7.3 just off highway knock - Ford Powerstroke Diesel Forum
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Old 02-14-2007, 06:14 AM
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7.3 just off highway knock

I am getting a repetitive knock just after leaving highway speed usually after a long run(100-200mi.) It comes and goes and is as consistant as weather in missouri but when it arrives it is disconcerting. Generally occurs with increased engine vibration.
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Old 02-14-2007, 11:58 PM
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does it kinda sound... like this?

If so, that is what is called "cackle" and is caused by aeration of the fuel, and the one injector that typically gets affected, is the #8 injector, which is the one that "knocks" really loudly in the above .wav

There are at least a couple reasons for that knock to occur (if in fact it is the same knock)

one, the quick connect fuel line is sucking air at the fuel pump inlet, two, your fuel level is very low and air is getting in that way.

three, your sock filter in the fuel tank is partially clogged, and is exacerbating #1, as most if not all PSDs with the frame mounted fuel pump, seem to have some degree of cackle. (The audio is an extreme example)

Let us know!

Last edited by ~CrazyDiesel~; 02-15-2007 at 12:03 AM.
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Old 02-15-2007, 06:46 PM
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crazy;

Yes that is the type noise, I just replaced the fuel separator drain valve as the ULSD we are getting now started it leaking at the o-rings and I have not heard it since, but it has been cold as bejesus and I have added PSvc. The other item you mentioned was the sock filter, I pull a gooseneck once in awhile but have no power problems, I also replace the separator element every fourth Oil change regardless and have found almost no contaminants. Truck is a '99 with 260k on it and still have a lot of OE components with (knock on my wooden head) little to no grief.
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Old 02-15-2007, 08:41 PM
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Basically, without changing the fittings on the Fuel Pump, it's something you're going to have to put up with, if it continues to come back at a later date.

If you're not wanting to change the fittings, (again if it comes back, which it likely will not do now that you found a leak) there are a couple of more options.

1. and this is the easiest, and the method I chose when i experienced the same thing

Fill your fuel tank with some BioDiesel, if available, B20 will swell the various o-rings in the system slightly( therby helping to seal up any places where air is being sucked), it will also totally clean your fuel system, from the tank to the injector tips, lubricate your injectors better than anything else, and also, as soon as that biodiesel hits the injectors after you fill up, the truck will change, run smoother, quieter, and overall better.

All those good things do come at a price, specifically your fuel filter..... After running that tank of biodiesel, your fuel filter will likely be nastier than you've ever seen it, it's best to check it after you fill up with normal diesel after that tank of bio.

You may find that, the benefits of biodiesel outweigh the extra few cents per gallon you may pay for it, however...

#2.. If you don't mind putting up with a holy mess if you ever have to replace the fuel pump, you can apply some silicone sealant(resistant to fuels of course) onto that fitting on the inlet side of the fuel pump to seal it up.

Last edited by ~CrazyDiesel~; 02-15-2007 at 08:55 PM.
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