No Guts at 50 MPH

courtesy of Bob, The Auto Answer Man

I have a 1974 ford F250 truck & lately it runs like new when it is cold but when it warms up it runs pretty good up to 50 mph then seems to flatten out & very slowly gain speed from there. As it gets hotter it gets worse. It does not overheat.

The plugs are a light brown, the points are not pitted and are gapped to tolerance, the condenser is new, the plug wires are new, the gas filter is new, the gas mileage is so bad it doesn't get a chance to go bad or get water in it as i keep it topped off. I also use a gas tank additive about once every 2 months to keep the carburetor tank & lines & fuel pump clean. The carburetor is a rebuilt, 3 years old. I also have an electric fuel pump that is on a switch & I can kick it in or out & it makes no difference. The coil is not very old. Is there any resistance wire or any thing connected to the coil that might make it act like that? What do you think is the problem? Any help is appreciated.

Sorry to hear about your problems! Yours seems to be the simplest question I received all week, but will take some time to explain it.

You mentioned that your truck is a '74. I bet that you have the original catalytic converter under there. What it sounds like to me is that it is plugged. The reason that it runs like a top when cold is that the air passageways in the converter actually expand with heat (just like everything else) and when they are partially plugged to start with, it just chokes off the exhaust and the car barely runs. The only way to really prove this, is to remove it, insert a piece of pipe to take its place and run the car till it warms up. I bet your problems will be solved. About 90% of all warm running problems are due to the cat being plugged. Okay, now that we have determined that it is the cat, what do we do about it?

  1. You can go to your dealer and have an OEM one installed for around $300-$400.

  2. Go to a muffler shop and have a aftermarket one installed for around $150-$200

  3. Try to clean it out. The only way that I know of is just getting it out on the highway and running on some hot gas for a while, but it may be too far gone for you (but heck, it's worth a try right). There are some chemicals out there that say they clean up cats, but most of them are just snake oil (they do nothing, but I have not tested them all). Try going to Pep Boys or Parts USA and check out what they have. These chemicals usually only cost a few dollars and it might be a lot cheaper than the other two options.

To all the other readers that have sent in requests, I will get to you. If not through the newsletter, personally. I answer all questions as best as I can. Just be patient. I kinda do a triage to the letters (you know like they did on the TV show M.A.S.H.) pick the quickest and the worst first and the ones that can wait, can wait. Since Gene's was an easy, I thought that I would get it out of the way. There was another reader (sorry, I forgot your name) That has a Ford Taurus with a 3.8, these are known to have oil problems. check the rear valve cover or the head gasket for a small oil leak that is dripping on the exhaust. Also, have the timing belt checked. I will get back to you, it's just that it's not so urgent (your car still runs).
Good Luck!
Drive Safely!
Bob, The Auto Answer Man

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