,500.
Give Caterpillar Corp a call with your engine serial number: 877 777-3126.
But I suspect your governed red line is around 2,400 RPM.
3,500 RPM and you would have things coming apart (assuming your Allison was broken to the point that it would allow such extreme RPM-- NOT LIKELY).
What is max RPM in each gear before upshift: Power mode? Economy mode?
I suspect max torque (lowest permissible RPM except no/low load is around 1,460 RPM).
Again, Caterpillar can give you the exact information on your engine.
Your engine RPM numbers (assuming the 3,500 was engine RPM and not full range of the tach) are both extremely high and shift points very low???
But, in looking at performance, when was the last time the fuel filters were changed? What was their condition? If fuel flow restricted, max throttle will NOT give more fuel than at part throttle. That is where to start with any diesel performance issue.
__________________
Brett Wolfe
Ex: 2003 Alpine 38FDDS. Ex: 1997 Safari Sahara. Ex: 1993 Foretravel U240
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09-05-2021, 09:34 PM
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#7
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"Formerly Diplomat Don"
Newmar Owners Club
Join Date: Apr 2005
Location: Moorpark, Ca.
Posts: 24,125
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Part of the problem with a DP, is you can't hear the engine when you accelerate. Mashing the pedal does no good and won't get you up to speed any faster.
I know my cruise control will operate at about 25 mph and up. When I enter an onramp, I get the coach up to about 25 -35 mph and the set the cruise. I then keep increasing the speed with the cruise control switch. The cruise control will only increase the throttle at what the engine will accept.
__________________
Don & Mary
2019 Newmar Dutch Star 4018 (Freightliner)
2019 Ford Raptor
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09-05-2021, 11:47 PM
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#8
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Senior Member
Join Date: Jul 2014
Posts: 35,445
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Modern diesels have governors and fuel control systems so they don't smoke. Its not like the old days where you poured the coal to it.
The throttle is just a suggestion to add more power, not a fuel valve. In pre-electronic engines, it pulls against a spring while the centrifugal governor spins up with RPMs allowing more fuel. Mechanical diesels will send out some black smoke under heavy load.
Now days, electronics control fuel delivery. There is litte, if any black smoke.
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09-06-2021, 12:02 AM
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#9
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Senior Member
Join Date: Apr 2011
Location: Powell River, B.C.
Posts: 31,495
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Dash and tach probably the same no matter what engine is in the chassis .
Cummins 5.9 L, ISB will rev higher than the Cat ,so the higher scale is required .
Cat is governed to 2400 under throttle but can rev to 2650 under exhaust brake use. My Allison trans will up shift at 2700 while using exhaust brake to prevent engine damage. So I apply service brakes to keep RPM between 2000 & 2500 on down hills .
Electronic fuel management will only inject the fuel the engine can burn at the RPM it's turning to prevent over fueling, cylinder wash down and black exhaust smoke.
__________________
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.
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09-06-2021, 08:03 AM
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#10
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Senior Member
Join Date: Sep 2020
Posts: 1,482
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Quote:
Originally Posted by wolfe10
NO, your tach is NOT correct if it ever shows engine RPM of 3,500.
Give Caterpillar Corp a call with your engine serial number: 877 777-3126.
But I suspect your governed red line is around 2,400 RPM.
3,500 RPM and you would have things coming apart (assuming your Allison was broken to the point that it would allow such extreme RPM-- NOT LIKELY).
What is max RPM in each gear before upshift: Power mode? Economy mode?
I suspect max torque (lowest permissible RPM except no/low load is around 1,460 RPM).
Again, Caterpillar can give you the exact information on your engine.
Your engine RPM numbers (assuming the 3,500 was engine RPM and not full range of the tach) are both extremely high and shift points very low???
But, in looking at performance, when was the last time the fuel filters were changed? What was their condition? If fuel flow restricted, max throttle will NOT give more fuel than at part throttle. That is where to start with any diesel performance issue.
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Tach never shows rpm over 2500 or so. Tach face has readings up to 3500…
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09-06-2021, 08:22 AM
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#11
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Senior Member
Join Date: Aug 2008
Location: Georgia
Posts: 8,638
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Quote:
Originally Posted by bpu699
Cat 3126, Allison 3060, 30,000lb class A.
Accelerating from a stop, 1/2-3/4 throttle and full throttle feel about the same…
Acceleration to 65mph is reasonable, no issues…
(Tach goes to 3500… but manual says redline is 2500 max?)
I don’t get there any faster if I slam on the accelerator…
How about you?
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You need to find a torque curve on your motor, you may find out more rpm means less torque.
__________________
2007 Fleetwood Revolution LE 40V
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09-06-2021, 10:02 AM
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#12
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Senior Member
Join Date: Sep 2018
Location: Fort Myers, FL
Posts: 1,694
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I seldom hear the difference in the engine between 1/2 and full throttle off the line due to the squealing of the rear tires...
But I do love burying those Maseratis in clouds of burning rubber!
__________________
2008 Phaeton 36QSH, Safe-t-Plus, Quadra Bigfoot
2017 Jeep Cherokee Trailhawk w/ flat tow wiring mod.
Blue ox, BrakeMaster + BrakeAway, diode lights and charge.
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09-06-2021, 10:09 AM
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#13
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Senior Member
Join Date: May 2002
Location: tn
Posts: 143
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Quote:
Originally Posted by Old-Biscuit
Full throttle from a stop just causes excess raw fuel washing down the cylinders
From a stop 1/2 throttle gets you rolling and then up to speed
It isn't a sports car
Pickup/trailer acts the same way so why waste the fuel
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that is in no way true on a fuel injected diesel... where does one get these facts?
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09-06-2021, 10:46 AM
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#14
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Senior Member
Join Date: Dec 2014
Location: High up in Arizona
Posts: 2,050
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Quote:
Originally Posted by bpu699
Cat 3126, Allison 3060, 30,000lb class A.
Accelerating from a stop, 1/2-3/4 throttle and full throttle feel about the same…
Acceleration to 65mph is reasonable, no issues…
(Tach goes to 3500… but manual says redline is 2500 max?)
I don’t get there any faster if I slam on the accelerator…
How about you?
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In all my coaches I feel no acceleration difference from a stop up to speed 1/2 or floored. It may hold the gear longer but you can do that shifting manually, which I do at times. When up to highway speed on hills I can get more power at full throttle vs half throttle and manually hold the gears. Slamming the accelerator pedal in these big machines does nothing.
__________________
2019 Allegro Bus 37AP towing a Jeep JK Rubicon Wrangler
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