I have a 2004 150 with 165,000 miles I sometimes pull a 5 by 8 trailer. when pulling trailer in overdrive and excelorating the engone will cough several times. I took it to a mechanic and he told me that there was nothing he could do that I needed a new engine. I can pull trailer out of overdrive with no problem. don't undrstand why I need new engine

 

U probably have a spark miss and a new set of spark plugs will suffice. Have the codes read to see if it is coding a misfire of a specific cylinder. Also look closely at vacuum hoses and the top of the motor for vacuum leaks/intake manifold leaks. It may possibly be a water leak into the cylinder from an intake or cylinder head gasket. A bore scope exam can help here. U should tow/haul with overdrive off. U add wear and heat to the powertrain otherwise, possibly creating pre-ignition or detonation depending on the fuel. These can vary in intensity/ very noticible/almost non-existant with a miss. I would add a tank of higher octane fuel when tow/haul is needed to help. Run a can of Techron thru it to decarbon the head. The motor has a lot of torque but can be overloaded depending on the circumstances. If the situation worsens possibly a combustion PSI test for bad valve will help. I would get a second opinions and look at the mileage on the motor. If you are approaching 200,000 miles it may be best to crate it. By then you are looking for trans problems probably also. With the history of the 2004's past, possibly trade for a newest generation model is wisest move!

 

You experience this problem only when having a load on the truck and your mechanic said right away that you needed a new engine and nothing he could do? WOW its time for a new mechanic to work on your truck.

I agree with Papa in that it is most likely a miss. At a 165k you may just be coming up on the point of needing to replace the plugs again they don't usually last as long the second time around just from the engine being older and having more wear on it. It also could be the COP and not a plug at all.

 

I wouldn't rule out fuel system either. With the miles you have on the truck the fuel pump could be getting weak from a volume perspective and would cause a misfire as well; or worse yet detonation. The platinum plugs do not withstand detonation well at all. The electrode usually breaks off and ruins the cylinder wall. If that happens you'll be able to tell by the oil smoke. When towing, always keep the engine RPM above 1600 RPM so you don't lug the engine down. That creates heat and a lean condition that is not good for the engine and transmission. It's also below the efficient operating range for the engine under load. That's it's wiser to tow out of OD.