I would definatly have him give you number like if 1 thru 7 were like 160 and 8 was 140 I don't think that would be so drastic. If you have any below 100 you have big troubles or over 15% of each other here is some one else's questions with same issues.
The first thing you should do is hook a a small outboard portable tank (like a 3 gallon) filled with fresh new fuel to the engines fuel pump and try it. This will rule out any issues with the fuel supply and fuel quality. If the engine performs better then you know the problem is either in the tank, lines, or fuel quality. If there is no change then you can rule this out.
Next is checking engine compression and fuel pressure. They both take time to check so it's up to you which you would like to check first. For compression, your results need to be 100psi or better on all cylinders, and all cylinders within 10 to 15% of eachother. If you get any cylinder below 100psi, then the engine has mechancial problems.
For fuel pressure, here is how you check it.
Checking Fuel Pressure and Fuel Supply Vacuum
1. Connect a fuel pressure gauge to the shrader valve on the fuel rail.
2. Cycle key switch 2-3 times (OFF to RUN position) at 3 second intervals to reach
maximum fuel pressure.
3. Verify that the pressure is within specification.
4. If fuel pressure exceeds 44 psi (303 kPa), replace the fuel pressure regulator.
5. If fuel pressure is less than 40 psi (276 kPa), but greater than 13 psi (90 kPa):
a. Relieve the fuel pressure in the fuel rail. Refer to section 2A for fuel pressure relief
procedure.
b. Use a tee fitting and connect a vacuum gauge to the fuel inlet side of the Cool
Fuel Module. Do not remove the fuel inlet fitting adapter.
c. Cycle the key switch 2-3 times (OFF to RUN position) at 3 second intervals to
reach maximum pressure.
d. Verify that the vacuum from the fuel source is within specification. If the vacuum
exceeds 2 in. Hg (7 kPa) , excessive fuel restriction exists. Correct the fuel
restriction before proceeding.
e. With the vessel secured to the dock and the engine running in neutral, restrict the
fuel supply with fuel shut-off tool and verify that the Cool Fuel Module has the
ability to cause an inlet vacuum reading of 11 in. Hg (37 kPa) or greater. If the
vacuum reading is less than 11 in. Hg (37 kPa) with the fuel supply restricted, but
fuel pressure is within specification, replace the low-pressure pump.
6. If fuel pressure is 13 psi (90 kPa) or less and inlet vacuum is less than 15 in. Hg (51
kPa), replace high-pressure pump and fuel pressure regulator.
Start with that and let me know how you make out. Post back with any questions
Good luck!
These were on a 2007 8.1 just a few things to ask your mech
