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Plan of Attack:
Please remember that this is a
documentation of my specific conversion. Components will vary depending on
the year & make of the donor TPI and the year truck you are converting.
TBI trucks from the years 87'-91' use an integrator harness/computer, whereas
the 93'-95' models require a different setup due to the 4L60E transmission.
And, 92' is its own special case. Whatever your variables are, the first
order of business is to contact the experts at
Street & Performance.
Since S&P has performed this conversion before, it
only seemed natural to use their expertise for this project. Not only is
S&P a good source for the conversion components, they offer customer service and
technical support that is second to none.
To simplify the conversion process, I decided to buy
all of the components from Street & Performance. Before
starting, please
visit S&P's on-line technical page:
TPI wiring Harness Instruction Sheet,
print it out and read it through completely. You will need Adobe Acrobat to
read this file. If you do not have it, no worries, get a free download
here
or at S&P's website. A few items included
with S&P's instruction sheet do not apply to my application because my TPI unit came off of a
1991 Pontiac Firebird GTA (5.7L). For instance, the cold
start injector and large cap HEI distributor. Also, if you are new to the
TPI system, I would highly encourage you to purchase S&P's two part video set.
This covers just about all aspects for rebuilding and working with the TPI
system. S&P also has some short videos available on their website.
Click here to view these videos.
My webpage will outline the
various components of the harness and computer and the installation of each
particular part. Please note, each number listed below corresponds to the
numbers called out on the S&P wiring harness diagram (reference the above link).
For each component, I have a picture of the harness connection and a picture of
that same connection in place. In some cases, the connections are not
applicable to my specific application. In this case, they should simply be
tied up out of the way.
Computer (ECM), Chip &
Harness: (NOTE: THIS IS A SPEED-DENSITY SYSTEM)
Click
Here for a Car Craft article titled "EFI: Mass Flow vs. Speed
Density. This article describes how each works.
The package I ordered from S&P
will use the TPI unit from my 1991 Pontiac Firebird GTA (5.7L). Although I could
have purchased a
less expensive computer, I opted for a heat resistant and water proof computer -
Service #122727. This will allow me to mount the computer under the hood
and if I ever decide to use it in another vehicle, it will make disassembly more
convenient. The harness that complements #727 computer and my
conversion also includes 4L60E jumpers. This is because I must leave the
original computer intact to control other functions such as the electric
transmission (4L60E), anti-lock brakes, etc. The 4L60E transmission
requires three critical inputs from the computer to function. They are
signals from the TPS, distributor and MAP. Because the new computer will
now control these engine functions, the jumpers are required to allow the
original computer (which still controls the transmission) to gather this
information.
There
are four harness plug connections with this computer, and each fits a specific
opening. Therefore, there is no chance of mixing up the connections.
The supplemental instructions for the 4L60E jumpers are not on S&P's on-line
tech, but are included at the bottom of this page. Note: The ECM operates on a negative (-) ground system. Inadvertent
connection of the battery leads in reverse will render the ECM inoperable.
Another tip: When installing the #727 computer under the hood, be sure to
tilt the plug end down so that any water getting into the plugs can drain out.
According to S&P, installing the removable door on top is fine and also permits
easy access to the chip if you ever want to make any changes.
Click Here for a List of GM TPI
Trouble Codes
Harness Connections:
(TPI wiring Harness Instruction Sheet)
[Top of Page]
1.
Check Engine Light and Fuse Block:
 Three 10 AMP fuses are utilized. One each for driver side and
passenger side injectors, and one for the ECM (computer) and "Check Engine
Light". This light has been mounted on the fuse block. It's use is
explained under the diagnostic aids. The diagnostic aids is page 8 of
the S&P TPI Wiring Harness Instruction Sheet. If you have access to
a scanner such as an Auto-X-Ray, the chip you are provided will indicate a VIN
number that can be used.
[Top]
2. Ignition Switch:
This is red wire is the ignition wire on harness and
must be connected to provide 12V with the key in the ON and in the START (crank)
position.
[Top]
3. Fuel Pump Relay:
The relay comes with the harness.
[Top]
4. ALDL Connector:
 The Automatic Line Diagnostic Link (ALDL): Used in
conjunction with Check Engine Light. See diagnostic aids. (Click Here for a List of GM TPI
Trouble Codes)
[Top]
5. Computer Plug
(Yellow): (Not Applicable for the #122727
Computer). Reference above picture.
[Top]
6. Computer Plug (Small
Black): (Not
Applicable for the #122727 Computer). Ref. above picture.
[Top]
7. 4K Pulse for
Speedometer & Cruise Control: (Green Wire) - Not Used
[Top]
8. Computer Plug (Large
Black): (Not Applicable for the #122727 Computer).
Ref. above picture.
[Top]
9. Park Neutral Switch:
(Black Wire) - Closed in park and neutral to ground. Used if Desired
[Top]
10. Brake Light Switch:
(Purple Wire)
Not used with the 4L60E application. Since my 94' Suburban came
stock with a 4L60E transmission, all the functions, including the TCC
lock-up/disengagement are controlled by the original truck computer, via the
4L60E jumpers.
The purple wire provided with the S&P harness would be used in the event that
you needed the new S&P computer to control transmission & torque converter
functions. The computer needs a brake signal to control the lock-up
converter on a 700R4 or 4L60. It requires a 12 volt ignition source, normally
closed switch. Be sure to reference page 12 of the S&P TPI Wiring Harness Instruction Sheet
if you only have a 2 prong pressure brake switch.
[Top]
11. Distributor Plug:
(White, purple, brown and black wires)
 The pig tail adapts from a large plug at the harness
side to a small black plug with a blue seal that plugs into the distributor.
Since the 94' Suburban comes with a small cap, remote coil distributor, I will
use the adapter. Note: A 12V ignition must be supplied to the distributor.
The harness plug does not supply this. Obtaining spark to the plugs is
independent of the harness and is a function of the distributor only. For
the 94' application, simply plug the other, original connection from the coil
into the distributor.
[Top]
12. EST Bypass: (Brown wire with black disconnect)
 Electronic Spark Timing.
Install in a location that will be easily accessible. This plug/connection
is used when setting the base timing. Disconnect the bypass, start the
engine, set the base timing at 2 to 4 degrees BTDC, shut the engine off and
reconnect the bypass, and finally restart the engine. Timing should now be
approximately 14 to 16 degrees.
[Top]
13. Engine Ground:
(Black
Wire)
  A good engine ground is critical for proper
operation of the system. Attach to the rear passenger cylinder head.
Note: Be sure that you have a good battery to motor or transmission
ground, motor to frame ground, and motor to body ground. Note: Be sure to
reinstall the original TBI harness grounds. There are four (2 black and 2
beige) attached just behind the water neck.
[Top]
14. MAP Sensor: (Gray, green and black wires to a green plug with a
green seal)
   Manifold Absolute
Pressure. Run a vacuum line from the rear passenger side of the plenum to
the port on the MAP sensor. In the right side picture, the
vacuum feed for the MAP sensor is the first one from the top, on the right hand
side.
[Top]
15. Knock Sensor: (Blue wire to a black plug)
  The knock sensor
provides engine knock (ping) information to the computer, which automatically
retards the timing. The original TBI knock sensor has a different
sensitivity level and should not be used with the TPI. Use S&P part no.
10456301 or 102456549.
[Top]
16. Oil Pressure Gauge:
(White wire)
For GM gauges only. Splice this wire into the
brown wire that sends a signal to the original truck computer. Note: With
aftermarket gauges, you must use their sending unit and tie this white wire out
of the way.
[Top]
17. Oil Pressure Sending Unit:
(Brown, orange, and white wire to a gray plug
with a green seal)
  The Oil Pressure Sending Unit is provided as a
back-up system in the event the fuel pump relay were to fail. With oil
pressure above 5 lbs., battery voltage is provided to the fuel pump. The
stock 94' OPSU will plug into this new harness and can be reused.
[Top]
18. Drivers Side Injector
Plugs: (Red and Blue Wires)
 Note: The
injectors are pulsed simultaneously, so any injector plug can connect to any
injector. However, the injector plug lengths will indicate which injector
to connect and will result in a neat and professional installation. Please
reference the S&P TPI Wiring Harness Instruction Sheet for an
illustration for the proper harness installation routing.
[Top]
19. Passenger Side Injector
Plugs: (Red and Green Wires)
 Note: The
injectors are pulsed simultaneously, so any injector plug can connect to any
injector. However, the injector plug lengths will indicate which injector
to connect and will result in a neat and professional installation. Please
reference the S&P TPI Wiring Harness Instruction Sheet for an
illustration for the proper harness installation routing.
[Top]
20. Manifold Temperature
Sensor: (Black and brown wires to a black plug
with a blue seal)
  The manifold temperature sensor operates in the same
fashion as the coolant temperature sensor, except it relates to the air
temperature in the manifold. The manifold temperature sensor and coolant
temperature sensor are the same and interchangeable. The one pictured below
is original and will be replaced before installing the TPI on the truck.
As you can imagine, being installed from the bottom of the plenum, it will be
difficult, if not impossible to change once the plenum is reinstalled.
[Top]
21. Starter Battery Terminal:
(Orange wire with a FUSIBLE LINK)
 A 14 gauge fused link wire is connected to the
starter terminal. This provides 12V to two computer terminals, the fuel
pump relay, and one side of the oil pressure sending unit. Note: If using a battery disconnect, this
orange wire must go to the hot side of the battery disconnect to maintain memory
to the computer. This is not applicable to my conversion.
[Top]
22. Oxygen Sensor:
(Purple wire to a black plug with a green seal)
 When exhaust temperature has reached 600 degrees F, the Oxygen Sensor places the
system in close loop and maintains an air fuel ratio of 14.7 to 1. This
input is ignored during wide open throttle. Note: The harness comes
equipped for single feed oxygen sensor. If you wish to install a three
wire oxygen sensor, you can buy a pig tail from S&P. This will plug into
the three prong sensor, and the single prong harness. The pigtail will
then need a 12V ignition source and an engine ground. For my swap, I will
be using the stock three wire oxygen sensor, but will splice the
sensor wire in in lieu of buying the pig tail.
[Top]
23. Hot Feed for Electric Fuel
Pump: (Brown wire)
  A 14 gauge wire is provided from the harness to
provide power to the fuel pump. This will provide power to the fuel pump
from either the relay and/or oil pressure switch circuit. For my 94'
Suburban, I spliced this wire directly to the gray wire
that runs along the driver's side frame rail.
[Top]
24. Coolant Temperature Sensor:
(Black and yellow wires to a black plug with a blue seal)
  The coolant temperature sensor returns a
proportional voltage to the computer that relates to the coolant temperature.
Cold = High Voltage and Hot = Low Voltage. Note: The new harness
plug will go to the coolant temperature sensor installed in the TPI base
manifold. The original TBI harness coolant temperature sensor plug should
remain installed in the driver's side cylinder head sensor. This is
necessary for the factory temperature gauge/dummy light function.
[Top]
25. Idle Air Motor:
(Yellow, white, brown and red wires to a black plug with a green seal)
 This connects to the Idle Air Motor or Control
Valve, which is a computer controlled stepper motor that adjusts engine idle at
different loads. Note: If the IAC is disconnected or reconnected
with the engine running, the idle speed may be wrong. It can be reset by
depressing the accelerator pedal slightly, start and run the engine for five
seconds, then turn the ignition off for ten seconds.
  As you can see
left, the original black plastic IAM needed a replacement.
The newer metal version was installed only a few thousand miles ago on the GTA;
therefore, I will be reusing this IAM. If this has not been replaced
recently on the donor vehicle, it is a good idea to do it now while the plenum
is off the car. Access with a big wrench is difficult when installed on
the car.
[Top]
26. Throttle Position Sensor:
(Black, blue and gray wires to a black plug with a green seal)
  This sensor returns a proportional voltage to the
computer that relates to the angular position of the throttle plates.
Relaxed throttle = Low Voltage (approximately 0.54V), whereas Wide Open Throttle
(WOT) = High Voltage (approximately 4.5V). Note: Setting this value
by using a real-time scanner such as an Auto-X-Ray is much more convenient then
using a digital voltmeter. If this is not available, please refer to the
S&P TPI Wiring Harness Instruction Sheet for a written description for
properly setting the TPS using a digital voltmeter.
[Top]
27. EGR Solenoid: (Red and
green wires to a black plug with a green seal) - Used if Desired
  Since I will be reusing the EGR, I will need to use the EGR solenoid. To
simplify the swap, I will reuse the GTA's EGR solenoid/bracket. It is
located at the lower left corner of the distributor in the picture below.
[Top]
28. Transmission Plug:
(White 4 prong plug with brown & purple wires to a white plug with a green
seal)
 Not used with the 4L60E application. This
would however be used for a standard 700R4 or 4L60 setup. This plugs into
the existing transmission connector. Note: S&P has an adaptor for
round 5 prong plugs.
[Top]
29. Vehicle Speed Sensor:
(Twisted purple and yellow wires to a black plug with a green seal)
 REVISED:
For this application, a functioning VSS signal is required to
prevent the engine from stalling when coming to abrupt stops or slow
downs (such as decelerating off an interstate exit ramp). The
EGR will also not function, as one of the operating parameters is
vehicle speed. The entire description of why the VSS is
necessary and how to make it work using the stock 128,000 ppm
signal. Click here
to see how it is done.
[Top]
30. 4 Pulses Manual Speed
Sensor: (NOT USED)
[Top]
31. 4L60E Jumpers (A,B,C):
  A - Plug the MAP jumper into the original MAP
plug.
B - Splice the blue wire head into the
original blue wire of the TPS plug.
C - Splice the purple wire head into the
purple wire with white stripe of the original distributor plug.
[Top]
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