Help! Tach Signal Disappears - Holley HP EFI

[dhutton]

Looks like Holley has programmable detection level and filtering for the crank signal. I can tell you that incorrectly setting one or both of these could very easily cause your problems.

http://documents.holley.com/199r10676rev.pdf

Minimum signal voltage and Filtering in the above document.

Don

[andrewb70]

Are we certain that the reluctor wheel has not moved on the crank? I've read multiple accounts of this happening.

Andrew

[andrewb70]

Originally Posted by dhutton

Looks like Holley has programmable detection level and filtering for the crank signal. I can tell you that incorrectly setting one or both of these could very easily cause your problems.

http://documents.holley.com/199r10676rev.pdf

Minimum signal voltage and Filtering in the above document.

Don

Don,

I had to double check, but those parameters are not accessible when the ignition type is set for LS engines.

Andrew

[ROKN69]

Originally Posted by dhutton

I thought you already swapped out the sensor.

I did, and am going to swap it again. I was told it is possible I got a bad sensor out of the box.

Originally Posted by dhutton

I suggested the scope because it is an ideal way to troubleshoot the problem. I am an electronics engineer and we troubleshoot problems like this by observing signal waveforms on an oscilloscope. I am pretty sure your crank sensor waveform has a lousy risetime for some yet unknown reason. One reason is because it may be too hot as suggested a couple of times.

I agree with you; sadly I am not an electronics engineer, nor do I or anyone I know possess the knowledge or the scope to perform the tests you're recommending. My best friend used to work for Lorial Space Systems and was an electronics engineer. He used to help me when I had need but he passed away about 10 years ago. It is a rare thing these days to know someone with your skill set.

Originally Posted by dhutton

Another idea I had is to get yourself a can of freeze spray and hit the sensor hard with it the next time it happens to see if it goes away briefly.

Don

That's a good idea. Now I just have to figure out how to make the issue occur when the car is on the trans brake. So far it only seems to happen when the car is moving. If we can get it to happen when the car is on the trans brake, then we can try it when it's on the hoist, and have someone under it with a can of freeze spray.

Or... maybe put the car in drive and bring it up to cruising speed slowly and get it to act up. When it does, hit it with the freeze spray.

I'll let you know how testing goes.

Thanks again!

[dhutton]

Originally Posted by ROKN69

I did, and am going to swap it again. I was told it is possible I got a bad sensor out of the box.



I agree with you; sadly I am not an electronics engineer, nor do I or anyone I know possess the knowledge or the scope to perform the tests you're recommending. My best friend used to work for Lorial Space Systems and was an electronics engineer. He used to help me when I had need but he passed away about 10 years ago. It is a rare thing these days to know someone with your skill set.



That's a good idea. Now I just have to figure out how to make the issue occur when the car is on the trans brake. So far it only seems to happen when the car is moving. If we can get it to happen when the car is on the trans brake, then we can try it when it's on the hoist, and have someone under it with a can of freeze spray.

Or... maybe put the car in drive and bring it up to cruising speed slowly and get it to act up. When it does, hit it with the freeze spray.

I'll let you know how testing goes.

Thanks again!

I was thinking that you would drive the car until it was good and hot and acting up, get out and quickly shoot the crank sensor with freeze spray and then drive it and see if it got better. Won't take but a few seconds to shoot the crank sensor.

Don

[71RS/SS396]

If you don't have the billet 24X reluctor wheel that's where I would look. The 2 piece ones GM and the aftermarket are using are prone to problems, I've seen excessive runout and also seen the welds let go.

[ROKN69]

Hi Guys,

We figured out the case of the disappearing Crank Signal issue. The shop had installed a driveshaft speed sensor, and I had requested they disconnect the sensor as part of the troubleshooting process. Basically, what was the last thing that changed? Undo that!

They disconnected the driveshaft speed sensor at the sensor (about 6 weeks or so ago), but not at the ECU. There was a wire that had gotten pinched in the transmission tunnel that was somehow causing issues with the ECU. They thought to disconnect from the ECU and the problem has completely cleared up.

Thank you all for your ideas and suggestions! Much appreciated.

[ROKN69]

Originally Posted by 71RS/SS396

If you don't have the billet 24X reluctor wheel that's where I would look. The 2 piece ones GM and the aftermarket are using are prone to problems, I've seen excessive runout and also seen the welds let go.

Thank you, Tim. We plan on installing a billet 24x reluctor wheel this winter.