Chevy 5.7 Throttle Body Injection

To answer the initial question briefly and succinctly: TBI was the term used by General Motors for Throttle Body Injection or, in technical jargon, also called central injection. In principle, TBI works like this: img-1258 There is a throttle body with 2 openings, above each of these openings sits an injection nozzle. So in the case of our two Caprice, 2 injectors feed 8 cylinders. In this article I would like to go into a bit of detail about how the TBI works and what parts are involved in making the engine run properly. Most of the parts that can be read out are more or less directly related to the injection and ignition or have influence on one of both. But before we go deeper, a short clarification: Even if the TBI looks a bit like a classic carburetor, it is NOT a carburetor with injectors added. It may look like that on the outside, and it may be regurgitated by the uninitiated, but that doesn’t automatically make it right. The whole system consists externally only of the throttle body, which was mounted like the old carburetors on the intake manifold, and the two injectors. These simply inject into the two openings of the throttle body. The whole thing looks like a large 2-fold carburetor. Hence the assumption that the TBI is a pimped carburetor, which does not make it right. There is more to the TBI than meets the eye and here we come to the point that a TBI is a real injection system after all. An important part of the system is that it can be read out with an ALDL cable. Many will now ask what ALDL should be again. We already had in another article, but here the short form. ALDL stands for Assembly Line Diagnostic Link and was GM’s OBD II precursor in the late 80s and early 90s. There are ECUs and multiple sensors attached to the TBI, otherwise the whole system wouldn’t run properly front and center either. It would run, but either not well or brutally inefficiently. Compared to modern fuel injection systems, the whole thing is of course quite simple, but for a layman then not so simple that you could deduce everything with common sense! ECM Let’s start with the most important part, the engine control unit. The MSG or in the American also ECM (Engine Control Module) called, processes all the data it gets from various sensors and passes these data to various places. We will come to that in a moment, let me just explain a little bit more Imagine the whole principle of TBI like a company. The ECM is the boss, the number one, the undisputed babo of the TBI Corporation. The sensors, which deliver the data to the ECM, are something like “suppliers” of the TBI Corporation. The data supplied by the sensors is recorded, processed, calibrated, calculated and passed on by the ECM. The “employees”, i.e. the components that then receive the data and instructions from the ECM, are things like the ignition, the injection nozzles, the fuel pump, the idle control valve, the engine control light and, of course, the ALDL port at the end, because you want to be able to read out all this stuff somehow. The MKL and the ALDL port have a kind of supervisory or revision function. Now that we have a rough understanding of the principle, we can break down the individual components. So let’s start with the “suppliers”. In the chapter “readout” I will go into the respective components again if they spit out a sensor value. So don’t be surprised if some info is duplicated or not mentioned in this part. At the end a shoe becomes from it, promised O2 Sensor o2 Also better known as lambda sensor. It measures the oxygen content in the exhaust gas and gives the engine control unit a further code number with which it then feeds the injection. This then adjusts the injection quantity and duration. Since most probes only have a very narrow measuring range, they only measure whether the mixture is in a certain ratio. This ideal ratio is 14.7:1, also called lambda 1, but we will go into this in more detail later. There are broadband sensors which can measure a much wider range, but these were at least then so expensive that the installation in the series was not worth it. Such probes also make more sense in the tuning area where you really go into detail when it comes to the mixture. ECT Sensor German drivers know the Engine Coolant Temperature Sensor as the coolant temperature sensor. The sensor measures the temperature of the coolant and tells the ECU when the engine is at its operating temperature. This sensor is controlled by the ECM via a 5V pulse. Depending on the temperature, the sensor returns a different pulse. The ECM compares this pulse with some kind of internal database to determine the temperature of the coolant. These values affect the injection amount, ignition timing, knock detection and idle speed. MAP Sensor map The Manifold Absolute Pressure sensor measures the pressure in the intake manifold. This helps the ECU to know what load condition the engine is in. When the throttle is closed, a vacuum is created in the intake manifold. If the throttle is open, the vacuum is gone, because the engine can now suck its air freely. Think of it as the forerunner of modern mass airflow sensors. Besides the injection, the ignition is also influenced by the MAP sensor. As the name suggests, it measures the barometric pressure in the environment. TPS tps Also known as Throttle Position Sensor. Like the MAP sensor, the sensor helps the ECU detect the correct amount of air. The sensor is basically a small resistor. The standard value here is 5V, at full throttle the value drops to 4.5V. Might be helpful for troubleshooting For example, if the sensor registers a load of 75% or more, this value is passed on to the ECU, which then heavily greases the mixture, which consequently assumes a strong load requirement, which usually results in a strongly opened throttle valve and thus a stronger air flow into the engine. The TPS also has an effect on the ignition timing. VSS veh-speed The Vehicle Speed Sensor, as people who know English have already guessed, gives the vehicle speed. However, this value does not have much influence on the rest. The value is mainly important for the idle control valve to know when the car is really moving and when it is really just idling. Ok, there is one nice thing about the sensor: You can use TunePro RT to read the sensor and see the actual speed. ESC Module ESC stands for Electronic Spark Control, so this module is responsible for controlling the ignition. The ESC gets support from the knock sensor. The knock sensor measures if the engine is ringing and sends this information to the ESC module. The ESC then passes the information to the ECM which then decides how much the engine is ringing and adjusts the ignition accordingly. Crank Signal Sensor This is what we know in Germany as the crank sensor. It measures the revolutions of the crankshaft and gives the signal that the engine is “moving”. This signal goes back to the ECM which then gives the appropriate instructions to ignition and injection. The sensor also ensures that your fuel pump relay gives the command to pump during the starting process. This command to the relay is maintained until the engine is running and has oil pressure. With that out of the way, let’s take a look at the other side of the system that receives the commands from the ECM. SES System SES stands for “Service Engine Soon” and is also known as “Check Engine Light” or “Idiot Light” in the USA. This light always comes on when the ECM has detected a fault. In our country it is more commonly known as the Check Engine Light. In times of OBDII in which cars are able to indicate already in the board computer what is broken such lamps become more and more rare whereby there is often the good old MKL still as addition. ALDL Our ALDL port is also connected to the engine control unit. As a predecessor of OBD II this port allows to read out the values of all possible sensors and error codes on GM vehicles of the late 80s and early 90s. I’ve already covered this topic a bit here (Follow me down the rabbit hole!). However, we will delve a little deeper into the various values in this article. IAC Valve iac This is our already known Idle Air Control Valve. It controls the airflow when the throttle is completely closed. Depending on the input it opens or closes. In the past there were chokes for this, today the injection does it all by itself. Fuel Pump Relay The relay of the fuel pump has been discussed before. As already mentioned, it gets its signals from the crankshaft sensor, so it is only active when the engine is turning but not running. The relay is also responsible for turning off the fuel supply when the ignition key is moved to the “off” position. The relay is also affected by the oil pressure sensor. If the oil pressure sensor does not indicate pressure, the fuel pump relay will shut off the fuel supply to the engine. This brings us to the question why the relay only switches off when the engine is running and oil pressure is present. Injectors Now we come to the injectors Our TBI has an incredible 2 of them The injectors get their instructions from the ECM and regulate the amount of fuel injected. Pretty simple! Interesting is that the nozzles are actually controlled separately by the ECU and not simultaneously. If you have seen the system in action, you know that the nozzles also inject asymmetrically. The injection rhythm at idle is a bit like milking a cow. On the picture above you can see the TBI above the valve cover. In the following video you can see the nozzles working: Distributor/Ignotion Control Module/Coil. Here we come to the topic of ignition. This consists of a classic ignition distributor for the TBI engines. This is supplemented by a control module and an ignition coil. The ECM feeds the ignition with data and thus ensures a good and above all healthy combustion without “knocking”. Readout So now we come to the part with the readout. There are a few values that can be read out with the ALDL cable and an appropriate reader/laptop. As promised, we will go into a few more points from above. This is also necessary because a few of the above mentioned sensors can be read and their values can give information about whether something is wrong. I use the software TunerPro RT for the readout. The TBI may be rather simple by today’s standards, but it is fascinating to see what values are processed that are somehow related to the mixture preparation. There are the following values: IAC (idle air control) position = position of the idle air control valve. This should be pretty self-explanatory The idle air control valve regulates the air flow during idling. Since an injection system, unlike a carburetor, can adjust to changing conditions based on the measured values, it makes sense to have an adjustable valve for the air at idle so that an optimal air/fuel mixture can be maintained. The idea behind this is the same as with the choke. Battery Voltage = Battery voltage battery-voltage Yes, the battery voltage also has an influence on the amount of fuel injected. This is due to the fact that the injectors react more quickly with a higher battery voltage. So if the battery voltage is low this has to be compensated somehow, that’s why the battery voltage is also measured to compensate this difference. But the battery voltage is not only important for the injection. The value is also very useful when you want to know the battery voltage. So you can see if the battery is still good or if the alternator is still working the way it should. OLDPA3 = Electronic ignition control oldpa3 measures if the engine is ringing and adjusts the ignition accordingly if something is registered in this direction. Vehicle Speed = Vehicle speed I think this is self explanatory The Vehicle Speed Sensor measures the vehicle speed. So far so logical, however it is fascinating what else the sensor does! The fourth generation Caprice is the first with a Vehicle Speed Sensor. While the older models were still driven by a speedometer cable, the 91-96 Caprice has no speed sensor. Since the sensor was needed for the standard ABS, it could be used to tell the speedometer what the speed of the vehicle is. The ABS needs the sensor to determine how fast the tires are spinning because it can tell when the wheels are locking and when they are not. But the Vehicle Speed Sensor can do even more! The signal is also used to determine the shift points for the transmission. Based on the speed, the transmission knows, depending on the load, when it has to shift. Engine Speed = Engine speed engine-speed I think this is self-explanatory. TPS (Throttle Position Sensor) = Sensor for throttle position. Measures how much load is currently demanded. The TBI adjusts the injection amount accordingly. BLM (Block Learn Multiplier) Here it gets a bit more complicated. Let’s try to describe it in a simple way. The BLM is something like a long-term value for the gasoline-air mixture. The system knows 256 states, from 0-255. 128 is the golden mean (if you know a bit about computers you will recognize a pattern here) and is the ideal value, so Lambda 1 in technical jargon also called stoichiometric (Ha, right off the bat and that without Google ) mixture. This is 14.7:1, i.e. 14.7 parts air and one part gasoline. Now at the latest it should become clear why engines are also often referred to as oversized air pumps. In order to burn one kilogram of gasoline in an ideal engine, 14.7 kilograms of air are needed. blm-int INT (Integrator) The INT value is closely related to the BLM value. The INT value is something like the short-term memory for the gasoline-air mixture. The INT value is the value that is permanently adjusted while the engine is running. This also has an influence on the BLM, as with the short and long term memory. Here again the 128 plays a role. 128 means that our mixture is perfect. A value above 128 implies that the engine has recognized that it runs too lean and injects more gasoline. A value below 128 implies that the engine is running too rich and that the engine is reducing the fuel supply. The values vary of course with different load conditions. Both values work hand in hand to ensure that the engine gets the right air-fuel mixture in the right amount under all possible load conditions. O2 Sensor = Lambda Probe This is the value that the lambda sensor outputs. Since most lambda sensors do not work until they are at operating temperature, the ECM calculates with fixed values until the sensor has reached its operating temperature. This mode is also called “open loop” mode. For this reason, cars never run as efficiently when cold as when warm. Because of the fixed values, the engine basically always runs the same way, so it does not adjust to the different environmental influences. At that moment, the injection reacts like a carburetor. In “closed loop” mode, the lambda sensor has reached its operating temperature and uses the exhaust gas to measure how well the combustion is running. In the Caprice, the lambda probe is warmed by the exhaust gas and operating temperature is reached at just over 50°C coolant temperature. Modern cars have heated sensors and usually several of them. Usually one in front of and one behind the catalytic converter. Here again BLM and INT play a role, because the values which the lambda sensor outputs influence both. If the sensor detects a too rich mixture, it returns the value to the ECM, which then instructs the TBI to reduce the injection quantity…….we have already discussed this before. MAP = Manifold Absolute Pressure The MAP sensor measures the pressure in the intake manifold. Since the pressure changes depending on the throttle position, this must also be taken into account by the injection. At partial load, a vacuum forms in the intake manifold. If full throttle is applied and the throttle valve opens, this vacuum naturally disappears. A low MAP value implies a high vacuum and thus a low power demand. At full throttle, this vacuum disappears and the MAP sensor outputs a high value. TunePro RT can give the values in kpA and bar. Coolant Temperature coolant This should also be self-explanatory The engine does not run efficiently until the engine is at operating temperature. Until then, the injection lubricates the engine to get it up to operating temperature faster. This explains, besides the not yet existing lambda control, why engines consume more fuel when cold. The engine also adjusts the amount of fuel based on the values of this sensor. A broken temperature sensor can cause the engine not to start at all when cold. If the engine starts from temperatures that are too cold, it will enrich the mixture too much and no ignitable mixture will be produced. TunePro RT can display the values in Fahrenheit and Celsius. MAT (Manifold Air Temperature) = Intake Air Temperature mat This value indicates the temperature of the air in the intake manifold or air filter. On the 91-93 model year Caprice, this sensor sits on the side of the air filter. The temperature of the air drawn in for combustion also affects the mixture. Simply put, there is more oxygen in cold air than in warm air. As we know, the more gasoline-air mixture an engine can burn, the more power it produces. Since the oxygen content determines how much gasoline can be burned, it is important to get as much oxygen as possible into the engine. This principle is used in supercharging. Here, a lot of pressure is used to force more air into the engine than it could naturally draw in. With the extra oxygen kick, more gasoline can be burned resulting in more power. That’s why cold air is so important for good combustion, and that’s why manufacturers have been shielding their air filters from heat as much as possible for years. So guys, throw your great open air filters that sit directly on the intake manifold away again The engine sucks in all the heated air that the engine produces and contains less oxygen. After this little digression comes the explanation why this is so important for the injection. As we already know, there is a perfect ratio between air and gasoline. But if the air has a different oxygen content or temperature than measured by the sensor, problems can occur. Bad engine running, loss of power or a too rich/lean mixture are the result. Depending on how much the values deviate, the engine may simply die. Finally, the most important standard values and other display data for the TBI engines, for the 91-93 Caprice. I don’t know to what extent these values are transferable to other TBI engines, but I think that they should at least fit for all L03 and L05 engines. It is important that the values are read under the following conditions: – Idle – Upper cooling hose hot – Idle (throttle closed) – Gear in N or P – Closed Loop (Lambda sensor warm and measuring) This is important because the values can deviate greatly if these conditions are not met. If you look at everything I have written before, this should be obvious Coolant Temperature: 85-105°C Throttle Position Sensor: 4-1.25 Volt MAP: 1-2 Volt INT: Varies between 0 and 255 BLM: 118-138 IAC: 1-50 Idle Speed: 650 rpm +- 100 rpm (550 rpm +-50 rpm in D) Lambda: between .001 and 999, varies constantly Closed Loop: Should be “closed” when engine is warm. A/C Request: No (“yes” if A/C on) VSS: 0 mp/h (at standstill of course) Batteriy: 13.5V – 14.5V MAT Temperature: 10-90°C (should be about the same as the engine temperature) Did you like the article? 4 out of 4 found the article worth reading. Chevy 5.7 Throttle Body Injection.

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