Need some help from all you inline six experts. Here is the scenario:


I have a 1986 F150 4X4 with a 300 six and a manual 4 speed that I use around the farm. Due to the loss of another truck, I have started driving the Ford to my "City Job". I have "modified" the Ford in the following way. I live in a non- emission/vehicle inspection state.

- Removed all emmision control equipment including the computer.
- Replaced the distributor and coil with a points unit from a '73
240 engine.
- Replaced the carb with a non-feedback model for an '82 300 engine.
It has an electric choke with a exhaust manifold heat tube. The
mixture screw is about 2 turns out.
- Replaced the cat exhaust with a manifold pipe from a '78 300 engine.
- I have gasketed the intake and exhaust manifolds due to prior leaks.

The carb and exhaust are new and the distributor and coil are wrecking yard models. I have all new points, condensor, cap , rotor, plugs and wires.

This truck is extremely cold natured. I will use yesterdays driving experience as my example.

I started the truck yesterday morning and let it run for about 10-12 minutes. It was 30 degrees outside at the time. I got in the truck, kicked it off the choke idle cam and it idled perfectly. I drove the 24 miles to work with only a few sputters in the first 4 miles. It sat outside at work for 9 hours. I started it up at work and let it run for 8 minutes. It was 52 degrees outside at this time. I kicked it off the choke idle cam and it idled just fine. I put it in gear and pressed on the accelerator and it sputtered and coughed and had no power at all. I left it running, stopped and popped the hood. I took the aircleaner top off to check that the butterfly was all the way open and that the choke had not stuck. The butterfly was fully open. I got back in and spit and sputtered with limited acceleration for the next 5 miles before it smoothed out and ran like a top.

I have this same driving experience almost everytime I drive it. If it warms up for 10 -15 minutes it runs better. Anything less than that it is a coughing, wheezing piece of scrap metal limping down the road. I can't for the life of me figure out what to do to make this thing run better with a shorter warmup. I know the 300 is an extremely cold natured engine and requires a warm up period before driving.

Any suggestions on were to look? It has something to due with the temperature of the engine or one of it's components. Whatever it is, it works fine when it is warm and not very well when it is cold. Until this truck, the best vehicles I have ever owned were Ford trucks with inline sixes.

Appreciate any help you can offer.
Thanks.

BigMac

 

[updated:LAST EDITED ON 19-Feb-02 AT 12:53 PM (EST)]Do you have the heated air intake duct, cowl, and door installed and operational? I think it's a sticky float problem. Sometimes something as simple as a fuel filter will give wierd erratic symptoms.

I re-read your post. It appears your choke is acting up. The old YFA's need a little fiddling with every season. Mine was working for about a week and then all this sudden it works again...

 

Ruby,

The heated air duct is piped into the snorkle of the air cleaner. The trap door has been removed. With or without the heated air supply, the results are the same. I remove the air duct for summer driving. The fuel filter is new.

It is definately engine temperature related. If the truck starts sputtering, I can pull over and let the truck idle for a few minutes and then take off like a scalded dog. Something needs to heat up before it runs right.

Could it be the coil? It is a junkyard replacement. I did not get a new coil.

When the engine is warm it runs perfect. When it is cold, start walking.

Appreciate any help.

BigMac

 

These trucks are by nature cold-blooded beasts. There are a few things you can do, depending on how far you want to go.
First, check to make sure the heat riser flap is operating. It's on the exhaust manifold, just below the "choke stove" portion where the exhaust mates with the intake portion of the two piece manifold. When the engine is cold, the flap is supposed to direct hot exhaust at the intake and warm it up. When the manifold gets warm, a heat sensitive spring opens the flap and exhaust flows normally.

More radical is to replace the intake/exhaust with a header and an aluminum mamifold, like the Offenhauser, that you can afix a water heat plate to.

I don't know if an electric block heater would work for you or not. Would be easy and cheap though.

 

A couple of years back when I removed the manifolds to put on gaskets, I removed the heat riser assembly in the exhaust manifold because it was all rusted out. You are right in that it heats the intake manifold and makes the engine run smoother.

That would explain why it runs fine when it is warm and like crap when it is cold. I had forgotten completely about the heat riser.

Give that motorhead a cigar!!!!!!!!!!!!!!

Is there anyone else out there that will second this motion as the cause of my symptoms?

I really appreciate the help and the knock on the side of the head with a 2 X 4.

BigMac

 

I will second that. Mine has everything on it stock for 1984 and it will do this for about a mile. What happens is that the intake is cold and causes the atomised gas in the air stream to condense backout believe it or not causing the clyinders to see a lean condition the choke tries to compensate for this by riching the mix up. You are not helping yourself with the old ignition system. the spark is a lot less potent on these then on the electronics and in cold start mode this can mean the difference between a miss and run.

 

Another thing to do, if you like simplicity, after you get the heat riser back on is to deep six that auto choke and install a manual choke. I've had four F-series Fords, three with I6's, over the past 33 years and they were all cold-natured. But the two that were easiest to deal with in that situation were the '68 and '69 with a manual choke on the dash. Makes it easier to start in the cold and you don't have to depend on the auto choke to keep the truck running right until it warms up. Just adjust the choke yourself to find the best warm-up idle and run it that way (gently) until the temp comes up and then choke off and you can run with the best of 'em.

 

I just did my manifold gaskets this weekend for the first time (third owner -'79). I had to swap on some legal manifolds for CA emissions that have the threaded EGR pipe hose and the hole in the top of the intake for the air injection - damn past owner just slapped on any old manifolds. Anyway, I always was curious how my Exhaust Fuel Evaportor valve (the flapper inside the exhaust manifold) was working. It was loose, but never appeared to close when the engine was hot. Well, after this weekend I finally got to look inside. The flapper part was gone. All that was there was the shaft going from one side to the other. I will have to say that I notice better driveability compared to before, but my truck rarely bogged like you described -when the valve wasn't on there. I don't think replacing / fixing the EFE in the manifold will stop the symptom (it's a bit of work to pull those suckers off).

 

I've found that simply removing the wire from the electric assist on the choke made a world of difference. The truck still has a wierd warm-up. I set the choke and let it run until the temp gauge hits the "C" it tries to die. I usually hop in it let it run for a minute then drive. It hesitates a lot less now. I've also upgraded the coil to an MSD aftermarket. The one thing I have noticed is my gas mileage dropped by a mile a gallon after the choke wire was removed.

-Kerry