36-1 wheel and sensor problems

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ast
MS/Extra Newbie
Posts: 2
Joined: Sat Jul 09, 2005 3:00 pm

36-1 wheel and sensor problems

Post by ast »

Hi!

I installed a Ford 36-1 wheel and sensor to a running megasquirt vehicle. I have modified MS so that I have LM1815 VR-sensor input. I connected the sensor there and configured MS for wheel decoder. Ignition is not yet controlled by Megasquirt.

It runs somehow but RPM is constantly changing betwheen two levels. It idle it might show around 800 and around 1000 rpm. I have good quality cable the between sensor and megasquirt and I have verified that the LM1815 circuit works, it gives out pulsetrain that corresponds to the VR-sensor output.

The problem is that I think the VR-sensor output is not correct. See pictures below

LOG:
Image

VR-sensor output at idle, missing tooth is where the longer falltime is shown:
Image

Wheel and sensor installation:
Image

If I measure the pulsetrain coming from LM1815 to MS CPU I would see a pulse approximately where VR-sensor signal goes from positive to negative. I thought that with 36-1 wheel there should be 35 pulses with equal time between them and then double time before next 35 pulses and so on. Now what I'm getting is 34 pulses with equal time between, then about 1.5 times pause, 1 pulse, again 1.5 times pause and then the next 34 pulses and so on.

Reading about the missing tooth wheel decoder I believe that it expects only one bigger time between teeth per rotation. Is my signal incorrect and what could be causing this? I can only think that it wasn't such a good idea after all to install the trigger wheel over unused pulley. As you can see in the picture, the pulley is quite close to the trigger wheel. Before I go, turn the wheel around and fabricate new mount for the sensor it would be nice to know if this is the cause of the problem...

Does anybody have oscillosscope trace from 36-1 wheel and VR-sensor?
Lancer EX2000 Turbo with Megasquirt
ast
MS/Extra Newbie
Posts: 2
Joined: Sat Jul 09, 2005 3:00 pm

Post by ast »

Problem solved. VR-sensor wires were reversed but it didn't solve the problem completely. I had also set second trigger event to incorrect teeth (not 180 degrees from the first trigger and even fire engine). Now RPM display is stable at least to 6000 rpm.
Lancer EX2000 Turbo with Megasquirt
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