Hesitation Issue
Thread Starter
|
New User
Joined: May 2012
Posts: 9
Likes: 0
Hesitation Issue
Hi All,
This is my first post here.
I have an 80 model 150 4x4 with the 4.9. I have a hesitation problem when stepping on the gas.. like when changing gears and accelerating. I have changed the motor and put in a new long block from Ford. The problem was there with the old engine. I have rebuilt the carb, but did not run it thru a cleaner. I have installed a new vacuum advance. My uncle desmogged the truck years ago before I got it from my Dad. I know the truck did not do this when my Dad drove it. It sat for a number of years before I started the rebuild. I put a manual choke on it and if you pull the choke out a little, the hesitation is gone. I would also love to be able to get rid of all the electronic ignition and go back with a new distributor.
Any help would be greatly appreciated.
This is my first post here.
I have an 80 model 150 4x4 with the 4.9. I have a hesitation problem when stepping on the gas.. like when changing gears and accelerating. I have changed the motor and put in a new long block from Ford. The problem was there with the old engine. I have rebuilt the carb, but did not run it thru a cleaner. I have installed a new vacuum advance. My uncle desmogged the truck years ago before I got it from my Dad. I know the truck did not do this when my Dad drove it. It sat for a number of years before I started the rebuild. I put a manual choke on it and if you pull the choke out a little, the hesitation is gone. I would also love to be able to get rid of all the electronic ignition and go back with a new distributor.
Any help would be greatly appreciated.
Posting Guru
Joined: Jun 2002
Posts: 2,091
Likes: 3
From: Suffolk, VA USA
Welcome to the club. Did you use the original intake & exhaust manifolds? Did you have them planed before installing them? The carbed manifolds had a tendency to warp, causing vacuum leaks that would drive you crazy trying to find. Recommend you use the old propane test around the manifolds.
Senior User
Joined: May 2007
Posts: 155
Likes: 0
Hey Dynamo, welcome to the forum.
You mentioned you had a carb, but what kind is it?
I had a hesitation in my 86 f150 when i'd step on the gas. i have a holey 4180 and i tried everything to get rid of the stumble. What it ended up being is the accelerator pump cam. I bought the kit and i would put a different color on, take it for a test drive and see how it performed. I did this until i found one that got rid of the hesitation.
What this does is, the cams have different profiles (shapes) this alows them to operate the accelerator pump at different times and more or less volume.
I may not be an expert on these trucks, but this has been my experience with hesitation and stumble.
Here's a pic of the different cams.
You mentioned you had a carb, but what kind is it?
I had a hesitation in my 86 f150 when i'd step on the gas. i have a holey 4180 and i tried everything to get rid of the stumble. What it ended up being is the accelerator pump cam. I bought the kit and i would put a different color on, take it for a test drive and see how it performed. I did this until i found one that got rid of the hesitation.
What this does is, the cams have different profiles (shapes) this alows them to operate the accelerator pump at different times and more or less volume.
I may not be an expert on these trucks, but this has been my experience with hesitation and stumble.
Here's a pic of the different cams.
Posting Guru
Joined: Jun 2002
Posts: 2,091
Likes: 3
From: Suffolk, VA USA
Running some choke would lessen the air in the combustion chamber, in a sense compensating for the extra air introduced by a vacuum leak.
Posting Guru
Joined: Jan 2012
Posts: 1,410
Likes: 1
From: Dallas, GA
I agree with both possibilities...especially with the note you stated about the choke. If limiting the air flow helps, then that mean maybe you have too much to begin with.
Either possiblity (vacuum leak or accelerator pump) would cause the engine to lean out. When you step on the gas, if you don't get that squirt of fuel as the throttle plates open up, that willl lean the engine out. Did you replace the accelerator pump when you rebuilt the carb? Is it adjusted correctly?
Look down the throat of the carb, with the engine off, and cycle the throttle wide open. Look to see that you have a nice solid stream of fuel squirting down the the throat.
On the distributor....you say you have an electronic ignition. I'm assuming you have a DS II. I would strongly recommend you keep this. They are very reliable and much better then the points type ignition.
Either possiblity (vacuum leak or accelerator pump) would cause the engine to lean out. When you step on the gas, if you don't get that squirt of fuel as the throttle plates open up, that willl lean the engine out. Did you replace the accelerator pump when you rebuilt the carb? Is it adjusted correctly?
Look down the throat of the carb, with the engine off, and cycle the throttle wide open. Look to see that you have a nice solid stream of fuel squirting down the the throat.
On the distributor....you say you have an electronic ignition. I'm assuming you have a DS II. I would strongly recommend you keep this. They are very reliable and much better then the points type ignition.
Trending Topics
Thread Starter
|
New User
Joined: May 2012
Posts: 9
Likes: 0
That makes a LOT of sense! I hadn't thought about it that way. I bet the intake is warped. I will definately check that.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
Posting Guru
Joined: Jan 2012
Posts: 1,410
Likes: 1
From: Dallas, GA
Well look down that carb and check for that squirt of fuel. That's a quick, and free, check to do. I'm not familiar with how the pumps on that carb is adjusted, if it's even adjustable. Your rebuild kit should have had some instructions.
For the vacuum leak check, if you don't have propane handy, you can also use some carb/choke cleaner or starter fluid if you have that.
For the vacuum leak check, if you don't have propane handy, you can also use some carb/choke cleaner or starter fluid if you have that.
Thread Starter
|
New User
Joined: May 2012
Posts: 9
Likes: 0
It's been some time since the engine install and carb rebuild. The new engine has only a few hundred miles on it. The truck has sat a lot. I can't remember about the adjustment and the instructions are long gone. I will do both checks and go from there. Thanks for the help.
Thread Starter
|
New User
Joined: May 2012
Posts: 9
Likes: 0
Looked down the carb and didn't see any fuel squirting in. This truck has a mechanical fuel pump so would any fuel be there without it running? Also sprayed some carb cleaner around the intake. Seems t o be a little change in rpm's around the #3 cylinder as well as #1. Also when the engine speeds up the hesitation is gone when you mash the accelerator quickly.
Moderator
Joined: Nov 2007
Posts: 22,415
Likes: 92
From: Denver Metro Area, CO
Yes, there would be fuel squirting, it would be coming from the Accelerator Pump. The pump's job is to provide a quick shot of gasoline to provide fuel to the air suddenly being sucked into the engine but for which the fuel circuit hasn't caught up yet.
If you don't have a properly-working accelerator pump, expect a short-lived hesitation when you initially step on the gas pedal.
If you don't have a properly-working accelerator pump, expect a short-lived hesitation when you initially step on the gas pedal.