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davew wrote:

Ah, I see where you misunderstood: In this particular context of course the 'base noise' is (using your choice of voltage) the 4V signal and the Timing reference signal is the 6V spike (triggering a positive on the leading edge and a negative on the trailing edge of the tooth in the PICO/Jag scope illustration I posted).

The main point again though is that we are just dealing with a few volts (AC) here between 'states' (ie. between tooth/no tooth/ or even double tooth..) and this can be very easily disrupted, particularly by the tooth-sensor 'air gap'; It makes more sense if/when you see a faulty P38 CKP signal in practice... I have (had ?) a photo of this -somewhere- posted up years ago on RRsnet, via a storage scope IIRC (along with the ECM illustration,) but I am not going to try to search for it on there thanks to their almost-useless 'search facility' !

If you do scope it mace take a photo ....

Not sure if your sensors work on starter motor teeth or on separate (for purpose) position sensing teeth? As I looked at it each 4v spike is signal from an individual tooth and I might assume the higher 6v spike after a position sensing gap is due to something related to magnetic flux causing a higher voltage pulse after a long period of no pulse but I'm no expert in the way these sensors work. Surely though the 4v spikes are not noise?

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No, it's a separate reluctor ring on the back of the flywheel/flex plate assembly. It has multiple teeth with a gap so the crank position sensor knows the crank position (oddly enough). It is the gap that the ECU looks for.

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I see you are in one of your overly-pedantic moods (again) Lpgc !

"Ah, I see where you misunderstood: In this particular context of course the 'base noise' is (using your choice of voltage) the 4V signal and the Timing reference signal is the 6V spike (triggering a positive spike on the trailing edge before the gap and a negative on the leading edge of the next tooth in the PICO/Jag scope illustration I posted). "

Happier now Lpgc ? I also note I wrote 'ECM' instead of 'ETM'..... although at least I tried to stay on the Reluctance/P38 topic !!
Again the main point is a Basic Coil, as we use for CKP, is really not ideal

Incidentally within RF/AC descriptions where there is a constant background signal it is totally valid/conventional to describe this as "base noise" and any 'event' occurring during that is the signal (of interest). Pedants may not agree with this entirely of course....

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mace; If you do get stuck let me know and I will 'scope my (working) CKP and post it up;
Incidentally what I also recall was that the (faulty) CKP signal was so erratic it was rather difficult to trigger the scope !

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davew wrote:

mace; If you do get stuck let me know and I will 'scope my (working) CKP and post it up;

I was never stuck WRT CKP :) you lot just hijacked my thread 🤣

Have you got a nanocom?

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Fair enough mace, we did ! Perhaps the CKPs in our heads are faulty ??

I suspect we went off on a tangent once you asked about monitoring the EAS handshaking with a 'scope...... which probably won't help (?) At risk of _another _tangent have you tried any other EAS diagnostics too (eg. RSW) ?. As you (may) know the EAS uses a dedicated pair of pins on the OBD connector and that may be the primary problem ??

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for those that don't know what the gap is for , it tells the ecu where top dead center is on start up, so it knows where it is and when to fire.

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davew wrote:

Fair enough mace, we did ! Perhaps the CKPs in our heads are faulty ??

:D

I suspect we went off on a tangent once you asked about monitoring the EAS handshaking with a 'scope...... which probably won't help (?) At risk of _another _tangent have you tried any other EAS diagnostics too (eg. RSW) ?. As you (may) know the EAS uses a dedicated pair of pins on the OBD connector and that may be the primary problem ??

It's definitely a nanocom problem, other diagnostics can talk to EAS both in multiple vehicles and in my bench setup, hence why I want to check a known working one for it's voltage levels.

Not interested in the actual comms chatter as such for the purposes of this issue.

From my probing, I'm pretty sure the green lead has some level of active electronics buried in it. Might not be much more than a couple of diodes or a transistor though, but hard to tell from the outside. I may see if I can borrow someone elses lead and see if that makes any difference - would explain why my extensive reverse engineering of the nanocom hardware has come up empty.

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A-ha ! Then why didn't you just tell us all that much earlier mace ?! :-)
Don't know if any of 'local' members could lend you their green lead
(I'm "dawn sarth" !!)

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davew wrote:

I see you are in one of your overly-pedantic moods (again) Lpgc !

"Ah, I see where you misunderstood: In this particular context of course the 'base noise' is (using your choice of voltage) the 4V signal and the Timing reference signal is the 6V spike (triggering a positive spike on the trailing edge before the gap and a negative on the leading edge of the next tooth in the PICO/Jag scope illustration I posted). "

Happier now Lpgc ? I also note I wrote 'ECM' instead of 'ETM'..... although at least I tried to stay on the Reluctance/P38 topic !!
Again the main point is a Basic Coil, as we use for CKP, is really not ideal

Incidentally within RF/AC descriptions where there is a constant background signal it is totally valid/conventional to describe this as "base noise" and any 'event' occurring during that is the signal (of interest). Pedants may not agree with this entirely of course....

Not being over pedantic Dave, just interested what those 4v spikes were. If they're noise fair enough but Gilbert's said the reluctor ring has multiple teeth besides the gap for TDC, could those 4v spikes be the other teeth? And if they are they're not background noise....

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Then it is probably just as well that i did _not actually describe it _as "background noise" then Lpgc, you would have blown a gasket ?!

  • In the specific context of a 'scope trace of an AC CKP I used the phrase 'base noise' and then 'background signal' above.

"Could it be" that you went off on an unhelpful (and irrelevant) Hall Effect tangent ? And if so that was not 'on topic' (either) !

Accordingly perhaps back on topic you could use your 'scope to provide mace with some voltage levels from your EAS instead ?

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I'm sorry for going off topic at the start but I continued to post because Mace said he'd found a problem with his CKP signal in the same way I had on a different model vehicle. I didn't want to take the topic completely off track but as an aside I thought at least you, Mace and I were interested in this.

I see what you mean.. If the object is to look for the 6v pulse which is a position reference point (for say TDC), the 4v pulses from other teeth (even though intended and necessary signals) could be considered noise - and you're saying it is the convention to consider the 4v signals noise even though they're intended and necessary? Fair enough. But you'll understand other people thinking that in the wider context the 4v pulses from the other teeth are not just base/background noise because they are intended and necessary, the engine wouldn't run properly without them?

Are the pulses from your reluctance sensors always 4v for teeth that are close together and 6v for the gap or do these voltages change with engine RPM (frequency)?

Are we correct in thinking that the 6v pulse is bigger than the other 4v pulses because of the wider gap between teeth, or is something else making the pulse from the bigger gap higher voltage than other pulses that are closer together (I would think it's due to the wider gap)?

Are you implying that the ECU looks for the higher voltage pulse to detect the (say TDC) engine position or would you say the ECU is looking for the missing tooth/pulse to detect TDC (I would think it's looking for the missing pulse)?

If the ECU detects the (say TDC) position by the missing pulse (and especially if voltages of pulses change with RPM) I still don't understand why you reckon the 4v teeth signals should be considered noise that might detract from the ECU's ability to properly detect the (say TDC) engine position?

Apologies to Mace again for keeping this up. Dave I'm not wanting to argue, I want to understand.

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Yes, Lpgc that summarises it all quite well. Yes the ECU 'just' wants to know when the engine is at TDC and the gap in the teeth (the spike) tells it ..!
Any other spikes etc due to air gap issues faulty CKP etc confuse it considerably. GEMS and THOR are different in that the 'reluctance wheel'
has teeth on the former and pegs on the latter. (These pegs can get bent as was described). On nether system is an OBD code raised though...

Sorry Mace, anyone offered to lend you their Green Nanocom Lead yet ?

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Teeth on gems are easily bent too.

Haven't had a chance to get a lead yet.