Carpokes

Thanks for the replies everyone, appreciate the help. I have less than a week with the kit installed. Give me a few more days to get my bearings and learn a few things. Then I can come back with better questions.

NP, good luck.

FWIW I had to move my crank sensor gap from 0.9mm (~OE gap) to 0.5mm with my standalone to get a high enough output voltage during cranking for my ECU to be happy. Cranking is the lowest RPM you’ll see, so if you’re going to have arming voltage issues due to sensor gap, that’s where you’re most likely to find it.

If you're running OE gap at the speed/reference sensors that might be one reason why the maxxecu is struggling.

Great info, thanks. That could be the issue as I never really took much care with gaping the sensors. So I don’t even know if I’m running stock OE gaps, could be much greater. I’ll start there.

SirLapsalot wrote: Thu Apr 10, 2025 9:14 am NP, good luck.

FWIW I had to move my crank sensor gap from 0.9mm (~OE gap) to 0.5mm with my standalone to get a high enough output voltage during cranking for my ECU to be happy. Cranking is the lowest RPM you’ll see, so if you’re going to have arming voltage issues due to sensor gap, that’s where you’re most likely to find it.

If you're running OE gap at the speed/reference sensors that might be one reason why the maxxecu is struggling.

Makes sense. If you watch that video I posted, you can see how dramatically the gap affects the strength of the signal. Makes me wonder how they came up with .8mm as the recommended gap. At least on my little test rig, I didn't see any down side to getting it closer to the flywheel -- at least up to the point where it starts touching... Of course, at 6500 rpms, with electrical noise everywhere, it might be a very different story.

during cranking there is a voltage drop on many systems. The Link ECU uses its own regulated sensor power suppply, i think the stock system does not.

Tom wrote: Thu Apr 10, 2025 9:44 am

SirLapsalot wrote: Thu Apr 10, 2025 9:14 am NP, good luck.

FWIW I had to move my crank sensor gap from 0.9mm (~OE gap) to 0.5mm with my standalone to get a high enough output voltage during cranking for my ECU to be happy. Cranking is the lowest RPM you’ll see, so if you’re going to have arming voltage issues due to sensor gap, that’s where you’re most likely to find it.

If you're running OE gap at the speed/reference sensors that might be one reason why the maxxecu is struggling.

Makes sense. If you watch that video I posted, you can see how dramatically the gap affects the strength of the signal. Makes me wonder how they came up with .8mm as the recommended gap. At least on my little test rig, I didn't see any down side to getting it closer to the flywheel -- at least up to the point where it starts touching... Of course, at 6500 rpms, with electrical noise everywhere, it might be a very different story.

Your example on the video really puts it together. Was not aware of the significant difference the gap could make. Of all the things Porsche over engineered, I wonder why a better solution wasn’t thought of to ensure proper sensor gap. Maybe there is I’m just missing it.

my 'official' way of gapping the crank sensor for my front mount set up is 3 layers of masking tape on the face of the sensor and set it up touching the trigger wheel. The tape is usually brushed off as soon as you start but even if that doesn’t happen it doesn’t interfere with the signal. Should be about .4mm

chris white wrote: Fri Apr 11, 2025 10:40 am my 'official' way of gapping the crank sensor for my front mount set up is 3 layers of masking tape on the face of the sensor and set it up touching the trigger wheel. The tape is usually brushed off as soon as you start but even if that doesn’t happen it doesn’t interfere with the signal. Should be about .4mm

Sounds like a good method, makes sense.

Seems blue paint edging tape should work, correct?

Looking back, you mentioned you had captured o-scope data of the trigger/crank sensor. That should clearly indicate if the sensor gap is the concern or not. What specifically did the vendor have to say about that data?

Basically, from what I have read and what I found personally, as long as the trigger voltage spikes are large enough to hit whatever your arming voltage table is set to and it is consistently showing a waveform that crosses 0V then it should be fine. At least to get the engine started.

Is your ECU able to show an engine speed signal while cranking if you monitor or log data?

Might be helpful to upload your calibration file and a data file during cranking. Can take a look and see if there’s anything obvious.

To clarify what I'm referring to regarding trigger scope data above…

Since you said you are using an OE sensor, you're using a variable reluctance (VR) sensor. That means the sensor outputs an A/C voltage with an amplitude as a function of speed (speed at which the falling edge of a tooth passes by).

When using a VR sensor the ecu needs to know at what voltage to start "arming" the circuit which looks for a falling edge of each tooth (point at which the signal crosses zero again). This arming voltage typically needs to be about 50% of the peak voltage. Meaning, if for example you find that your peak voltage output from your crank sensor while cranking the engine is 6V, then your arming voltage will need to be 3V at ~400 - 600rpm (typical cranking speed for our engines I think).

Where this can become tricky is at these low voltages we see during cranking. Unless it is documented in your ECU's help section, only the engineers who designed your ECU HW/SW will know the minimum arming voltage an ECU needs in order to give it enough time to "arm" itself and start its internal processing for recognizing a zero cross point (tooth passing by) to then calculate an engine speed and subsequently use the reference sensor trigger to understand where the engine is in its 720deg cycle so that ignition can happen at the correct point according to the ignition timing table (critical to actually start combustion and start the engine…).

So if your gap is too large, your peak output voltage amplitude from your crank sensor will be very low, if it is so that that there is not enough time for the ecu to calculate engine speed, then you will never be able to start the engine.

Here is an example from my ECU when I went through this process:

Crank sensor gap was 0.89mm. Peak amplitude was ~0.2V. This was so low that with an arming voltage at 0.1V (50% of 0.2), the ECU had a hard time properly calculating engine speed, and as such would not start. Crank sensor gap was 0.5mm. Peak amplitude was ~0.65V. With an arming voltage of 0.3V, the ECU can properly calculate engine speed no problem. My current arming voltage calibration table for reference. I get no trigger errors with these settings, but I would not necessarily copy paste to your ECU's calibration table. For reference only: As FYI, in the above screen shots the trigger scope logging function actually has a pretty low logging rate, so this is why the waveform doesn't look as pretty as a traditional A/C waveform. At higher engine speeds the trigger scope does look more like you'd expect, but since we're talking cranking, the point comes across I think..

Of course, if you have wiring issues you may have a completely different problem than sensor gap and arming voltages I described above, but it is a good place to start. Especially considering you have oscilloscope data already.