All Vehicles:

f. ALL Vehicles:

Do four (4) WOT accelerations from a running start in 3rd gear, or with the shift indicator in 2nd gear on automatic transmission vehicles. These accelerations should be done on level, dry, smooth, paved roads; running two (2) tests in each direction on the same road. The maximum wind velocity should be not greater than 18 mph when conducting this test. Start the test at the "starting speed" and accelerate to the "end speed" given in the following appropriate vehicle performance charts. Rerun any test for which time differs greatly from the other test runs. When four (4) good tests have been finished, average the results.

g. Compare the average with the "acceptable performance" numbers given in the appropriate chart. Use the chart for the transmission, and axle ratio combination that matches the vehicle equipment. Use only the vehicle weight and frontal area from items b and c above. Enter the vehicle weight across the bottom of the chart. Go down the left side of the chart to the frontal area equal to the frontal area of the vehicle.

NOTE: FRONTAL AREA IS LABELED FOR STANDARD TRUCKS (EXAMPLE F-250 4X2 PICKUP). THE NUMBER WHERE THE VEHICLE WEIGHT AND THE FRONTAL AREA MEET IS THE "ACCEPTABLE PERFORMANCE" FOR THE VEHICLE BEING TESTED. RECORD BOTH THE AVERAGE OF THE VEHICLE TEST RUNS AND THE "ACCEPTABLE PERFORMANCE" NUMBERS IN THE COMMENT BOX ON FORM FPS-8512-A.

h. If the test result is less than the "acceptable performance" number, continue with steps 12 through 14. If the test result is greater than the "acceptable performance" number, proceed to step 11.

11. Do this step only if directed to by step 10h. Complete step 12 of the 7.3L Diesel Engine Diagnostic Guide (Form FPS-8512-A). If the crankcase pressure is within specification, replace the fuel injection pump. Refer to the appropriate Light Truck Shop Manual, Section 22-08.

NOTE: WARRANTY CLAIMS FOR THE INJECTION PUMP WILL NOT BE ACCEPTED UNLESS ALL TAMPER-RESISTANT SEALS ARE INTACT AND THE COMPLETED ENGINE PERFORMANCE CHART, FPS-8512-A, IS SUBMITTED WITH THE RETURNED PART.

12. Check manual transmission gear ratios for the truck's application. Two different sets of gear ratios are available in the ZF-M50D. The Close Ratio M50D (4.14 / 2.37 / 1.42 / 1.00 / 0.77) is the standard production transmission. However, a limited number of mainly F-350 DRW Chassis Cab vehicles have been built using a wide ratio (5.72 / 2.94 / 1.61 / 1.00 / 0.76) gear set. This wide ratio M50D was available as a limited option of F-350 DRW Chassis Cab vehicles with 4.10 axle ratios only, but a smaller number have been special ordered in other 7.3L Diesel applications. This wide ratio gear set results in potential performance concerns due to the wide split between third and fourth gears when towing trailers. The vehicle could be accelerated in third gear up to 3400 engine RPM shifted to fourth gear and lose speed forcing a downshift back to third gear. Therefore, the wide ratio M50D is not recommended for use in on-highway trailer tow applications. Vehicles used as wreckers or other start-up applications, but not used for highway trailer towing could benefit from the use of the wide ratio M50D.

NOTE: CHANGES IN TRANSMISSION GEAR SETS ARE NOT AUTHORIZED OR WARRANTED BY THIS TSB.

13. Check rear axle ratio for the truck's application. Three different axle ratios have been used on vehicles equipped with the 7.3L diesel engine.

^ The 3.54/3.55 axle ratio should be used for vehicles used at empty to moderate loads or for occasional or light trailer towing (Max GCW 12,000 lbs).

^ The 4.10 ratio is recommended for trailer towing, performance intensive and high altitude applications (Max GCW 14,000 lbs).

^ The 5.13 axle ratio is standard and available only for thr F-Super Duty Chassis Cab (Max GCW 17,000lbs).

NOTE: CHANGES IN AXLE RATIO TO IMPROVE VEHICLE PERFORMANCE MAY REDUCE FUEL ECONOMY AND ARE NOT AUTHORIZED OR WARRANTED BY THIS TSB.

Other things that may add to the customer's belief of poor engine performance are:

a. Dual versus single-rear wheels causing added rolling resistance and increased wind resistance of the vehicle with dual rear wheels.

b. Four-wheel versus two-wheel drive vehicles causing the loss of horsepower because of the additional drivetrain components, additional rolling resistance, weight, and increased frontal area of the four-wheel drive vehicles.

58Gc. Auxiliary equipment such as PTO operated equipment, larger alternators, air conditioning systems that are operated during vehicle acceleration causing reduced performance.

d. Added coolers or equipment mounted in front of the radiator reduce the cooling system's efficiency resulting in increased cooling fan loads which reduce vehicle performance.