Turbo boost has diminished

David Anderson · October 21, 2026, 09:24:02 AM

My turbo boost has dropped from around 15 psi to 9psi max. I used to be able to get up to 18 psi in cold weather.
I noticed this in July when I went to Wyoming. I changed my air filter in Wyoming, and that did not help. When I got home I changed my fuel filters. I have not driven the bus until yesterday.The results are still the same. I'm only getting about

9 pounds of pressure at full throttle going 65 mph. I'm having somewhat of a struggle just to get up any small hills. I had my turbo charger rebuilt by M&D Diesel in San Antonio for $1345 in 2019. It has about 50,000 miles on it now. It has worked fine up until that trip to Wyoming. I checked for turbo leaks and have found none. I can't see any exhaust leaks around my manifold either. I have no black smoke or any smoke to speak of while driving. I can make a little black smoke with a full throttle kick down taking off from a stop light.
I'm not sure what to do next. Does anyone have any ideas?
Thanks
David

luvrbus · October 21, 2026, 10:49:55 AM

Manifold gaskets blow out or the manifold cracks causes the drop you have a leak some place ,the 6v92 is usually around 20 to 25 lbs. under a good load it doesn't take much of a leak to drop the PSI boost pressure and they can be hard to trace at times, and a worn turbo can cause it very often if one has a small amount of drag on the compressor (hot) side

David Anderson · October 21, 2026, 01:06:33 PM

If it is a leak, there are a lot of places it could leak. It could be somewhere around the blower because the charged air inlet goes in at the side of the blower.

If there is a manifold leak would I see signs of stains near the escape point? I would think the escaping exhaust would discolor the area at the pipe flange where it would be leaking.

Is there a way to test the turbo charger either on the engine or off of it on a bench? I have to eliminate devices one at a time.

luvrbus · October 21, 2026, 03:45:34 PM

You can check the turbo on the bus a little pay up and down you can fell is ok but side movement is not ok,you have to check the manifold on top and bottom not just the upper.If the engine has a throttle delay leaking it will drop the boost too

David Anderson · October 21, 2026, 06:32:34 PM

I pulled the intake boot off and wiggled the fan. No slop or play. I don't see any issues there.

I can't do a thorough inspection until I go home in 3 weeks.

Would it be possible to force air into the intake tube at the blower and spray soap solution around the six manifold gaskets using something like a leaf blower?

luvrbus · October 22, 2026, 08:01:52 AM

Quote from: David Anderson on October 21, 2026, 06:32:34 PMI pulled the intake boot off and wiggled the fan. No slop or play. I don't see any issues there.

I can't do a thorough inspection until I go home in 3 weeks.

Would it be possible to force air into the intake tube at the blower and spray soap solution around the six manifold gaskets using something like a leaf blower?

I use a smoke tester but a leaf blower may work

David Anderson · October 22, 2026, 08:12:59 AM

Ok thanks
David

David Anderson · November 09, 2026, 10:01:15 AM

I am back home now. I set up a test system to air charge the turbo charger. When I put air to it I only got it up to about 10 pounds on the gauge. I can feel air coming out of the tailpipe which means it is bypassing through the turbo fan out the exhaust. Is it supposed to be that way? Am I testing this correctly to try to find any leaks on the induction side?

David Anderson · November 10, 2026, 10:02:54 AM

I found the leak. I have a blown gasket on the exhaust on the radiator side that is blowing like crazy when I pressure up the system. I'm gonna have to take the radiator out to get to this. Ugh.

Here are my home made air stops to pressure the system.

luvrbus · Reply #9 - Re: Turbo boost has diminished

If the manifold has blown a section out it is not always just the gasket the manifolds with age gets thin and blows out I have the manifold if you need it.soak the nuts good some of the studs go into the water jacket you don't want those come out. When reinstalling the manifold sets on a ledge if not resting on the ledge they will break when you tighten the nuts lol BTDT with some of my help

David Anderson · Reply #10 - Re: Turbo boost has diminished

Quote from: luvrbus on <strong>Today</strong> at 02:59:34 AMIf the manifold has blown a section out it is not always just the gasket the manifolds with age gets thin and blows out I have the manifold if you need it.soak the nuts good some of the studs go into the water jacket you don't want those come out. When reinstalling the manifold sets on a ledge if not resting on the ledge they will break when you tighten the nuts lol BTDT with some of my help

You were right, Clifford. I actually got all four nuts off without using heat. I pulled the manifold off and there was still a piece sticking on there. It is in the picture. How much do you want for your manifold?

David Anderson · Reply #11 - Re: Turbo boost has diminished

This manifold was replaced in 2006. It was a takeoff that I bought from a boneyard in Harlingen Texas.

I had a feeling the exhaust leak was an issue because I would get the smell of it in the coach while driving sometimes. My wife noticed it, also.

David Anderson · Reply #12 - Re: Turbo boost has diminished

Cliff, let me know if I can get your manifold. I need to get this back together quickly. Have a thanksgiving trip planned. I have two numbers for you ending in 309 and 162.
Or call me. I think you have my number. Ends in 729.

David.

David Anderson · Reply #13 - Re: Turbo boost has diminished

I guess this has been somewhat of a blessing. Close inspection of the fan hub shows wobble, and the bearings are noisy. I got the hub off and pushed the bearings out. Will replace them.
Also the fan drive belt has cracks in it. I'll get this stuff ordered tomorrow.
I found a few other leaks in clamps in the system too. Will get all this buttoned up.
She may run like a scalded dog after this stuff is done. 😇😇