idle and operating rpms
Thread Starter
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Senior User
Joined: May 2002
Posts: 298
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From: San Diego, CA
idle and operating rpms
Hey Guys, a few questions for you. Not sure if my tachometer is running right or wrong.
When warm, my idle is about 450-500rpm.
I've got a gear vendors over/underdrive unit and 285/85/16 tires. At about 65 mph my rpm is around 1000-1100 rpm.
My transmission always changes gear around 1100rpm. I've never seen this engine above maybe 1500rpm.
Is this normal?
After calculating everything including mileage adjustments to compensate the tire size, I get about 15.6 mpg and that's with a few 60 mile trips in the hills.
Erik
When warm, my idle is about 450-500rpm.
I've got a gear vendors over/underdrive unit and 285/85/16 tires. At about 65 mph my rpm is around 1000-1100 rpm.
My transmission always changes gear around 1100rpm. I've never seen this engine above maybe 1500rpm.
Is this normal?
After calculating everything including mileage adjustments to compensate the tire size, I get about 15.6 mpg and that's with a few 60 mile trips in the hills.
Erik
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 16
From: Nutter Fort, WV
Idle should be around 650 to 700 with a warm engine.
800 to 850 cold at high idle.
Do you have the overdrive gear vendors unit or the under drive unit?
Also what transmission?
Do you know what gears are in the rear end?
If you have a C6 transmission and 3.55 gears with the overdrive gear vendors unit in overdrive and 285/75-16 tires, at 1900 RPM you should be going 65 MPH.
Same setup with the overdrive off 1900 RPM will get you 51 MPH.
For a test lock it in second gear with the overdrive locked out and put it on the floor.
The governor should cut you off at 3300 to 3400 RPM and the fastest it would go with the above setup and overdrive off is 60 MPH at 3300 or 64 at 3400.
800 to 850 cold at high idle.
Do you have the overdrive gear vendors unit or the under drive unit?
Also what transmission?
Do you know what gears are in the rear end?
If you have a C6 transmission and 3.55 gears with the overdrive gear vendors unit in overdrive and 285/75-16 tires, at 1900 RPM you should be going 65 MPH.
Same setup with the overdrive off 1900 RPM will get you 51 MPH.
For a test lock it in second gear with the overdrive locked out and put it on the floor.
The governor should cut you off at 3300 to 3400 RPM and the fastest it would go with the above setup and overdrive off is 60 MPH at 3300 or 64 at 3400.
Thread Starter
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Senior User
Joined: May 2002
Posts: 298
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From: San Diego, CA
I think my tach might be broken. In my possession my engine has never seen the other side of 1500rpm.
The gear vendors switch says Over/Underdrive unit.
At 65-70mph i'm at about 1100-1200rpm.
The gear vendors switch says Over/Underdrive unit.
At 65-70mph i'm at about 1100-1200rpm.
New User
Joined: Dec 2005
Posts: 9
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If its a 94 and older I would check the RPM sensor.Its mounted on the left front of the engine with two wires into a connector and if i remember its about a 11/8 hex I think they are about $50+ - from Ford.Way less than the tach Around $100.
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 16
From: Nutter Fort, WV
The tach is no longer available from Ford for the 86 dash style.
The tach pickup that mounts in the IP drive housing is available at Ford for 47 dollars.
Salvage yards are your only hope to find a replacement if the gauge is bad..
The diesel tach is different than a gas tach.
I have been thinking about making a custom insturment cluster for mine so I can install a six speed transmission.
There are aftermarket diesel tachs, but I have not started checking it out that close yet.
We are normally kinda slow in the excavation business this time of year and I get to work on my truck. This year the winter is so mild we are covered up with work.
No time to work on the truck.
The tach pickup that mounts in the IP drive housing is available at Ford for 47 dollars.
Salvage yards are your only hope to find a replacement if the gauge is bad..
The diesel tach is different than a gas tach.
I have been thinking about making a custom insturment cluster for mine so I can install a six speed transmission.
There are aftermarket diesel tachs, but I have not started checking it out that close yet.
We are normally kinda slow in the excavation business this time of year and I get to work on my truck. This year the winter is so mild we are covered up with work.
No time to work on the truck.
Last edited by Dave Sponaugle; Dec 30, 2005 at 05:35 PM.
