12.7 Detroit power loss when hot

What year is engine, or ddec model? That is important.

 

You might check fuel pressure before and after acting up. Check between the secondary filter (last before head) and head.

 

I’d second that suggestion.

It sounds like fuel starvation to me. I replaced all my fuel lines on a 1995 a while back, all those rubber components have a shelf life.

I don’t know how the barometric pressure sensor affects fuel delivery adjusted for elevation, and if a bad sensor leads to lost power, but if your engine is surging, I’m thinking fuel system.

 

Is the filter on the frame a glass bowl Davco, or a solid filter with a tap on the bottom?

 

Just connect a t-fitting between the filter head and fuel line to the head, and use the third hole on the fitting for a pressure guage. My 2002 DDEC 4 430 hp runs at 75lbs. If the pressure is the same before and after, fuel restriction before the head shouldn't be the problem. I believe you can also run down the road with a diagnostic computer connected to your data port to check fuel pressure.

 

And run a cylinder cut out test while you’re at it.

 

I'd start with checking fuel pressure as mentioned. Then bypass all the suction lines, and run a fuel line straight from the fuel pump and drop it in the tank and test drive.

If your problem persists, you know all your suction lines are good. If it's gone, you've narrowed it down.

Diagnose without the thought of "well, that wouldn't be affected by temp"

Just diagnose as normal. A laptop or prolink will help.

My first thoughts,
Boost pressure sensor is very likely a possibility, throttle position sensor also likely.

Both can be monitored while driving with a Pro Link or laptop.

DDEC II did not have the intake air temp sensor.

You don't have fuel heaters do you?

 

Ddecll who will even hook diagnostics to those?