mpdive
Chief Petty Officer
- Joined
- Apr 23, 2011
- Messages
- 567
A lot of post's lately deal with drive ability problems which were much easier to diagnose in the "old days". With the advent of fuel injection and computer controls, the same sub systems exist but are either monitored or controlled by the on board computer (ECM). This post is directed at the laymen to help better understand what is controlling their engine and to aid in possible diagnoses before hauling it to the dealer. I am in no way a guru of these systems, but working in the automotive field for many years, has led me to find easy, non garbled ways to explain engine problems to customers.
First and foremost, is the question of why computer control and fuel inject an engine?
The auto industry is always striving for performance and fuel efficiency in an engine. The goal is "stoichiometric" or "perfect combustion". This is almost impossible to achieve since the engine loads and speed are never constant. The addition of fuel injection is one step closer to being able to achieve that goal. The addition of the ECM allowed the computer to monitor multiple engine systems and make finite adjustments to try to achieve stoichiometric balance. What does all this mean, and how does it work? Let's start with a typical morning on a nice summer day. The fish are biting, and your stomach is full from the McDonald's sausage mcmuffin and two hash brown's you ate on the way to the dock. It's gonna be a great day.
You get the boat in the water and turn the key. The fuel pump is instantly energized, and the fuel rails are pressurized. You start the engine. The instant the engine is started the ECM is running in what is known as "open loop". All this means is that a prescribed set of values have been stored in the computer for a cold engine start up. These would include an enrichment circuit meaning the dwell or "on time" of the injectors is increased. This serves as your choke. A timing setting and air flow is also controlled. The ECM is looking at several sensors during this warm up especially your coolant temp sender. The ECM watches these sensors by supplying a fixed voltage to the sensor and "watching" what comes back. Since they are mostly resistor sensors, the computer knows the state of the engine. For example, when the ECM sends the 12V signal to the coolant sensor and receives back 4.5 volts it now knows the engine temp. There are other sensors it is watching such as manifold pressure sensors that tell if the engine is under a load condition, mass air flow or MAF which measures the velocity and density of the incoming combustion air etc..They all operate on the same principle of voltage in voltage out. OK. So anyhow we are finishing our coffee as we wait for the engine to warm up. In our exhaust is the all important O2 sensor. It is a little different than the other sensors because there is no voltage supplied to it. It has a single wire and in all aspects is a self contained battery. Two dissimilar pieces of metal stay separated by an electrolyte which when cold resembles parafin wax. As the exhaust heats up the "wax" begins to melt and the O2 sensor begins to generate it's own current. It can usually generate up to 1 volt. As it begins to generate current, the ECM receives this signal. As you take your last sip of coffee, the ECM goes into "closed loop" operation largely due to the O2 sensor beginning to operate. All this means is that instead of the prescribed values that it was running on in open loop, it now has the ability to monitor and change engine conditions based on values received from the sensors. OK, so were out past the now wake zone and the sausage mcmuffin is not sitting well, but there's fish to catch. You open the throttle. This is when the amazement of the ECM and the "feedback" system of sensors really shines. When you cracked the throttle, within thousandths of a second the ECM looked at multiple sensors to verify this is what you wanted to do. It looked at your throttle position sensor "TPS" to verify there was an increase in throttle body angle. It looked at the MAF to see if there was an increase in air velocity to the intake. It looked at the MAP sensor to see if there was a pressure differential in the intake manifold. At the same time it looked at those sensors it also looked at the return voltage of the coolant sensor to see what the engine temp was while also looking at the O2 sensor to see the voltage it was producing to see if the exhaust stream gas was lean or rich. All these calculations in a split second. The ECM then decided how long to keep the injector's on or "pulsed" for. The whole time we are driving the boat whether under a load, cruising, trolling or idling, the ECM is constantly monitoring and adjusting the fuel and timing based on sensor values and the feed back from the O2 sensor. All we know is the boat is operating fine but we need to find the nearest restroom because......you know why. As you can see, the system is not that complicated, but, failure of one of these sensors can greatly mimic starving for fuel etc....Many post's here have had situations where they mention the boat runs great but at wide open throttle it starts to bog down. Certainly filters or bad fuel could be a culprit but we also have to look at the other less known devices. The throttle position sensor is nothing but a resistor lever sliding on a conductor. It is technically a potentiometer but all that matters is that it is a wear item that does wear out and usually it is in a certain area of the contact surface. Hence someone stating that the boat cuts out at exactly 4,000 rpm's, it could very well be the TPS fails at this point in the lever. When that happens, the return voltage to the ECM is the signal that the boat is at idle and not moving. See the problem...A coolant sensor could become defective and sends a hot engine value to the ECM even though you have not even started the engine yet.
I don't want to use up all the ink in my computer so I'll stop there. There are simple voltage checks that can be done on many of these sensors if they are suspect I just wanted to bring some clarification and take away the mystification for those that might feel duped by the whole computer thing. I hope this helps in some diagnoses and thankfully the marina did have a restroom.
God Bless
Mike
First and foremost, is the question of why computer control and fuel inject an engine?
The auto industry is always striving for performance and fuel efficiency in an engine. The goal is "stoichiometric" or "perfect combustion". This is almost impossible to achieve since the engine loads and speed are never constant. The addition of fuel injection is one step closer to being able to achieve that goal. The addition of the ECM allowed the computer to monitor multiple engine systems and make finite adjustments to try to achieve stoichiometric balance. What does all this mean, and how does it work? Let's start with a typical morning on a nice summer day. The fish are biting, and your stomach is full from the McDonald's sausage mcmuffin and two hash brown's you ate on the way to the dock. It's gonna be a great day.
You get the boat in the water and turn the key. The fuel pump is instantly energized, and the fuel rails are pressurized. You start the engine. The instant the engine is started the ECM is running in what is known as "open loop". All this means is that a prescribed set of values have been stored in the computer for a cold engine start up. These would include an enrichment circuit meaning the dwell or "on time" of the injectors is increased. This serves as your choke. A timing setting and air flow is also controlled. The ECM is looking at several sensors during this warm up especially your coolant temp sender. The ECM watches these sensors by supplying a fixed voltage to the sensor and "watching" what comes back. Since they are mostly resistor sensors, the computer knows the state of the engine. For example, when the ECM sends the 12V signal to the coolant sensor and receives back 4.5 volts it now knows the engine temp. There are other sensors it is watching such as manifold pressure sensors that tell if the engine is under a load condition, mass air flow or MAF which measures the velocity and density of the incoming combustion air etc..They all operate on the same principle of voltage in voltage out. OK. So anyhow we are finishing our coffee as we wait for the engine to warm up. In our exhaust is the all important O2 sensor. It is a little different than the other sensors because there is no voltage supplied to it. It has a single wire and in all aspects is a self contained battery. Two dissimilar pieces of metal stay separated by an electrolyte which when cold resembles parafin wax. As the exhaust heats up the "wax" begins to melt and the O2 sensor begins to generate it's own current. It can usually generate up to 1 volt. As it begins to generate current, the ECM receives this signal. As you take your last sip of coffee, the ECM goes into "closed loop" operation largely due to the O2 sensor beginning to operate. All this means is that instead of the prescribed values that it was running on in open loop, it now has the ability to monitor and change engine conditions based on values received from the sensors. OK, so were out past the now wake zone and the sausage mcmuffin is not sitting well, but there's fish to catch. You open the throttle. This is when the amazement of the ECM and the "feedback" system of sensors really shines. When you cracked the throttle, within thousandths of a second the ECM looked at multiple sensors to verify this is what you wanted to do. It looked at your throttle position sensor "TPS" to verify there was an increase in throttle body angle. It looked at the MAF to see if there was an increase in air velocity to the intake. It looked at the MAP sensor to see if there was a pressure differential in the intake manifold. At the same time it looked at those sensors it also looked at the return voltage of the coolant sensor to see what the engine temp was while also looking at the O2 sensor to see the voltage it was producing to see if the exhaust stream gas was lean or rich. All these calculations in a split second. The ECM then decided how long to keep the injector's on or "pulsed" for. The whole time we are driving the boat whether under a load, cruising, trolling or idling, the ECM is constantly monitoring and adjusting the fuel and timing based on sensor values and the feed back from the O2 sensor. All we know is the boat is operating fine but we need to find the nearest restroom because......you know why. As you can see, the system is not that complicated, but, failure of one of these sensors can greatly mimic starving for fuel etc....Many post's here have had situations where they mention the boat runs great but at wide open throttle it starts to bog down. Certainly filters or bad fuel could be a culprit but we also have to look at the other less known devices. The throttle position sensor is nothing but a resistor lever sliding on a conductor. It is technically a potentiometer but all that matters is that it is a wear item that does wear out and usually it is in a certain area of the contact surface. Hence someone stating that the boat cuts out at exactly 4,000 rpm's, it could very well be the TPS fails at this point in the lever. When that happens, the return voltage to the ECM is the signal that the boat is at idle and not moving. See the problem...A coolant sensor could become defective and sends a hot engine value to the ECM even though you have not even started the engine yet.
I don't want to use up all the ink in my computer so I'll stop there. There are simple voltage checks that can be done on many of these sensors if they are suspect I just wanted to bring some clarification and take away the mystification for those that might feel duped by the whole computer thing. I hope this helps in some diagnoses and thankfully the marina did have a restroom.
God Bless
Mike
