Automotive Technology Course | Fuel Injector Testing Procedures

Automotive Technology Course | Fuel Injector Testing Procedures


Oh you you you the fuel injector is an electromagnetic valve in charge of delivering fuel to each cylinder the construction of the fuel injector employs an internal coil that drives the fuel injector pintle into an open and closed position this fuel injector coil and internal components may become corroded dirty or contaminated over time causing fuel delivery problems however other problems associated with the fuel injector are cloudy pintle and heavily sulfated and corroded fuel injector connector terminals excessive corrosion on the fuel injector connector will also render this electromagnetic valve inoperative due to the fact that the high resistance will cause the injector not to open the fuel injector coil which is inside the injector casing itself provides an electromagnetic field which is the one that actually drives the pintle open seen here on screen the fuel injector in itself is made into a closed position by an internal spring through careful analysis of the current and voltage waveforms of the injector circuit we can actually ascertain the viability ethyl and proper injector operation for example problems such as weak springs inside the injector itself clogged injector Pindell problems even problems with excessive resistance at the connector or injector circuit can all be detected through a waveform analysis of the signal let’s check out the actual injector in operation and then later on do a waveform analysis to see what kind of information we can derive from it this is an actual injector and voltage waveform here we can see the actual transition between injector off and injector on you can actually know whether the injector is grounded properly and test injector pulse would by testing the actual spike from the collapsing magnetic field around the coil from this wave information we can make a determination as to the condition of a fuel injector unit the first part of a voltage waveform is the injector turned on point and this is signified on screen by the vertical red line this is the point at which the injector actually turns on and it is very important because any problems inside the ECM with the injector driver or internal transistor that turns the injector on will actually be seen immediately at the turned on point of the injector waveform by studying the very bottom of this injector turn on point we can prove and verify whether the injector is grounded properly this ground is provided by the ECM so in a way this waveform test point tells us if the ECM is properly grounded most injectors will draw around 950 million of current this is not a whole lot of current but in order for the ECM to drive the injector open the ECM has to be grounded properly being that in the event of a ground fault at the ACM circuitry the ECM driver will not be able to ground this injector at all 95% of all the injectors on the market worked through a trigger ground principle they have steady power going to one side and the other side is grounded or pulse grounded by the ACM internal transistor this determination of whether the ECM is grounded properly can be deduced by studying the bottom part of this injector turn off portion of the waveform as a rule of thumb no more than 100 milli volt should be seen from the bottom part of the injector turn on point and a zero line and always remember that the injector turned on point should be clean and vertical signifying that the actual injector driver has a good switching ability the next part of the injector waveform is the injector open time this injector open time or pulse would should coincide with the ECM commanded injector open time this parameter can also be read using a scan tool but remember that the actual injector open time and the value indicated by the scan tool may not coincide this is due to the fact that the scan tool will report this value in a calculated method by the ECM and not necessarily the true real-life value in order to know the exact open time for all the different engines on the market you would have to have your own database of previously recorded values at idle most engines should range at between three point five to six milliseconds of injector on time but this is a wide range and it is only to be used as a generalized idea of what you should have a dipole if you have an injector pulse that’s over eight milliseconds at idle then you know that you indeed have a problem in this case you should look at why the ECM is increasing the injector pulse with so much another fact to remember about injection time is that it will remain steady throughout the entire rpm range in other words the injector pulse may coincide with 3.5 milliseconds at 3000 rpms but may also stay at 3.5 milliseconds at idle the reason for this is that although the injector pulse remains the same the frequency with which the injector is triggered is going to increase obviously you are not going to have the same rate of pulsation at dipole as you would at 3,000 rpms the injector pulse width should not be confused with duty cycle the best indicator of an engines fuel consumption is the duty cycle value of the injector pulse as a rule most engines will have a duty cycle of between two point two and two point nine percent at idle the duty cycle is simply the ratio of on to off time you are going to have higher than 2.9 percent on an engine that is running rich and vice versa if you have an engine that also has a lean condition such as a vacuum and leak you are going to have a duty cycle of less than 2.2 percent there are a few exceptions on the market of engine systems that will need more than 2.9 percent of duty cycle for injector pulse at idle the VW Audi brand being one of them but again this is the exception to the rule the duty cycle of the injector is an easy information to acquire by simply tapping into the pulsed wire of a fuel injector and setting your multimeter for graphing multimeter to duty cycle and percentage you can immediately measure and record the duty cycle throughout the different engine rpm range if you’d happen to the pulsed side of the injector and you see a duty cycle value of 95 to 98% then simply swap the multimeter leads right at the equipment so remember that injector pulse width is used as a fuel consumption indicator often times the duty cycle is used to compare the two separate banks of cylinders on a p-type engine if one bank gets richer or leaner than the other then both duty cycle values will not match if you need an exact value do not take into account the injector pulse width since this is not going to change throughout the RPM range you could use pulse width as a generalized indicator of injector fuel output but not as a pinpointed indicator of fuel consumption also injector pulse width is not a wave for me that’s you actually record with the oscilloscope it is simply a value taken with the voltmeter or graphing multimeter and it is always expressed in a percentage value the final part of the injector voltage waveform is the injector turnoff point this is a vertical line normally clipped at the top to around 35 volts and denotes the collapsing magnetic field of the injector coil if the spike is too low it is indicative of shorted injector coil windings but oftentimes this vertical spike is clipped by the internal circuitry of the ECM to around 35 to 45 volts one of the very first steps during any injector testing routine is to expose the wires start by cutting the sheathing leading to the injector connector right on top of it be aware of the fact that sometimes the two injector wires are coiled together this is done to prevent electromagnetic interference so if you have to uncoil these two wires make sure you put them back to the way it was originally the first step is to test the power feed at one leg of the injector connector as said before 95% of all injectors have steady power going to one side and the other side of the injector is pulsed to ground by taking a test light and verifying power at one side of the injector you have a strong indication that the injector is receiving steady power an exception to the rule as if you are dealing with the Chrysler vehicle which has NASD really on which all injector power shuts off with engine off and key on if you are dealing with a Chrysler vehicle then simply cycle the key on and off to activate the relay jump the asd relay or activate the asd relay using us and tool chrysler vehicles feed a steady power to the injectors through the asd relay which is triggered on by the ECM when an RPM input is received from the crank sensor the other side of a Chrysler vehicle injector is also ground pulsed just like a normal injector unit at this point in time we have actually verified that we have power applied to one leg of the injector unit a further refinement of this technique is the use of a higher amperage load such as a headlight bulb to verify power it is possible to have the right to mount a voltage but not enough current going to the injector circuit as a rule of thumb most port fuel injectors will draw around 950 million second we proceeded to do an oily light test the noid light is a simple tool which is a sort of test flight for injectors and may prove valuable to ascertain whether the injector is pulsating but remember noid lights do not determine if the circuit can actually provide the current or power needed by an injector unit so simply connect this noid light with the two prongs terminals to the injector connector this light is very useful for injector pulse testing the light snaps right across the injector connector as we can see on screen and allows you to verify injector pulse immediately there are different noid lights available which attach to the different injector connectors on the market injector on pulse testing is one of the basics when it comes to automotive diagnostics so always verify that you have your basics such as spark fuel pulse fuel pressure and compression we are now going to the basics and verifying that we at least have a pulsation at the injector unit again most injector circuits are ground pulsed unless you have a Chrysler vehicle Chrysler’s are also ground pulsed injectors but the power comes through the ASD relay which is activated by the ECM in this case the asd relay has to be activated with a scanner or jump to apply a steady power feed to one side of the injector unit as you can see we have verified that there is an actual injector pulse present at the injector wires keep in mind that the injectors circuit is directly controlled by the ECM injector driver this driver provides an actual ground path for the injector to turn on all the injectors reiver does is simply control the amount of time that the ground is applied to the injector coil this is what’s going to determine the injector on time and therefore the amount of fuel injected into the intake manifold runner if we are to go deeper into testing the actual injectors rival our transistor then a current ramping test should be performed current ramping is a technique using the clamp on amp probe and a graphing multimeter or oscilloscope to take a current waveform of the signal the current ramping technique is very useful because it stresses the circuit and allows the technician to verify proper operation during actual working conditions this is the low current amp probe used to test injectors circuits at the center of a clamp on amp probe there is a switch which can be set to different current settings depending on the component being tested by simply clamping on either of the two injector wires a current waveform can be captured using the right equipment it doesn’t really matter which wire the amp probe is clamped on to the amp probe detects the expanding magnetic field around the injector wire and translates it into a waveform on the screen that the technician can view we now see that with the engine off there is no signal present remember that 95% of the injectors in the field will draw a nominal 950 million or very close to 1 amp now we can see the current waveform with the engine running on the screen being picked up by the clamp on amp probe this hump in the middle of the screen is the nominal current being drawn by the injector unit by studying this hum very carefully we can know the entire operating characteristics of that particular injector it is called a current hump and if you freeze the wave very carefully the technician can do an extensive analysis of it we are looking for around nine hundred to nine hundred seventy five milliamps remember we are dealing with current or amount of electrons flow and not voltage the clamp on amp probe simply translates this current into a voltage to be plotted on the equipment screen during testing let’s analyze this way for in detail right away we see the injector open time in between the two yellow dots on the screen a little bit further up we see the pintle opening right where the cursors are we can see that this particular injector is drawing 787 milliamps if we multiply the measured amount at the bottom of the screen by the setting that we have on the amp probe we immediately arrive at a 787 milliamps figure so now we know exactly how much current this injector is drawing unless we do a current ramping test it is almost impossible to know if the ECM internal injector driver is operating properly you may have an injector pulse but excessive resistance in the circuit faulty driver faulty injector coil shorted injector coil or any other problem related to the injector circuit that may prevent that injector from working so remember nominal current for an injector is between 900 and 975 million an exception to the rule where the old peak hand-hold injectors found on throttle body fuel injection systems but these injectors are no longer being used there are nominal current draw West between 4 to 5 amps again you can see the injector pintle opening which is created by the metal Pindell interfering with the magnetic field around the injector coil this in turn creates the small hump that you can’t see on screen the higher quality oscilloscopes can show this hump with much greater definition then we can see the open time of the injector which is a space in between the cursors signified by the yellow dots on the screen that is the injector open time and again may not coincide with the scanner injector pulse width injector open time in this case is that 4.3 milliseconds which is normal for most idling engines not all engines are the same and a good library proves very helpful duty cycle is the best way to determine fuel consumption you step number three prepared to do a voltage waveform analysis of the injector signal this is done by tapping into both of the injector wires using wire crimpers or any means necessary you are measuring a different waveform which is called a voltage waveform and by analyzing it a different set of characteristics can be derived this is an intrusive test and involves piercing the wires to get to the copper element in other words a physical contact isn’t did this type of waveform yields a totally different type of information than the current ramping waveform seen before we are using the Vantage graphing multimeter and by using the waveform viewer part of the menu and connecting the black and red leads we can immediately acquire and capture a voltage waveform from the injector wires connect the black and red multimeter leads to each one of the injector wires if they waveform is inverted simply flip the leaves here we have the waveform viewer which is a setting that allows the technician to graph a wave from an oscilloscope will also do the trick but you can do the waveform analysis using only the graphing multimeter as soon as we get set up we go to the ground control circuit and then we plot the waveform on screen by centering the trigger level or the small X you can clearly see the injector waveform now on screen this is a lot easier than actually plotting numbers using a digital multimeter following we see the trigger mark and the injector waveform inverted then we see the injector open time which is the space between the two vertical lines there are three points of interest when analyzing injector voltage waveforms these are the injector pulse switch or open time the injector pulse which can also be determined from a current waveform as we did before by using a voltage wave it becomes a lot easier to determine the open time for that injector unit the spike following the injector shut down vertical line is clipped by the internal circuitry of the ECM by studying this spike we can know if there are shorted injector coil windings within the injector itself this spike is generated by the self induced voltage of the collapsing magnetic field around the injector coil you should not have anything less than 35 volts this spike is never clipped below 35 volts in actuality this measurement is a sign of the general health of the injector coil if the injector coil windings are semi shorted the spiked vertical line is going to be much lower than 35 volts next we see the injector pintle closing or the actual physical closing of the injector pintle this is not the point of electrical turn off which is denoted by the vertical line preceding it it simply takes the injector pintle a few milliseconds for it to close completely this delayed time is captured by the graphing multimeter or oscilloscope and plotted on screen the injector pintle closing point denoted by the small hump is indicated here by the yellow dot again the small hump is created by the interference with the collapsing magnetic field on the metal pintle closing even though our waveform is inverted the point is the same if this point is too far down or close to the zero line then it is a good indication that it is taking the injector a long time to close this is a sign of weak injector Springs the small spring inside the injector weakens over time and caused the injector to be open for too long a period as a result more fuel is delivered to the engine skewing the fuel trims and the entire fuel injection control system if on the other hand this point is too far up or further away from the zero line then it is a good indication of a cloud injector unit the less fuel inside the injector the faster its pendel will close these readings however should only be used as preliminary indicators of a problem always follow up on these diagnostic tests with for their manual testing to prove your faulty issue this also includes an injector leak down tests and carefully monitoring the fuel pressure drop a manual injector leak down pressure drop differential of 1 psi points to a clogged injector unit now we’ve actually flipped the actual waveform and we can see the magnetic spike or the collapsing magnetic field going straight up again as spike is clipped by the ECM s internal circuitry even though the waveform is now right-side up the end result is still the same always look for a minimum of 35 volts sometimes this spike could go as high as 60 or even 90 volts then we see here a different way of connecting our test equipment we can always go from battery positive to injector triggered negative wire or from injector positive power feed to injector trigger and wire the end result however is always the same as we sent her the pulse we can see again the injector open time injector turn-on point and the high voltage spike again the hump is indicating that the pendulous closing this of course does not coincide with the actual command an injector pulse closing time here we see in between the two yellow dots the actual ECM command injector pulse but it does take a certain lag time for that pintle to overcome the inertia and go completely closed here we see that the injector pulse width is at 3.9 milliseconds remember not to use the injector pulse width as an indicator of fuel delivery this pulse width is not going to change throughout the different rpm range but it could be used as a general indicator for fuel delivery however always use duty cycles as the main indicator for fuel delivery on an engine you would never know whether the engine is running rich or lean by looking at the pulse width alone you could have an idea if the fuel control it’s way off but not with pinpoint accuracy you may be able to compare two separate banks on a v-type engine by comparing the two pulse widths of separate injectors on each bank so if one bank is running richer than the other you will know because you have a reference point but it is extremely difficult to use pulse wood as a fuel indicator normal duty cycle percentage for an idling engine is between two point two and two point nine percent anything higher than two point nine indicates that the engine is running rich and lower than two percent sand indication that the engine is running Liam now we can see how to test the ECM grounds and the way we do that is by actually measuring the bottom of the injector pulse and comparing it to ground here we see at the bottom of the injector pulse has a voltage level of about 240 me levels again it depends on the vehicle that you are working on the rule of thumb is nothing higher than 100 millivolts of ground voltage drop or between battery ground and ECM ground but in case of an injector there are other resistance values in between such as the injector coil connector resistances and the rest of the wiring harness which may add up to a voltage level of it higher than 100 millivolts normal ground voltage drops for a cranking engine should be no higher than 500 millivolts but this should only be seen with a cranking engine in this particular case we were having a bit of a problem with this vehicle there was actually a ground problem at the main computer ground feeding the ECM which is the reason why we use this vehicle for our video example the bottom side of this injector is that 240 millivolts indicated by the 0.2 4 volts seen on the bottom of the screen during this test again this is a fast way to look and analyze our ECM ground by simply knowing how much the computer grounds the injector we can know right away if the ECM is having a ground problem between the two lines you are going to see the injector pulse the bottom of the injector waveform is used to determine ground faults as we said before normal engine grounds voltage drops should not be higher than 100 millivolts of course this figure should not be taken to the extreme a few millivolts above or below is fine this 100 millivolts rule can always be applied to any computer ground circuit if the engine is cranking you should be looking at a maximum of 500 millivolts between battery negative and ECM ground this is a simple and fast way to know whether the computer is grounded properly we are still seeing the voltage waveform and trying to measure the injector real-life open time and this can be deduced by setting our cursors at the injector closing hum and the injector turn-on point here we can see the mechanical lag time between the two white lines as said before this point can always be used as an indicator of whether the injector is clogged or the injector Springs are weak this is by no means a conclusive test but it is a fast way to ascertain whether the injector is faulty or if the problem lies elsewhere the spike that you see on screen now is the collapsing magnetic field again don’t be confused if a spike proves to be lower than normal oftentimes this spike is clipped by the ECM s internal transistor here we can see that this particular spike gives at 54 to 55 volts this injector waveform is not clipped by any internal circuitry the reason why the spike is clipped if it is indeed clipped is to protect the rest of electronics from the high voltage induced by the collapsing injector magnetic field around the coil the clipping circuitry is oftentimes found in the Asian vehicles to protect the ECM here we see a healthy 54 volts for the collapsing magnetic field or injectors spike at the waveform further on to the right then we see the actual injector pendel pulsing you you


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