I started having some surging at startup when cold.

So I’m thinking of some fueling issues.

I have an MM3 and monitoring some rail pressure.

See the image, for example.

There’s actual, desired, and rail pressure rationality for the PIDs.

What does rationality mean?

Also, what does the FCS fuel Control State mean?

Numbers go from usually 8 up to 96.

I will do some data logs to see fluctuations between desired and actual. So I’ll report back on that. I don’t have any codes.

The truck only has 60k, 2017 with exhaust and EGR upgrades”.

It sounds a little more “ rattled” throughout all RPMs.

I also notice at idle; the actual pressure seems to jump around and doesn’t stay constant.

I know many things to consider, but right now, I am just trying to understand correct rail pressures and how to diagnose them.

You can see on the monitor picture that the actual rail pressure hit 28,045. Seems too high?

Also, notice so far that it is always lower than desired.

316941F0-B2A0-4507-BB98-E3846CEE09EC.jpg


F2B2CB7E-90F0-42DB-9C1A-FAB5EC37449F.jpg


4956B79D-D20D-475D-91C9-40FC45CE718B.jpg