Steep grades and engine braking
Thread Starter
|
Senior User
Joined: Sep 2006
Posts: 110
Likes: 0
From: Fair Oaks, Ca
Steep grades and engine braking
I have a 94 f250 460 e4od that I use to haul a 2700 lb camper.
On steep hilly mountain roads I like to gear down, sometimes 1st to use compression to hold back on a hill. The problem is that emission controls keep the RPM above <>2000, thus I'm forced to use the brakes intermittently to go slower than the 2000 rpm allows. If the rpm is above 2000 the engine will hold back the rig just fine but then your traveling at 25-30 mph.
Is it as simple as using a switch to disable the IAC?
I'm going to install a tranny temp gauge but can someone answer this question also. When using low gears and on compression going down a hill does the tranny heat up?
My other f250 460 was the 5 speed zf tranny. Put that sucker in 1'st and a 3000 lb load and you didn't even need to touch the brakes even on the 27% Sonora pass grade. It was wonderful.
On steep hilly mountain roads I like to gear down, sometimes 1st to use compression to hold back on a hill. The problem is that emission controls keep the RPM above <>2000, thus I'm forced to use the brakes intermittently to go slower than the 2000 rpm allows. If the rpm is above 2000 the engine will hold back the rig just fine but then your traveling at 25-30 mph.
Is it as simple as using a switch to disable the IAC?
I'm going to install a tranny temp gauge but can someone answer this question also. When using low gears and on compression going down a hill does the tranny heat up?
My other f250 460 was the 5 speed zf tranny. Put that sucker in 1'st and a 3000 lb load and you didn't even need to touch the brakes even on the 27% Sonora pass grade. It was wonderful.
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
I don't think this has anything to do with emission controls. That's just how automatics are. Above 1500 RPMs with your foot off the gas I'm pretty sure the IAC is shut and I know for a fact the injectors are.
Just another advantage of having a manual tranny.
Just another advantage of having a manual tranny.
Thread Starter
|
Senior User
Joined: Sep 2006
Posts: 110
Likes: 0
From: Fair Oaks, Ca
andyum, thanks for the reply......
It doesn't feel like the tranny is doing it. If the hill is steep and the rpm has settled at, say, 3000 and holding the truck at that speed, when the grade decreases and the rpm begins to go down and the truck slows down something changes. and doesn't allow the rpm to drop below <>2000 until the grade decreases more or you put the brakes on.
The manual tranny did the same thing but 1'st gear is so low that 2000 rpm is like 5 mph whereas the e4od is geared higher in 1'st and the speed is somewhere around 15-20.
Originally Posted by andym
I don't think this has anything to do with emission controls. That's just how automatics are. Above 1500 RPMs with your foot off the gas I'm pretty sure the IAC is shut and I know for a fact the injectors are.
Just another advantage of having a manual tranny.
Just another advantage of having a manual tranny.
The manual tranny did the same thing but 1'st gear is so low that 2000 rpm is like 5 mph whereas the e4od is geared higher in 1'st and the speed is somewhere around 15-20.
Thread Starter
|
Senior User
Joined: Sep 2006
Posts: 110
Likes: 0
From: Fair Oaks, Ca
alz, that is one of my listed projects to do but in this case, something is keeping the rpm up on the engine. Naturally the emissions system is doing it, but what device is aiding in keeping the rpm up?
I want the tc locked when I'm climbing a hill/steep road and want the tc to stay locked 2nd and 3rd.
I don't know at this time if the tc stays locked when going down a hill in 3rd and your using the engine for breaking.
I do know that if your cruising along and let off the gas the tc unlocks, but the question is does it stay unlocked as you slow down?
I want the tc locked when I'm climbing a hill/steep road and want the tc to stay locked 2nd and 3rd.
I don't know at this time if the tc stays locked when going down a hill in 3rd and your using the engine for breaking.
I do know that if your cruising along and let off the gas the tc unlocks, but the question is does it stay unlocked as you slow down?
Thread Starter
|
Senior User
Joined: Sep 2006
Posts: 110
Likes: 0
From: Fair Oaks, Ca
Originally Posted by andym
I don't think that's a valid assumption to make at all.
I'll assume that my assumption is correct but will wear my bathing suit in case I'm all wet....
Jim
Trending Topics
Elder User
Joined: Feb 2007
Posts: 601
Likes: 1
From: Chicagoland
One other thing to keep in mind is that the fuel injectors don't fire under deceleration when the RPM is greater than 1500. I'd imagine an engine that's not adding any energy is going to hold a lot more than one that is.
Calvin
Calvin
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Thread Starter
|
Senior User
Joined: Sep 2006
Posts: 110
Likes: 0
From: Fair Oaks, Ca
Originally Posted by mprice
One other thing to keep in mind is that the fuel injectors don't fire under deceleration when the RPM is greater than 1500. I'd imagine an engine that's not adding any energy is going to hold a lot more than one that is.
Calvin
Calvin
Is it the IAC that keeps the engine from holding back? The injectors are shut down, if they weren't they would be dumping gas into the cyl's and the throttle body were closed you would just be dumping unburt fuel out the exaust. Compression is the only thing holding back, so, what allows the engine to not develop the high vacuum required to enable the engine to act like a brake? That is my question.
The diesel guys need an exaust brake because they can't develop the high vacuum pressure us gas burning guys can.
Jim