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Megajolt - VR sensor voltage
Hugh_ - 3/5/10 at 06:59 PM

I'm at the trying to start stage and all is good except the coil & MJLJ aren't registering anything from the VR sensor.

I adjusted the mounting so it is very close (~0.2mm), square too and in line with the pulley which has increased the voltage to from 0.2V to 0.5V (measured at the pins of the VR sensor). It isnt close to any other pulleys.

It is a tuned pinto but still running the standard starter motor so is turning over a bit slowly, at a guess ~100rpm, is there a minimum cranking speed that the VR sensor needs to reach its operational voltage range?

Any thoughts appreciated.
Thanks
Hugh

omega 24 v6 - 3/5/10 at 07:04 PM

Not much help I know but Scudderfish is having EXACTLY the same problems ( see his thread). One of you will be helping the other when you solve it.

RichardK - 3/5/10 at 07:05 PM

I would unplug the megajolt and try to start up just using the edis, it should start ok but will be in limp home mode, maybe swich the wire to the crank sensor around as the are a specific polarity, check the gap in the toothed wheel is at 90 degrees at tdc, do you have a spark whist cranking?

Couple of things to check fella first.

Rich

Hugh_ - 3/5/10 at 07:30 PM

Thanks for the replies.

Thanks for the heads up on Scudderfish's thread, there are a couple of things on there I havent tried.

I've tried running in limp home mode (with VR connectors both ways round) and checked the wiring and wasnt getting a spark so assume that I'm not getting enough voltage from the VR sensor.

The AutosportLabs site suggests it should be reading 2.5v. It doesnt say whether that is the requirement for the MJLJ or the EDIS (or more likely, both). Also my my A-level physics escapes me, as I cant remember whether the magnet oscilating in the coil (I assume that is how the VR works?) faster would increase the voltage or the current?

RichardK - 3/5/10 at 07:43 PM

It should run without the megajolt plugged in so it seems to be a problem with the edis or the grounding/shielding of the crank pos sensor (very important that its shielded) and only grounded at one end too.

Cheers

Rich

scudderfish - 3/5/10 at 07:52 PM

EDIS won't work in limp home if it doesn't think the engine is turning. Right now I've removed my megasquirt and EDIS from the car. I've directly wired the VR sensor to my multimeter. I've got it up to about 1.3v.

I think cranking speed might have something to do with it as the voltage generated is dependent on how fast the magnetic field is disturbed.

What would be a great help would be is some kind soul with a working set up could measure the AC volts they see on cranking to see if the 2.5V autosports talk about is obtainable or a typo.

Hugh_ - 3/5/10 at 07:59 PM

It should but it doesnt... The VR connects to the EDIS and not to the MJ and is needed to run in limp home mode. The 0.5V I've got at the moment is measured directly off the VR sensor, so it isnt interference giving me a low reading.

The VR sensor cable is shielded and earthed at the EDIS end. The PIP/SAW cable (same stuff) isnt yet earthed but that's irrelevant at this stage.

Does anyone know what voltage the EDIS requires?

Hugh_ - 3/5/10 at 08:02 PM

quote:
Originally posted by scudderfish
What would be a great help would be is some kind soul with a working set up could measure the AC volts they see on cranking to see if the 2.5V autosports talk about is obtainable or a typo.


I've got a colleague with a working MJLJ setup in a Tiger, I'll see if we can go round to his tomorrow and have a measure. Only possible downside is it's a Zetec and the ZR is mounted on the flywheel so each tooth is larger/more distinct; it should give us an idea though.

dhutch - 3/5/10 at 08:04 PM

quote:
Originally posted by scudderfish
EDIS won't work in limp home if it doesn't think the engine is turning.

Mine does, unplug the MJLT, bridge to get power to the coil (running hard cut limiter pack) and it will start, run, and drive fine. All be it on a fixed advance.

Cant really help the op however, as i was one of those annoying sods who just plugged it all together in an afternoon and had it all work perfectly first time and ever since.


Daniel

scudderfish - 3/5/10 at 08:08 PM

quote:
Originally posted by dhutch
quote:
Originally posted by scudderfish
EDIS won't work in limp home if it doesn't think the engine is turning.

Mine does, unplug the MJLT, bridge to get power to the coil (running hard cut limiter pack) and it will start, run, and drive fine. All be it on a fixed advance.

We're talking about the VR sensor not working, unplug that and the EDIS will die.

RichardK - 3/5/10 at 08:17 PM

If you tell me which pins you are using I can do the same tomorrow if that would help.

Rich

scudderfish - 3/5/10 at 08:18 PM

Sorry for hijacking your thread

I scan read the EDIS patent, but it made no obvious mention of voltages. According to http://www.megamanual.com/ms2/EDIS.htm

quote:
In fact, the EDIS module has a built-in VR signal hysteresis - when the VR signal is passing from negative to positive polarity (next tooth is approaching), the signal must reach +0.5 volts before the EDIS module will "arm".

It then will "trigger" when the signal passes through zero on a positive to negative transition, which occurs when the VR sensor tip is aligned with the crank wheel tooth.


According to http://www.dainst.com/info/edis/edis.html
quote:
The VR sensor drives an input detector which fires on the falling zero crossing of the signal at -300mv.


So my 1.3v should be enough. Maybe I should plug it all back together instead of chasing the next 1.2v.

Hugh_ - 3/5/10 at 08:33 PM

quote:
Originally posted by RichardK
If you tell me which pins you are using I can do the same tomorrow if that would help.

Rich


I've disconnected the cable from the VR sensor and am measuring directly off the sensor. It would be helpful if you could see what yours is giving during cranking.

quote:

Originally posted by scudderfish
Sorry for hijacking your thread

...


No problem at all, that is very helpful and suggests I'm probably not too far from getting it to work. The next thing I am going to try is offsetting the sensor the oposite way to how it was originally incase that yields anything (it shouldn't, but you never know...)

[Edited on 3/5/10 by Hugh_]

omega 24 v6 - 3/5/10 at 09:00 PM

When we check the sensors on truck wheel abs systems we usually get a reading of around 1.5 volts so I.d expect yours to be similar at 300rpm. I will however try my running v/hall set up either tommorrow or wed to see what cranking voltage i get.
we went to help scoobylav with his avon a couple of years back and he had the ford sensor as well. It was a right bugger to get it sparking. He tried 3 or 4 before he got one to work.
Now we all know it should not be like that surely. Possibly try it with a v/hall sensor or any sensor may do the same job. well on a generic setup it should.
I had to muck about with resistors in my vr circuit after I got it running as it would not rev above 2500rpm due to the strength/interference of the vr signal.

iti_uk - 3/5/10 at 10:24 PM

Wait, am I missing something? Measuring VR generated voltage with a multimeter? Is that even possible? I always though an oscilloscope was required... you're dealing with a (near as damn it) sinusoidal voltage...

It wouldn't surprise me if you hooked it up to an oscilloscope and found that you had your 2.5V after all - I'd put my money on it being another problem. Bad EDIS module? Bad earths? Stretched/damaged wire?

Chris

[Edited on 3/5/2010 by iti_uk]

Hugh_ - 3/5/10 at 10:38 PM

I dont know, but thought AC current was sinusoidal??
I'm using a fairly standard multimeter in AC mode

MikeRJ - 4/5/10 at 07:29 AM

quote:
Originally posted by Hugh_
I dont know, but thought AC current was sinusoidal??


Not always, all "AC" implies is that the net DC level is zero. The output from a VR sensor certainly isn't sinusoidal.

A cheap multimeter on the AC setting will assume you are measuring a sinusoidal waveform, and the scale will be calibrated to give you the RMS voltage of a sinusoid. A signal with a higher crest factor (e.g. a VR sensor) will give an inaccurate reading.

If you are seeing 2.5v on a multimeter then I would suspect that would be sufficient. Is the coil pack definitely wired correctly and receiving an ignition switched 12v supply on the correct terminal?

Is the coil pack a known good item? (duff coil packs on Fords are not unknown).

[Edited on 4/5/10 by MikeRJ]

omega 24 v6 - 4/5/10 at 07:22 PM

quote:

The output from a VR sensor certainly isn't sinusoidal


This page sugest it is
Vr sinusoidal wave form

I have just been out and measured mines. During cranking I have 1 volt ac measured on a std multimeter that is using the std vauxhall c20xe sensor.

scudderfish - 4/5/10 at 08:22 PM

quote:
Originally posted by omega 24 v6
I have just been out and measured mines. During cranking I have 1 volt ac measured on a std multimeter that is using the std vauxhall c20xe sensor.


Thanks for that, it implies that if I hook it all up again it may work. 1V is a much more achievable figure than 2.5V

If the multimeter is doing RMS, and the autolabs 2.5v comes from a peak reading on an oscilloscope then that would explain the discrepancy.

I've made a new simpler bracket that has the sensor horizontal and I used a laser to check the alignment. However I want a night off tonight so I won't be testing it until tomorrow.

[Edited on 4/5/10 by scudderfish]

MikeRJ - 4/5/10 at 08:39 PM

quote:
Originally posted by omega 24 v6
quote:

The output from a VR sensor certainly isn't sinusoidal


This page sugest it is
Vr sinusoidal wave form


I can't see a single diagram on that page that shows a sinusoidal waveform, unless I really am going blind

Hugh_ - 5/5/10 at 05:58 PM

I have a spark

I tweaked the VR sensor again and this time it was actually touching the wheel albeit very lightly. It has taken a minute amount of plastic off the end of the sensor but nothing to worry about.

I also forked out for a high torque starter as I wasnt convinces the standard pinto starter was man enough for my 2.1 high compression setup, and it does spin slightly faster now.

The multimeter now reads 0.7V when cranking. Just got the get the carbs and timing right so it runs now...

scudderfish - 5/5/10 at 06:12 PM

Good news! I'll have to have a go myself tonight now.

RichardK - 5/5/10 at 08:23 PM

Soz, somethings come up, will try and get it done over the weekend.

Cheers

Rich

RichardK - 5/5/10 at 08:27 PM

Good news, just read your post, yep mine was touching for a few secs How thick is your trigger wheel as I've had my doubts about the really thin ones. Here is mine off a cvh sierra 1.8.



Cheers

Rich