1970 Ford F100 Stalls At Highway Speed

Asked by MyBoyBlue Jan 09, 2017 at 09:18 PM about the 1970 Ford F-100

Question type: Maintenance & Repair

I bought a 1970 F100 this week. After two days of
running perfectly on two long trips - morning of day
three started fine and at highway speed of 65
started to lose power as if running out of gas.
Engage clutch and down shift and fine but it would
occur again after a min. By pulling over and letting
truck idle it would go away but then occur again at
full speed. The problem persisted so I eventually
towed balance of trip home. Seems to start fine
every time but struggles to get fuel at highway
speed if given enough time. Thoughts?

F_O_R answered 7 years ago

I would change the fuel filter and maybe the fuel pump too if the filter change does not fix it.

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MyBoyBlue answered 7 years ago

Initially I thought filter/pump too but Ford dealer confirmed filter and pump are new. They mentioned common issue is a faulty Engine Control Module, which prior owner replaced points w. Truck has a Montgomery Ward ECM, which is 30+ yrs old. I went to NAPA but he couldn't discern proper replacement part - he thought it was an Echlin TP85. He was wrong - truck won't even turn over. I'm not sure how to find correct replacement of ECM or whether I should go back to OEM points and condenser. Another friend who knows old Ford trucks said he thought gas tank was creating vacuum and not allowing fuel to carb... I could test by driving on highway at 65 MPH for a while without gas lid but not sure how safe that is. Thoughts on finding correct ECM replacement or vacuum issue in fuel tanks?

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