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Hi folks, I just purchased a 1976 Bronco and need some help. The truck runs well until I run it for a while in 3rd gear. The Bronco starts to cut out - like a fuel filter issue - but I just changed the fuel filter and the issue is still happening. It’s episodic - sometimes it runs fine, sometimes it starts to cut out in 3rd gear. Any suggestions?
If the Bronco still has the original style of mechanical fuel pump you need to look at that. I've had several of these pumps in a variety of cars and trucks fail and give similar issues.
You'll need to put a T in the fuel line going to the carb and add a pressure gauge, typically about 4.5 to 6.5 psi at idle. If it's lower than 4 you have fuel starvation, higher than 7.0 and you can overfill and flood it out. Either way you would need to replace the pump but If it's high you can just add a pressure regulator.
They act up more with warmer temperatures. Why we used to have "Vapor Lock", when the volume of gas being pumped to the carb is not enough to keep it cool so it boils off in the line, increases pressure so the pump cant overcome and will not provide liquid to the float bowl.
Agree with the fuel pump being a possible culprit. But don't forget to look for other filters that any number of PO's might have added.
My '79 had three filters! Well, five if you include the stock ones at the carburetor and the in-tank sock filter.
And speaking of the sock, if it's original it might just be self-destructing as we speak.
Much of the fuel systems don't like modern gasoline, and they absolutely HATE sitting around for long periods of time after they've been used for a bit. A brand new pump might be fine for five years on the shelf in a box, but put some fuel and heat through it and then let it sit for a couple of months, and that's a recipe for a dead pump.
Especially modern replacements.
So if you end up replacing any parts (ANY parts) on your Bronco in the future, don't get rid of the old ones until the new ones have proven themselves worthy. Much of the new stuff is crapola.
Great looking Bronco by the way. What all has been done to it? Maybe it's an ignition coil or ignition module cutting out with heat, or if the stock Dura Spark setup has been changed to something else, maybe it's acting up.
One thing you can check if it's Dura Spark is the distributor trigger. Pull the connector apart and with an ohm-meter, check between the Orange and Purple wires (or whatever color they are other than Black) and you want to see a reading well within the 400 to 800 ohm range. If it's anywhere near the limits, this could be your issue.
X2 on the mechanical fuel pump, but usually they either works or don't. X3 on ck ALL fuel filters and or has the tank ever been dropped and cleaned out? And or the sending unit been pulled and check the the pick up tube end filter sock is still there?
X4 Possibility it is a heating up issue, causing vapor lock? Fuel lines by the headers and or elec issue from the distributor? Still points or Durspark II conversion?
Any recent work done on any of the fuel/elec systems? Have you checked for a vacuum leak around the intake? Nice Bronco BTW.
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