VR Sensor Air Gap
Discussion
Thanks, this is inline with my research.
This weekend I checked my VR sensor air gap and it had been set by my engine management installers at just 0.4mm!, this was not slippage as the sensor is very secure as is the bracket, the bracket bolts were found to be extremely tight too so the air gap had been intentionally set to 0.4mm
, I regapped to a far more reasonable but still conservative 0.8mm and the car immediately idled and ran smoother, noticeably smoother!
I have since researched the outcome of a VR sensor that's been set too close to the trigger wheel and essentially it gives the ECU are really hard time making sense of the signal, set the air gap too tight and the sensor output signal becomes unstable, the wave form it produces becomes inconsistent and can indeed be completely lost for a few milliseconds.
The ECU struggles to process this poor input signal and the results are poor ignition coil and injector control, micro misfires are the common result of a VR sensor being set too close to the trigger wheel causing an erratic idle and poor drivabilty. Both the way too tight 0.4mm gap the installers set my VR sensor at and my recently discovered battery terminal/cable connection issues clear have combined to make some significant improvements in the way the car idles and drives.
My idle is even smoother, throttle response is sharper and drivability especially below 2,000rpm is greatly enhanced. The engine and so the whole car feels way more refined, even above 2,000rpm there seems to be a smoothing effect like all the high frequency vibrations once felt throughout the car but especially through my metal Leven throttle pedal have gone.
It wasn't like it was dreadful before, more that the changes have brought something so much better that the comparison is very pronounced. Even the wife without me even prompting her said "wow the TVR feels a lot smoother", she would be the first to admit she has no mechanical aptitude whatsoever so believe me for her to say that is praise indeed.
I knew I had voltage/earthing/charging issues which is why I've been focussing on this area for a while now, but it turns out the issue I was looking for were all at my battery terminals, this and opening up my VR sensor gap have together delivered fantastic improvements.
My research has also revealed setting a VR sensor too close to the trigger wheel can damage it, not necessarily physical damage as such although this is always a consideration, but internal electrical damage within the sensor. I believe my 7 year old pattern part sensor has had a hard life being run so close to the trigger wheel all these years, its also been covered in a thick jacket of oil and road dirt for a lot of this time, I only noticed the build-up of grime a few weeks ago and cleaned a ton of goo from it.
So with all this in mind and the the real improvements I've seen from increasing my VR sensor air gap I've decided to treat the car to a brand new genuine Ford sensor, with such a critical job to do I figured its not worth messing about with a cheap pattern part as it only saves be £18 and to be frank I've become very fed up with finding myself at the side of the road because of poor quality components being fitted to my car.
Fuse holders that fail before the fuse itself and no name pattern part idle valves are all now banished to the bin where they belong, all to be replaced with genuine Bosch, Ford and GM sensors and components and proper MtA midi fuse holders and fuses.
Dave.
This weekend I checked my VR sensor air gap and it had been set by my engine management installers at just 0.4mm!, this was not slippage as the sensor is very secure as is the bracket, the bracket bolts were found to be extremely tight too so the air gap had been intentionally set to 0.4mm
, I regapped to a far more reasonable but still conservative 0.8mm and the car immediately idled and ran smoother, noticeably smoother! I have since researched the outcome of a VR sensor that's been set too close to the trigger wheel and essentially it gives the ECU are really hard time making sense of the signal, set the air gap too tight and the sensor output signal becomes unstable, the wave form it produces becomes inconsistent and can indeed be completely lost for a few milliseconds.
The ECU struggles to process this poor input signal and the results are poor ignition coil and injector control, micro misfires are the common result of a VR sensor being set too close to the trigger wheel causing an erratic idle and poor drivabilty. Both the way too tight 0.4mm gap the installers set my VR sensor at and my recently discovered battery terminal/cable connection issues clear have combined to make some significant improvements in the way the car idles and drives.
My idle is even smoother, throttle response is sharper and drivability especially below 2,000rpm is greatly enhanced. The engine and so the whole car feels way more refined, even above 2,000rpm there seems to be a smoothing effect like all the high frequency vibrations once felt throughout the car but especially through my metal Leven throttle pedal have gone.
It wasn't like it was dreadful before, more that the changes have brought something so much better that the comparison is very pronounced. Even the wife without me even prompting her said "wow the TVR feels a lot smoother", she would be the first to admit she has no mechanical aptitude whatsoever so believe me for her to say that is praise indeed.
I knew I had voltage/earthing/charging issues which is why I've been focussing on this area for a while now, but it turns out the issue I was looking for were all at my battery terminals, this and opening up my VR sensor gap have together delivered fantastic improvements.
My research has also revealed setting a VR sensor too close to the trigger wheel can damage it, not necessarily physical damage as such although this is always a consideration, but internal electrical damage within the sensor. I believe my 7 year old pattern part sensor has had a hard life being run so close to the trigger wheel all these years, its also been covered in a thick jacket of oil and road dirt for a lot of this time, I only noticed the build-up of grime a few weeks ago and cleaned a ton of goo from it.
So with all this in mind and the the real improvements I've seen from increasing my VR sensor air gap I've decided to treat the car to a brand new genuine Ford sensor, with such a critical job to do I figured its not worth messing about with a cheap pattern part as it only saves be £18 and to be frank I've become very fed up with finding myself at the side of the road because of poor quality components being fitted to my car.
Fuse holders that fail before the fuse itself and no name pattern part idle valves are all now banished to the bin where they belong, all to be replaced with genuine Bosch, Ford and GM sensors and components and proper MtA midi fuse holders and fuses.
Dave.
spitfire4v8 said:
First time I've ever heard of this ..
I always set my sensors up by eye, I learned years ago that as long as there's a gap which is there-abouts then that's fine.
I do use a trigger wheel that's a bit larger diameter than most people though, so the effective linear speed of the sensor past the teeth is greater than with a small diameter wheel, which might help me.
On that point though, I've seen sensors actually being ground away on the trigger wheel with no apparent issues. This is incredibly common on the later tvrs - unless the sensor has been spaced out with a small washer .. you remove the crank sensor for cleaning at service to find the end ground away by the wheel.
Maybe the canems is more sensitive to this, or maybe the non OE sensor type makes the effect more noticeable, but the effect on your car's running that you've experienced isn't something I can say I've experienced before.
If it's better, it's better though, so worth doing in your case.
Knowing the principles of variable reluctance a change in the trigger wheel size will quite clearly make a difference as the signal developed by the VR sensor is proportional to speed.I always set my sensors up by eye, I learned years ago that as long as there's a gap which is there-abouts then that's fine.
I do use a trigger wheel that's a bit larger diameter than most people though, so the effective linear speed of the sensor past the teeth is greater than with a small diameter wheel, which might help me.
On that point though, I've seen sensors actually being ground away on the trigger wheel with no apparent issues. This is incredibly common on the later tvrs - unless the sensor has been spaced out with a small washer .. you remove the crank sensor for cleaning at service to find the end ground away by the wheel.
Maybe the canems is more sensitive to this, or maybe the non OE sensor type makes the effect more noticeable, but the effect on your car's running that you've experienced isn't something I can say I've experienced before.
If it's better, it's better though, so worth doing in your case.
- would have been interesting to see a data log or osciloscope trace to prove it
It's always been my experience there are very good reasons why clear specifications exist for this type of critical sensor clearance so I try to follow them, I found my air gap to be set by the installers at 0.4mm which is a lot tighter than the Canems manual recommends at 1.5mm.
Strangely even the installers own manual states 0.5mm to 1.0mm so I have no idea why I got 0.4mm.
I'm not quite sure why the installers would quite different figures to the ECU designer but there it is, perhaps this and the 0.4mm air gap I got was the function of being an early adopter and maybe things have been learned since my car received its engine management installation, actually that's not a maybe as I know an awful lot has been learned by everyone since then!
Anyway, I open the gap from my tight as a nun's chuff 0.4mm setting to 0.8mm which I felt walked a nice line and go for a drive to find the car is most definitely smoother idling and driving, it's not a maybe a bit better thing..... its an unquestionably better thing!
Thems the facts and very happy I am with them too
ric355 said:
I run a hall sensor. I noted when building my system that the most common problem people had was with VR sensors and loss of sync / wrong sync / weird triggering issues, so I just stayed away from them.
The above is of interest to me as is an option I am exploring myself, my Canems ECU will accept a Hall sensor and I hear they are less susceptible to EMI issues which I've most definitely suffered from in the past.Let me try my new and genuine Ford VR sensor, following this a Hall sensor may well be my nest step
Edited by ChimpOnGas on Monday 10th June 14:57
spitfire4v8 said:
I use inductive triggers so the amplitude of the wave is proportional to the speed of the trigger past the sensor. It's the reason why I use a slightly oversize trigger wheel compared to most kits as at cranking I want the ecu to properly "see" the wheel at around 100rpm or so. The oversize wheel gives a higher signal amplitude for any given angular velocity, because the equilavlent linear speed of the teeth past the sensor is greater.
Here's a great test of wheels and speeds :
https://trigger-wheels.com/store/contents/en-uk/d2...
My Canems system definitely takes a few seconds to pick up the crank signal, I'd be interested to know how quickly your setup picks it up?Here's a great test of wheels and speeds :
https://trigger-wheels.com/store/contents/en-uk/d2...
The gap increase I'm covering here was definitely an improvement and that includes starting, the ECU clearly likes a bigger gap so I most certainly will not be returning to the 0.4mm I was given
ric355 said:
I guess to an extent it depends on which signal conditioning IC is being used by the ECU and what the supporting circuitry does. The trick is clearly to make sure that the signal to noise ratio is correct, and I can see that if there are other electrically noisy components in area that noise may be picked up on the sensor input, but I don't understand how a smaller sensor gap could cause that noise to be amplified. A smaller gap should just produce larger signal voltages at the sensor (I suppose the conditioner might ignore them if they got too large?). I would be interested to see the reference material on it.
I don't think linear speed of the teeth will be having an effect in your case as a larger diameter wheel will naturally have wider teeth thereby keeping the frequency constant (assuming the same number of teeth).
I run a hall sensor. I noted when building my system that the most common problem people had was with VR sensors and loss of sync / wrong sync / weird triggering issues, so I just stayed away from them.
What I'm being told is for VR you need a quality conditioning solution and apparently not all VR conditioner boards are created equal, maybe this fact combined with me running a well used pattern part sensor is the reason I saw such an improvement from open my air gap?I don't think linear speed of the teeth will be having an effect in your case as a larger diameter wheel will naturally have wider teeth thereby keeping the frequency constant (assuming the same number of teeth).
I run a hall sensor. I noted when building my system that the most common problem people had was with VR sensors and loss of sync / wrong sync / weird triggering issues, so I just stayed away from them.
While I'll take the improvements with a smile something is definitely still not right in the VR department, very occasionally at around 1,600rpm I am seeing an RPM drop out accompanied by what what I would describe as a monetary hard misfire.
I'm not a fan of the parts darts approach but before I get scoping it's getting a new genuine Ford VR sensor, after all my pattern part sensor has done 7 years service and on my TVR that means during that time it's been subjected to not inconsiderable levels of oil contamination, heat and vibration.
With very real improvements found in a simple gap change and the nature of the fault also pointing me in the VR direction, I don't feel the investment in a new genuine sensor is the greatest leap of faith... especially given the very affordable cost of the thing.
While these things are generally pretty reliable VR sensor failure is far from uncommon, I know the one fitted to my car is not a genuine part made to strict OEM standards and I know it's had a hard life...... so lets hope I'm on the right track
ric355 said:
ChimpOnGas said:
The above is of interest to me as is an option I am exploring myself, my Canems ECU will accept a Hall sensor and I hear they are less susceptible to EMI issues which I've most definitely suffered from in the past.
Let me try my new and genuine Ford VR sensor, following this a Hall sensor may well be my nest step
My hall sensor is a BMW 1214170327. I'm running it with a 5v supply. It switches to ground if I remember correctly but I wasn't sure whether it floated or supplied the input voltage when not switched, so I stuck with 5v so that I was sure it could go straight into the ECU.Let me try my new and genuine Ford VR sensor, following this a Hall sensor may well be my nest step
Edited by ChimpOnGas on Monday 10th June 14:57
Dave.
This is an interesting read:
https://fullfunctioneng.com/info/Hall%20vs%20VR.pd...
Its especially worth digesting the part about how VR sensors make more voltage the closer they are set to the trigger wheel, of course as voltage increases so does the potential for noise/interference (EMI), actually the paper discusses how increasing the distance from the ferrous material is a solution to the inherent flaw all VR sensors come with...... IE by design they are perfect little EMI generators themselves!
Closer = higher voltage and increases EMI while further away decreases voltage reducing EMI until eventually its so far away the effects of reluctance are lost, this all makes perfect sense, moreover it tells us why VR sensor air gap specifications never just say from as close as you can get it to say 1.0mm.
Clearly too close is actually a very bad thing! Indeed in many respects too close is worse than too far away because at least if the gap is too wide the engine most likely will simply fail to start!
We now have very strong evidence to support a theory that says the reason my engine idles and drives so much better since I opened the gap from the ridiculously close 0.4mm the installers gave me to the much more reasonable 0.8mm is because my sensor voltage is now within the design limits of both the sensor and what my ECU can tolerate in the way of EMI produced by said sensor.
I also now understand why I was advised by a reputable source that a VR sensor can actually become damaged electrically when placed too close to the trigger wheel, too close and the sensor may make more voltage than it's designers intended, not only will it generate more EMI than the engine management system can tolerate it could also be enough to start damaging the sensor's delicate internals IE is fine wire coil windings.
See, a little study goes a long way
https://fullfunctioneng.com/info/Hall%20vs%20VR.pd...
Its especially worth digesting the part about how VR sensors make more voltage the closer they are set to the trigger wheel, of course as voltage increases so does the potential for noise/interference (EMI), actually the paper discusses how increasing the distance from the ferrous material is a solution to the inherent flaw all VR sensors come with...... IE by design they are perfect little EMI generators themselves!
Closer = higher voltage and increases EMI while further away decreases voltage reducing EMI until eventually its so far away the effects of reluctance are lost, this all makes perfect sense, moreover it tells us why VR sensor air gap specifications never just say from as close as you can get it to say 1.0mm.
Clearly too close is actually a very bad thing! Indeed in many respects too close is worse than too far away because at least if the gap is too wide the engine most likely will simply fail to start!
We now have very strong evidence to support a theory that says the reason my engine idles and drives so much better since I opened the gap from the ridiculously close 0.4mm the installers gave me to the much more reasonable 0.8mm is because my sensor voltage is now within the design limits of both the sensor and what my ECU can tolerate in the way of EMI produced by said sensor.
I also now understand why I was advised by a reputable source that a VR sensor can actually become damaged electrically when placed too close to the trigger wheel, too close and the sensor may make more voltage than it's designers intended, not only will it generate more EMI than the engine management system can tolerate it could also be enough to start damaging the sensor's delicate internals IE is fine wire coil windings.
See, a little study goes a long way
And directly from the Canems manual, I give you.......
Maybe all we need is a little help from Edwin Hall
Maybe all we need is a little help from Edwin Hall
ric355 said:
I run a hall sensor. I noted when building my system that the most common problem people had was with VR sensors and loss of sync / wrong sync / weird triggering issues, so I just stayed away from them.
Lets give the new sensor a go, if it fails to resolve the hard misfire condition where I have poven the ECU is losing the engine speed signal it will be time to get the scope out.
The Canems system has crank sensor diagnostics of sorts, you can set output 1 to crank sensor diagnostics mode and attach an LED to it. Any flashing of the LED indicates a sensor fault, but I suspect the same wire could be scoped for a more complete analysis of whats actually going on.
Anyway apart from the very occasional hard misfire the engine has never idled better, and drivability is excellent so I am very close to the end game and have confidence the genuine Ford sensor is a logical purchase.
The Canems system has crank sensor diagnostics of sorts, you can set output 1 to crank sensor diagnostics mode and attach an LED to it. Any flashing of the LED indicates a sensor fault, but I suspect the same wire could be scoped for a more complete analysis of whats actually going on.
Anyway apart from the very occasional hard misfire the engine has never idled better, and drivability is excellent so I am very close to the end game and have confidence the genuine Ford sensor is a logical purchase.
Sardonicus said:
Dave I have set those crank sensors from 20/40 thou no issues they are fairly tolerant but like you say is the conditioner circuit lots of variable's with after-market management , tooth logger within tuning software is OK but you cant beat a proper scoped analysis , this may be useful too https://shoptalkforums.com/viewtopic.php?f=66&...
Cheers Simon, I'll have a read of that this evening lots of variable's with after-market management , tooth logger within tuning software is OK but you cant beat a proper scoped analysis , this may be useful too https://shoptalkforums.com/viewtopic.php?f=66&...Gassing Station | Chimaera | Top of Page | What's New | My Stuff