I have 76 F-100 (360 2 BBL). On the passenger side of the intake manifold between the carb and the valve cover is a small device with two electrical leads at the top and a vacuum line in that runs from the front of the manifold and a vacuum line that runs to the front bottom of the carb. It bolts to the top center bolt of the valve cover. What is this and is it needed and how can you tell if it's bad. My worthless Haynes manual says nothing of it. Please help, thanks!

 

It's hard to pin-point what you have exactly...but it sure sounds like you have an electrically controlled vacuum switch there. Trying to find out precisely what it's for will be hard without a vacuum and wiring diagram. As far as whether or not it's needed....I can tell you that Ford wouldn't have spent the extra money if it weren't. Question is whether the rest of the system itr goes to has all ready been removed. You might try to locate a similar truck in your area to compare notes. Good luck to you.

Stock Man
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Doop:

Like Stockman said, from what you gave us, it’s hard to tell exactly what you have.

Does the unit extend into the intake or is it merely attached to the engine by the center valve cover bolt?

The reason why I ask is that I have an ’84 Bronco with a 302. It originally came with a 2-bbl setup but I have converted it to a 4-bbl Edelbrock intake and Autolite carb. The original 2-bbl intake had a device on the passenger side between the carb and the valve cover. It actually attached to the intake and extended into it. It had two vacuum lines connected to it.

Beginning in the early ‘70s most V8 intakes included an exhaust gas passage under the intake. Its connected from about mid-point of both banks of the engine, i.e. the heads. It’s function was to circulate hot exhaust gasses under the intake, therefore warming it up faster upon startup. If the intake warmed-up faster then the fuel would atomize sooner and emissions would be reduced. The choke would also warm-up faster and open-up sooner after a cold start.

The problem is that you want the intake and carb to warm-up sooner but after the engine has warmed up you don’t want to overheat the intake. This would cause a reduction in power and torque. On my Bronco there is a vacuum-operated valve in this exhaust passageway. Once the engine warms up, vacuum is applied to valve and it closes, thus preventing exhaust gasses from circulating under the intake. This valve is rare in 302s but is very common in 351s.

If this is what you have then you want to make sure it is functioning properly. To test it you need to remove it and use a hand-operated vacuum pump to test it. If it fails then your preference is to have it frozen in the closed position. This will prevent exhaust gasses from circulating under your intake. This means it will take your truck slightly longer to warm-up, but it won’t affect your normal engine operation.

If this isn’t what you have, the unit may have something to do with the choke since this is about the time that most auto manufacturers began using the exhaust crossover in the intake manifold to heat the choke. The wires may go to a thermoelectric coil in the unit which further shortens the time before the choke opens fully.

Good Luck

Bruce