87 ford f-150 with 4.9 engine and the pickup keep fouling plugs and runing badly. I was wounding if that if the valves on the head might be bad and if I would need to have the head rebuilt?

Answer 1

Assuming that it runs crappy even after putting new plugs in (before they get fouled again I mean), either your mixture is too rich or you have a weak spark causing the intake charge to not burn completely and fouling your plugs. Since your engine is fuel-injected it's rather unlikely that your mixture is so rich that the plugs are being fouled up. I'd check the following in this order, which should be from cheap and easy to time-consuming and expensive:

1. Plugs. Determine exactly what they're fouled with...if you can't tell, bring them to someone as it makes a huge difference. If they're oil-fouled, then your fouling problem may be unrelated to your performance problem entirely. If they're carbon-fouled, check your points, ignition coil and wires. Check that your plugs are in the proper heat range for your engine. Try ones in a higher heat range, even if you have the "right" ones already.

If they're carbon-fouled:

2. Check the intake from the airbox to the throttle body. Make sure the filter is clean and there's no obstructions.

3. Check your sensors...don't know off the top of my head which ones the 4.9 has, but it should most definitely have an oxygen sensor on the exhaust manifold and some kind of intake sensor (either a MAP or MAF sensor and possibly an IAT sensor). Info on how to remove and test them is readily available, so you can Google it :) I can't see this possibly solving your problem completely, but a bad sensor may be making a minor problem worse and more difficult to diagnose.

4. Do a compression test. Again, plenty of info elsewhere for the tools and procedure. If any of the cylinders tests lower than spec, your engine will most likely need to be rebuilt entirely, although it could be a valvetrain problem.

If they're oil-fouled:

2. Check that your PCV valve isn't clogged and that it's operating properly. A clogged or stuck valve will cause pressure to build up in the crankcase, forcing oil past your rings and/or valve guides.

If you've checked all of the above then you've pretty much eliminated all the problems with easy fixes. It's probably either bad valve stem guides or bad piston rings. At this point it would be cheaper to just pick up a new motor (or head if it turns out to be the guides) from a yard than get yours rebuilt...the motors are plentiful and cheap. My friend bought an '85 F-150 with the same engine for $200. He's had it for three or four years now and it's still going strong.

Good luck!