No tach signal on LS

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No tach signal on LS

Postby PJF » Wed Dec 03, 2014 7:43 pm

Hello all-

Specs are as follows:

MS-2 V3.0 built by me
5.3L LSx with 24 tooth reluctor wheel
Install has been running for two years but has troubling syncing while cranking so the VR conditioner was an attempt to fix that



I installed a Dual VR board following instructions recieved from Jean.

I am seeing no tach signal at all.

The composite logger is also showing nothing.

I have good grounds to the board, I have good voltage to the board, and I can see voltage on the VR+ from the sensor on the engine.

I will have access to a scope in the next couple of days but I am hoping that maybe I am just stupid and missed something simple. Has anyone got any advice?
PJF
 
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Re: No tach signal on LS

Postby jbelanger » Wed Dec 03, 2014 7:48 pm

Can you mention specifically how you wired everything? I just want to check that I didn't miss anything in what I told you or that something was misunderstood.

Jean
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Re: No tach signal on LS

Postby PJF » Wed Dec 03, 2014 7:59 pm

Wow you are fast Jean! :lol:

I wired the V+ to +5 volt source from the rail on the proto area (This is an internal VR board)

I wired the GND to a generic ground on the MS2 board and a VOM confirmed I have good ground.

I wired the VR1+ to TACHSELECT

I wired the VR1- to a generic ground on the MS2 board. I did this as I have a relay board and ground wire from the GM sensor is wired straight to the sensor grounds. I verified this with a VOM before I removed any jumpers.

I wired OUT1 to TSEL


I hope the above makes sense!

Thanks again for your help.
PJF
 
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Re: No tach signal on LS

Postby jbelanger » Wed Dec 03, 2014 8:07 pm

It would be better if you could disconnect the sensor wire from the ground and connect it directly to VR- using a spare pin on the DB37 connector. But the rest is correct.

Having said that, you should still get a signal when using ground as the VR- connection. Using a scope will be the most obvious way of finding the issue.

Jean
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Re: No tach signal on LS

Postby PJF » Wed Dec 03, 2014 8:10 pm

Okay, when I get my hands on the scope I will report back what I find.

Thanks for the advice.
PJF
 
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Re: No tach signal on LS

Postby PJF » Fri Dec 05, 2014 7:37 pm

The scope confirms that there is no output on OUT1.

On your advice Jean I hardwired VR- on the conditioner directly to the sensor but no improvement.

I think I may have found the problem however. I looked up the data sheet on the MAX chip and it appears that it is only capable of handling 5V DC +/-.3V on the input side.

This is an older LS engine that uses the 12V VR sensor. The conditioner is seeing about 10 volts while cranking which is above the limit in the data sheet. Could I have burned up the chip? Should I rewire the sensor for 5V and see what happens?

Here is a picture of what the VR Conditioner is seeing. This was taken straight from the VR+ tap on the conditioner so obviously the signal is getting there but at almost 10 volts it is far above what the chip is rated for.

Thanks for any help.

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PJF
 
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Re: No tach signal on LS

Postby jbelanger » Fri Dec 05, 2014 8:04 pm

I'm not sure what you saw but the chip can handle a lot more than 5V.

The issue from your scope trace is that this is not a VR sensor so there is no zero-crossing. To get a correct output from that type of input, simply leave VR- on the dual VR board not connected to anything. And you'll need to ground your sensor again to another ground.

Jean
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Re: No tach signal on LS

Postby PJF » Fri Dec 05, 2014 8:41 pm

I guess I misread the datasheet Jean.

You were right about the conditioner though. I did as you said and instantly had a signal!

However it is still not clean enough for the MS to fire. It will cough a bit but is not syncing up.

Got any other suggestions to try?

I took a composite log and it is showing occasional sync but not very often.

Here is how the output looks on the scope.

Image
PJF
 
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Re: No tach signal on LS

Postby jbelanger » Fri Dec 05, 2014 8:45 pm

Try changing the edge on the ignition input capture. The MAX9926 may invert the signal compared to the circuit you used before.

Jean
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Re: No tach signal on LS

Postby PJF » Fri Dec 05, 2014 9:27 pm

That didn't work Jean but I somehow managed to fry something else on the board. :o

My TPS is now stuck at 117% and the coolant is showing 180 degrees even though the engine is cold.

So I will need to sort that out before I go any further!

Thank you very much for your help on this. I hope I can get it sorted!!
PJF
 
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