1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks Discuss the Early Eighties Bullnose Ford Truck

Causes of Rough Idle when.....

Thread Tools
 
Search this Thread
 
  #1  
Old 11-16-2002 | 01:01 PM
XJeepGuy's Avatar
XJeepGuy
Thread Starter
|
Senior User
Joined: Aug 2002
Posts: 212
Likes: 0
From: Okanagan BC
Causes of Rough Idle when.....

What are the causes of rough idle when the truck is in gear ? Put it in neutral and smooth as silk . (1980)400M/C6 4x4 . There are no vacuum leaks , new plugs , cap / rotor etc...
If it idled erratic in park/neutral I`d suspect a vacuum leak but its smooth . Ideas , thoughts ??

Thanks

Jeff
 
  #2  
Old 11-16-2002 | 03:04 PM
Franklin2's Avatar
Franklin2
Moderator
Joined: Jan 2001
Posts: 54,658
Likes: 1,990
From: Virginia
Club FTE Gold Member
Causes of Rough Idle when.....

Low compression on one or two cylinders could be one cause.
 
  #3  
Old 11-16-2002 | 03:12 PM
Ford_Six's Avatar
Ford_Six
Hotshot
Joined: Oct 2002
Posts: 18,488
Likes: 20
From: The Big, Oregon
Club FTE Gold Member
Causes of Rough Idle when.....

check your timing- retarded timing will cause smooth idle, but no power and roughness under load.

Jared
 
  #4  
Old 11-19-2002 | 04:00 PM
enginenine's Avatar
enginenine
New User
Joined: Nov 2002
Posts: 14
Likes: 0
From: Loxley,AL
Causes of Rough Idle when.....

It could possibly be a bad brake booster. does it do it all the time in gear or just with your foot on the brake? it could be sucking air through the booster
 
  #5  
Old 11-19-2002 | 06:14 PM
XJeepGuy's Avatar
XJeepGuy
Thread Starter
|
Senior User
Joined: Aug 2002
Posts: 212
Likes: 0
From: Okanagan BC
Causes of Rough Idle when.....

[updated:LAST EDITED ON 19-Nov-02 AT 07:15 PM (EST)]You know thats a darn good idea because now that I think of it , putting on the brake , it does get worse . I`m going to check that as soon as the monsoon around here stops
Last weekend I checked the vacuum at idle , with the truck in park and the reading is rock steady at 14 . No fluctuations at all on the gauge , if it was worn engine components , the vacuum would wander or jump . At least thats been my experience so far with engines . Thanks for the tip .


Jeff
 
  #6  
Old 11-22-2002 | 10:25 AM
dwebb210's Avatar
dwebb210
New User
Joined: Oct 2002
Posts: 20
Likes: 0
From: Moline USA
Causes of Rough Idle when.....

I remember dad's '81 bronco did that.
The brake booster's diaphram had torn.
Caused the engine to suck air, and run
VERY lean on one cylinder.

Melted the piston.

Engine had to be rebuilt.


 
  #7  
Old 11-22-2002 | 05:22 PM
XJeepGuy's Avatar
XJeepGuy
Thread Starter
|
Senior User
Joined: Aug 2002
Posts: 212
Likes: 0
From: Okanagan BC
Causes of Rough Idle when.....

I checked into the brake theory and its not that . I`ll keep fiddling around till I find the culprit


Jeff
 
  #8  
Old 11-25-2002 | 07:28 PM
Franklin2's Avatar
Franklin2
Moderator
Joined: Jan 2001
Posts: 54,658
Likes: 1,990
From: Virginia
Club FTE Gold Member
Causes of Rough Idle when.....

 
  #9  
Old 11-27-2002 | 04:29 AM
seymour's Avatar
seymour
Freshman User
Joined: Mar 2002
Posts: 44
Likes: 0
Causes of Rough Idle when.....

>I checked into the brake theory and its not that . I`ll keep
>fiddling around till I find the culprit
>
>
>Jeff
Jeff check the booster by taking of the vaccuum line going to the booster and blocking the end. If the idle smoothes out then you definitely have a bad booster. I just recently had to change mine.
 
  #10  
Old 11-27-2002 | 06:16 PM
XJeepGuy's Avatar
XJeepGuy
Thread Starter
|
Senior User
Joined: Aug 2002
Posts: 212
Likes: 0
From: Okanagan BC
Causes of Rough Idle when.....

Thanks Seymour , I never did get that far but I have Friday off and its going to be SUNNY so I`ll mess with that first . You know , like some other 400M`s I`ve heard , I have a couple(few) noisey rockers and I`m wondering if that would be enough to make it idle lumpy ??


Jeff
 




All times are GMT -5. The time now is 05:56 PM.