Jeep RENIX differential mag crank sensor signal

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vprtech
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Joined: Tue Apr 30, 2013 11:26 pm

Jeep RENIX differential mag crank sensor signal

Post by vprtech » Tue Oct 30, 2018 12:57 am

Hello, I'm working to try and simulate, at least the crank signal, for use with a OEM Jeep Renix ecu for bench testing. What I've found is that the crank input and output are biased by about 4-6 volts. If VR- is tied to sensor or battery ground with a running engine, the engine dies. The ecu will run the engine without the cam trigger in batch fire mode, but even then, I have not been successful simulating a crank signal that the ecu recognizes. I cannot find a datasheet on the VR chip, but I'm considering using the oscilloscope to probe each pin to see if I can find its output, and then just bypass the chip altogether for testing work on the bench. Before I do that, I thought I would post up to see if anyone had any ideas or possibly has already had success triggering the factory Renix ecu using JIMSTIM. Any input is appreciated.
Attachments
crank signal only between VR- and VR+ Jeep Renix.JPG
crank signal only between VR- and VR+ Jeep Renix.JPG (251.81 KiB) Viewed 999 times
cam and crank VR- not connected to scope.JPG
cam and crank VR- not connected to scope.JPG (204.71 KiB) Viewed 999 times

vprtech
Posts: 8
Joined: Tue Apr 30, 2013 11:26 pm

Re: Jeep RENIX differential mag crank sensor signal

Post by vprtech » Fri Mar 13, 2020 1:36 am

Bumping this topic.

I've figured out that the issue has to do with the fact that the Jeep Renix ecu crank signal input is floating, or not tied to ground. It would appear that I need to use a small transformer to duplicate this floating output.

@Jean : have you had any experience or can you provide any assistance as to how one could connect a small transformer to your JimStim in order to duplicate a floating output ?

Thanks.

jbelanger
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Re: Jeep RENIX differential mag crank sensor signal

Post by jbelanger » Fri Mar 13, 2020 12:05 pm

I'm not sure what you mean about the floating signal and it not being tied to ground. Can you elaborate on this and give a link to whee you got the information that you would need a transformer?

I should add that if you use the VR emulator tach signal on the JimStim, the signal is not tied to ground.

Jean
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vprtech
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Re: Jeep RENIX differential mag crank sensor signal

Post by vprtech » Thu Apr 02, 2020 6:22 pm

Hi Jean, thank you for the reply. What I mean by floating is that the - signal input to the ecu is not tied to ground. In fact, when I was scoping the cam - crank signal I found that connecting the VR - signal to ground would immediately cause the engine to die.

Searching around, I noticed there was mention from several people and vendors of this need for a floating output, and that it could be achieved with a small transformer. Here are some links below:

Excerpt from http://www.daqarta.com/dw_0okk.htm

Inductive sensors may produce quite a bit more than that at high speeds, but that doesn't mean the ECM/ECU needs the higher voltages; it's typically just looking for zero crossings to tell where the teeth are, so the sound card output may be enough as-is.

Otherwise, you will need a transformer for isolation and voltage boost, and possibly an external amplifier if your transformer doesn't boost it enough.


This person made his own simulator incorporating transformers:

https://www.lotus7.club/forum/techtalk/ ... -simulator

So in summary I'm trying to get the zero crossing output to float, as opposed to sharing it's VR- with common ground so that I can get the ecu to use the signal.

- Chris

jbelanger
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Re: Jeep RENIX differential mag crank sensor signal

Post by jbelanger » Sat Apr 04, 2020 1:17 am

From what you describe, that's not really a floating zero-crossing signal but rather a signal that needs to cross some bias voltage value. The JimStim will generate a zero-crossing signal which is why you can use ground as VR- because that's the zero reference.

Without knowing what the detection circuit is in the ECU, it would be difficult for me to say what is needed. And that is beyond the scope of the JimStim.

Jean
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