1973 f-100 dies when hot.
 

Hey all, this is my first post since i got my truck 4 months ago so bear with me. I purchased a 1973 F-100 2wd with a 390 and have absolutely loved it since i got it. I had been driving it around town for a month or so when i decided to take it on a camping trip. The truck did awesome until the very end of the trip, all of a sudden i lost power almost like i was out of gas. This was the farthest i had ever driven this truck and i was traveling at 55 most of the way. I pulled to the side and the truck just sat there and idled. I pumped the gas peddle and it was as if nothing was wrong. when i started off again as soon as i got over 45 it did the same thing. Since then every time i run the truck at hi speed(55+) for any length of time it will do this, yet i can drive it at 45 for an hour with nothing happening. any ideas on what is happening and how i can fix it would be great.

Howdy and welcome to FTE.

Does the engine try and stall out like it's out of gas, or is it more like it's getting too much fuel and bogging down? Are the fuel lines and fuel filter in good shape?

Hopefully some others will chime in too...

Sounds like a clogged fuel filter, dying fuel pump, or low float height.

So update since the last time i wrote. I have rebuilt the carb and replaced the filter. A friend said he used to have a close problem with an old car of his and fixed it by replacing the points and condenser so i also replaced those. Seemed to be fine but then it started to act like it was running out of fuel while i was driving it. I would rev it up and in a minuet it would seem to clear up.This went on for two days until it finally died on the road. Thinking that it was something in the carb, got the truck home opened up the carb and applied a liberal dosage of carb cleaner checked the jet and and the fuel filter and tried again. Started easier and quicker than ever before and ran smooth for about two miles then did the same thing. The filter was a wix filter at the carb because the previous owner removed the inline filter that came with the truck so i decided to ad a performance inline glass filter after the fuel pump. This morning i tried to take the truck to work and it did not make, it did the same thing. It starts losing power and starts backfiring as i pump it to try to get it going then dies. Had a mechanic friend come and try to help me get it going. First turned it over to try to get it started it acts like it wants to start but won't. He said that the carb had plenty of fuel and when he squeezed the fuel line he could feel the pump working and when i pumped hear the fuel squirt into the carb, so that kind of ruled out a fuel problem. He pulled off a spark plug wire and tested the spark as i turned it over he said he would get spark when the engine acted like it was going to start and then he said he would loose spark all of a sudden. He then checked the timing with a timing light and said it was right on. So I ran down to the parts store and got a new ignition coil and we plugged it in. Nothing. He is kind of out of ideas. Please help, I am now going to ice my wrists from all this typing.

You need 3 elements to get a motor going...air, fuel, and spark. You obviously have the first two covered so something electrically must be wrong.

Id start from the battery and work all the way to the plug wires looking for a short, frayed wires, bad connections, proper voltages, etc and if something looks worn replace it to eliminate variables.

Keep communicating man the people here will help you solve for problem for sure:-X22

Connect a test light from the negative terminal of the coil to clean, unpainted metal on the engine (ground). The negative terminal is the side with the wire coming from the distributor. Crank the engine over with the key, and the light should BLINK. Report your results.

Also, I strongly recommend against cleaning a carburetor the way you did. Opening it up and spraying it down only serves to move stuff around, only to cause other problems later on. If you're going to clean a carburetor, you need to completely tear it down, soak all the metal parts in a chemical bath, spray down, blow out with air, then re-assemble with a rebuild kit.

Alright I know it has been a while but it has been winter and I haven't done much to the truck until now. So I did to the best of my ability what you all suggested, checked the wires and hocked up the test light and it blinked just like you said. On top of these I have been replacing parts to eliminate problems. My brother said it my be the distributor so I bought a new one and we replaced it, the truck ran for about a day after this then died again seemingly the same problem. Called my friend and he said it might be the timing chain said that the gears used to be covered in nylon teeth so I bought a new timing chain set. That took me a while but finally got it done not too long ago and he was right gears were covered with nylon teeth and were cracked and broken off. So replaced the gears and chain and even replaced my fuel pump while I was down there. Made sure the timing was right and turned it over and it started fine than went back to the same thing that was happening before. Starts running real rough missing barely staying running then dies. The fact that occasional it will run great for like two minuets really throws me and most theories I have out the window.

The square electronic box on the fender should be checked, probably replaced.

OP's F100 is a 1973. No such thing as DuraSpark Electronic Ignition until 1974 and some vehicles didn't come with it until 1976.
The factory installed 352/360/390 timing gear had nylon teeth. You could not buy this gear at the parts counter, only came on new trucks.

Ford installed this gear because it was quieter than the aluminum timing gear sold at the parts counter.

C4AZ-9365-B .. Fuel Filter (Motorcraft FG-1A) / Myriad 1964/76 FoMoCo I-6 & V8 vehicles / Available from Ford/autoparts stores.

This corrogated paper cartridge fuel filter is located inside a metal cannister that threads onto the fuel pump.

Some people are unaware, so they install an in-line fuel filter. Meanwhile the cartridge filter is getting more clogged up every day.

When a vehicle sits for long periods of time when the fuel tank is low or partially full condensation on the inside of the tank occurs especially in parts of the country where you have a real Winter .. The fuel becomes contaminated with water and the fuel itself becomes bad as it ages .. This can eventually result in clogged filters and carb .. If the fuel tank was never dropped in your truck and thoroughly cleaned out you have not eliminated a highly potential suspect of problems that occur in vehicles that have sat for longer periods of time .. before you jump into dropping the tank I would perform these tests .. Take a gas can with known good fuel run a fuel line from the can to the tank side of fuel pump and start/test .. If the problem persists then the fuel tank may not be of immediate concern however if the problem is eliminated check fuel line backwards to the tank by disconnecting it at the tank and blow through it to determine if it has obstruction .. If it is clear or not proceed to drop the tank and thoroughly clean out the tank ..

If after doing the gas can test you found the problem wasn't eliminated then next take a vaccum gauge and hook it to the tank side of fuel pump and with the coil wire disconnected have an assistant crank the motor over as you read the readings from the gauge (post them here).. After determining the fuel pump is operating at it's rated pressure we move up the line to filters in line to the carb .. pull the line at carb and at engine side of pump and blow through the line to determine if any obstruction exists .. If none move to the carb take it off and rebuild or have someone rebuild it for you .. This is the way to eliminate any suspicions of a fuel delivery problem and insure that any problems of future fuel delivery won't occur/reoccur ..

note: on the line going back to the tank a lose hose clamp may not show an actually fuel leak but still allow air to be sucked in thus degrading fuel delivery .. Make sure all clamps are tight

Is it possible the filter (sock) on the pickup tube in the gas tank is partially clogged allowing enough fuel for the engine to run at low speeds only?

D1AZ-9A011-A .. Plastic Mesh Filter Screen 3/8" I.D. / Slips over the end of the fuel tank sending unit pickup tube / Available from Ford/autoparts stores.

Applications: 1964/79 all FoMoCo vehicles except 1964/77 F100/750's with in-cab fuel tanks & except Maverick/Comet/Pinto/Bobcat (D1FZ-9A011-A ~ 5/16" I.D.).

This sounds more like an electrical problem, than a fuel or mechanical problem.
This is only a possibility.
First, when you put the new coil on, it was bolted to the engine, not just "laying there", correct?
Next, my "guess" is maybe a bad ignition switch or, less likely, Ford uses a resistor wire in the ignition circuit. When running, the coil "sees" 6-7 volts not a full 12 volts.
This wire is part of the wiring harness. It's pink and says "resistor wire do not cut or splice" on the insulation. If this is going bad it could cause these symptoms.
If it is the resistor wire, to repair, either the harness needs to be opened up or it can be "wired around" using regular primary wire and a ballast resistor.

COLF-12250-A .. Resistor Wire-Ignition Coil (Motorcraft DY-37) / Obsolete ~ Available from autoparts stores.

61.49" long / Color coded pink / 1.30-1.40 ohms resistance / #20 gauge wire.

ALL 1960/73 FoMoCo vehicles / 1974/75 FoMoCo vehicles without DuraSpark Electronic Ignition.

In my reading of the thread with a truck which has a long history of sitting, fuel delivery must be completely eliminated and IMHO it hasn't been completely eliminated yet .. This needs to be done regardless of other issues for a whole host of reasons ..