When the fuel injector flow becomes flow restricted, the computer will attempt to adjust the fuel flow by opening the fuel injector longer through the use of its longterm fuel trim function. How to ensure fuel injectors are receiving the correct. The longer the ground signal is on, the more fuel is injected into the engine. We typically measure pri as the time from the beginning of one pulse and the. Initially, the waveform voltage on the switchedearth side of the injector is at. Chrysler injector characterization injector dynamics. When it comes to injector duty cycle or pulse width though a diesel engine uses direct injection where the available time to inject fuel is much shorter than the full engine cycle time. A single intensity signal is sent to a fuel injector which causes the valve to open. As part of a larger project, i want to be able to measure the width of a fuel injector pulse, allong with the vss vehicle speed sensor to determine mpg. The white line is the high slope which is a straight line approximation of the linear portion of the flow vs pulse width curve.
How to interpret fuel injector waveforms a scannerdanner. Simply connect the power leads to a 12 volt car battery, hook up the injector, select the pulse width, and press the button. How to test a fuel injector with a voltmeter it still runs. This type of driver works by supplying 12 volts to the injectors and the ecu turns. The last carburetorequipped car came off the assembly line in 1990. If a noid light was designed for the other type of driver. It uses the pulse width and the engine rpm to compute the duty cycle. Initially, the waveform voltage on the switchedearth side of the injector is at battery voltage, 14 to 15 v, and the injector is off. Complex triggering system used to capture and filter data. The airfuel o2 monitor, pulse width monitor, and fuel controller are all on one. My question is what would the expected maximum injection pulse that this or a similar system might show at full load, in this case at approx 3400rpm we get a maximum engine load of 54% and max injection pulse of 7. Injector duty cycle calculator want to calculate your injector duty cycle. The injector duty cycle calculator is used to find out if your injector is the right size for your engine.
Injector flow curve tech corner performance fuel systems. Check fuel pulse width fuel pw while cranking check. The dynamic flow rate is the flow through an injector while it is pulsed on and off for a given number of pulses. The waveform 2 shows that the injector current pulse consists of two stages. A typical pulse width is 2 to 4 milliseconds at idle and as high as 15 to 18 milliseconds at wide open throttle. The relation between injection pulsewidth and loss of icp. The blue line is the raw flow vs pulse width curve for our id2000 injector at 14v, 100hz, 7bar fuel pressure. Unlike peakhold, a saturated injector remains on for the entire pulse width. Injector drive types can be divided into three categories. If the longterm fuel trim reading from the scan tool shows the computer is correcting the airfuel mixture by more than 10%, the fuel system is in need. Detailed analysis of a saturation type fuel injector waveform. The injector data given is based on manufacturers published data and are given for the specific base fuel pressure listed recommend high. Offers realtime features, like fast fourier transform fft offers features unique to digital systems, like protocol analyzers. See how a snapon lab scope and diagnostic software can help you check voltage.
The cars computer turns the ground signal on and off to rapidly pulse the injector. Positive voltage is supplied to the injector as long as the engine is running. Simple threshold or pulsewidth triggers used to show a steady waveform. Find out how fuelinjection systems work and about the various configurations used in the cars today. The time between the start of each pulse is called the period or pulse interval pi. During normal engine operation, the fuel injector fires once during the four strokes of the otto cycle, which last for 2 revolutions of the engine. Observing injector waveforms for the first time can be somewhat confusing. Injector pulse width is the amount of time, measured in milliseconds ms, that a fuel injector stays open delivers fuel during a cylinder intake cycle. If the valve is pulsed on at variable durations called pulsewidth modulation, the duty cycle varies. About injector pulse injector pulse is a focused service with one purpose, effective and affordable fuel injector cleaning.
The time the injector is actually energized during the period is called the pulse width pw. The electric fuel injector has been around for more than 50 years. Design of the electrical drive for the highpressure gdi injector in a. The purpose of this test is to monitor the injector voltage within a multipoint injection system. These graphs depict the characteristics of various fuel injectors with effective pulse width in milliseconds with 19 ms being equivalent to 100percent injector duty cycle and injector flow rate in ccmin. The constants used are 160 cfm per 100 hp, and an 85% duty cycle for maximum injector pulsewidth. This is a scannerdanner premium video on chapter 17 of my book engine performance diagnostics where i will be introducing how to read and interpret fuel injectors waveforms. The problem is, the injector is always powered with the engine on, it is fired when the ecm grounds the other side of the injector. An electromagnetic coil moves a pintle in a chamber that has pressurized fuel on one side and a nozzle on the other.
A shorted injector coil that draws too much current, a bad injector driver, an ecm. During the first stage, the force developed by the solenoid is not enough to open the valve. The regular software and driver updates are a real bonus. Current flow through the winding will result in the creation of a large magnetic field, which has the effect of attracting the pintle valve into the winding. Waveforms injector pattern tutorial 1990 nissan 240sx general information waveforms injector pattern tutorial please read this first note. The chart below shows the raw flow vs pulse width of the stock hemi injector at the 7 voltage points defined in the stock tune. Waveforms injector pattern tutorial volvo owners club.
Honda civic dual tbi units use an auxiliary injector which has a saturation driver and a main injector that uses a pulse width modulated driver. Here is an example of a negatively controlled pulse width modulated driver. Saturated injector autoditex automotive diagnostic tools. Three different pulsewidth current waveforms may be supplied to the solenoid valve in the injector. Generally youll inject the fuel somewhere close to tdc on the compression stroke and continue some way into the power stroke. How to test a fuel injector using a oscilloscope and current probe. I performed a cylinder cutout test on a series 60 detroit. Real time monitoring of diesel engine injector waveforms for. The switch allows either the primary or secondary injector pulse to be monitored. This paper presents the development, experimentation, and validation of a reliable and robust system to monitor the injector pulse generated by an engine control module ecm which can easily be calibrated for different engine platforms and then feedback the corresponding fueling quantity to the realtime computer in a closedloop controller in the loop cil bench in order to achieve optimal. Crd bosch solenoid injector circuit current the purpose of this test is to check the actuation current within a boschtype common rail diesel crd solenoid injector circuit across a range of engine load and demand conditions. The shorter pulse width will cause the injector to deliver less fuel. At this point valve opens, changing the inductance of the solenoid and so causing a dip in the waveform before the current rises again. Pulse repetition interval pri is the time between sequential pulses.
Although a pcm in closed loop can alter injector flow by reducing injector pulse width, it cannot control a single faulty individual injector. To make this measurement repeatable and accurate, we use the 50% power level as the reference points. The time during which the injector is powered or activated is called the injector pulse width ipw. This article is intended for general information purposes only. Pwm works by switching the 12 volt ground to the injector on and off very rapidly in about 0. Effective pulse width is the ipw value before any battery or ignition voltage offset values are added to compensate for delays in injector. Hopefully this information will help to make things clearer and speed things up on the road to proper injector diagnosis. This duration or period is referred to as the injector pulse width. The corresponding electrical pulse is sent to the injector stators or the inductor. Base pulse width bpw ideally, n pv rt and then injector pulse n injector flow constant. We have a peugeot boxer camper van 1997 4 cylinder 2. If this is confusing, consider a secondary ignition pattern.
Since then, fuel injectors have been the primary means of getting gasoline into the engine cylinder so it can combust and you can drive. From the pits to your garageprofessional quality injector cleaning is. Here, you should also measure pulse width from the beginning of the peak section to the end of the pulse modulation section as the cursors show. If the air flow meter is properly sized, the reduction in pulse width will cause the new, larger injectors to deliver the same amount of fuel as the stock injectors did at the original pulse width. A typical pulse width is 2 to 4 milliseconds at idle and as high as 15 to 18 milliseconds at wideopen throttle. Real time monitoring of diesel engine injector waveforms. At 0 ms, the engine control module ecm provides an earth path to battery negative, 0 v, which marks the start of injection. The pulse width modulated waveform is filtered to produce an analog. The typical injector pulse width for an idling engine at normal operating temperature is between 2. The waveform shows an example of an engine with inefficient combustion flagged in yellow by the software s cylinder and bar.
Programmable fuel injector current waveform control and method of. In this example, the pcm needs to increase the injector pulse width to reach the correct airfuel ratio. The fuel injector duty cycle idc is the percentage of time the injector is supplied with power. Gm introduce the concept of base pulse width or bpw to reduce the v and r terms. What you see below is a screenshot of the worksheet we use to develop ford injector characterization files. Waveforms injector pattern tutorial 1995 volvo 850 general information waveforms injector pattern tutorial. When an engine needs to make more powerto accelerate onto a highway, for examplethe onboard computer increases the pulse width of the fuel injectors to deliver more fuel. Professional fuel injector pulsewidth calculator this calculator will generate pulsewidth values for specific rpms, from idle to peak speeds. The coil is typically energized by a driver pulling the circuit to ground. Looking at the battery compensation table to the right, you can see that we have a pulse width value in microseconds vs battery voltage. Lets say the air flow meter and injectors are designed to support double stock.
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