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Crank Sensor Wiring - Mi16 Transplant, Std Bosch 60-2 Wheel And Crank


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19 replies to this topic

#1
chownr

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OK nearly got the car running but currentl;y dont have fuel or spark which I think is related to Crank Sensor Wiring. The Omex wiring Diagram shows only one connection between ECUY and sensor but I think this is for an Omex Crank sensor which is only a 2 pin plug - Sensor Out and Sensor Earth.

This has confused the heck out of me cos the Pug sensor is a 3 pin plug - 12v, Sensor Out (Signal) and Earth.

So am I right in thinking that the reason for no Crank Signal is simply I need to give the sensor a positive feed?

If so should this be from a relay source or just a direct 12v feed from the battery or other source?

Thanks in advance

Rich

#2
Super Josh

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Hi Rich, no the CAS doesn't need a supply, it is only a coil, with a permanent maget. So 2 connections between the coil and ECU, the third connection is the screen, which has to be earthed at the ECU end. I sent DrS a PM about this a few days ago. I didn't keep a copy of it, but if he still has it I'm sure he won't mind forwarding it on.
One other thing, how have you configured the sensor type in the OMEX software?




Josh

#3
petert

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read this:
http://forum.205gtid...a...ost&id=2079

You'll notice that it puts out a sine wave on pins 1 and 2, so the polarity doesn't matter. Is it possible that the Omex is looking for a 12V square wave output? The Motronic output is very low and the Omex would need to have a software setting to recognise the Motronic output.

#4
DrSarty

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This what Obi Josh Sine Wave-Kenobi sent me. It's clear and I understand it; BUT, I am in the same boat as you now, where my Megasquirt seems to be only expecting one CAS input :lol: ! See below Josh's work.

...the ECU uses it to work out where the engine is rotation wise and therefore it can calculate the timing.

The system we use on our Pugs is the Bosch 60-2 system. The 60 refers to the number of timing teeth around the circumference of the flywheel, so each tooth is 6 degrees of rotation. The 2 refers to the number of missing teeth, which gives the ECU a reference for working out the timing.

The CAS is actually a coil of wire(inductor) wrapped around a permanent magnet, hence it has two pins, the third pin is connected to the screen around the cable. Because the signal is at such a small level it is really susceptible to interference form things like the HT etc. So the screen picks up the interference and routes it to ground. So that you don't get a ground loop with current flow down the screen it is only connected to ground at one end, the ECU end.

Each time on of the teeth on the flywheel passes through the CAS's magnet field a small voltage is induced in the coil and this is sent back to the ECU. At low revs the voltage may only be around 0.5V, whereas at 7K it could be over 100V.

The pinout should be something like this.

1. Earth Return to ECU

2. Output Voltage to ECU

3. Screen, connected to ground at the ECU end only.

So you should be able to get out your trusty multimeter and measure the resistance of the coil, between pins 1 and 2. And check that the screen isn't short circuited to the coil either.

So something like this, I reckon.

Pins 1-2 300-500 Ohms, as this is directly across the coil, don't worry about the exact value, but anything above 100 Ohms and less than 1000Ohms should be okay

1-3 open circuit (infinity) These two measurements make sure the screen isn't short circuit to the coil

2-3 open circuit (infinity)

Even before the first turn of the key you should be able to prove that the majority of sensors are returning sensible values to the MS, using the PC based software.


This is an extract from the MS ECU main (DB37) pin map:

Pin 2 - Shield (coax wrapping) - Ignition input shield for pin 24
Pin 24 - Shielded white wire - Ignition input signal (tach)

I gather here one of the CAS coil wires goes to pin 24 and the shielded coax wrap goes to pin 2. But where does the other end of the CAS coil (earth return) go to?.

When I bought the MS ECU from Bono via James R, James' MS like mine I was told needed to be converted (by Anthony I gather) to work from the Bosch 60-2 system. Perhaps this type of mod is what we both need?

This is NOT a hijack, as I think we're in the same boat and some expert advice will help both of us.

HELP PLEASE - BOTH OF US.

EDIT: Peter - Judging by that PDF document of a Magneti Marelli sensor (showing both 2 & 3 pin variants) and as I suspect they all work in a similar fashion, bottom right of the document under the sine wave diagram it says:

OUTPUT VOLTAGE ON THE POSITIVE
TERMINAL GENERATED BY ONE TOOTH
(NEGATIVE TERMINAL CONNECTED TO GROUND)


My mind says that means that on the 3 pin Bosch variant, signal/positive terminal goes to ECU, negative terminal can simply go to a local ground (engine block) and the shield can be earthed on the ECU casing. Is this a correct assumption?

Edited by DrSarty, 12 March 2008 - 12:44 PM.


#5
DrSarty

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Again, I hope this is not viewed as a hijack as I think CHOWNR & myself are facing the same issue, ie. running an aftermarket ECU off the standard Bosch Flywheel/Crank Angle Sensor (CAS for short).

I''ve been forced to do lots of searching and reading (mostly on Megasquirt forums etc) but I've gleened the following and just want someone to check please.

1) MS2V3 (just like ChownR's Omex) has one input for a tach signal, sent by the CAS.

2) This signal wire is shielded, and we both have to earth this shield at the ECU to avoid interference in this delicate signal line.

3) I am convinced that the Bosch standard sensor IS a 'VR Sensor'.

4) VR (Variable Reluctance) sensors receive no power; they just create an AC/sine wave output based on them being a magnet with a coil of wire wrapped around it, and the flywheel teeth moving past the magnet generate an output voltage between approx 0.6v at idle, 3v at mid RPM & around 50v at rev limit, and this voltage alternates plus/minus based on approaching/departing tooth on flywheel.

5) The Bosch VR sensor's 3 wires are signal output (positive - one end of coil) into ECU, earth (negative - other end of coil) to local ground, & finally shield (metal shielding around signal wire) going to ECU casing/dedicated ECU earth.

Much of the above is assumptions made from the following and needs verification or correction please:

MEGAMANUAL VR SET WIRING

All MegaSquirt® EFI controller installations must have an input (tach) signal to determine engine speed. This signal comes in on pin #24 of the DB37 (Correct for MS2v3 board). A variable reluctor (VR) input (tach) sensor is shown (above) for the input.

You must ground the VR other lead of the sensor as well (2nd pin to earth?), and pin #7 is shown for this. However, pin 7 is not a 'dedicated' or specialized ground for the VR sensor, it just happens to be a ground. The VR sensor can be grounded to any pin that connects to the board's ground, and it can be connected externally (I.e., in the DB37 connector for the harness, or even in the wiring loom).


I have extrapulated (sp? :P ) from the above description and these three diagrams :lol: (below) that the standard MS2v3 board has pin 7 as a VR sensor earth (not shield) and where needed - pin 2 not being used. But, the DIYautotune.com ready made loom takes pin 7 and just merges it with the ECU's main earth cable, and VR sensor shield goes to pin 2.

Posted Image
The footnote on this ^^^ one seems to explain it to me. It's stating that you can use the shield as a shield or as the ground for the VR sensor. This means to me I/we can either take 2 earths back the ECU (one shield one VR ground), pair the VR sensor's earth to the shielding at the sensor and wire up as per the diagram OR even ground the VR locally and take just the shield and the signal wires back to the ECU.

This is the supporting, enclosed diagram that came with the ready made loom:
Posted Image

Compared to this the standard MS2v3 diagram: (Note the change over of pins 2 & 7)
Posted Image

Are my conclusions correct? In summary - 3 pin Bosch VR sensor: signal+ to OMEX or MS ECU tach input pin. Earth to local earth (chassis). Shield to ECU casing or dedicated shielding pin on OMEX/MS ECU.

And FINALLY (phew) to perhaps answer ChownR's intitial two questions: no, it doesn't have a power feed. BUT, what he could need to do is swap to a different pin on the VR plug (not the shield), as he may be feeding the ECU a negative rather than positive feed or vice-versa, as this is a common cause of problems for MS users as well; it gives odd timing signals. MS needs the positive feed.

And Peter: I believe MS2 is designed to accept an AC sine wave (as shown in the below diagram) which a circuit internally converts for processing.
Posted Image

Sorry; I find this fascinating. ;)

Edited by DrSarty, 12 March 2008 - 03:08 PM.


#6
Tom Fenton

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I think you are wrong. The + goes to the signal pin (24 on MS), the - goes to the signal earth (pin 7 on MS), and the shield is wired to earth at the ECU end.
The standard Peugeot sensor has three pins in the plug as the shield is used just as a shield, not as an earth return path.

#7
Super Josh

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^^^ Agreed ^^^ Needs to run to the MS earth, NOT locally at the gearbox end.



Josh

#8
DrSarty

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I think you are wrong. The + goes to the signal pin (24 on MS), the - goes to the signal earth (pin 7 on MS), and the shield is wired to earth at the ECU end.
The standard Peugeot sensor has three pins in the plug as the shield is used just as a shield, not as an earth return path.


Thanks Tom. I actually want to use the shield as that's the best way to do it to avoid any interference. Even the standard Pug wiring is done thay way. Perhaps what I mean to ask is whether " - " on the VR sensor can be grounded locally to a main earth bolt on the gearbox (which is incidentally where my MS main earth is anyway) or it MUST go back the ECU?

Edited by DrSarty, 12 March 2008 - 03:52 PM.


#9
Tom Fenton

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Well up to you, do it however you think is best, however I think you are wrong and I'll be doing it as outlined above as I know this works from experience. There is no such thing as a VR sensor "earth", the VR sensor provides a small (mV) AC signal that the ECU then decodes. Therefore both the + and - polarity of the crank sensor needs to be fed into the ECU.

#10
welshpug

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this thread http://www.306gti6.c...h...0340&page=1 has extracts from Autodata that shows that the signal is 1-4v AC, resistance of the sensor is 300-400 ohm.

#11
Craigb

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This may be of some use or not , but mine is wired up as Tom suggests ie back to the ecu, albeit with my emerald , and not omex or MS.

#12
DrSarty

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Yep. Tom, Josh etc (and I wasn't arguing or disagreeing by the way) are all correct. And you've also said the good thing that 'it works'.

What it means for me and Mr Topic Starter is that his VR+ goes to his tach input pin, and that there will be a sensor return that he needs to use for his VR'-' which goes back to the OMEX. The shielding just needs to be grounded at the ECU.

What I was clearly missing was that both diagrams show the earths from the ECU ALL combined which they're not. They both can be if you are not using one of them as sensor return. My MS loom has 2 earth lines, as it states in the pin listing (grayscale list).

Edited by DrSarty, 12 March 2008 - 05:58 PM.


#13
DrSarty

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After much searching I found the attached, pretty much all encompassing document. It explains how VR sensors work and how to test pin outs and whether it's working or not. So first off CHOWNR you could test your sensor.

It also explains what I mentioned earlier about how you may have the 2 signal pins switched, meaning your Omex ECU is getting a neg (falling signal) when it should be receiving a pos (rising signal). Both will work but the ECU (MS at least) needs to be configured so it knows what to do. This likewise could fix your issue; swapping the wires.

Also in the highlighted areas at the bottom, it explains wiring. I hope this info is useful to others.

Attached Files



#14
chownr

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Well, intresting and informative reading guys

I called Omex this afternoon for some help (and they were very very helpful). Explained that the ECU wasnt receiving cranking signal. They suggested that the only reasons for not receiving a signal were faulty CAS (I knew my sensor to be OK) or a wiring fault. Suggested checking resistance across pins 1 and 2 on the disconnected CAS (Signal and Signal grd I believe), then connecting CAS and checking rsistance across the CAS pins at the ECU (2 - Signal and 13 Signal Grd in my case). I had approx 370ohms across the CAS, but open circuit at the ECU plug. Closer inspection showed a poor contact at pin 13 which once corrected showed wiring to be OK. Plugged it back in cranked it up and it fired almost straight away - boy was I chuffed!!!!

Having chatted to Omex for about half an hour over the last couple of days I have to say that as a layperson observer the DIY enthusiast seems to think this sort of stuff is complicated and often over complicates matters. I also have a feeling that whislt everything should be shielded even an unshielded CAS connection should provide enough signal for the engine to run even if a little rough

My Advice is Keep things simple, keep a Multimeter close by, be methodical and take a break if you hit a dead end.

Omex has a single common pin for all sensor grounds - Pin 13. It also has one common Earth - Pin 15. The CAS signal is on Pin 2. My understanding is that the Sensor Grds and ECU Earth are effectively one of the same so it doesnt matter which the shield is connected to. I do agree that the shield should be grounded at the ECU end though - gut instinct not science

Dr S I apreciate you dont have a helpline like Omex do but I honestly believe ther is a simple solution to your problems.

Hope you find it soon Ill (and Im sure others) will be watching with interest - best of luck and thanks to all of those who have contributed to this topic

Rich

Edited by chownr, 12 March 2008 - 09:41 PM.


#15
DrSarty

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Well done Rich & good old Omex. Incidentally, your thread timing (i.e. you having a bad connection at pin 13) made me get to the bottom of understanding VR sensors for engine timing signals. That was my only problem.

I understand a great deal more now thanks to your thread, the contributors and all the reading it made me do.

You are right as well - as I learn everyday - this stuff really isn't difficult. And the MS is exactly the same in principle as your Omex having a main ECU earth and sensor return (earth). These can actually be joined and earthed together on a high quality earth, but they are supposed to be used as you've stated as it means in essence that all of the sensors are 'singing off the same song sheet' with a single earth reference, right at the ECU.

So as a result my MS ECU main earth will go to a chassis & engine bolt, along with my coil earths.

My MS ECU earth/sensor return will only go to the following sensor earths (this is MS pin 7 amongst others):

1) - VR sensor
2) - IAT sensor
3) - TPS
(& 4) - ECU coolant temp sensor IF it has an earth pin and does not earth through its body
(& possibly 5) - LC1 lambda too (NOT the element earth) when I've read up on it

The VR sensor's shield will go to the dedicated shield pin (MS pin 2) which from the reading I've gathered is attached to naff all at the sensor end. It may be fixed into the plug but I think it's connected to nothing. I say this because the MS gray scale chart (above) & one other document says about just isolating the braided shield cable at the sensor end using shrink wrap or insulating tape. Its only 'connection' is at the ECU.

As I've found this set-up also on a DTA site, on MS and now your Omex seems identical I can only conclude that they're all pretty much identical in practice.

Well done again Rich

errrmm....Rich :unsure:

Edited by DrSarty, 12 March 2008 - 10:24 PM.


#16
pugrallye

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Rich (chown).... have you connected your CPS earth to pin13 or 15??? Good practise would suggest pin 15, which if i remember it was originally connected to as 13 you may get slight interference if you have any sensors not dropping 12v across them but this all depends on what omex have suggested??

#17
chownr

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Just spoke to Omex again (Im sure they are getting fed up with my calls!!) to confirm how the CAS earth/grd and Shield shoul dbe connected up. They said join them both together at the ECU end and connect to Pin 15 - ECU power Grd/Earth pin

As suggested by Jon (pugrallye) think this is best practice to avoind any interefrence from other sensors shoul dthey be breaking down/faulty

Many thanks for everyones input

Rich

#18
maxi

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Having chatted to Omex for about half an hour over the last couple of days I have to say that as a layperson observer the DIY enthusiast seems to think this sort of stuff is complicated and often over complicates matters. I also have a feeling that whislt everything should be shielded even an unshielded CAS connection should provide enough signal for the engine to run even if a little rough

My Advice is Keep things simple, keep a Multimeter close by, be methodical and take a break if you hit a dead end.



Couldnt agree with you more. It makes me laugh whenever I read responses to topics like this where some idiotic keyboard electronics expert, has read something once, repeated it 5times and uses it in the wrong context and then, as a result, think they know the mathmatical solution to life itself. WAKE UP.

A lot of problems like this are due to a dodgy contact and have f*** all to do with testing the resistance of pin5 of the main IC through a potential divider. Its bulls*it. These are mass made, aftermarket management systems that even a chav in burberry pyjamas could install. Any hitches are 99.9% of the time due to contacts or a fault missed in the factory when being maufactured.

I must also say, this is why I stay away from UTTER S HIT like mega squirt. Id rather pay a few hundred quid for a second hand ECU (yes OMEX offer complete support for all of their ecus whether your its 1st or 5th owner) that works properly, has the support and makes the most of your efforts in building your engine.

Rant over.

Maxi

#19
Miles

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After installing a few of the Omex ECU's over the years there support is second to none, I have used a couple of other's and they don;t come close and hense why I only use them now and well having a local mapper helps too now.
But back on subject and I wire them up with on the CAS end (Both 500 and 600 series)
Red > pin 1
Blue > Pin 2
Sheild > Pin 3

But the sheilding always makes me laugh on std 8v's, it's only ever connected on one end.

#20
Sandy

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I wish Omex would have a clean up of their software, it's far more complicated than it needs to be, especially the crank sensor settings.