Turbo not building boost in high gear

[Bai]

For the past few weeks when the truck shifts into overdrive I
loose boost. When it drops back into 3rd it makes good boost. I
cleaned the airfilter and changed oil and it didn't help. There are no
error codes in the computer and no check engine light. Someone
suggested maybe it is the map sensor. Any suggestions.

[mschn99]

When was the last time u replaced ur fuel filter?

[Bai]

6000 miles ago. The truck has 102,450 miles on it.

[strokermann]

well inn overdrive at 75 i am only making about 4 psi. and when it drops down to 3rd it builds right back up. when your in overdrive and you push in teh pedal does it build boost. sounds pretty normal to me. slowly push teh pedal in when you in overdrive so you don't make it kick down a gear and watch your gauge see if it builds boost. and let us know what it does. i do that to mine and i can build some pretty good numbers on teh gauge. just don't mash teh pedal or it will kick into teh 3rd.just my 2 cents

[Bai]

when its in high gear and I slowly give it fuel it starts falling on its face when i'm pulling a load. When I'm empty I don't notice it quite so much. I've had the truck for a few years and know it well. Something is definitely not right.

[strokermann]

well when your in overdrive you engine is at less rpm and not needing the boost. when it shifts to 3rd teh engine works harder so your boost goes up. thats normal for it to fall on its face when it overdrive whoile pulling a load. trying starting off in 4th gear with a manual tranny and see how far you get.

[Bai]

I found part or maybe all of the problem today. The Y pipe that the exhaust manifolds attach to is leaking on one side. So i'm losing some of the power
there..

[lilredpowerstroke]

I'll betcha its leakin on the other side too!!!!!!!!

[straycat]

Yup,I agree with lilred, you might be running into surge as well.

Gord.