Cummins ISX CM871 Technical discussion

You definitely have an unsafe condition. Sounds like fuel being sprayed on a hot
exhaust manifold. Potential fire hazard. Check for rusted through fuel supply line
or loose connection at fittings. Check fuel lines up on top of engine at fuel pump

 

I agree with what vandgtransport has to say, at the clamped joint on the back side of the doser elbow there should be a gasket on that connection, I've had several driver complaints like what you describe and every time the gasket at that connection has been bad.

 

The part number for the gasket on the Prostar is 3846392C1, it's a international part #, it costs around $6. Ask your driver if when parked, after it's hot or when first starting the truck, if he/she smells exhaust. If so, it's more then likely this gasket. If it is this gasket and it's replaced, then the same exhaust smell returns but no visible "mist", run a parked regen with the hood open and watch for the "mist". If it's still present but very light you can double up on the gasket and your problem is solved.

 

If you have fuel misting the first thing I would check is the fuel line to the doser valve, or "7th injector" as Cummins calls it.
Cummins upgraded the coolant lines, they now have a short section of braided line to abate vibration fractures.
The fuel line is routed behind the engine, a great place for problems to hide.
Anybody that has had a mechanical pump engine has at some point probably had a cracked injector line, symptom is the same.

I just changed the doser on our 386 Pete. In the process I found that the SS flex pipe was split.Not visable to the naked eye.
I had to take it apart to find it. If you have an exhuast leak down stream from the doser this would also be another point to check.

 

Got code 3751 scr mechanical failure or out of adjustment? Anyone else had this problem?

 

That would be a code for a cm2250 or newer engine so you'd probably get more help making a new topic for it

 

I have a buddy that has a 05 Pete with the isx in it. The fuel inside the tanks is black, looks like soot? Any help would be appreciated..

 

Black fuel is normal. It's called asphaulting. Heat from the engine causes it.

 

If you need help on your 2250, make a new topic and I can help.

 

This could also be algae build up which will totally clog the filters. There are treatments to kill it but you should get the tanks drained also if that is it.