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77 F150 - 400 Intermittent stall - Troubleshooting Suggestions?

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77 F150 - 400 Intermittent stall - Troubleshooting Suggestions?

Old 08-03-2018, 12:17 PM
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Default 77 F150 - 400 Intermittent stall - Troubleshooting Suggestions?

Looking for suggestions on troubleshooting options. Have a 77 F-150 with a 400 that recently starting having intermittent stalling problems at lower speeds. This happens typically at a stop sign or when backing in the driveway. Here is what I know:
- Cold starts great
- Idles fine when in park
- Accelerates with no hesitation
- Has been running great since intake manifold gasket was replaced ~6 months ago
- Scenario of what happened today: Started truck up in the driveway, started great and it idled fine for about 5 minutes. Left driveway and it ran great for .5 mile but started to hesitant / sputter as I came to a stop sign. It did not stall at the intersection and ran fine until back to my driveway. As I put it in reverse it started to sputter again and did so until it stalled when I came to a stop in the driveway. Tried to start it again, it took 10 seconds of cranking and some gas for it to start again. Idled fine while in park after it started.

Vehicle details
Ford 400 with an edelbrock 1406 carb and edelbrock intake.

Any suggestions would be appreciated!
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Old 08-10-2018, 08:44 AM
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This REALLY sounds like a vacuum leak. I would recommend getting a vacuum gauge.
https://www.harborfreight.com/fuel-p...ter-62637.html

Put the vacuum gauge on the manifold vacuum port on the carb. I have added a picture. I would watch the gauge and see as it warms up does the vacuum drop and then die. If it does, Id start to look for a vacuum leak. Being that its a 77, there shouldn't be too many lines. If that isnt it then I would adjust the idle mixture screws.


Adjusting the idle adjustment screw:
If the truck is idling nicely, set the idle adjustment screws to get the highest manifold vacuum on the gauge. This should normally be done after the engine is warmed. This will give you the best A/F ratio. Newer cars do this by adjusting the fuel based on the O2 sensor feedback. You are using the vacuum gauge.




The other thing it could be is the Ignition coil. When its cold, everything is good, and then heats up and the resistance changes and you run rough. Good news is that the coil starts to do this and then dies. I would replace it anyways as its cheap.

Hope this helps.
​​​​​​​Dave
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