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erroneous trigger causing ignition cut and erratic tach


S4-VR6
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The part number to my crank sensor is BOSCH 0261210107.

"Neither the + or - pin on the sensor would have continuity to ground normally". How is this the case, in your first diagram the - pin is wired to ground? are you referring to chassis ground? 

If Roll the + and - then the + is on the sensor ground and creates the cross talk as demonstrated in my second waveform capture. Again referencing your first diagram above. 

I must be missing something... 

I rang out all the wires and have not found an issue yet...  all grounds and shields are to sensor ground and sensor inputs are wired to the ECU. 

Is it safe to conclude that my cam sensor was working properly according to my first wave form and the crank sensor is still where I need to focus?

I plan to hook it back to the scope today or tomorrow and stepping through this again and to see if I can see the inverse wave form, which I have not been able to produce.   

Thanks!

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It is pretty simple.  In your original scope you didnt have cross talk but your crank signal was inverted.  In your second scope you had cross talk.  So what ever you changed caused the cross talk - and usually that would mean one of the common grounds is missing somewhere.  It could be that you have swapped the wrong two pins or it could be that a terminal is not pushed all the way home or a bad connection somewhere.  

Pinout for your sensor below.  Sensor ground is the center pin, trig 1 is the left, right is the shield.

vkSirBs.png

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Thanks for looking this up! This confirms what I measured with my meter and is how it was wired when the trigger error was gone, the signal was not inverted, and cross talk was on the the cam sensor. 

According to the manual, the figure in section 8.1.1, the sensor ground and shield are tied together and wired to the sensor ground pin on the ECU plug. Therefore it would not matter what pin I moved it to, center or right, it would ring out at the sensor ground pin at the ECU Plug. My cam sensor ground is also wired to this pin, figure in section 8.1.2, and this is what I believe is the source of the cross talk. Doing this did not invert the signal, just induced the cross talk...

Did I miss-interpret the figures or missed a nuance potentially?  

Thanks and sorry for being soo slow... :)

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Well I think I finally got it. 

Quick run down if anyone cares. 

First waveform displayed inverted crank but good cam. 

Second waveform still showed inverted crank and cross talk to cam. 

I retraced all my steps and was able to re-produce the first waveform (inverted crank, good cam). I then rolled my signal and ground in hopes to invert it and ended up with the cam waveform on both channels, or what looked like cross talk from the cam. At this point I started to question my second waveform as crank cross talk and started to examine my connection to the ECU.  

After adjusting the probes (staple and paperclip) over and over I was finally able to capture this waveform and there are no trigger errors accumulating at high RPM or erroneous tach spikes that I have observed yet. 

In hind sight I must not have inverted the wires like I thought the first go around. 

It looks like it shifted the crank profile to a valley from a peak on the falling edge. Does this correlate into an advance or retard of the spark? At this point, should I re-calibrate the trigger offset and delay?  

I really hope to get your blessing, finally, then it is off to the tuner for some real boost! 

Thanks a million for the continued support!  

Bob O

    

correct waveform.jpg

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Perfect, will do. 

Does everything look good with the waveform or do you see something else that needs to be addressed? 

On a different note, do you know of a tachometer that can be driven by the v88? 

Thanks, 

When we started this conversation you mentioned my trigger set up looked suspect. I am still currently using them in as they were in the config file I shared. Do these need some attention now? 

Thanks, 

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5 hours ago, S4-VR6 said:

On a different note, do you know of a tachometer that can be driven by the v88? 

Any aftermarket tacho should be fine, most OEM tachos will be fine. Does the factory one not work?  Is it CAN bus or was it originally a high voltage tacho drive off the ignition coil?  

 

5 hours ago, S4-VR6 said:

When we started this conversation you mentioned my trigger set up looked suspect. I am still currently using them in as they were in the config file I shared. Do these need some attention now? 

It is not clear from your posted scope captures if the cam has 1 tooth or more.  Need to confirm that.  

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I believe the stock is high voltage. I purchased a tach that is also driven off the coil that did not work. after a little research I tried a signal converter from DYI Auto and it still didn't work. I did a brief search for a low voltage driven tach but had not luck. 

Is there a way to confirm cam teeth with a capture or is it inspection only? The picture you provided is likely what I have (embarrassing that I don't know, long history...). If I assume it is, what would be the next step? 

Thanks!    

IMG_1508 (1).jpg

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I havent tried the DIYautotune tach adapter, but some of them dont have a transistor in them so the ecu aux will clamp the flyback and prevent it generating high voltage, try connecting it to a spare ignition drive instead of aux.  

The scope can be used to see the cam pattern but all your previous pics are too zoomed in, you want to see 2 ful crank revolutions, so that you will have 3 "missing tooth gaps" on the screen.

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So I got bored this weekend and decided to pull my cam sensor to see what it could see. I took some photos using a mirror and it looks like I have the early style with only one tooth. Would this suggest my setting for Trigger 2 are correct at 1x cam pulse? 

Is there anything else within my trigger set up/calibration/ignition set up/dwell or just in-general set up that you see as an issue? 

For the tach, do I hook the spare ignition drive directly to the tach input and leave it set up as an ignition output? I assume leave the tach set for 6 cyl?   

Got a bit more aggressive with boost settings so now I really need a tach... :)

Thanks!

IMG_1512.jpg

IMG_1516.JPG

IMG_1515.jpg

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Hi Adam, 

I don't have Tacho as an option in my ignition drive menu? Is it something I can add?

here is a link to the tach adapter I have. 

https://www.diyautotune.com/product/axm-100-high-voltage-tach-adapter/#tab-ywtm_78211

Thanks! 

tacho.PNG

Also worth mentioning that I wired the tach directly to the ecu using Aux 3 set to tacho and at one point the needle drifted to the mechanical stop and stayed there until I shut the car off. The tach still sweeps under its own function when I turn the key on so don't believe the stepper motor is damaged but I cant be sure at this point. It never did a thing when I wired it to the adapted.   

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 I assigned and wired ign 8 to the input of my signal converter as a tacho signal and still nothing. 

The tach still sweeps on its own so I am not sure if it is damaged or not.  

Any other thoughts or things I can try?

Thanks!!  

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  • 4 weeks later...

Hi Adam, 

I finally was able to get some time to do this simple test. 

I was able to see a signal from the ECU into the signal converter, the test light flickered but just barely. 

At the tach I was able to see a signal but it was not flickering like at the ECU output, it was just solid on. 

Does this suggest my tach is toast? 

Thanks!

Bob O 

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Yeah that woulkd be expected if there was a tacho booster fitted.  Most of those have some sort of 12V powered coil in them, so your test light will show this 12V, when the ecu sends a tacho pulse to the convertor then that 12V will spike to ~50V+.  So a test light on that side will just show a constant signal. 

But if you see a pulse going into the device then the ecu is doing all it can, the problem lay elsewhere.  

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