I'm scratching my head here. I've got an '85 F250 with a 6.9. I use this to pull a horse trailer and my horses. It has been doing a really good job and I've never wanted more. Nothing noteworthy has happened that I'm aware of, but today when I went to pull the horse trailer, it's as if there was no ***** behind it. When I gave it gas, it just didn't respond. I gradually could get my speed up, but there was just not the same acceleration as before.

I noticed something new that I've never seen before. When I really gave it gas to try and get it to move, black smoke started coming out the exhaust. When I let up on the accelerator, it went away. It's never done that before. (I've seen big rigs do this, so I'm not sure if it's normal or not)

I checked all the wheels on the trailer to see if maybe one was locked up and thus causing more drag, all is good there. I also checked my air filter to see if there was any blockage that was keeping air from getting to the engine, and I found nothing there as well. All engine fluids are fine, and there are no injector leaks.

Seems I've checked all I can think to check. Anyone have any ideas? It's been a few thousand miles since I replaced my fuel filter. I also replaced my throttle cable a few months back (just in case that might have caused something). Any comments or help is appreciated. I gotta haul horses all week and would appreciate getting some power back.

 

Suggest you do the fuel filter replacement first.........always... pre fill the filter with diesel fuel additive before installation....... saves on the starter. ( Power service, Hayes diesel treat, Stanadyne pro, etc)

Then do the below test to ensure fuel is being pumped........

Do a pressure and flow test of the fuel pump at the Schrader valve on the filter header (FSS- fuel shutoff solenoid disconnected on IP). Remove the tire valve core and hook a hose and pressure guage on it should see 4-6 psi when starter cranking engine over. Then do a fuel quantity test same place, should see 1/3 pint in 10 seconds of starter engine cranking, route fuel to a suitable container with a hose. When all finished hook up the FSS wire .

If there is a problem with the lift pump and you are changing it, ensure the new pump comes with instructions as to correct installation procedure if it is the newer model pump with the almost straight arm.

 

Thanks for the input! Just out of curiosity, could you just put a normal tire pressure guage on the schrader valve on the filter to check for pressure?

Also ... where is the FSS wire at? Is IP the Injector Pump? Sounds like a pretty simple test.

Another thought I had was that my water separater has never been emptied. It's an aftermarket one and I've never been able to figure it out. Any chance that is full of water and fouling things up?

 

Yes the IP is the injection pump. The test is really easy...however i've never heard of anybody trying to use a tire pressure gauge to check pressure. I have a hose i screw onto the schrader valve and i can start cranking....all i do is remove the gauge to do the second half of the test.

 

You can use a tire pressure gauge to check the fuel pressure at the schrader valve, but it usually will ruin it if it is for dry tires. You can get a tire pressure gauge for liquid filled tires (ballast in farm tractors) that will work better.
How long since the air filter was changed out? Is the snorkel from the air cleaaner to the grill still there? If so check to see if it is blocked or kinked off. Heavy black smoke tells me you are getting more fuel than air.