TPI swap

Tuned Port Injection (TPI) Swap - By Craig McCormick (craig at

Tuned Port Injection in my 85 Monte Carlo SS has been a dream of mine ever
since I first looked under the hood of a TPI Camaro. I love the look of the
aluminum runners and throttle body. I have always been a sucker for the
computer-controlled fuel injection stuff too. I finally got a 5.7 (L98)
motor from an 89 TransAm GTA.
For anyone planning such a swap - you've come to the right place. The first
thing you need to do is order a book called 'Chevrolet TPI & TBI Engine
Swapping' which you can get from Summit Racing or places like that. The
book doesn't tell you step-by-step stuff but rather it is an invaluable
tool at the planning stage of your project. It tells you things like; how
to buy a motor, what components are required and what kind of problems you
WILL run into.
This project will take you a lot of time and a lot of money. If you don't
have both, I'm sorry to say you will have to put this idea on hold. There
are no shortcuts - Period.

MAF (Mass Air Flow) vs. SD (Speed-Density)
Up until 89, TPI motors used a MAF system. From 90-92 they used
Speed-Denisty. Each system has has its own advantages and disadvantages. My
preference is for MAF. The benefit of the MAF system is that it measures
the amount of air entering the engine with the MAF sensor so that if you
modify the engine and increase the amount of air flowing through it, the
ECM will compensate for it automatically. With a Speed-Density system the
ECM makes a calculation of the amount of air-flow based on the speed of the
engine and the density of the air in the intake manifold. The problem with
this is that the ECM does not recognize if modifications affecting airflow
are made to the engine and therefore cannot compensate for it. To get
around this you must have a new chip programmed so the ECM can once again
accurately calculate the amount of air entering the engine. For each change
you make to the engine you must also have a new chip made.
The reason that some people prefer the Speed-Density system is that the air
duct routing can be simplified. Since the speed-density system doesn't need
a MAF sensor you can just stick a filter onto the end of the throttle body
and that's all. With MAF, you usually need to turn the air duct to the left
or right so you have room for the MAF and then add a filter.

Buying a Motor
TPI motors were first used in 1985 in F-bodies (Camaro & Firebird) and
Corvettes and are available in 5.0 and 5.7 litres. In 87 GM began using
roller camshafts and center-bolt valve-covers. In 88 a serpentine belt was
added. In 89 the cold-start injector was removed from the system which
cleans up the harness a bit. 90-92 systems, as mentioned earlier, use SD so
I do not recommend those. Any of the earlier systems would be a good
choice, especially 87-89. If you can find one, get a 5.7. The 5.0's are
good but if you're going to do all this work you might as well do it right
with a 5.7. For G-body swaps, most people recommend a motor from an F-body
rather than a Corvette because the bodies are more similar and things will
fit better. I believe the Pontiac cars always used an electric speedometer
so if you get the trans too you will have to buy a mechanical speedometer
drive. Another problem with the 90-92 motors is that they use a 4-pulse VSS
(vehicle speed sensor) whereas the 85-89 used a 2-pulse VSS which is the
same as your 80's G-body. When you buy the motor, make sure you get the
complete system. That means, wiring harness, ECM and ALL sensors. I also
recommend you get the accessories as well, especially for 88 & up because
of the serpentine belt. Get as much of the air ducting as you can as well
as the throttle cable and transmission TV cable.

Wiring Harness
Assuming you've got the old engine out:
-Remove the wiper motor so you can access the connector that goes into the
fuse block.
-There will be a small bolt in the centre of the connector which holds it
to the firewall. Once you get it out you will see that half of this
connector is for the body harness, i.e. headlights, wipers, etc. The other
half is for the engine wiring harness. You can separate the two parts of
the connector.
-Remove the passenger side wheel-well by removing all the bolts from the
underside as well as the battery and battery tray. Now you can access the
firewall where the harness goes through to the ECM. Remove the metal clip
that holds the harness to the firewall.
-Remove the passenger-side kick panel and unplug the ECM and the 15-pin
-Push the rubber grommet out from the inside of the car and feed the wires
through.At this point you should be able to completely remove the engine
wiring harness from the car.

Throttle cable
Dig out some of the tar around the cable where it goes through the
firewall. Inside the car, unhook the cable from the pedal and pull off the
rubber washer at the firewall. Use a screwdriver to pry the tabs that hold
the cable to the firewall and push the cable out from the inside. I had to
make the hole a little bigger to fit the F-body cable. The connector to the
pedal is the same.

Transmission TV (kick-down) cable
You must use a kick-down cable from a TPI / 700-R4 vehicle. The bottom end
of this cable is the same as a TH200-4R cable so it will fit either
transmission. I used my original 200-4R transmission because I was running
low on cash. If you get the 700-R4 transmission that is with the TPI motor
(which I highly recommend if you have the cash and time) you will need to
do the following as well:
-Replace tail-shaft on 700-R4 to fit G-body cross-member. Refer to the
chapter on Automatic Transmissions in 'Chevrolet TPI & TBI Engine Swapping'
-Have driveshaft shortened and balanced
-Re-calibrate speedo or else change speedo gears in trans to match your
rear-end gears

Power steering
The hose fittings from the TPI power-steering pump fit my steering gear
with no problems.

Heater hoses
The TPI motors have only one coolant outlet from the block at the throttle
body. The return is through an extra inlet in the rad. Since the G-body rad
doesn't have his extra inlet you must splice a T-fitting into the lower rad
hose. My TPI motor also has an oil cooler that routes coolant through the
oil filter adapter. The outlet from the throttle body is 5/8". This routes
to the same size pipe in the heater core. The other pipe from the heater
core is 3/4" which then routes to the oil cooler pipes which are also both
3/4". The return from the oil cooler pipes is then routed to the T-fitting
the lower rad hose. I got this plastic fitting from Home Depot for about
$4. It is 1-5/8" on the straight through part and 3/4" on the T.

Electric fan
You will need an electric fan, as large as you can find. My donor car had
two fans - the second one was for the A/C which I don't have so I was able
to omit that one. I used a fan from a mid-eighties FWD (cutlass I think)
and it works great and pulls a lot of air. I connected the fan to the TPI
harness so the ECM controls the fan.

Fuel delivery
TPI systems require high fuel pressure - 35-50 PSI. This means you will
either need an in-tank pump or a high-pressure external pump. External
pumps are easier to install but they are usually noisy. An in-tank pump
requires a fuel-sender from a fuel-injected car such as a 4.3 TPI Monte

Battery relocation
I decided to relocate my battery to the driver's side because the battery
hookups were on that side of the engine. I think you could re-route the
wires to the other side if you wanted.

The manifolds on my TPI motor were quite a bit larger than the L69
manifolds and the exit is at a slightly different angle. Fortunately I got
the Y-pipe with the TPI motor so I just had to take it to an exhaust shop
to get it modified to hook up to the Monte's catalytic converter.

Required changes to wiring harness
NOTE: These pin-outs may or may not be the same for different years. You
will have to check yours but this will be a useful guide.
15-pin connector
-Cut wire on Pin B (orange) on car-side of connector
-Cut wire on Pin C on car-side of connector and route directly to the
'check-engine' light (the original circuit goes through a 'light driver
module' which will not work with the TPI ECM. I had to modify the light
socket because it originally plugged into a ribbon cable that I couldn't
easily tap into. The wire from Pin C is the ground for the light so you
also have to run an ignition circuit (I used Pin F) to the other side of
the light socket.
-Pins B & G on engine-side of connector are power for the injectors. These
need to be connected to an ignition source (I used Pin F).
-Pin D on engine-side is goes to the alternator. On the L69 harness, this
wire comes from the fuse-block connector so you will have to run a wire
from the small brown wire on the L69 fuse-block connector to the
brown/white wire (Pin D) on the engine side of the 15-pin connector.
-Pin J provides serial data from the ECM and must be routed to ALDL Pins E
& M.
-Pin L is the circuit for the VATS (Vehicle Anti-Theft System) module (if
equipped). If you don't have a VATS module and matching key you will have
to make a signal generator to provide the equivalent signal. You can make
one with about $10 of electronic parts and an electronics whiz.
-Pin P is the purple wire that runs to the transmission. I believe it is
the TCC control. On the TPI wiring harness, this wire runs through the
fuse-block connector so you will have to run a wire form this pin to the
purple wire on the fuse-block connector.

Fuse-block connector
To remove the spade connectors from the fuse-block connector you must first
carefully remove a clip that resembles a comb that keeps the spade
terminals from sliding out. On one connector the clip was blue and on the
other it was white - I forget which. You will be re-using the L69 connector
and inserting the spade terminals from the TPI harness into this connector.
Be careful when removing the old spade terminals because you will have to
get the equivalent ones from the new harness into the same slots. On mine
all the spades were the same size except for one. The two thick red wires
had one wide spade and one narrow one. It is the same on the other
connector too so make sure you get those right.

-Pink/Black wire is for the canister purge solenoid and needs to be on an
ignition circuit
-Purple wire, as mentioned above, must be connected instead to the 15-pin
-The following wires are for the cruise control which I did not use: small
pink, grey and
-There is a purple and yellow wire that go together. They run from a
connector at the transmission are for the VSS/electric speedometer.
-Another purple wire is for the wiper motor.
-White wire is the tach signal. The original tach wire on my car was
clipped to the firewall near the distributor.
-Lt.Green wire is the temperature sender wire for the gauge.
-Brown wire is the oil pressure sender wire for the gauge.
-Small Red wire should be routed to ALDL pin G.
-Brown/White wire is the power for the fuel pump.
Two wires from the L69 fuse-block connector were not needed: Green/White
and Brown. These were both for an oil pressure switch on the L69 engine.
The small brown wire, as mentioned above, must be routed to Pin D on the
15-pin connector.

ALDL connector
I used my original ALDL connector but I got an additional ALDL connector
from a wrecker so I could get extra terminals from it. The ALDL for the TPI
engine uses more terminals in the connector so I carefully removed them
from the extra ALDL and inserted them into mine. The extra terminals are
for serial data and fuel pump testing. This is one step that a lot of
people skip but if you ever break down on the road and have to get another
mechanic to diagnose it this will make it a lot easier.

Costs (Canadian $$ - wholesale)

$1875     Engine (incl. complete wiring harness, ECM, all sensors except
MAF, Y-pipe, throttle cable and accessories)
$296 AC-Delco MAF
$247 AC-Delco fuel sending unit (hanger for in-tank fuel pump)
$80  AC-Delco electric fuel pump
$15  AC-Delco weather-pack connector to mate with connector on fuel sending
$110 Misc. items for fuel delivery (3/8 tubing, 5/16 tubing, fittings,
hoses, filter)
$20  Used TPI kick-down cable
$50  Y-pipe modification
$53  Upper rad support from Grand National
$50  Used air-filter box from Buick T-Type
$20  3" air tubing
$100 Other misc. parts

Other items purchased
$7   New heater hoses
$182 New upper nose support (from rad support to nose - old one was badly
$60  New coolant, oil, filter, power steering fluid, spark plugs, etc.

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