Runs fine when cold but...
Thread Starter
|
Senior User
Joined: May 2002
Posts: 353
Likes: 1
From: Bayonne NJ
Runs fine when cold but...
When I first start my 79 F100 it runs fine. smooth idle and good smooth power. After 20 min or so, once it warms all of the way up, it begins to run real rough and stumbles, cutting offanytime I give it gas. What gives?....
Thanks
BTW it has a 302 and a 2 bbl carb. also a c4 transmission.
Thanks
BTW it has a 302 and a 2 bbl carb. also a c4 transmission.
New User
Joined: Apr 2003
Posts: 12
Likes: 0
Runs fine when cold but...
I have the same problem with my 1986 F250. It has a v8 engine with Edelbrock carburettor. I think that there may be a problem with the cooling system, it looks as though the thermostat may be stuck or the waterpump is no longer working. does anyone know if this could cause extremely poor performance as soon as the engine warms up? Performance is great when it's cold but as soon as it warms up it hardly wants to go.
Posting Guru
Joined: Dec 2002
Posts: 1,297
Likes: 3
From: Billings MT
Runs fine when cold but...
If your tstat is stuck or the water pump doesn't work, you'll have over heating problems. That will only affect performance once it gets too hot.
It could be that you have a bad temperature sending unit. If the comp isn't getting the right signal from the temperature sending unit and the comp thinks that the engine is always cold and therefore keeps it running rich. It cold be the O2 sensor. Until that gets to 600*, the computer ignores what it says.
That's only for MikeConolly, it doesn't apply to JoeBlow.
JoeBlow, I don't know if you have an O2 sensor or not.
It could be that you have a bad temperature sending unit. If the comp isn't getting the right signal from the temperature sending unit and the comp thinks that the engine is always cold and therefore keeps it running rich. It cold be the O2 sensor. Until that gets to 600*, the computer ignores what it says.
That's only for MikeConolly, it doesn't apply to JoeBlow.
JoeBlow, I don't know if you have an O2 sensor or not.
New User
Joined: Apr 2003
Posts: 12
Likes: 0
Runs fine when cold but...
Thanks, I will check to see if I have an o2 sensor. I also didn't mention that the hydraulic lifters also become very noisy when the engine warms up. Could that effect the performance to such an extent?
Thread Starter
|
Senior User
Joined: May 2002
Posts: 353
Likes: 1
From: Bayonne NJ
Runs fine when cold but...
I know this sounds stupid, but I have never messed with the carb. Where is the choke and how do I check to see if it is opening all of the way up? i have the motorcraft 2bbl carb.
Thanks
Thanks
Trending Topics
Posting Guru
Joined: Dec 2002
Posts: 1,297
Likes: 3
From: Billings MT
Runs fine when cold but...
Mike,
How many miles and what motor? If the lifters are getting noisy, I would think that they are not moving the valves like they are supposed to. If the valves are not opening correctly you will have either too much or too little fuel in the chamber at combustion. That'll definetely cause poor performance.
I'm pretty sure that you should have an O2 sensor. Not positive, but fairly sure.
How many miles and what motor? If the lifters are getting noisy, I would think that they are not moving the valves like they are supposed to. If the valves are not opening correctly you will have either too much or too little fuel in the chamber at combustion. That'll definetely cause poor performance.
I'm pretty sure that you should have an O2 sensor. Not positive, but fairly sure.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
Rezvani's Latest Post-Apocalytic 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
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
New User
Joined: Apr 2003
Posts: 12
Likes: 0
Runs fine when cold but...
Take off the air filter. At the top of the carburetor you will see a flap (butterfly) that can open and close. In the case of an automatic choke this flap will close on it's own thereby "choking" the airflow into your carburetor. When the engine warms up this flap will automatically open.
Normally, with a manual choke you would have a **** inside the cab to enable and disable the choke manually. If however the previous owner changed the carb from an auto to a manual they may not have installed a cable to adjust it. Please note that I am not an expert and you should confirm what I have said.
Normally, with a manual choke you would have a **** inside the cab to enable and disable the choke manually. If however the previous owner changed the carb from an auto to a manual they may not have installed a cable to adjust it. Please note that I am not an expert and you should confirm what I have said.
Posting Guru
Joined: Dec 2002
Posts: 1,297
Likes: 3
From: Billings MT
Runs fine when cold but...
JoeBlow,
No problems, that's what we are all here for.
You should have a round black dial on the passenger side of the carb with 3 screws with 1 or 2 wires going into it. When cold, you should not be able to look down and see the butterfly flaps in the carb. As the engine warms up, it should open to a vertical position and you can see the butterfly flaps in the bottom of the carb, right before the intake.
If the choke is set too far, it will never open enough. If you loosen the three screws, you should be able to turn the black portion clockwise and the top flap should open. To set the choke, turn it back counterclockwise, until the flap stops moving, and then back it off just a little.
If this doesn't make sense, let me know and I'll see if I can post a picture.
Now, if it has a manual choke, ignore all of my previous statements and make sure that the cable isn't broken.
No problems, that's what we are all here for.
You should have a round black dial on the passenger side of the carb with 3 screws with 1 or 2 wires going into it. When cold, you should not be able to look down and see the butterfly flaps in the carb. As the engine warms up, it should open to a vertical position and you can see the butterfly flaps in the bottom of the carb, right before the intake.
If the choke is set too far, it will never open enough. If you loosen the three screws, you should be able to turn the black portion clockwise and the top flap should open. To set the choke, turn it back counterclockwise, until the flap stops moving, and then back it off just a little.
If this doesn't make sense, let me know and I'll see if I can post a picture.
Now, if it has a manual choke, ignore all of my previous statements and make sure that the cable isn't broken.
New User
Joined: Apr 2003
Posts: 12
Likes: 0
Runs fine when cold but...
Joe, I am not sure about the mileage as this is a vehicle that I just recently bought and I know that this is not the original motor. By the way what do I look for to know that I have an o2 sensor, where should it be and what does it look like?
Thanks for your help.
Mike
Thanks for your help.
Mike
Posting Guru
Joined: Dec 2002
Posts: 1,297
Likes: 3
From: Billings MT
Runs fine when cold but...
Mike,
You're backwards on the choke, it opens as the engine warms up. It closes when cold to make the fuel mixture richer. Since the fuel and air are cold, there is less atomized fuel, and is harder to burn. Once things get warm, the fuel atomizes more and therefore requires less fuel and more air to burn.
Mike,
The O2 sensor will be on the driver side exhaust, after the manifold, but before the crossover. It will be about 3/4" in diameter and will have either 1 or 3 wires coming out of it. It should be easy to spot. You should be able to see it from the engine compartment.
Mike,
If you can start the truck in the morning with the choke open, there is a problem with the air/fuel mixture. Unless you like where the temp never drops below 60*.
I would fix that choke and get the air/fuel mixture set. Whoever put that carb on probably set the air/fuel mixture so rich that when the engine is warm, there is too much fuel and it runs rich now
You're backwards on the choke, it opens as the engine warms up. It closes when cold to make the fuel mixture richer. Since the fuel and air are cold, there is less atomized fuel, and is harder to burn. Once things get warm, the fuel atomizes more and therefore requires less fuel and more air to burn.
Mike,
The O2 sensor will be on the driver side exhaust, after the manifold, but before the crossover. It will be about 3/4" in diameter and will have either 1 or 3 wires coming out of it. It should be easy to spot. You should be able to see it from the engine compartment.
Mike,
If you can start the truck in the morning with the choke open, there is a problem with the air/fuel mixture. Unless you like where the temp never drops below 60*.
I would fix that choke and get the air/fuel mixture set. Whoever put that carb on probably set the air/fuel mixture so rich that when the engine is warm, there is too much fuel and it runs rich now
New User
Joined: Apr 2003
Posts: 12
Likes: 0
Runs fine when cold but...
That is very possible re: the mixture because I am getting very poor mileage at the moment. Could that not also cause what they call "pinging" and maybe I am mistaking it for the hydraulic lifters? To be honest I am not sure what the lifters would sound like if they were worn.