GM TBI on Ford 351W HOWTO
Max
I've been getting quite a few requests for how to install GM
TBI (Throttle Body Injection) on Ford 351W powered vehicles, ever
since I posted about the success I had in doing it.
I hope this makes it easier for y'all.
The GM TBI is well understood and supposed to be simpler to understand than
similar types of injection from other auto makers. It is cheap and
plentiful (available on V8 trucks from 1987 to 1992) and extremely reliable.
A number of shops make commercial kits available for earlier Chevy engines
and these have been reported on in the car and truck magazines. Also the
Holley Projection unit is similar in concept and execution so this is very
accessible technology.
Originally, I had intended to purchase the Holley system, but had difficulty
in finding a company who would sell it to me, and then I began to hear
rumors about teething problems, which well may be fixed by now. In addition,
the Holley appeared to be far from turnkey when applied to a Ford engine.
The commercial kits for GM TBI also appeared not to support engines other
than GM very well and I would be required to fabricate once again, despite a
steep cost rivalling Holley's offerings.
I then began to investigate the feasability of rolling my own with parts to
be obtained from a wrecking yard. After some thinking, the whole setup was
obtained by me from a wrecker for around $200, except for the adapter plate
which I had fabricated, wire, fuses, connectors, nuts, bolts, fuel
filter, neoprene injection fuel line, and a different 02 sensor, all
available from local discount auto parts stores.
I wanted to get something from a vehicle with similar engine size and
weight, to avoid ECM PROM reprogramming issues, at least initially. Since
the host vehicle was to be a 1975-1/2-1986 Ford van with a new 351W V8
installed (I had earlier converted the vehicle from a 6 to an 8 cylinder) I
chose the donor vehicle that best matched in the yard I had good rapport
with, a 1989 GMC extended cab pickup with Chevy small block 350 V8 and auto
transmission without overdrive.
You can either make or obtain an adapter plate to mate the TBI unit
itself to a square bore intake manifold. I previously had a 650 cfm
Holley four barrel installed there. You mount the TBI unit with
3 bolts to the adapter, and then mount the adapter and unit in the
usual way with four studs and nuts to the manifold.
You remove the mechanical fuel pump and and block off the opening with
a suitable plate, available either commercially or from a Ford small
block V8 in the wrecking yard. I did the latter.
Use a distributor with a magnetic pickup coil. A 1978 era stock
distributor from 351W will work. Disassemble it and remove the weights
and rotate the assembly the weights attached to until it locks in
place, then reassemble. Remove or modify the vacuum advance until
that is locked. You may need to index the teeth position to TDC. I
used silicone sealer to do this. There are three wires from the
distributor. The black is ground; mount it to a surface on the
distributor housing. The other two connections go to the GM
electronic module that came off the original GM distributor; you
may need to be able to swap these on the original GM connector
to the module to whatever gives best results. The connections from the
module, which I mounted to the distributor body using the remains
of the vacuum advance mechanism, use sealed plug assemblies to the
original GM coil which mounts on the intake manifold, and to the
ESC module and ECM (computer).
You need to get the proper sensors. The anti-knock sensor will
mount in the block on the passenger side of the motor, next to
the motor mount, which will need to be slightly ground down
for clearance. The anti-knock sensor attaches by wire to the ESC
module, mounted on the passenger side of the engine next to the
TBI unit, along with the MAP sensor and EGR solenoid. The MAP
sensor has a vacuum attachment to the rear of the TBI unit, as
well as a connector to the ECM. The ESC module, which retards
ignition timing when the knock sensor senses preignition, is
mounted here as well and has connections to the ECM and module.
You also need the manifold temperature sensor. This I mounted
where the original gauge temperature sensor went; it uses
the same threads. I relocated the gauge sending unit to the
thermostat housing - I obtained one with a threaded opening.
You need to get an oxygen sensor for the exhaust stream. I decided
to use a preheated one with 3 wires. The original is one wire.
The three wire is better since the sensor needs to be around 600 degrees
before the computer can go closed loop, adjusting mixture
dynamically for better emissions and drivability. The +12V wire should
be connected to the same wire as the electric fuel pump, so that
it is drawing current only when the fuel pump is running - that is,
when the engine is actually running, not just the ignition on.
The other connections are ground and the original 02 sensor to ECM
connection. I had installed headers, so I welded a nut of the same
thread dimensions as the sensor threads to a hole I had drilled in the
collector to exhaust pipe connection, and installed the sensor using
the anti-seize compound on the threads. Since the sensor is further
away from the exhaust outlet than with the original manifold, I
used the heated sensor since it takes longer to reach operating
temperature. Also, headers dissipate heat more than the original
cast iron manifolds, so I found this sensor worked better. It's
available from discount stores for around $30 - I used an aftermarket
3 wire sensor from Tomco (TI), part 11014.
For an intake, I used an aluminum Performer 351W from Edelbrock. I
recommend the EGR version, because although the engine will run
without EGR, the ECM will generate trouble codes under certain
conditions. When it thinks EGR should be on, it will find that
the exhaust stream is not as lean as it wishes, and remains
richer, which it will flag as an EGR trouble code.
You need fuel supply and return lines. Don't use the evaporative
canister line for return - it isn't big enough. Keep it
and connect the canister to the TBI connection for that purpose.
I used plastic lines from a 1989 Ford van, as well as its fuel tank
which supports a submergible elctric pump. Get the original pump
from the TBI setup; it will mount with very little modification
where the Ford pump went. (Both are AC, but the Ford pump is
a 9 psi, the TBI a 15 psi.) I also used the plastic reservoir from
Ford that mounts inside the frame under the driver, and which connects
the plastic lines. I used rubber fuel injection hose on the other
side of the reservoir to mount to the TBI fuel in/out fittings.
On injected Fords, a 55 psi pump is used between the fuel rail
and the reservoir, but instead I mount a GM fuel filter for
EFI applications using appropraite fittings and clamps. Be sure to
route all fuel lines well away from exhaust parts, especially away
from catalytic converters. I recommend keeping any lines at least two
feet away from exhaust components.
What else? Basically, there are three +12V connections for the ECM
and fuel pump relay circuits. +12V from the battery, fused
appropriately, that is always live; Starter +12V, and Run +12V. The
Run +12V is live when the ignition key is on. The Starter +12V can be
obtained from the starter solenoid/relay, from the same connection as the
starter uses. Use a 3.5 amp fuse for Start/Crank, and 10 Amps for the
other two.
The fuel pump relay is usually mounted somewhere on the firewall;
and in the fuel pump circuit there is a sensor that must be mounted
into the same fitting as the oil pressure sender. A steel plumbing fitting
"T" connector and pipe threads can be used to adapt the oil pressure
connection to two outlets. The oil pressure sensor cuts off +12V to
the fuel pump when oil pressure drops below 5 psi. This is important
so that both fuel pump and 02 sensor aren't powered when the engine
is not running, except for the relay bypass during Start to bring up
pressure so that the injectors will deliver fuel. This is also a
nice feature as the engine will stop if oil pressure is ever lost. Run
the fuel pump circuit wire back along the frame to the pump, following
the same wiring path as the fuel tank gauge sender wires.
Speed sensor... you need to modify the Ford speedo to accept the GM
speed sensor pickup. Get the sensor from the original GM speedo and
see how it works. It uses an LED and sensor that uses the
interruption of the light beam by the speedo mechanism as it
spins. It is fairly easy to modify a mechanical speedometer that
uses the same principle.
I used the hot fuel handling module. This turned out to be
important to avoid vapor lock when the engine is hot. The engine
would not start without this module when it was hot. The module
allows the fuel pump to circulate extra fuel to cool the TBI
so that the injectors will actually have fuel to deliver when
starting instead of vapor.
It's important to get the entire original wiring harness, from both
the engine and behind the dash. Get the Chilton manual for 1989
GM pickups and use the ECM wiring diagram for reference. Get all
the sensors from the donor vehicle. Get the distributor and ECM
(under the dash) from the same originally running vehicle, as
well as the TBI unit. Get the fuel pump relay and get an extra to
wire in as a neutral/drive switch off the existing transmission
neutral safety switch.
Stock throttle cables are usually able to be used with only
minor modifications to the mounting plate. To get full throttle
travel, I found it necessary to saw off the throttle to cable
mount on the TBI, and screw attachment hardware (stud and nut)
from a carburetor into a conveniently existing hole just
below the original.
This covers most of it; my initial problem was that the injectors
were stuck closed since I had stored the TBI unit outside for
several months. Once I had that problem fixed (whacked with a
big hammer while applying +12V, not recommended!!) I drove the
vehicle trouble free 5000 miles across country, and more
thousands locally since without it failing.
It is helpful to have a running vehicle as the donor; that means you
know it all once worked, and you should have all working parts,
a very good assurance when you are making custom installations
like this.
I recommend getting a logic probe for troubleshooting digital
computer circuits from Radio Shack; this is only $20 or so and
will allow you to see if there are pulses from the module
and on the injectors from the ECM. Nice to see if signals are
being properly generated, believe me!
Without prior experience with this setup, I completed installation
in several days under an outside roof in my back yard.
It's been running with easier starting, better economy, far better emissions
and at least equal power for 6 months and thousands of trouble-free miles.
Hope this helps!