A B737-800's Fuel Totalizer froze after becoming erratic in flight. The QRH instructed the crew to manually enter the fuel information in the FMC. However neither the FMC PERF INIT nor PROG pages could be updated manually.

Narrative

Started to get various fuel messages on FMC. Fuel readings on EICAS showed left fuel reading erratic. Finally went blank. Fuel totalizer froze at last reading for some time. Followed QRH which states to update performance utilization page manually. This procedure does not work. You cannot update fuel on the performance utilization page. You cannot update fuel on page 1 of the program page. You can update your gross weight on the performance utilization page but this lowers or raises your ZFW making for inaccurate predictions. The only thing worth updating with a failed fuel reading is the utilization reference page for your approach speed. I checked this the rest of the aircraft I flew during my sequence. the MEL and the QRH both state to update the performance utilization page and are therefore misleading and wrong. The only thing you can do is select fuel used on the EICAS and check for excessive fuel flow/engine readings. This is totally inadequate as the FMC on the F-100/B-757/767/777 all allow for a 'manual' insertion of fuel on the performance utilization page which then updates your gross weight and fuel calculations appropriately. Fuel reading on left engine came back to life upon shutdown.