GM TBI Swap
This page is for information about GM Throttle Body Injection
EFI swaps. TBI is a fuel injection system that uses a pair of injectors mounted
in a single housing that is mounted and functions much like a carburetor, except
that the injectors replace the venturis, jets, air bleeds, fuel bowls, and
For general-purpose EFI information, please refer to my
EFI Basics page. For GM TPI systems, please refer to
my GM TPI Swap page. For Ford systems, please refer
to my Ford EFI Swap page.
Goals for this Web Page
This page exists to contain all of the TBI-specific information I have run
across during my work on my TPI swap. Rather than
try and explain the differences in one page, I have chosen to collect them here.
Note that I have not actually done a TBI swap yet - this page exists to gather
the details I gave into one place. I would prefer a TPI system, but I do recognize that many people will prefer a TBI style swap
over a TPI style swap because of the ease and simplicity of mounting the TBI
throttle body and injector assembly to existing intake manifolds that were designed to
accept a carburetor. A simple adaptor plate is all that is needed to accomplish
this, and many folks sell them. If you are willing to drill a hole in the
firewall and mount the computer inside the passenger compartment (which I am
not on all of my cars) then this swap becomes very attractive for both cost and ease of
I've been gathering parts for this swap, and I need to keep track of what I
have and what I need, so here's the list.
||From a 1992 Blazer with a 5.7L and an automatic. The one I got was
#16146299. Based on my (minimal) research, it appears that it plugs into
the same harness as the popular #1227747, shares the same pinouts, and
the main difference I could find is that this computer does not have the "Highway
Mode" in it. For a beginner like me, that's no big deal.
also acquired two #16144288 computers from a local wrecking yard. These
are for 4.3L V6 applications from 1990-93, with Astro vans being a
popular source for these computers - that's where mine came from.
||From 1989 Suburban with a 5.7L and an automatic. Has wiring stubs to
connect to interior wiring, the ALDL connector with a wiring stub, a
connector + stub for the O2 sensor wiring, and the TH700R4 wiring was
cut near the rear of the engine. Includes the small HEI module to coil
||Has TPS, IAC, and regulator attached.
|Fuel Lines and Filter
||These are the factory high pressure braided line from the fuel
filter to the TBI unit, and then from the TBI unit back down to the
return line connection near the transmission.
||Small cap unit, with module attached.
||Remote coil style to match small cap HEI distributor.
|Fuel Pump Relay
||Came with the harness.
|Water Temp Sensor
||Came with the harness.
||Came with the harness and included a small wiring stub.
||Local wrecking yard
||Measures the vacuum in the manifold to tell the computer what kind
of load the engine is under. Most common ones are 1-BAR, there are also
2 and 3 BAR versions available for forced induction systems.
is the typical/usual 1 BAR sensor.
||Listens for engine knock (detonation, pre-ignition). They are
basically a very highly tuned and specialized microphone that only
responds to a very narrow frequency band.
||Translates the signal from the knock sensor into something the
computer can understand.
I have two - 16065711 and 16128251. Both were
used on V6 and V8 applications from what I can tell.
|EGR Solenoid Valve
||Controls the vacuum flow to the EGR valve. On the 5.7L and 7.4L
engines this is labeled as an EVRV Solenoid, which stands for Electronic
Vacuum Regulator Valve, and is a three wire device. On the 4.3L and 5.0L
engines, it's labeled as a EGR Solenoid and is a two wire device.
one is a two-wire unit off of a 4.3L V6.
|Oil Pressure Sensor
||Senses oil pressure and helps control the fuel pump - if there is no
oil pressure (such as if the engine stalls), the oil pump shuts off. The
one I got is a three wire sensor.
|Exhaust Air Control Solenoid
||Controls the vacuum flow to the diverter valve for the air (smog)
pump. Used to divert the air from the smog pump to atmosphere instead of
sending it to the exhaust system.
||Use a four wire heated sensor with a dedicated ground if possible -
AC Delco AFS75 and pigtail PT368 is suggested to hook it up. Don't buy used
O2 sensors except for mock-up purposes! They are a "wear item" and it's
just not worth it trying to tune your TBI system with an O2 sensor of
|Vehicle Speed Sensor
||Used to tell the computer how fast the vehicle is going. Can use a
factory style unit (if appropriate for the vehicle/transmission) or an aftermarket unit -
it just needs to be a one-wire 2000 pulse per mile unit.
of good ones, in particular the #2PRS and #2PRS-EXT, but they are
|Air Filter Assembly
||A stock TBI air cleaner assembly can be used, or possibly any standard 4-bbl
air cleaner can be substituted. Emissions compliance requires a hot air
controls in some cases - check your donor engine to be sure. K&N
and other companies sell various appropriate filters. Make sure the
injector wiring is not pinched or subject to chafing if a non-stock air
filter housing is used.
|Air Inlet Ducting
||May need to be custom fabricated if you want to get a "cold air"
source. JTR sells
a lot of good pieces for this. It looks like you can also just use a
simple 4-bbl open element air cleaner if needed?
||Used to adjust the engine RPM as you go into and out of park/neutral
and any gear. The computer needs to have a specific wire grounded only
when the transmission is in park/neutral. If the factory switch can't be
used, then a relay setup needs to be fabricated off the original starter
Park/Neutral switch and wiring to make this work.
|Service Engine Soon Light
||Fabricate something inside the vehicle to handle this. It simply needs to be
visible from the driver's seat. A small bulb mounted somewhere on the
instrument panel works fine and the cost should be negligible - under
||Shuts off the fuel pump in case of an accident. They are a purely
mechanical switch that responds to any sufficiently hard "jolt" by
opening the connection and turning off the fuel pump. I can't seem to
find out if these are used on the stock GM TBI systems, or if they use
only the oil pressure as a surrogate for this. More research is
|High Pressure Fuel Pump
||Needs to be appropriate for pressure and flow of a TBI system.
Various choices are available, see my main EFI swap page for details.
||Optional. Used to provide a constant source of fuel for the high
pressure fuel pump, even if the fuel level in the gas tank is low. See
my main EFI swap page for details.
|Low Pressure Fuel Pump
||Optional. Only used if you are using a surge tank. See
my main EFI swap page for details.
||Hooked up to the starter solenoid circuit and is used to tell the
computer that the starter is engaged. This is simply a wire that has
power when the key is in the "start" position.
||Hooked up to the AC clutch control wire and is used to tell the
computer that the AC is on so it can raise the idle a bit. This is
simply a wire that has power when the AC compressor is turned on.
||Total without cruise and other misc bits below
|Partial wiring harness
||local wrecking yard
||From an Astro with a 4.3L V6, circa 1990. It has been cut in a
couple places, but it has most of the connectors still on it and is only
missing the transmission connectors and one of the TBI injector
|Water Temp Sensor
||Came with the partial harness.
|Cruise Control System
||From 1989 Suburban with a 5.7L and an automatic. Includes brain,
wiring, switches, some vacuum hoses, throttle actuator that mounts to
the engine. Does not include VSS as these were mounted in the
speedometer in this era truck. I grabbed it because it was a good deal
and it can easily be used with the TBI setup - it just needs to get
access to the right kind of VSS pulse via one wire that goes to the
cruise control system.
||Total with cruise and other misc bits
Knock Sensors and ESC Modules
The knock sensors and their associated modules were matched by application -
this includes engine size, year, and sometimes transmission (manual vs.
automatic, for example). The knock sensors are basically a tuned microphone that
listens for a very specific frequency, and when the module takes note of that
frequency being heard, it sends a signal to the computer that engine knock is
occurring. The computer then retards the timing to stop the knocking. This is
strictly a safety feature and not a tuning feature - the knock sensor can only
detect knock after it happens, not before, and by then engine damage may have
This is a list of the ESC modules and knock sensors that I have been able to
glean from various websites and parts catalogs. It is by no means complete, it
is more representative of what information I have run into cross with what parts
I have grabbed out of a junkyard and tried to decode their application data.
||4.3L V6, 5.7L V8
||4.3L V6, 5.7L V8
Given that some modules and sensors were used on both V6 and V8 applications,
I can only conclude that the specific combination of knock sensor and ESC module
is highly tuned for a specific application
Here are some pictures of a 4.3L V6 GM TBI unit that I scrounged out of a
junkyard to use for mock-up purposes. The small block V8 and V6 units are
identical and use 1 3/4" bores. The big block V8 units use 2" bores. I believe
the mounting pattern and the bore centers are the same, they just put slightly
larger holes on the big block V8 units. These pictures also highlight the
unusual mounting pattern of the GM TBI units - they use a triangular bolt
pattern with 3 bolts, and the base plate on the TBI unit is a decidedly
non-square pattern. The second picture also shows the maze of vacuum passages on
the underside of the TBI unit that must be properly sealed to whatever the
mounting surface is - this will be very important if you are using some form of