Fuel Injector Waveform Questions
www.scanshare.io/share/heEVuXVVWkiYjDa8EEhdSQ
Interesting that you saw the CEL flash, but didn't notice a miss. Maybe that's why the owner threw a CKP at it - the PCM is falsely flagging misfires? :huh: I don't recall there being a CKP pattern learn on these...
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If the A/F sensor doesn't go low, that'd be another strike against the fuel system.
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Tyler wrote: I haven't forgotten! :blush: Was just working out a reply, gimme a few minutes.
Sorry Buddy, wasn't sure if you got my message and didn't want to be a pest.
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So, I gotta clarify a bit. KOEO, #4 injector unplugged, you saw B+ on the common injector power feed. But on the PCM control wire, you saw 2.9V? Then later, with the injector power feed fuse out, you saw the same 2.9V on the power feed? :huh:
I went over all the available diagrams a couple times, and couldn't find anything that ties into the same circuit that fuse #55 feeds (for the injectors). Unless that 2.9V is coming from the PCM, I can't see where it'd be coming from.
Was it misfiring when you ran that power balance test?
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I was getting ready to pull the intake to test the pressure while activating each injector with my injector tool when I decided to see if the Maxisys would do it so I wouldn't have to pull the intake. "Module not supported" (of course).
For no particular reason I fired up the car and started a power balance test. Injectors 1, 2, & 3 made the RPM drop as expected as I shut off each injector. But when I commanded #4 off, the RPM picked up to about 1100 instead of dropping and the car seemed to even smooth out.
It's got me completely thrown. Getting it again tomorrow.
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Tyler (or anyone), I notice on the wiring diagram that the BRN/YEL wire that feeds all the injectors (from fuse #55) has a dotted line on part of it. I know this means that there are other circuits or wires connected at the dotted location, but I can't figure out how to locate on the wiring diagram what those other circuits or wires could be? Any ideas?
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On a side not i quickly read through these posts a couple days ago and I don't remember has a compression test been done to verify you don't have a base engine problem?
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An outside possibility that came to mind today... Is #4 at the end of the rail, or at the beginning (relative to the fuel line)? I ask because whenever I'm A.) Running an injector flush with the MotorVac machine or B.) Dealing with water in the fuel, it's my experience that whatever isn't gasoline tends to end up at the ends of the rails. Whatever cylinders have injectors at the ends of the rails end up misfiring.
Probably unlikely, but maybe there's a fuel quality issue? If there's been more than one tank of fuel run though this thing since you started diagnosing this issue, disregard and proceed as normal. :silly:
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rockp2 wrote: What are your thoughts on the voltage on the control wires?
I didn't know what to think at first. :silly: So I decided to have a look at a Nissan we had at the shop, see if it's the same way. It's an '08 Altima 2.5L, so not the same year/model/engine/anything. But I figured if that 2.9V is a common Nissan thing, this one might use it, too?
Grabbed an injector waveform for reference:
With the injector disconnected, I got 12V on the feed wire, and 2.9V on the control wire. :blink:
This Altima has no engine performance issues that I know of, so I think you're definitely looking at a bias voltage on the injector control wire.
It's interesting that Nissan O2 sensors also use a 2.9V bias on their O2 sensor signal circuits. Maybe it all comes from the same place?
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