1999 f-250 7.3 power stroke . With straight single 3inch pipe. Power pup set at the 40 hp for towing k&n filter. The boost at a cruising speed drops to 0 on the gage and you can hear the wast gate open wile driving at a cruising speed. The truck has 165k miles on it. And it didn't start doing this until it got cold out. It won't hold its boost at any speed below 55mph.

The most common reason is that all of the compressed charge air is not getting to the engine. It's leaking somewhere, causing a fuel-rich condition. Check the hose between the intercooler and the intake manifold. Also, check the hose between the turbo and the intercooler.

The wastegate's normal job is to keep boost pressure from becoming excessive. However, the following can happen:

. Valve can stick open--there may be a boost control solenoid.

. Seal for the valve can crack.

. Spring can break.

. Turbo can fail. It may not be spinning. Turbo failure is much greater on trucks that don't use full-synthetic diesel HDEO.

. Wastegate is not receiving the correct pulsed pressure from the computer.

Personally, I would use the standard Ford air filter. I would not trust my F-250's turbo to a K&N Filter. Air filter problems are prime causes of turbo failure. It's imperative on diesels to closely monitor air and fuel filters.

Thanks. Yesterday the temp outside was 45* . And the wast gate didn't open up near as much as when it was 20* outside. And on the k&n filter, I popped the lid of the box off and drove it for a bit. I had all kinds of power. Is the box and duct chocking off the air. The filter has been in the truck for 9 months. Cleaned 2 times.

Sounds like you found the cause of the problem. I would install Ford's original air induction system and filter (change every 10,000 miles). Check your turbo--turbine blades may be bent. Air restrictions can take out a turbo in a heartbeat.

Other tips:

. Change coolant (32 qts.) every two years, using a 50/50 mixture of approved antifreeze (Ford Premium Green) and distilled water. Add 10 oz. of Supplemental Coolant Additive (FW-16) every 15,000 miles. This will help prevent cavitation problems. Disconnect batteries and remove 2 hex head engine drain plugs. One is above starter and one is on driver's side. Rear two cylinders are prone to cavitation.

. Change ATF and filter every 30,000 miles with Mercon ATF. On 1999 F-250 trucks, it's easy to drain the converter. I prefer to use Mobil 1 Full Synthetic Multi-Vehicle ATF or either Amsoil's Torque Drive or Universal Synthetic ATF.
Change synthetics every 60,000 miles. With the standard 26 plate ATX cooler, total fill is 17.7 qts; initial fill is 6.5 qts. Pan gasket is reuseable and should be tightened to 11 ft.-lbs.

. Change brake fluid every two years--easy job. Valvoline SynPower Brake Fluid is Ford HBH approved and what I use on PSDs. Remove left-rear off-the-road protection bracket to gain access to the bleeder screw.

. Change fuel filter every 15,000 miles.

. Power Steering Unit--Change and refill with Mobil 1 Synthetic Multi-Vehicle ATF.