Boost Control Problems

[Ezzie]

Looking for some help to diagnose a problem with my 1995 6.5 TD pickup. I recently completed a 5000km. haul of a 7000GVW cargo trailer. For the first half of the trip, all was fine, max. boost of about 7.5 lbs., EGT's in the 900-1100 degree range. On the return trip, I noticed the truck down on power and only maxing at about 2.5psi. The "check engine" light then started going on and the boost dropped to zero until I lifted off the throttle. The light would then go out and boost would return to a max. of 2.5 psi. My EGT's are also now higher and can creep over 1200 if I don't back off. I checked the wastegate actuator and it moves freely when the engine is off. All the vacuum lines seem intact with no leaks and the vacuum pump is relatively new. I also now get a "Service Throttle Soon" light coming on when I turn on the key at startup.

I don't notice anything unusual with the smoke levels or anything. Is this a bad wastegate control solenoid symptom?

[john8662]

Sounds like a loose connection.

Check out the MAP sensor connector on the top of the upper intake manifold. It's the sensor that is black. If yours is like mine, it's clip is broken and may have wiggled loose, most of these are broken.

Also check the connection to the wastegate solenoid on the driver's side rear head (follow vacuum lines).

When turning the key to run before starting the engine, all check lights are supposed to illuminate.

So, does your service throttle soon light turn on after starting the engine?

If so, you're likely going to need a new APP.

But, of course, check what codes you've got stored in memory on your truck.