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

1981 F100 Misfire & Run-On Problem

 
  #16  
Old 02-09-2019, 08:37 PM
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A common cause for the engine to run on when you turn the key off is the idle speed being too high. It may have been set high to keep it running if the EGR was on all the time. Leave the EGR disconnected. Try to get the idle speed down.
 
  #17  
Old 02-09-2019, 09:48 PM
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That Dorman kit should repair that

That copper tubing is not part of the kit, just the silver tubing.
I am running EFI exh manifolds and they do not have provisions for the hot air tubing so I had to make a system up using the copper.
Fresh air into the tube

A few wraps around the manifold to get heat

The heated air tube under blanket

And the choke still uses the wire from the ALT. the money shot

Got to do what you got to do LOL
Dave ----
 
  #18  
Old 02-11-2019, 12:54 PM
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It appears that the distributor vacuum hose is attached to the lower vacuum port, which is most likely manifold vacuum. This will cause the ignition timing to be advanced and will raise the idle speed, which could cause the "running on" condition.

Looking at the photo where you are showing the vacuum hose and where it is connected on the carburetor [post #12]... the vacuum "tree" which has about 6 outlets, is the one FuzzFace2 spoke about. There is a vacuum port on the backside of this "tree", which is pointing toward the cab and is nearest the engine and exhaust manifold. It has [had?] a rubber cap when new, but often falls off or is severely cracked after 30+ years of exposure to high heat. It is difficult to hear it hissing due to the exhaust and spraying with carb cleaner sometimes does not find the leak due to its location. If this port is open, it will cause a significant vacuum leak which will raise the idle speed and will cause poor running and can cause "run on".
 
  #19  
Old 02-11-2019, 01:39 PM
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Originally Posted by 1986F150six View Post
It appears that the distributor vacuum hose is attached to the lower vacuum port, which is most likely manifold vacuum. This will cause the ignition timing to be advanced and will raise the idle speed, which could cause the "running on" condition.
Going to have to disagree. That's the spark port, it's hooked correctly.


Stole this from another thread, good info.


You still have the emissions sticker above the grill. Care to post a picture?
 
  #20  
Old 02-11-2019, 01:54 PM
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Thank you for the correction.
 
  #21  
Old 02-13-2019, 10:03 PM
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Originally Posted by 1986F150six View Post
Looking at the photo where you are showing the vacuum hose and where it is connected on the carburetor [post #12]... the vacuum "tree" which has about 6 outlets, is the one FuzzFace2 spoke about. There is a vacuum port on the backside of this "tree", which is pointing toward the cab and is nearest the engine and exhaust manifold. It has [had?] a rubber cap when new, but often falls off or is severely cracked after 30+ years of exposure to high heat. It is difficult to hear it hissing due to the exhaust and spraying with carb cleaner sometimes does not find the leak due to its location. If this port is open, it will cause a significant vacuum leak which will raise the idle speed and will cause poor running and can cause "run on".

Ive got 5 caps on the tree. That i see. Are any of these the ones you were talking about?

 
  #22  
Old 02-13-2019, 10:05 PM
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  #23  
Old 02-13-2019, 10:17 PM
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**NEW INFO**
I feel like this has gotten to long and confusing. I've got some new information though.

I did get a tachometer. And at idle the truck is idling at 1,400 RPM'S! Keep in mind that I previously timed the truck accourding to the white marks on the crank pulley.

I tried to Retard the engine and get the RPMs down and at about 1200 RPMs the truck starts to shut down. What could be causing these insane idle speeds? I feel like I'm in over my head at the moment. Do I need to replace the carb and EGR completely and have a professional hook it up??
 
  #24  
Old 02-14-2019, 07:55 AM
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Originally Posted by Jakehx F100 View Post
**NEW INFO**
I feel like this has gotten to long and confusing. I've got some new information though.

I did get a tachometer. And at idle the truck is idling at 1,400 RPM'S! Keep in mind that I previously timed the truck accourding to the white marks on the crank pulley.

I tried to Retard the engine and get the RPMs down and at about 1200 RPMs the truck starts to shut down. What could be causing these insane idle speeds? I feel like I'm in over my head at the moment. Do I need to replace the carb and EGR completely and have a professional hook it up??
Don't try to slow it down with the timing. Make sure the vacuum hose to the distributor is unplugged. Clean your marks off good, I like to put white out on the 10 BTDC. Then start by setting the timing at 10. Leave it there for now, it should run fine at that setting.

Then try to get your idle speed down. Turn the idle stop screw all the way back. If it is not touching the throttle arm anymore, and it is still idling high, check your choke. Make sure the choke door is all the way open. If it's not open all the way, pull it open with your finger and goose the throttle, the idle speed should drop down and the throttle arm should touch the idle speed screw.

If pulling the choke open doesn't help, you need to make double sure the fast idle cam over on the choke area is not holding the throttle open. It's a complicated mess of levers and rods on the choke side of the carb.

If you get the throttle arm to come back and hit the idle stop screw, and you back it all the way out, the butterfly in the bottom of the carb is shut, and the idle speed is still high, you have a massive vacuum leak somewhere, letting air into the engine.
 
  #25  
Old 02-14-2019, 08:31 AM
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Originally Posted by Jakehx F100 View Post

Ive got 5 caps on the tree. That i see. Are any of these the ones you were talking about?
Yes, the one on the left [towards the cab] and nearest the engine.
 
  #26  
Old 02-14-2019, 09:05 AM
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I know I'm an ignorant old hillbilly, BUT, if you'll turn off truck IN GEAR, your dieseling (or run on) should diminish, maybe even stop, due to lower rpm.
 
  #27  
Old 02-14-2019, 10:04 AM
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All new caps are on the tree. And no your not a hillbilly because I tried to shut of off in gear as well. The only problem is that the RPMs don't lower in gear. I'm at work and I'll do those throttle tests when I get home.
 
  #28  
Old 02-14-2019, 12:51 PM
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Have you temporarily disconnected the throttle cable to see if it is holding the throttle plate open?
 

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