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Old June 14th, 2011, 08:33 PM   #1
78ford460
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Default 1978 ford f-150

I have a 1978 Ford F-150 with a 400. Motor runs good until about 2000 rpm and then cuts out really bad and will not rev up any further. I have ran a compression test, and have tried 2 different carburetors. Has new spark plugs and wires. has a new set of aussie heads, and new valve train. Any suggestions.
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Old June 14th, 2011, 08:52 PM   #2
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coil/ cap and rotor?
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Old June 14th, 2011, 08:59 PM   #3
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fuel filter? is it plugged? fuel pickup plugged? hows the air filter does it look like a swap?
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Old June 14th, 2011, 09:12 PM   #4
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Sounds like a fuel delivery issue as Masterbeatty stated. Check the fuel pump as well, is it mechanical or electric? Pickup a cheap low pressure gauge and check the fuel pressure, if that comes back good then check the flow. Flow should be about 7-10 gph for a mostly stock 400, heavily modded could require MUCH more. How to check flow http://www.73-87.com/7387garage/drivetrain/fuelpump.htm.

Another thing that comes to mind since you swapped heads and a cam. What CFM rating are the carbs you've tried? You might be running out of Cfm at the carb with the improved heads. What are the specs on the heads? Is the RPM verified with a Tach or just an educated guess?
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Old June 14th, 2011, 09:19 PM   #5
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It has a clear see threw fuel filter, and is clean. It uses a mechanical fuel pump, and have also replaced that. I have tried a 600 holley designed for the ford 400 and is rebuilt, and have tried a 750 edelbrock. The air filter is new and clean. The motor ran fine for about two months with the edelbrock, then one day out of the blue it started cutting out. At first it would clear up and run fine then after awhile it wouldnt clear up at all. On a computer dyno the motor has around 450 horse and runs on 110 octane fuel. And yes the rpm is verified with a tach.
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Old June 14th, 2011, 09:29 PM   #6
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The 750 should be a good fit for that engine. I would see if you can get the pump warrantied and try a new one without paying for it, just because something is new doesn't mean its working properly.

Maybe coil or ignition module, the duraspark boxes are a fairly common replacement item. Unless you have MSD, in which case you should check battery voltage when everything is running to verify a constant 10 volts to the control box, they don't like to work on much less than that.
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Old June 14th, 2011, 11:45 PM   #7
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Quote:
Originally Posted by bigblockford79 View Post
I would see if you can get the pump warrantied and try a new one without paying for it, just because something is new doesn't mean its working properly.
I've gotten fitted radiator hoses for older vehicles that have cracked and or bulged within weeks of being installed. For a 400M engine, there's no telling how long that pump has been sitting on a shelf.
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Old June 15th, 2011, 06:36 PM   #8
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The Ignition module was the problem.
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Old June 15th, 2011, 09:50 PM   #9
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The Ignition module was the problem.
Sweet!!!!!!!
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