GMC 1989 Light Duty Truck, Repair Manual, Page: 626 / 998

6C3-2 MODEL 220 THROTTLE BODY
DESCRIPTION
The fuel control system has an e le ctric fuel pum p,
located in the fuel tank with the gage sending unit, which
pumps fuel to the TBI through the fuel supply line, then
through and in-line fuel filter. The pump is designed to pro­
vide pressurized fuel at about 125 kPa (18 psi). On vehicles
with two fuel tanks, there is an electric fuel pump and gage
sending unit in each fuel tank.
A pressure regulator in the TBI keeps fuel available to the
injectors at a constant pressure between 62 and 90Kpa (9
and 13 psi). Fuel in excess of injector needs is returned to
the fuel tank by a separate line.
The ECM controls the injectors that are located in the fuel
meter body assembly of the TBI. The injectors deliver fuel in
one of several modes.
In order to properly control the fuel supply, the fuel pump
is operated by the ECM through the fuel pump relay and oil
pressure switch.
MODEL 220 TBI UNIT
Model 220, used on V6 and V8 engines consists of three
major casting assemblies:
• Fuel meter cover with:
— Pressure regulator
• Fuel meter body with:
— Fuel injectors
• Throttle body with:
— Idle air control (IAC) valve
— Throttle position sensor (TPS)
Figure 1— TBI Identification
Model Number
Day of YearJ
Year —
Assembly Plant CodeJ
Shift Identification—
Source CodeJ
F-6736
THROTTLE BODY DISASSEMBLY
IDLE AIR CONTROL (IAC) VALVE
N O TIC E: The IA C valve is an e le c tric a l c o m p o ­
n e n t an d m u st n o t b e so a k e d in any liq u id c le a n e r
o r solvent. O th erw ise d a m a g e c o u ld result.
Important
All IAC valves on TBI Model 220 units (except those
on the 7.4L engine) are thread-m ounted and have a
dual taper, 10mm d iam eter, p intle. On the 7.4L
engine, the IAC valve is flange-m ounted and has a
12mm diameter, dual taper pintle. Any replacement
of an IAC valve must have the correct part number,
with the appropriate pintle taper and diam eter for
proper seating of the valve in the throttle body.
Remove or Disconnect (Figures 3 and 4)
1. IAC valve.
• On thread mounted units, use a 32mm (11/4")
wrench (figure 3).
• On fla n g e -m o u n te d u n its , re m o v e s c re w
assemblies (figure 4).
2. IAC valve gasket or O-ring and discard.
TH R O TTLE P O S IT IO N SENSOR
(TPS)
N O TIC E: The TPS is an e le c tric a l c o m p o n e n t and
m u s t n o t b e s o a k e d in any liq u id c le a n e r o r so l­
vent, as d am ag e m ay result.
Important (Figure 5)
On 2.8L (V-6) engines, the TPS is adjustable, and is
supplied with attaching screw retainers. On all other
engines, it is non-adjustable, w ithout retainers. In
addition, on 2.8L (V-6) and 7.4 (V8) engines, the TPS
has a horizontal electrical connector; whereas, on all
other engines, the connector is a vertical one. Since
these TPS configurations can be m ounted inter­
changeably, be sure to order the correct one for your
e n g in e w ith th e id e n tic a l p a rt n u m b e r if b e in g
replaced.
Remove or Disconnect
1. Two TPS attaching screw assem blies and retainers,
(if applicable).
2. TPS from throttle body assembly.