Engine Power Improvements - Redesigned Components
Article No.93-16-13
08/04/93
^ ENGINE - 7.5L - NON-INTERCHANGEABILITY OF CERTAIN ENGINE COMPONENTS - ENGINES BUILT AFTER 11/16/92 - SERVICE TIPS
^ ENGINE POWER IMPROVEMENT - 7.5L ENGINES - VEHICLES OVER 8500 GVW BUILT AFTER JOB 1, 1993
LIGHT TRUCK:
1993 ECONOLINE, F SUPER DUTY, F-250, F-350, F-53
ISSUE:
The 7.5L engine was recalibrated for increased power and performance by incorporating several design improvements. These changes are effective with engine build date, 11/17/92, and with vehicle Job 1 in mid February 1993. Many components in the 1993-1/2 version of the 7.5L engine are NOT interchangeable with past models.
ACTION:
Refer to the following information for changes to the 1993-1/2 version of the 7.5L engine. A quick and easy way to distinguish the new engine is to locate the calibration number. The new calibration numbers begin with the digit "3". The following component groups are affected:
^ Cylinder Head
^ Pistons/Rings
^ Exhaust Manifold
^ Rocker Cover
^ Vacuum Reservoir/Harness
^ Thermactor System
^ Powertrain Control Module
^ EGR Valve
^ IAC Valve
DETAILED DESCRIPTION OF COMPONENTS
Cylinder Head
The internal porting of the cylinder head casting is changed to improve air flow. Internal cooling passages are improved for more efficient heat dissipation.
The intake valves and cylinder head intake ports are larger, Figure 1. These changes ensure more air is available for combustion and increases swirl flow of the fuel/air mixture, as well as increase the volume of air ingested per intake stroke.
Pistons/Rings
New aluminum pistons are installed to initiate a faster combustion cycle, Figure 2. There is a closer piston to bore clearance and the ring pack end gap is smaller. These changes add up to a more effectively sealed combustion chamber which reduces combustion gas blow-by. This provides more control of oil loss into the combustion chamber.
The pistons are also higher in "crown to deck height", Figure 3. The combustion bowl is enlarged to accommodate the change of raising the deck height. The piston crown has a deeper valve recession to improve combustion and prevent interference with the intake/exhaust valves when they open. The "squish area", or area above the piston at top dead center (TDC), is more efficient. It provides for a more rapid burn of the fuel-air mixture.
Previously, the deck height of the piston crown was -0.010" (-0.254 mm) nominal. For the 93-1/2 the deck height has been changed to 0.0" (0.0 mm) or flush, Figure 4.
NOTE:
NEVER INTERMIX A CURRENT PRODUCTION PISTON IN A PRE-93-1/2 ENGINE AND VICE VERSA. SEVERE DAMAGE MAY RESULT TO THE VALVE TRAIN/PISTON ASSEMBLY. USE ONLY THE PISTON THAT IS PROVIDED UNDER THE SERVICE NUMBER FOR THE INDIVIDUAL MODEL YEAR.
Exhaust Manifold
A new exhaust manifold is now fitted to allow injection of Thermactor air, directly into the manifold. A rifle drilling is bored in the manifold and plugged on the end, Figure 5. Cross drillings intersect the rifle drilling to connect the exhaust ports to Thermactor air. This provides better oxidation of the exhaust gas, by injecting air to the highest temperature point in the exhaust (upstream air).
A Ni-Resist material is used for vehicles with catalyst, to protect the catalyst against internal erosion (A conventional cast iron material would flake off and get in the catalyst causing erosion). The Ni-Resist material has been used in EFI systems since 1988.
For the F-Super Duty trucks over 14000 pounds (6350 kg) a Hi-Sil-Moly manifold is fitted for durability instead of using gray cast iron. Since the vehicle uses no catalyst, it is not required to use the Ni-Resist material.
CAUTION:
IT IS NOT RECOMMENDED THAT THE HI-SIL-MOLY MANIFOLD BE USED 014 CATALYST EQUIPPED VEHICLES. HOWEVER, THE NI-RESIST MANIFOLD COULD BE USED IN PLACE OF A HI-SIL-MOLY MANIFOLD, WITHOUT CAUSING HARM TO THE EXHAUST SYSTEM.
Rocker Cover
Improvements for customer satisfaction are included in the 93-1/2 program. A new style PCV valve and mounting boss are integral with the rocker cover. The PCV valve body now screws into a threaded boss located on the cover. Leakage is prevented with a compression type nylon seal between the threaded boss and valve body flange.
Vacuum Reservoir and Harness Assembly
The vacuum reservoir has been increased in size from a single tank with a 90 cu.in. (1475 cu.cm) displacement to a double tank system. One compartment serves the EGR system, containing a 90 cu.in. (1475 cu.cm) volume while the other displaces 180 cu.in. (2950 cu.cm), and services the Thermactor system.
The purpose for this change is to meet the emission control requirements for the vehicle. The vacuum harness for the dual reservoir design has been updated.
Thermactor System
The exhaust manifold section pointed out that a new manifold is used for Thermactor Air injection. This is known as "Upstream Air". Its purpose is to improve oxidation of exhaust gases. For the 93-1/2 program, the Thermactor plumbing is revised to accommodate a downstream and upstream system. Following is an outline of the changes from 1992 to 1993-1/2, Figure 6.
Powertrain Control Module (formerly EEC Processor)
The increased power and revised layout requires that the Powertrain Control Module (PCM) contain a new strategy to manage the engine. Therefore, PCMs are not interchangeable with pre 1993-1/2 versions.
EGR Valve
The EGR valve, is double the capacity of the 1992 EGR valve. The new valve is not interchangeable with the prior valve.
Idle Air Control Valve
The new Idle Air Control Valve (IAC) is incompatible with previous PCMS. The new valve improves the idle of the revised engine.
OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: INFORMATION ONLY
OASIS CODES: 499000