@jdubb408 Thanks for posting. We thrive to make our videos better all the time, while keeping them free for all. We appreciate your suggestions and thanks again. Keep posting.
@5ohMan Hello, thanks for participating and posting. We thrive to give people another perspective on automotive technology. We're also a full fledged auto repair advice and help center. We encourage folks to post and participate. We also have lots of viewer from beautiful India and encourage participation. Our American and English computer narrations are the best solution to this FREE service. So, if you ever have car issues, ask away and let us help you. It's FREE.
I am now thinking that even if the car is on a lift, as the RPM is increasing, engine load will increase with RPM due to the inertia inherent in the powertrain. Once the increasing of the RPM has reached a plateau constant value of let 's say 5000 RPM and allowed to stay at that constant level, then engine load will go back down to it's idle level, since the powertrain is no longer accelerating but instead moving at a constant velocity. Is that right? Or even close?
There's always some load at higher RPMs. Effort to suck in outside air, engine parts friction, etc. These questions are probably outside the scope of engine diagnostics and more for engineers, but I applaud your logical reasoning. You can give our comments a shot. Buy an inexpensive DMM, with CD and PW or if you have access to an oscilloscope and try in on your own vehicle. THe problem with using a DMM is that all of them use avaraging circuitry and therefore not won't give an exact mSec value.
If it is impossible to simulate this condition either in the lab/shop or on the road, then I guess you are right about the relationship of RPM and injector PW being difficult to put into perspective.
Use an oscilloscope and plot the injector pulse waveform. You'll see that at idle is value A, as you accelerate it widens to break the inertia and provide more power, and at a stable high RPM is goes down to value A. Value A signifies whatever calls for your engine type.
Is it possible to simulate a condition in the shop/lab where the RPM is increased but the engine load stays the same, and then measure both injector duty cycle and pulse width.
I am thinking that a good way to keep the load the same would be to raise all 4 wheels off the ground using a lift and putting the vehicle in drive and stepping on the gas pedal. Stepping on the gas pedal will increase RPM, and since the car is off the ground, I assume this means there is no load on the engine.
The above was ADPTraining's response to a personal message I sent to him. I said to him that according to a fuel MAP chart (which is a look up chart the PCM uses to determine base injector pulse width) if engine load stays the same, then injector pulse width does in fact increase if RPM increases. If you google "how stuff works injector pulse width", the first web page listed explains fuel MAP.
PW also differs depending on the injector design, inj. chamber size, electrical characteristics, etc, which is the reason why PW at any RPM is deferent from one maker to the next. DC has all the diagnostic value that you'll ever need.
engine to another. We've done extensive testings on many 4 cyl, V6 and V8s engines, on some units with completely re-learned adaptive memory, the RPM change will not even reach 1 mSec. Theoretically there should be a minor increase to make up for the losses mentioned before, but not in practice or very little change. Simply put, PW stays the same for practical diagnostic purposes, pulsation frequency increases, DC increases and so does fuel consumption.
Under normal conditions there may be a very small increase with engine RPM, due to excess friction, water and oil pump losses, as well as volumetric efficiency losses. It takes more work to suck a large amount of air at higher RPMs. However, on a larger V8 this may be negligible. That's why I stresses that PW changes a lot from one
First of all, there's a huge difference between theory and practice. Hence the need for adaptive memory factors on fuel injection systems. It's not all mathematical, since mechanical systems have huge physical discrepancies.
What factors influence the base injection width? Does base injection width increase and/or decrease with crankshaft position sensor signal, MAP signal, MAF signal, and/or TPS signal?
Very nice try. The problem is that FT are part of an algorithm that only the manufacturer knows. Remember, such formulas are highly guarded secrets. We employ such formulas on our Scan-1 (ADPScan-1) diagnostic system to perform automated testing using the scanner PIDs, but we also guard the algorithm that we use to detect faults. That feature makes our product second to none.
Suffice it to say that you're missing a few variables from your formula, but that's OK. Good try.
Looking at one cylinder, does the PCM pulse the injector only once per 4-stroke cycle? I am guessing that the fuel injector opens during the compression stroke. Or maybe this is only true for engines with synchronized fuel injection. Are my assumptions correct?
The ECM pulses the injector once per two revolutions of the crank. The fuel is injected when the intake valve closes, right before compression. The fuel stays on the intake manifold runner for a split second before the intake valve opens and sucks in the fuel.
However, on rare direct injection systems the fuel is injected right into the combustion chamber. To my knowledge there are no DI gasoline engine's on the market (production). Direct injection is used in production Diesel engines (VW).
What you refer to as synchronized injection is called sequential injection. That just means that the injectors are NOT group fired. They're pulsed as stated above independently, or one at a time. This takes advantage of the air swirl and the injection is also tailored for better fuel economy. Most newer engines (even 4 cyl) have 2 front O2 sensors. One O2 sensor per 2 cyl. Again, better A/F control and fuel economy.
Hello to all. Injector pulse-width is the last parameter that any technician should ever use. Why? It's simple, injector pulse-width can be used to determine fuel delivery, but it's very difficult to put into perspective.
EXAMPLE: Normal Inj. PW at idle it's about 3.5 mSec. However at 4000RPM it's also 3.5mSec. The difference is a higher rate of pulsation.
The best determinant of fuel delivery is injector duty-cycle or the ratio of ON to OFF time.
Continued: An almost perfect inj. DC is 2.9%. I won't go into the details of DC. Suffice it to say that negative fuel trims means the ECM is reducing injection duration to the BASE injection timing factor, to correct for a rich condition. Positive FT equals the ECM adding to the base injection pulse to correct for a LEAN condition (most common). There are many reasons for a skewed FT value: O2 sensor, MAF, Vacuum leak, fuel-Pressure Regulator, leaky injector, etc.
Continued 2: Only a scan tool can show the FT value. FT is a calculated value (by the ECM), which means that if the ECM is detecting the wrong data it'll reflect as a skewed FT value. Wrong data as in an O2 sensor or MAF sensor ground fault.
The final measurement during a FT diagnosis should always be done with direct measurement. Use a Multi-meter or scope for final measurement.
Fuel-Trims is an indicator of what the ECM is perceiving and not necessarily reality.
@ADPTraining Yeah, but what about the graph in the video? I am assuming the horizontal axis is fuel trim. What I can't figure out is the vertical axis.
This is not a graph as in X and Y axis. It's a horizontal chart. 0.00% is perfect A/F ratio for gasoline. -10 to +10% is within range on all makes and models. Below = ECM reducing injection due to RICH cond. Above = ECM increasing pulse due to LEAN cond.
Continued 3: Whenever trying to asses the engine's fuel consumption in real life use a multi-meter set to duty-cycle and measure at the injector wires. Then, compare to the scanned Fuel-Trim value. If the DC is at 2.9% but FT are skewed, then suspect external fault, such as a ground fault.
Use Injector pulse width as a very generalized measurement and to detect an extremely off balanced mixture. Such as normal Inj. PW should be 3.5mSec and it's at 7mSec. That's way off. Then cont. to manual measurements
Some vehicles will give you injector pulse-width but it's a calculated value and not accurate (useless). NO duty cycle can only be ascertained with a multimeter that has DC capabilities. Not even with an oscilloscope.
Duty-Cycle is the actual working part of a pulse cycle or the part of the cycle with ability to do real work.
As I said above, some vehicles have it, but it's useless. If you want PW use an oscilloscope and measure directly. Even if you can get the PW from a scan tool, disregard it. It'll skew you off.
This is information is priceless and has taken us much research to implement into our software tools.
As a rule 2.5 to 2.9% DC at idle is perfect, regardless of engine size. Remember, DC is fuel contribution per each cylinder separately. So it doesn't really matter if it's a 4-cyl or 8-cyl.
In our research we did encounter one specific make (VW/Audi) which was the only engine manufacturer that deviated from the rest.
For some reason, especially on the VW/Audi 4 cylinder engines the DC at idle is pegged at around 3.1 to 3.2%. It doesn't seem like much, but when it comes to DC a minute deviation is important. On most systems, if DC above 2.9% the vehicle is running RICH. This is by far the best way to determine if the engine is OFF balance.
Remember, the ECM may say one thing, but reality may be another. As a technician you always have to prove what the ECM says.
YES, absolutely, DC is direct measurement of fuel delivery or consumption, for that matter. Pulse-width on the other hand stays the same regardless of RPM. It increases with LOAD, but it's hard to use a determinant of real fuel delivery or A/F (air fuel) balance.
A combination of Fuel-Trim and duty-cycle analysis will give you the whole picture. These two parameters should always support each other, depending on engine condition.
The entire process is called Closed-Loop operation and relies on the O2 sensor for A/F feedback. If the O2 sensor is defective or sluggish, the whole process would be out of sync and A/F balance will be off.
cant stand this gay computer voice
jdubb408 3 weeks ago
@jdubb408 Thanks for posting. We thrive to make our videos better all the time, while keeping them free for all. We appreciate your suggestions and thanks again. Keep posting.
ADPTraining 3 weeks ago
OMG..can someone shoot this computer voice.... Id rather listen to a guy from India narrate this..sheesh
5ohMan 3 weeks ago 2
@5ohMan Hello, thanks for participating and posting. We thrive to give people another perspective on automotive technology. We're also a full fledged auto repair advice and help center. We encourage folks to post and participate. We also have lots of viewer from beautiful India and encourage participation. Our American and English computer narrations are the best solution to this FREE service. So, if you ever have car issues, ask away and let us help you. It's FREE.
ADPTraining 3 weeks ago
I am now thinking that even if the car is on a lift, as the RPM is increasing, engine load will increase with RPM due to the inertia inherent in the powertrain. Once the increasing of the RPM has reached a plateau constant value of let 's say 5000 RPM and allowed to stay at that constant level, then engine load will go back down to it's idle level, since the powertrain is no longer accelerating but instead moving at a constant velocity. Is that right? Or even close?
nobleheight 2 years ago
There's always some load at higher RPMs. Effort to suck in outside air, engine parts friction, etc. These questions are probably outside the scope of engine diagnostics and more for engineers, but I applaud your logical reasoning. You can give our comments a shot. Buy an inexpensive DMM, with CD and PW or if you have access to an oscilloscope and try in on your own vehicle. THe problem with using a DMM is that all of them use avaraging circuitry and therefore not won't give an exact mSec value.
ADPTraining 2 years ago
If it is impossible to simulate this condition either in the lab/shop or on the road, then I guess you are right about the relationship of RPM and injector PW being difficult to put into perspective.
nobleheight 2 years ago
Use an oscilloscope and plot the injector pulse waveform. You'll see that at idle is value A, as you accelerate it widens to break the inertia and provide more power, and at a stable high RPM is goes down to value A. Value A signifies whatever calls for your engine type.
ADPTraining 2 years ago
Is it possible to simulate a condition in the shop/lab where the RPM is increased but the engine load stays the same, and then measure both injector duty cycle and pulse width.
I am thinking that a good way to keep the load the same would be to raise all 4 wheels off the ground using a lift and putting the vehicle in drive and stepping on the gas pedal. Stepping on the gas pedal will increase RPM, and since the car is off the ground, I assume this means there is no load on the engine.
nobleheight 2 years ago
You don't have to raise the vehicle. At Park or Neutral there's no load and it'll work the same for your calculations.
ADPTraining 2 years ago
PART 7
" (END QUOTE)
=============================
The above was ADPTraining's response to a personal message I sent to him. I said to him that according to a fuel MAP chart (which is a look up chart the PCM uses to determine base injector pulse width) if engine load stays the same, then injector pulse width does in fact increase if RPM increases. If you google "how stuff works injector pulse width", the first web page listed explains fuel MAP.
ADPTraining requested I post his reply.
nobleheight 2 years ago
PART 6
PW also differs depending on the injector design, inj. chamber size, electrical characteristics, etc, which is the reason why PW at any RPM is deferent from one maker to the next. DC has all the diagnostic value that you'll ever need.
nobleheight 2 years ago
PART 5
Also, a curiously similar effect happens on the coil dwell (pulse width for the coil), which doesn't change much if at all with a higher RPM.
NOTE: I am assuming that in all this discussion the LOAD stays the same.
Now, if the LOAD is always changing, as it normally does, then it makes it even harder to use PW for diagnostics.
nobleheight 2 years ago
PART 4
engine to another. We've done extensive testings on many 4 cyl, V6 and V8s engines, on some units with completely re-learned adaptive memory, the RPM change will not even reach 1 mSec. Theoretically there should be a minor increase to make up for the losses mentioned before, but not in practice or very little change. Simply put, PW stays the same for practical diagnostic purposes, pulsation frequency increases, DC increases and so does fuel consumption.
nobleheight 2 years ago
PART 3
Under normal conditions there may be a very small increase with engine RPM, due to excess friction, water and oil pump losses, as well as volumetric efficiency losses. It takes more work to suck a large amount of air at higher RPMs. However, on a larger V8 this may be negligible. That's why I stresses that PW changes a lot from one
nobleheight 2 years ago
PART 2
First of all, there's a huge difference between theory and practice. Hence the need for adaptive memory factors on fuel injection systems. It's not all mathematical, since mechanical systems have huge physical discrepancies.
nobleheight 2 years ago
PART 1
Hello all:
The following is a personal message I received from ADPTraining in response to a question of mine.
==========================
"Re: Relationship of RPM to injector pulse width
Hello nobleheight, thanks for the response. The issue of PW in relation to RPM is highly confusing to a lot of my students. Let me try and explain:
nobleheight 2 years ago
This has been flagged as spam show
What factors influence the base injection width? Does base injection width increase and/or decrease with crankshaft position sensor signal, MAP signal, MAF signal, and/or TPS signal?
nobleheight 2 years ago
(At least as far as the PCM is concerned), I am assuming the mathematical formula to get pulse width is:
pulse width = (base injection width) * [1+(short term fuel trim % + long term fuel trim %)/100]
Is that correct? Is my assumption even close?
nobleheight 2 years ago
Very nice try. The problem is that FT are part of an algorithm that only the manufacturer knows. Remember, such formulas are highly guarded secrets. We employ such formulas on our Scan-1 (ADPScan-1) diagnostic system to perform automated testing using the scanner PIDs, but we also guard the algorithm that we use to detect faults. That feature makes our product second to none.
Suffice it to say that you're missing a few variables from your formula, but that's OK. Good try.
ADPTraining 2 years ago
Looking at one cylinder, does the PCM pulse the injector only once per 4-stroke cycle? I am guessing that the fuel injector opens during the compression stroke. Or maybe this is only true for engines with synchronized fuel injection. Are my assumptions correct?
nobleheight 2 years ago
The ECM pulses the injector once per two revolutions of the crank. The fuel is injected when the intake valve closes, right before compression. The fuel stays on the intake manifold runner for a split second before the intake valve opens and sucks in the fuel.
However, on rare direct injection systems the fuel is injected right into the combustion chamber. To my knowledge there are no DI gasoline engine's on the market (production). Direct injection is used in production Diesel engines (VW).
ADPTraining 2 years ago
What you refer to as synchronized injection is called sequential injection. That just means that the injectors are NOT group fired. They're pulsed as stated above independently, or one at a time. This takes advantage of the air swirl and the injection is also tailored for better fuel economy. Most newer engines (even 4 cyl) have 2 front O2 sensors. One O2 sensor per 2 cyl. Again, better A/F control and fuel economy.
ADPTraining 2 years ago
This video shows a graph. What is that graph of? Is that graph supposed to represent the injector pulse width?
If yes, then shouldn't a negative 10% short term fuel trim decrease injector pulse width?
The current graph shows the injector pulse width increasing for both a negative and positive 10% short term fuel trim.
nobleheight 2 years ago
Hello to all. Injector pulse-width is the last parameter that any technician should ever use. Why? It's simple, injector pulse-width can be used to determine fuel delivery, but it's very difficult to put into perspective.
EXAMPLE: Normal Inj. PW at idle it's about 3.5 mSec. However at 4000RPM it's also 3.5mSec. The difference is a higher rate of pulsation.
The best determinant of fuel delivery is injector duty-cycle or the ratio of ON to OFF time.
ADPTraining 2 years ago
Continued: An almost perfect inj. DC is 2.9%. I won't go into the details of DC. Suffice it to say that negative fuel trims means the ECM is reducing injection duration to the BASE injection timing factor, to correct for a rich condition. Positive FT equals the ECM adding to the base injection pulse to correct for a LEAN condition (most common). There are many reasons for a skewed FT value: O2 sensor, MAF, Vacuum leak, fuel-Pressure Regulator, leaky injector, etc.
ADPTraining 2 years ago
Continued 2: Only a scan tool can show the FT value. FT is a calculated value (by the ECM), which means that if the ECM is detecting the wrong data it'll reflect as a skewed FT value. Wrong data as in an O2 sensor or MAF sensor ground fault.
The final measurement during a FT diagnosis should always be done with direct measurement. Use a Multi-meter or scope for final measurement.
Fuel-Trims is an indicator of what the ECM is perceiving and not necessarily reality.
ADPTraining 2 years ago
@ADPTraining Yeah, but what about the graph in the video? I am assuming the horizontal axis is fuel trim. What I can't figure out is the vertical axis.
nobleheight 2 years ago
This is not a graph as in X and Y axis. It's a horizontal chart. 0.00% is perfect A/F ratio for gasoline. -10 to +10% is within range on all makes and models. Below = ECM reducing injection due to RICH cond. Above = ECM increasing pulse due to LEAN cond.
ADPTraining 2 years ago
Continued 3: Whenever trying to asses the engine's fuel consumption in real life use a multi-meter set to duty-cycle and measure at the injector wires. Then, compare to the scanned Fuel-Trim value. If the DC is at 2.9% but FT are skewed, then suspect external fault, such as a ground fault.
ADPTraining 2 years ago
Continue 4:
Use Injector pulse width as a very generalized measurement and to detect an extremely off balanced mixture. Such as normal Inj. PW should be 3.5mSec and it's at 7mSec. That's way off. Then cont. to manual measurements
ADPTraining 2 years ago
@ADPTraining Is there a scan data PID for fuel injector duty cycle? Or is hooking up a multi-meter the only way to get it?
nobleheight 2 years ago
Some vehicles will give you injector pulse-width but it's a calculated value and not accurate (useless). NO duty cycle can only be ascertained with a multimeter that has DC capabilities. Not even with an oscilloscope.
Duty-Cycle is the actual working part of a pulse cycle or the part of the cycle with ability to do real work.
ADPTraining 2 years ago
@ADPTraining Is there a scan data PID for fuel injector pulse width?
nobleheight 2 years ago
As I said above, some vehicles have it, but it's useless. If you want PW use an oscilloscope and measure directly. Even if you can get the PW from a scan tool, disregard it. It'll skew you off.
ADPTraining 2 years ago
How do you know what duty cycle values correspond to what fuel trim values. Is there a chart to look this up?
nobleheight 2 years ago
This is information is priceless and has taken us much research to implement into our software tools.
As a rule 2.5 to 2.9% DC at idle is perfect, regardless of engine size. Remember, DC is fuel contribution per each cylinder separately. So it doesn't really matter if it's a 4-cyl or 8-cyl.
In our research we did encounter one specific make (VW/Audi) which was the only engine manufacturer that deviated from the rest.
ADPTraining 2 years ago
For some reason, especially on the VW/Audi 4 cylinder engines the DC at idle is pegged at around 3.1 to 3.2%. It doesn't seem like much, but when it comes to DC a minute deviation is important. On most systems, if DC above 2.9% the vehicle is running RICH. This is by far the best way to determine if the engine is OFF balance.
Remember, the ECM may say one thing, but reality may be another. As a technician you always have to prove what the ECM says.
ADPTraining 2 years ago
Does duty cycle increase with increasing RPM?
nobleheight 2 years ago
YES, absolutely, DC is direct measurement of fuel delivery or consumption, for that matter. Pulse-width on the other hand stays the same regardless of RPM. It increases with LOAD, but it's hard to use a determinant of real fuel delivery or A/F (air fuel) balance.
A combination of Fuel-Trim and duty-cycle analysis will give you the whole picture. These two parameters should always support each other, depending on engine condition.
ADPTraining 2 years ago
The entire process is called Closed-Loop operation and relies on the O2 sensor for A/F feedback. If the O2 sensor is defective or sluggish, the whole process would be out of sync and A/F balance will be off.
ADPTraining 2 years ago