3406b laggy power

Hello,
We have an 89 9300 with a 3406b. The truck has really laggy power in the low end. Meaning it takes a long time to build boost, but when it does it has good power. It builds about 17 psi of boost under a load. Im not sure how normal that is. I have driven another 9300 with same engine and the truck felt like it had way more power at all RPMs.

Sometimes though randomly when I upshift then accelerate you can hear and feel the raw power and the truck takes right off with a "cloud" of black haze. It almost feels like it should be that way all the time. Can anyone explain this? I'm not doing anything differently that I know of when shifting. It doesnt happen very often.

Thank you

 

I changed that Diaphragm in the AFC. did not fix the problem. After researching about the timing advance I think you are right. Truck is in a shop I was told I was going to get a guy that knows 3406b in and out but I have a 20 something year old kid working on it and seems to think it's the air to air or turbo. I mention the timing advance and he is clueless. Trying to find an older mechanic still.

 

I made a mistake on my turbo boost. It's a new to us truck, I was looking at the manifold pressure gauge. There is no boost gauge. Found a kenworth dealer that has some old time mechanics that think they can diagnose it. seemed to be pretty knowledgable on the phone. Will post what they come up with. Thanks for all the help!

 

Oh. I was under the impression there was slight differences.