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Post by ezimoto on Dec 27, 2022 19:25:08 GMT 1
Hi guys
Wonder if anyone has a cranking waveform (not running) for a common rail piezo injector?
Can't seem to find a cranking one anywhere, plenty of idle etc but not what I need for a non running vehicle.
Thanks in advance
Ezi
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Post by givusaclue on Dec 28, 2022 12:44:32 GMT 1
Picoauto forum is probably the best place, failing that simply diagnostics network forums may have what you want.
can I ask why you are looking for one? Never found piezo patterns very informative personally other then to confirm the ecu is sending a signal to the injector & a current clamp to check if the injector is using the current available
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Post by ezimoto on Dec 28, 2022 13:13:59 GMT 1
Thanks for the reply.
On both of those I've only found waveforms at idle or above. I've asked this same question on the Scannerdanner site but no response as yet.
I have a non starting common rail diesel which has good rail pressure / crank signal etc but doesn't appear to be getting fuel as it will run but not keep running on a squirt of brake cleaner.
I managed a quick amp scope which shows a current of some sort (started pouring with rain so no scales set etc or chance to scope voltage) but hoped I could find a known good in the meantime for when I return to the vehicle.
Thanks again for your input.
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Post by valhalla on Dec 28, 2022 23:47:46 GMT 1
The piezo waveform at cranking will be very similar to an idle-speed waveform on most cars. It would depend on the engine make & model, but I very much doubt whether you would fail to make a diagnosis using an idle waveform, as it will typically be of similar rail-pressure setpoint, and similar injector timing and separation pilot-to-main injections.
If you are seeing something dramatically different, then you have your diagnosis in the bag.
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Post by givusaclue on Dec 29, 2022 0:27:00 GMT 1
Thanks for the reply. On both of those I've only found waveforms at idle or above. I've asked this same question on the Scannerdanner site but no response as yet. I have a non starting common rail diesel which has good rail pressure / crank signal etc but doesn't appear to be getting fuel as it will run but not keep running on a squirt of brake cleaner. I managed a quick amp scope which shows a current of some sort (started pouring with rain so no scales set etc or chance to scope voltage) but hoped I could find a known good in the meantime for when I return to the vehicle. Thanks again for your input. Get your injectors tested, or at least one, sounds like they may be blocked, if they are then obviously there’s a lot of work & expense to rectify |
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Post by ezimoto on Dec 29, 2022 17:20:30 GMT 1
Thanks to everyone for their input.
Had the chance to return to the vehicle today (for reference it is a 2018 Peugeot Boxer 2.0 Blue HDI).
On one injector wire I get a similar pattern to good idle waveforms I have found with around an 80 volt peak however on the other wire I get absolutely nothing.
Perhaps I have misunderstood but from various articles on these injectors it seems there should be a positive feed one way to open the injectors and then another the other way to close them? If this is the case I guess I only have the closing feed as the injectors are certainly not stuck open.
I have tried this on three accessible injectors with the same result.
Perhaps someone could suggest if I am testing incorrectly or have a thought on what direction I should now follow.
Thanks again, nothing worse than testing a system which is not fully understood!
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Post by givusaclue on Dec 29, 2022 19:22:55 GMT 1
The injectors on those fail for fun, they also seize in, I’ve extracted several for my local Peugeot dealer for failure, oldest was probably 2017.
if it runs on a sniff but won’t pick it up on diesel & you’ve got good fuel pressure you can spend 3 days testing everything unobtrusively with a scope like some of the gurus will, but what’s the value of that Labour vs. Removing an injector to get it tested? I suppose it depends who’s paying, I know which way I’d personally go though.
if you want to know more about scope testing procedures on simply diag Fullscope is your man & on pico forum & a few others Robski is a very accomplished scope diagnostician
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Post by ezimoto on Dec 29, 2022 21:47:24 GMT 1
Thanks again, great answer and I've posted on Simply diag.
Seems a bit odd that at least three injectors could fail at the same time, looking at how rotted in they appear to be I can see what you're saying about removal which is pretty sad when only four years old.
Keep seeing reference to voltage on both injector wires, I'm drawn more to an ECU fault at present (or even drivers that have damaged injectors or vice versa).
I can justify diag time on this as knowledge will make diagnosing the next one much quicker. Don't have another same vehicle here until next week, if I don't find my answers by then I'll kill the fuel and get some known good waveforms from that.
Thanks again, keeps the grey cells working!
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Post by valhalla on Dec 30, 2022 0:11:45 GMT 1
The thing to remember on piezo injectors is that when testing them, the voltage is less important than measuring the current; secure a current-clamp around one of the twisted-pair wires into the injector connector plug, and look for a current (a charge) being moved first onto the injector, then off the injector.
Don't forget that if anything is wrong, whatsoever, with the injector harness, the connectors, or the injector piezo unit itself, then the end-stage of the engine management computer that handles the charge onto and off the injector piezo stack will just shut off, to protect both the ECU and the injector. The on-charge must equal the off-charge, 30 times a second at idle speed.
The big rule is - don't move or pull an injector plug/harness whilst the engine is running. If you interrupt the flow of charge on/off the piezo stack, you will likely destroy the injector i.e. the testing must be done in a way that does not interfere with the electrical continuity of the injector circuits, otherwise a failed injector is a self-fulfilled prophecy!!  |
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Post by remmington on Dec 30, 2022 1:26:27 GMT 1
The thing to remember on piezo injectors is that when testing them, the voltage is less important than measuring the current; secure a current-clamp around one of the twisted-pair wires into the injector connector plug, and look for a current (a charge) being moved first onto the injector, then off the injector. Don't forget that if anything is wrong, whatsoever, with the injector harness, the connectors, or the injector piezo unit itself, then the end-stage of the engine management computer that handles the charge onto and off the injector piezo stack will just shut off, to protect both the ECU and the injector. The on-charge must equal the off-charge, 30 times a second at idle speed. The big rule is - don't move or pull an injector plug/harness whilst the engine is running. If you interrupt the flow of charge on/off the piezo stack, you will likely destroy the injector i.e. the testing must be done in a way that does not interfere with the electrical continuity of the injector circuits, otherwise a failed injector is a self-fulfilled prophecy!! +1 for current clamps. Non intrusive method to test injector drive circuit. |
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Post by givusaclue on Dec 31, 2022 15:41:50 GMT 1
The thing to remember on piezo injectors is that when testing them, the voltage is less important than measuring the current; secure a current-clamp around one of the twisted-pair wires into the injector connector plug, and look for a current (a charge) being moved first onto the injector, then off the injector. Don't forget that if anything is wrong, whatsoever, with the injector harness, the connectors, or the injector piezo unit itself, then the end-stage of the engine management computer that handles the charge onto and off the injector piezo stack will just shut off, to protect both the ECU and the injector. The on-charge must equal the off-charge, 30 times a second at idle speed. The big rule is - don't move or pull an injector plug/harness whilst the engine is running. If you interrupt the flow of charge on/off the piezo stack, you will likely destroy the injector i.e. the testing must be done in a way that does not interfere with the electrical continuity of the injector circuits, otherwise a failed injector is a self-fulfilled prophecy!! +1 for current clamps. Non intrusive method to test injector drive circuit.like wot i sed in the second post  unfortunately they'll likely be goosed, it's a common problem |
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