I am starting this thread because of intrest in the operation of CFI in the DOD, CFI, and "Norms whatever" threads. This is purely academic, no relation to the other threads/arguements, other than that the subject is the same. This is for CFI, not the LT-5.
or "The CrossFire Vault" Yesterday. After doing some digging, I came up with some good stuff on how this system operates, and its "inherent problems". I will use their s/n's, but they are of no signifigance.
Fundamentally, the crossfire system is a small crossram manifold with two single barrel throttle body injectors, one over the right bank of intake runners and one over the left bank. throttle body injectors are essentially computer controlled carbuerators. a crossram manifold is like a tunnel ram that has been flattened by laying the runners down across each other, so you get the torque benefits of long intake runners
This is the theory in a nutshell. Will post pics of intake as soon as I find them.
In 1982 the L83 was equipped with an electronic fuel injection system dubbed "Cross Fire Injection". The engine
was called L83 and had the same block casting# as the L81 and 1980 late production L82's.
The Cross-Fire Injection system had two throttle bodies with ECM controlled fuel injectors. The 1982 ECM has
more functions than just the spark advance and smog pump that the 81 ECM has. It also controls fuel and air
flow to the engine and transmission converter lockup. Idle air flow is controlled in the same way as in the
L81, with an Idle Air Motor located in each of the two Throttle Bodies. Fuel requirements are controlled by
monitoring the engine load, throttle position sensor and combustion efficiency. Combustion efficiency is
monitored by the O2 sensor. It indicates the amount of oxygen in the exhaust system.
When there is too much oxygen in the exhaust system it is assumed that not all the oxygen has burned and the
engine is running lean. The ECM enters fuel "enrichment" mode and more fuel is added. This is done to the
point that the O2 sensor senses no oxygen in the exhaust. Then the ECM enters "enleanment" mode. Less fuel
is added and the engine will start to run leaner to the point that the O2 sensor notices a lean condition.
Then "enrichment" mode is entered again. It does this several times a second.
This way the engine will always (theoretically) run in the vicinity of an ideal fuel/oxygen mixture.
Emissions are controlled by:
* Optimizing combustion efficiency:
Optimizing combustion efficiency is done by adjusting spark curves according to the
requirements of the engine. These requirements differ when circumstances change. When for instance
the engine is put under load the fuel requirements are of course different than when at idle.
* Pumping fresh air into the exhaust system
The smog pump (aka A.I.R. pump, = Air Injection Reactor pump) pumps fresh air into the exhaust
system to stimulate the burning of unburnt hydrocarbons.
This is done in two seperate locations; in the catalytic converter and in the air tubes in the
headers. When the engine is cold, open loop mode (Coolant temperature low, O2 sensor not at operating
temperature), air is pumped through the airtubes into the exhaust runners of the cilinder heads, this
is done to speed up O2 sensor warmup. When the engine is at operating tempreature (closed loop mode)
the ECM energizes a solenoid in the smog pump switching valve and routes the air to the catalytic
converter. This helps the catalytic converter to convert NOx (nitrogen oxides) and unburned
hydrocarbons.
This is an exploded view of the two Rochester 400 throttle bodies that are part of the Cross-Fire System. The
throttle bodies each feed a bank of cilinders, the right Throttle body feeds the left bank and vice versa.
The numbers in the picture above correspond to the following parts:
Front Unit (passenger side) Rear Unit
1 Screw & Lockwasher (2)-Fuel Meter Cover (short) 1 Screw & Lockwasher (2)-Fuel Meter Cover (short)
2 Screw & Lockwasher (3)-Fuel Meter Cover (long) 2 Screw & Lockwasher (3)-Fuel Meter Cover (long)
3 Fuel Meter Cover & Accumulator Assembly 3 Fuel Meter Cover & Regulator Assembly
4 Screw & Lockwasher (4)-Diaphragm Cover 4 Screw & Lockwasher (4)-Diaphragm Cover
5 Cover-Spring & Diaphragm 5 Cover-Spring & Diaphragm
6 Retainer Spring 6 Spring-Pressure Regulator Diaphragm
7 Spring-Accumulator Diaphragm 7 Diaphragm Assembly-Pressure Regulator
8 Diaphragm Assembly Accumulator 8 Dust Seal-Pressure Regulator
9 Gasket-Fuel Outlet Passage 9 Gasket-Fuel Outlet Passage
10 Gasket-Fuel Meter Cover 10 Gasket-Fuel Meter Cover
11 Injector-Fuel 11 Injector-Fuel
12 O-Ring-Fuel Injector (small) 12 O-Ring-Fuel Injector (small)
13 Filter Fuel Injector 13 Filter Fuel Injector
14 O-Ring-Fuel Injector (large) 14 O-Ring-Fuel Injector (large)
15 Washer O-Ring Back Up 15 Washer O-Ring Back Up
16 Fitting-Fuel Inlet 16 Fitting-Fuel Inlet
17 Gasket-Fitting 17 Gasket-Fitting
18 Fitting-Fuel Return 18 Fitting-Fuel Return
19 Gasket-Fitting 19 Gasket-Fitting
20 Screw & Lockwasher (3)-Fuel Meter Body 20 Screw & Lockwasher (3)-Fuel Meter Body
21 Fuel Meter Body 21 Fuel Meter Body
22 Gasket-Fuel Meter Body 22 Gasket-Fuel Meter Body
23 Valve-Idle Air Control 23 Screw & Lockwasher w/ Retainer (2)-Sensor
24 Gasket-Air Control Assembly 24 Sensor-Throttle position
25 Throttle-Body Assembly 25 Valve-Idle Air Control
26 Gasket-Air Control Valve
27 Throttle Body Assembly
As you can see a throttlebody consist only of a few parts when gaskets and O-rings are not included.
In comparison to a carb it is very easy to rebuild but normally it could go thousands of miles without ever
needing a rebuild.
The two throttlebodies are mounted on a decklid wich in it's turn is mounted on a manifold bottom. The manifold
is a single plane type manifold with relative small and long runners. The small long runners promote low end
torque but hurt high end horsepower.
The pulsing of the injectors is controlled by the ECM this is known as Pulse Width Modulation (PWM). The ECM (
Electronic Control Module) is a computer, wich is mounted in the drivers side storage compartment in front of
the battery.
The ECM is the "brain" of the fuel injection system.
This one is a '7747 ECM from Turbo City
The '82 ECM is the 1225550, the 84 manual is the 1226430 and the 84 auto is the 1226026.
The ECM is devided into three major sections:
The ROM (READ ONLY MEMORY.)
The PROM (PROGRAMMABLE READ ONLY MEMORY) also known simply "the chip".
There's also a CALPAK, wich is the calibration for the type of engine. Some ECM's have been used in bothe V8 and V6 engines, the '7747 is such an ECM. These have different calpaks (can be swapped out).
The RAM (RANDOM ACCESS MEMORY).
The ROM contains the basic set of instructions for the ECM to follow. The programming in this chip cannot be
erased or changed. The ROM is NON Volatile.
The PROM works along with the ROM to fine-tune the functions of fuel and timing control. The PROM can be
replaced by a "power" chip (also a prom) or an EPROM (or even EEPROM) from wich the data can be erased and
changed. The PROM is NON Volatile.
The RAM has three primary functions:
To act as scratchpad (temporary memory) in case of a mathematical calculation.
To store BLM (Block Learn Multiplier) information when the engine is off or the ECM is in open loop.
To store fault (trouble) codes. These codes are stored for 50 starts or whenever the power (orange wire on
juction block for '82 vette) is disconnected. Unlike the ROM and PROM the RAM is volatile.
The ECM controls the injection system, it fuctions in either one of 3 different modes:
* Shutdown Mode..
When the ignition is off for 2 or more seconds. Only the RAM (trouble codes) and the BLM remain powered.
* Startup Mode.
When engine is cranked. Timing is locked at initial starup and air/fuel ratio is enriched. This mode is on for
about two seconds after starting to ensure the engine will continue to run.
* Running mode
devided in:
o CLOSED LOOP.
The red arrow doesn't indicate a signal, it's an event. Due to the more/less pulsing of the injectors a
rich/lean condition will be observed and the ECM will compensate for this.
In closed loop mode the ECM has 2 differend modes;
+ Enleanment Mode
When the throttle is closed.
+ Enrichment Mode.
# At wide open throttle.
# High engine load.
# High engine RPM.
# Overheating engine. (the cold fuel is a great contributor to engine cooling)
The ECM is normally in enleanment mode, it constantly lowers fuel addition. When the oxygen sensor detects a
lean condition enrichment mdode is entered untill the oxygen sensor doesn't sense a lean condition anymore.
Than enleanment is entered again. This (theoretic) gaurantees an "ideal" air/fuel ratio.
o OPEN LOOP.
+ Fuel cutoff Mode.
When the throttle is closed and the MAP sensor notices a negative load (deceleration) untill about 1500 RPM..
+ Clear flood Mode.
When throttle is depressed more than 80% while cranking. Injectors are turned off or air/fuel ratio is lowered
to 20:1.
+ Limp Home Mode.
When there is major trouble with any of the critical sensors/actuators.
The ECM monitors different sensors and controls the injectors and actuators to respond to changes/demands.
The different sensors and actuators are:
* The Oxygen
sensor is the only sensor on the car that creates it's own voltage and has therefore only one wire
coming from it. It's actually a chemical voltage generator, based on the potential difference between the
oxygen rich condition in outside air and the lean condition in exhaust gas.. When it's at it's operating
temperature of about 600ºFahrenheit it will produce a Voltage ranging from 100 to 900 mV. At operating
temperatures the sensor will respond to changes in the oxygen content in the exhaust gasses. It creates a
potential difference between the "clean" oxygen rich outside air and the oxygen poor exhaust gas. The voltage
potential is developed due to chemical imbalance between the two oxygen concentrations. When the voltage is
low (oxygen levels in exhaust high) the ECM will assume the engine is running lean and thus enter the enrichment
mode. Lean conditions usually produce voltages lower than 450mV, rich will be over 450mV. As you can see there
is a very critical value for "ideal" air-fuel ratio. This is done to ensure that the engine never runs very
lean/rich. This way a nearly ideal air fuel ratio is always obtained, the engine never gets the chance to
run off this point by far without the ECM noticing it.
Due to the nature of the oxygen sensor it has a hard time distinguishing between a perfect and a rich running
engine, when all oxygen is burnt the mixture can be ideal or rich. The oxygen sensor doesn't recognise surplus
(unburnt) fuel in the exhaust. Therefore the ECM will always assume the engine is running rich unless it
notices a lean condition.
* The Tach Signal
The Tach signal is used to synchronise and sometimes (WOT) sequence the injectors. At very high engine RPM the
ECM always enters enrichment mode.
The TPS is actually a three wire potentiometer. It's got a 5V reference sent to it
by the ECM. The TPS is grounded through the ECM. The 5V is lowered to a different voltage through the
potentiometer (read variable resistor) When at no throttle the resistance is lowest and the voltage is also
lowest (normalle set to 0.525V ±0.025) When at full throttle the resistance between the 5V and the ground is
highest (theoretical infinity) and the potential difference (voltage) will be 5V.
* The Idle Air Control valve or IAC (stepper motor)
The IAC is a motorised plunger that regulates the idle speed of the
engine by regulating the incoming airflow. The IAC has 256 positions. At normal idle it's somwhere around
position 20. When full throttle is applied the IAC valve completely opens.
The EST retards timing when the knock sensor (a sort of microphone) notices
detonation. Normal spark timing is controlled by the EST, commanded by the ECM.
* The EGR or Exhaust Gas Recirculation
EGR is a method to decrease emissions by venting exhaust gas into the intake
(about 7% of the intake volume is rendered "useless" due to this). It also decreases detonation due to the
uncombustable (inert) exhaust gas. The EGR position is ECM controlled via the EGR position control solenoid.
This is a solenoid that regulates vacuum to the EGR valve thus opening/closing it.
* The AIR system or Air Injection Reactor
The A.I.R system consists of an AIR pump or just SMOG pump, that pumps fresh air into the headers/catalytic converter.
When the engine is in closed loop air flows into the headers (and cylinder head exhaust ports) to speed up O2
sensor warmup. When the engine is running in closed loop air is pumped into the catalytic converter to speed up
the chemical reactions taking place there. Also during deceleration the air is vented to the atmosphere to reduce
detonation in the exhaust. The route the air travels is regulated by a control solenoid (that is ECM controlled)
* The TCC or Torque Converter Clutch (lockup converter)
The TCC is engaged when the car is travelling at about 30mph at
relatively light load and in a high gear and when a relatively steady signal is observed from the TPS (steady
throttle) This is done to maximize fuel efficiency.
* AC compressor clutch
When the Air Conditioning compressor clutch is on the ECM increases the RPM at idle to account for the increased
load.
* The Auxiliary cooling fan
The Cooling Fan is engaged when the ECM detects a high signal from the coolant temperature switch. On the Cross-
Fire system the auxiliary fan is NOT ECM controlled
* CTS or Coolant Temperature sender
The Coolant Temperature sensor on the manifold sends a signal to the ECM. The one on the drivers side cylinder
head goes to the temperature gauge, the passenger side one controls the auxiliary fan.
* The MAP sensor or Manifold Absolute Pressure sensor
The MAP monitors the manifold pressure and is an indicator for engine
oad. Also the ECM calculates the quantity of incoming air from the signal of this sensor.
Maintaining the Cross-Fire Injection system
When all service parts of the Cross-Fire system are changed at the right intervals the Cross-Fire system needs no
or only minor upkeep to keep it functioning properly, thus the claim of some that buying a Cross-Fire vette or
camaro is asking for trouble is a myth.
Most people that experience problems with the Cross-Fire system have mingled with parts they don't understand or
have a vacuum leak somewhere.
To service the system you need several basic tools and parts:
* A fuel pressure gauge
* A multimeter
* A decent repair manual
* Tool J-33047 or duct tape (or grounding the ALDL connector)
* A torque wrench
* Electrical cleaner
It would be beneficial if you also have:
* An ALDL scanner
* Manometer
The manifold is known for leaking, but only does so if it has been apart and the decklid is not retorqued to about
20-25 lbs/ft or the gasket is misaligned. Problems can also occur when the idle balance screw has been tampered
with. GM welded it to the connection rod to prevent tampering.
Also the throttle stop screws can be adjusted. These are originally plugged with caps, but they can be removed.
Some manuals let you drill holes from the top of the throttlebody base down under a 30 degree angle right into the
stop s crew cavity and let you drive the cap out with a center punch.
I have another method wich I think is better because only the cap will be destroyed ( with the other method they
also won't survive and even if they did you couldn't and wouldn't replace them) and there is no chance of iron
curlings falling into the manifold.
First remove the brake booster vacuum fitting from the intake manifold to get some clearance. Take a small drill
and drill a hole in each blockoff cap. Take a small screwdriver and peer out the cap and.....PRESTO, the screws
are accesible and no damage is done to the throttlebodies themselves.
If the engine has collected a lot of miles balancing the two throttlebodies and adjusting minimum air (the amount
of air that seeps past the throtlleplates at idle) may be required.
Adjusting minimum air should be done with the engine warm.
You'll need to acquire a (water or mercury)manometer to measure vacuum.
You'll need to block off the idle air control solenoid air feed passage with special tools (part# J-33047) or something fabricated yourself such as strong duct-tape. You can also ground the ALDL so the IAC motors close. Then disconnect the IAC's from the engine harness so the ECM can't reset them
* First hook up the manometer to a drivers side throttlebody vacuum port.
Be sure all other vacuum ports are either capped or attached and won't leak air.
* Now adjust the throttle plate stop screw so that 6 inches water or 0.45 inches Hg of vacuum is obtained.
* Move over to the other throttlebody and hook the manometer up (cap the port of the other throttle body).
* Now using the idle balance screw (if it's still welded break the seal) obtain the same amounts of vacuum.
* Now only the throttle position sensor needs to be adjusted so that it reads 0.525 ±0.025V at no throttle.
This guy deserves a gold medal. Lots and lots of useful info in this post. I think this explains it pretty well, but let's discuss. Again, I will post pics as soon as I find them.
