Mag sensor voltage levels

[Alex B]

Hi everyone,

Working with Subarus I have come across number of cases when Mag sensor (Ref or Sync) voltage levels were quite high (15-20V and on one occasion 30V ! on the scope readings) causing ref/sync errors and sometimes totally confusing the ECU resulting in erroneous rpm and/or position reading. Moving the sensor further from the trigger wheel does improve the situation with mid and high rpm, however care is needed to maintain high enough signal for the ECU to sync on cranking. I observed it on old M4, M8 as well as on x00 series ECUs, however the old ECUs seem to suffer more from this problem.

Is there other solution to this issue rather then messing with the sensor gap? How come the factory ECU works without such problems? Is it possible to make a circuit that would limit signal to say 9V that ECU can safely use?

Best regards
Alex

[Dragon]

Which model year of Subaru are you talking about?

[MarkMc]

Hi Alex,
All of our ECUs clip the voltage at 9.8v, people who are familiar with the ref/sync capture feature will have seen this.

I have actually heard of over voltage problems before where people claim the ECU inputs were being saturated and this caused problems but to be honest I have never seen it. Some Porsche sensors we have used can deliver well over 120v..!!! And I have never had a problem like this with a Porsche.

Some of the later model Subarus (about 2002-2005) did have a slight issue with sensor allignment causing ref/sync errors at high RPM, usually if you were reving past 7500 but this could be fixed in the setup by using the "wrong" edge setting and an offset on the Trigger Level setting.

Another quick fix that had been used was to swap the sync sensor for a GT101 hall sensor which apparentl bolts straight in. The hall type signal allowed you to choose the different signal edge in the software and fix the missalignment.

I could see that moving the sensor further away could change the voltage profile of the signal and fix a problem but I really do not think it is to do with too much voltage but I am quite happy to be proven wrong........but you would have to prove it.

PLEASE NOTE: This only happened every now and then so don't panic and start the usual industry rumours.

[Alex B]

Hi Mark,

We did have problems with Subaru ref/sync sensors, more with older ECUs on GC8 and fewer with newer ECUs. Moving the sensor away helped the situation. I will show it to you once we have a "proof" in our shop Perhaps I overlooked the alignment problems thinking it was signal level problems.

I had the alignment problem last week on 2005 JDM Spec C last week. After looking at the ref/sync capture it was apparent that ref/sync signals almost merged into one line. Changed the ref edge to rising and reset CRIP. Problem solved. Interestingly, it came up only when we changed to new VF42 turbo and switched to VP Q16 fuel. RPM affected - 7000+, 6500+ with high boost of 1.6 bar.

I'll note the solution with GT101

So you say that no matter how high (say within +/- 50V) the voltage is at the ECU ref/sync input it will read signal correctly.

Who said I am panicking? Just discussing some issues we had. I'm calm and relaxed

Dragon: I've seen this in GC8 ver 3-4 EJ20K (EJ20G in Europe), GC8 ver 5-6 EJ207, GDB A-G EJ207.

Cheers
Alex

[Dragon]

Changing the Ref filter table may help.

[oversteer]

Hello

I believe I have a car experiencing the issue mentioned in marks above post, car has a missfire at 7200rpm, built engine 2.35, big aftermarket cams, adjustable wheels etc, ~700whp 2.3bar.

Problem has been around for a while and it can be traced back to when later model(2001 - ref/sync mode 26) was used as opposed to old head/cam set-up using early subaru cam and crank wheels...

Mark mentioned above being able to get around issue by using wrong edge setting and a voltage off set, which sensor should be set to Rise ? and what voltage offset should be used ?

Only trigger scope I have handy is a cranking one, can be seen here that crank & cam look a bit close !?


While idling trigger voltages are around 8v, can someone suggest a appropriate voltage level table and filter setting to use, .5 - 3v@7000rpm is what has been used and 124 - 80@6000rpm for filter. but that has been played around a lot trying to solve issue with lots of worse running, but nothing to solve 7200 rpm trigger missfire !

[stevieturbo]

Do a trigger scope when the problem is occurring.

[oversteer]

That would be nice yes, but car is not on dyno now, need to have a solution to test and then go back to dyno.

Any suggestion on what settings to change/try ie, which sensor set to rise and what voltage offset ?

[Stephen Dean]

This is caused by the crank and cam pulleys moving slightly in relation to each other due to the way that the cambelt runs on these engines, it is worse on engines that have have the head and block skimmed as doing so reduces the alignment tolerances.

The best fix if you have this is to change the sensor to a hall effect unit, as this generates a square wave that has two usable edges so the better option can be selected of the two, where as the Mag sensor only gives a single working option.

The swap the edge and use an offset as suggested is to use a Rising edge instead of the falling edge that would be used in the capture shown, and then set the SYNC Trigger Voltage to 1V.

[stevieturbo]

That would be nice yes, but car is not on dyno now, need to have a solution to test and then go back to dyno.

Any suggestion on what settings to change/try ie, which sensor set to rise and what voltage offset ?

Until you know what the trace looks like, voltages seen and whether there is any noise....any settings would be a guess.

But the thresholds at high rpm could be quite high ( say 5v ), as the voltages themselves would be high...ie, well over the clip level of 10v

Certainly on other ecu's I've had no trigger issues to around 4 figure power on Subarus with all standard sensors and trigger wheels.

I've only used an old M800 on one Subaru years ago, it'd probably be in the 7-800hp range and it had no issues ( 01, 36-2-2 trigger )