Topic: "66 289 misfire problem

[Ponygirl66]

Hello! I am new to the forum and looking for some help with a a problem with my 66 289 Automatic Coupe. The car runs fine below 65 mph. SOMETIMES when I get it to 65 mph the engine begins to jerk a bit like it is not getting enough fuel. I had it tuned up, new coil, put in a fuel filter with no success. Since the problem is intermittent it can't be identified. There was oil on a spark plug when it was tuned. Mechanic talks of needing a new engine. Car runs beautiful except on these occasional spurts.
Any ideas on what it could be?

[jethat]

I'd replace the fuel pump. Cheap and easy to install on that engine.

[Soaring]

First, welcome to the site. Until you can get it to an honest mechanic, I would just keep it under 65.  That annoying miss could be a number of things to include old gas that needs replacing to water in the gas to any number of electrical problems.  Take it to  a reputable mechanic.  Those are usually found at the Ford dealership. 

[Ponygirl66]

Will a Ford Dealership look at my car? I wasn't sure they even dealt with the the old Mustangs. Truth be told I am having a hard time finding a good mechanic. Most don't deal with carburators anymore, or can't function without a chip telling them where to find the problem!
My last mechanic may have something to do with my current problem..he replaced the fuel lines a few years ago and did not put a fuel filter on. I did not discover it until we had a falling out and took it to a new place to have it tuned up last week...perhaps the lines are filled with years of unfiltered gas junk?

[Soaring]

If you can do some work on your own car, you might want to take the fuel line off from the sending unit under the tank, and also take it off at the inlet to the fuel pump and add some air pressure to test your theory.  If you don't have an air tank, a  good blast from your lungs will be sufficient.     Just remember to blow out and not suck in, or else get a mouthful of gas.  Not very tasty.     If that is clear, then take the line off from the outlet of the pump and the carb and blow toward the carb.  Now, if that is clear, you have to know that you have a filter in the gas tank of these old dinosaurs.  It's called a sock.  You must first drain all the gas out of the tank and take the sending unit out.  My 65 has a plug on the bottom corner of the gas tank.  Hopefully yours does too. The sock is attached to the sending unit.  The tank may have rust particles in it, and the sock is clogged, not allowing enough gas to get to the pump.  If that is the case, I would replace the entire sending unit with the new sock.  And, if that is the case, you may want to consider replacing the gas tank in the near future.  You are right about some mechanics won't touch a carbureted car, but some will.  I just had a local mechanic who I know well to work on my 1981 F-150 with a 351 Windsor with a Motorcraft 2100 carburetor.  My problem was vacuum line problems though. 
You are just going to have to realize that in order to drive these dinosaurs, you are going to have to do most of the work yourself.  I have been working on my 65 for almost 20 years now, and still learning. 

[jethat]

Find a mechanic who is 45+ they know carburators. If you can work on it at all your self I would start off replaceing the fuel pump, $25 part and its got 2 fuel lines attached to it and its held on with 2 bolts. I can put one on in a half an hout in my drive way.

[Soaring]

I don't see where it might be a fuel pump problem if the car runs fine from 0-65.  That pump is working just fine.  After 65 causes the engine to require a stronger flow of gas, pointing in the direction of a lack of fuel pressure, not caused by the pump, but by a possible restriction in the line.  A fuel pump in a 66 Mustang either works or it doesn't. 

[jethat]

My experiance has been when old mechnical pump get weak they are unable to maintain flow. What she is describing could very well be a weak pump. Its a cheap part no mater. I would eliminate it.

[Soaring]

The only way a fuel pump loses pressure is if the diaphragm gets a hole in it.  But, you are right about the price of it and one more thing to eliminate in the process of elimination of the problem.  Obviously, the engine is starving for fuel at high speeds. 

[Ponygirl66]

I will try replacing the fuel pump (I have someone who can replace it for me) and check the fuel lines as well, and let you know what happens. Thanks so much for your help! It's nice to talk to people who know about Mustangs. I am learning a lot just from reading the posts.

[cybercanvas]

Hello,
We have a similar problem with our '66 Mustang, but the misfire happens at lower rpm's. While accelerating from first to second or second to third, the car lunges or jerks forward. We recently had a new carburetor installed and the car ran fine for about a week. We have read it could be a fuel pump, etc., however, what would be our first line of attack? Any help would be greatly appreciated!