Stick To Your Diagnostic Game Plan!
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Date: 2020-08-05
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Comments and reviews: 10
Brian
Eric: I am NOT a mechanic, even if I do troubleshoot & repair quite a few agricultural implements here where I live. I know nothing about this vehicle you repaired, but without seeing the cabling to the injectors, I would offer a guess that the injector wires are not shielded, are carried in a bundle & then fanned out to the individual injectors. I would further suggest that the high current to the shorted injector is inducing current pulses into the other injector wires, causing the affected injectors to have limited pulse height, and/or narrower pulse width. I would guess that the longer the engine idles, the lower the shorted injectors input resistance becomes & the higher the short circuit current becomes, exacerbating the problem. I offer this as a possible explanation for the multiple misses which disappear when the #1 injector cable is unplugged. Once again, I emphasize that I am NOT a mechanic, hold NO qualification as a mechanic ( the local single moms bring vehicles to me to fix because they can't afford to pay the outrageous rates shops charge ) but I lay a modest claim to understanding a bit about electrics & electronics.
At 80 years of age when I am confronted with a perplexing electronic problem, I wistfully wish I was 16 again when I knew EVERYTHING. It is amazing how much my knowledge & understanding have diminished over the years. Sometimes I even ask for opinions from people who are smarter than I (a significant portion of the population. I love your videos Eric, & you have the best understanding of electrics & electronics in vehicles of any mechanic I have encountered. Keep up the good work & all the best to you & your family.
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Eric: I am NOT a mechanic, even if I do troubleshoot & repair quite a few agricultural implements here where I live. I know nothing about this vehicle you repaired, but without seeing the cabling to the injectors, I would offer a guess that the injector wires are not shielded, are carried in a bundle & then fanned out to the individual injectors. I would further suggest that the high current to the shorted injector is inducing current pulses into the other injector wires, causing the affected injectors to have limited pulse height, and/or narrower pulse width. I would guess that the longer the engine idles, the lower the shorted injectors input resistance becomes & the higher the short circuit current becomes, exacerbating the problem. I offer this as a possible explanation for the multiple misses which disappear when the #1 injector cable is unplugged. Once again, I emphasize that I am NOT a mechanic, hold NO qualification as a mechanic ( the local single moms bring vehicles to me to fix because they can't afford to pay the outrageous rates shops charge ) but I lay a modest claim to understanding a bit about electrics & electronics.
At 80 years of age when I am confronted with a perplexing electronic problem, I wistfully wish I was 16 again when I knew EVERYTHING. It is amazing how much my knowledge & understanding have diminished over the years. Sometimes I even ask for opinions from people who are smarter than I (a significant portion of the population. I love your videos Eric, & you have the best understanding of electrics & electronics in vehicles of any mechanic I have encountered. Keep up the good work & all the best to you & your family.
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Antonio
I went down a few of these rabbit trails because I didnt do my normal procedure them days was working on a 2000 4runner with the 3. 4l v6 and couldn't figure out why it was missing on 3 different cylinders found out that the timing was fine and the fuel was fine spark was fine but the number 1 cylinder coil was bad causing the other cylinders to not get there spark as well so thought it was spark plugs and these Toyota have 3 coils on passenger side and 3 wires on driver side 2 of the miss fires were on 1 coil because the coil runs one wire and the spark plug connected to the coil and the 3rd was a coil that was going bad if it would have been left longer would of been 4 cylinders missing out of 6 was frustrating to say the least 19 years on factory coils isn't bad though
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I went down a few of these rabbit trails because I didnt do my normal procedure them days was working on a 2000 4runner with the 3. 4l v6 and couldn't figure out why it was missing on 3 different cylinders found out that the timing was fine and the fuel was fine spark was fine but the number 1 cylinder coil was bad causing the other cylinders to not get there spark as well so thought it was spark plugs and these Toyota have 3 coils on passenger side and 3 wires on driver side 2 of the miss fires were on 1 coil because the coil runs one wire and the spark plug connected to the coil and the 3rd was a coil that was going bad if it would have been left longer would of been 4 cylinders missing out of 6 was frustrating to say the least 19 years on factory coils isn't bad though
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thehappyTexan
Just a theory- its possible that a shorted injector would put too much demand on the injector driver in the ecm, which would then have increased resistance as it started to overheat from being overloaded. I saw that happen twice on Cummins engines about 7 years apart. You can bet your paycheck I remembered real quick the second time around that the computer isnt always right. They would both misfire until you hooked up the laptop and did a cutout test. As soon as I clicked start on both trucks, the miss went away. Cummins said its because their t/s software actually forces the drivers to put out max power to all 6 injectors during the test.
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Just a theory- its possible that a shorted injector would put too much demand on the injector driver in the ecm, which would then have increased resistance as it started to overheat from being overloaded. I saw that happen twice on Cummins engines about 7 years apart. You can bet your paycheck I remembered real quick the second time around that the computer isnt always right. They would both misfire until you hooked up the laptop and did a cutout test. As soon as I clicked start on both trucks, the miss went away. Cummins said its because their t/s software actually forces the drivers to put out max power to all 6 injectors during the test.
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autos
In a previous career, I was managing some on aircraft testing (it was a two day test. I had a well defined plan that should have worked. Near the end of day two, some of the crew was getting anxious to clean up. I let them convince me that they could start pulling some equipment unrelated to the test I was performing. All of the sudden my test went to sh! t. It turns out there was one connection that they pulled that they shouldn't have. I was pissed. almost as pissed as the Major that scheduled two days of aircraft downtime for us to do the testing.
Since then, I ALWAYS stick to my plan! Some lessons come hard.
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In a previous career, I was managing some on aircraft testing (it was a two day test. I had a well defined plan that should have worked. Near the end of day two, some of the crew was getting anxious to clean up. I let them convince me that they could start pulling some equipment unrelated to the test I was performing. All of the sudden my test went to sh! t. It turns out there was one connection that they pulled that they shouldn't have. I was pissed. almost as pissed as the Major that scheduled two days of aircraft downtime for us to do the testing.
Since then, I ALWAYS stick to my plan! Some lessons come hard.
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Dave
When I was in my automotive electrical class we would have to diagnose bugs that the teachers would put into the car. One team got a headlamps inoperable on what I think was a Toyota Camry from the early to mid 2000s. They spent a solid two days trying to figure it out. They checked fuses, current draw, continuity, everything and then some. Turns out that model has a weird switch that is kinda hidden away. Its this little push button thing. All they had to do was hit the switch and the lights worked perfectly. That team was so pissed. I thought they were going to cry.
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When I was in my automotive electrical class we would have to diagnose bugs that the teachers would put into the car. One team got a headlamps inoperable on what I think was a Toyota Camry from the early to mid 2000s. They spent a solid two days trying to figure it out. They checked fuses, current draw, continuity, everything and then some. Turns out that model has a weird switch that is kinda hidden away. Its this little push button thing. All they had to do was hit the switch and the lights worked perfectly. That team was so pissed. I thought they were going to cry.
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StarionGuy
Is that shorted injector actually opening and spraying fuel? maybe the shorted windings and subsequently weak magnetic field is keeping that injector from opening, or maybe just reducing it's on time open resulting in a lean AF mixture reading at that bank AFR sensor. The PCM then sees that lean mixture on that bank and tries to correct by enriching that bank, resulting in an incorrect AF mixture on the other cylinders of that bank and them running poorly or misfiring. Then when you unplug the injector the PCM sees that fault and goes into open loop?
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Is that shorted injector actually opening and spraying fuel? maybe the shorted windings and subsequently weak magnetic field is keeping that injector from opening, or maybe just reducing it's on time open resulting in a lean AF mixture reading at that bank AFR sensor. The PCM then sees that lean mixture on that bank and tries to correct by enriching that bank, resulting in an incorrect AF mixture on the other cylinders of that bank and them running poorly or misfiring. Then when you unplug the injector the PCM sees that fault and goes into open loop?
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Moon
I haven't scoped my own car yet so I haven't learned. But I remember you saying something along the lines of a misfire is counted by checking the engine speed at a certain point in time, if the ECU is not what it expects it to be, it counts a misfire. Something along those lines. Generally injectors are driven from the ECU. So It's possible that the injector going short is pulling parts of the ECU low and is making the ECU go wonky? I dunno, this is pure speculation, there's a reason I'm not a mechanic.
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I haven't scoped my own car yet so I haven't learned. But I remember you saying something along the lines of a misfire is counted by checking the engine speed at a certain point in time, if the ECU is not what it expects it to be, it counts a misfire. Something along those lines. Generally injectors are driven from the ECU. So It's possible that the injector going short is pulling parts of the ECU low and is making the ECU go wonky? I dunno, this is pure speculation, there's a reason I'm not a mechanic.
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YH
Great job Eric. Great video. I'm curious to know if any other misfire source malfunction (i. e. ignition coil) would have the same effect on the other cylinders, or is this problem unique to the fuel injector. It sounds like perhaps it could be an ECU software issue unique to that make/model car. I'm wondering if the ECU has the latest software update that may affect that issue. Just a thought.
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Great job Eric. Great video. I'm curious to know if any other misfire source malfunction (i. e. ignition coil) would have the same effect on the other cylinders, or is this problem unique to the fuel injector. It sounds like perhaps it could be an ECU software issue unique to that make/model car. I'm wondering if the ECU has the latest software update that may affect that issue. Just a thought.
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ice44567
That's the weirdest thing I've ever seen. I wonder if the one injector being shorted was pulling down the current for the rest of them and causing them to not fire correctly? But that doesn't explain why their per firing amperage didn't go up after you disconnected #1, or at least I didn't see it go up. I'm curious as to what the fuel pressure was reading during these tests.
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That's the weirdest thing I've ever seen. I wonder if the one injector being shorted was pulling down the current for the rest of them and causing them to not fire correctly? But that doesn't explain why their per firing amperage didn't go up after you disconnected #1, or at least I didn't see it go up. I'm curious as to what the fuel pressure was reading during these tests.
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bookerol
I'm going to have to put my scope to work, from now on. That was very enlightening Eric.
Recently had an Acura in the shop with all the cylinders throwing misfire codes. I didn't draw that job, but those involved assumed the INTERNET fix of valve adjustment, was the way to go. I doubted it, but if it returns, most likely it will come my way.
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I'm going to have to put my scope to work, from now on. That was very enlightening Eric.
Recently had an Acura in the shop with all the cylinders throwing misfire codes. I didn't draw that job, but those involved assumed the INTERNET fix of valve adjustment, was the way to go. I doubted it, but if it returns, most likely it will come my way.
reply
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