Hi all, I have a 1989 F-350 with the fuel injected 460 (7.5), completely stock (is far as I know) with manual transmission, and approx 140K miles.
The truck has been running fine until about a week ago when my son was driving it, he was at highway speeds when the truck started losing power, he tried to give it some gas and then he says that he heard a Pffftttts sound (kinda like a small backfire) the motor then no longer had/has any power over 2K-22K RPM it just starts cutting out and bogging.

When the truck is cold or hot it idles fine, but when it's cold it will rev over 2K RPM fine until it hits the rev limiter at around 3K, but after it starts to warm up it boggs and cuts out at around 22K RPM, but still idles fine, it also appeared to be over heating because I would get boil over out of the overflow container.

OK.... I have replaced the fuel filter, checked MIL codes (KOER) first code was the TPS, so I replaced that, then I recived the code for the ECT sensor so I replaced that, no more codes execpt 111, engine still felt like it was putting off a lot of heat, and was still boiling out of the overflow so I replaced the water pump, I also not too long ago (2-3 months) replaced the thermostat, and the radiator cap. I have checked the oil and do not see any signs of water in the oil so I do look OK as far as internals and gaskets.

So I'm at the point of engine still will not rev over 2K when warm, no more signs of over heating, and no failure codes, so I'm stuck and hope somebody here has any ideas.

Thank you for your time
Greg

 

Check the exhaust for a restriction.
Could be a plugged catalytic converter or collapsed muffler internals.

Have someone rev it up and check the sound at the tailpipe. If it sounds like a jet exhaust, or you get a very fast/hot exhaust stream, you have a restriction somewhere.