FIXED! : Tach drops to 0 when accelerating
 

As the title says, the tach drops to 0 when I start to accelerate.

*this issue did not happen before the cam swap I just did.
*Happens around 3000 rpm. Once I let off, the tach starts reading just fine.
*HP tuners data log shows no issue with RPM. The rpm is logging the entire time.
*No other issues with the car, starts and runs good.
* Codes p0342 and p0343 are popping up

I performed a crank relearn procedure but that didnt help.

I know it could be a crank sensor or a cam sensor issue but I wanted to ask you guys for any other ideas.

Thanks

Definitely not the cam sensor and I'm pretty sure any issue with the crank sensor would kill the engine or a least show RPM problems in the scanner.
I'm thinking just a loose wire going to the tach or in the tach itself. Maybe that new cam is giving you stronger acceleration than before and some marginal connection is coming apart.

Here is a video of the Tach loss

Does the tach drop out if you are stationary and raise RPM or only while driving?

Good question. I'm not sure but I'll will give that a try.

Tach is driven by the cam sensor. It's either the cam position sensor/wiring, the cam reluctor itself is wonky, or the cam is moving forward/backward in the block... and yes I've seen that before when the bolts loosen up.

Okay thank you! I'll will be investigating all of that.

https://cimg8.ibsrv.net/gimg/ls1tech...9746540e67.jpg
https://cimg9.ibsrv.net/gimg/ls1tech...231951fbed.jpg

It drops out stationary as well

Does the RPM drop out on a scanner or only the dash?

"HP tuners data log shows no issue with RPM. The rpm is logging the entire time."

That tells you its either cluster or harness related after the pcm.

No it doesn't, the PCM uses the crank position sensor for engine RPM and that's it.

But engine RPM doesnt drop out at the PCM. Its reading correctly on HP tuners at all times.

So far I've tried a new cam sensor, crank sensor and adding a resistor between the white tach wire and a 12v wire...nothing worked.

Yesterday I pulled the blower cam out set it next to the OEM Ls6 cam and it looks physically identical. The over length is exactly the same, and the cam reluctantors measure out exactly the same as well.

Spoke to a Comp Cam tech rep and he said if it was the new blower cam causing the issue, it would happen all through the rpm band. He said, in his opinion, I'd be waisting my money sending it back to them for inspection but if I wanted to, it would be $75 and 2-4 weeks turn around time.

I decided to put it back in the car.

Might look at the crank relearn procedure again because when performed it before, I never got a notification saying that "crank relearn was successful"

Try a test PCM or cluster.

Thanks, I will give that a try.

Did you ever get this sorted?

No I haven't. I put it on the back burner. I will be sure to update this thread once I get it figured out.

I fully believe it has something to do with the cam swap I did. I've read that I need to do a crank relearn because now the PCM thinks there's a miss fire and doing the crank relearn procedure with HP tuners is hit or miss and Ideally I should find someone with a Tech 2. I've also read and was told that it could be my IAC stepper motor. I just put a new one in today but didn't get a chance to test it out.

I found a few people on this site that had this exact issue. The one guy said after the crank relearn the issue was fixed. The other guys never replied to my PM.

I had the dealership look at my car for this issue. He used a Tech 2 and successfully did a crank relearn but that did not fix the issue.
He believes the issue is with the cluster or the PCM.

I am now getting the cam sensor codes p0342 and p0343 codes as well.He called it a class 2 communication issue and believes its either the cluster or the PCM.

Another thing, Occasionally My fuel gauge is randomly dropping to empty, triggering the "check gauges" light. I figured it was the float getting suck.
I wonder if this is related to the tach issue.

definitely going to be swapping in another cluster and if that doesnt work, going to try another PCM

Those codes are kind of opposite each other so it's weird it's throwing both, circuit low and circuit high. Those codes are directly from the PCM thinking there is a problem with the cam position sensor/circuit, it's NOT a class 2 communication issue as it has nothing to do with it. The cluster is not the issue either. The tach signal comes from the PCM along with the other data over the class 2 databus and everything else is working just fine, and if there was a class 2 databus issue it still wouldn't throw those cam sensor codes.

Just to confirm, you didn't convert this to a front cam gear/sensor cover setup did you? It's still just using the OEM position cam sensor in the rear top of the block correct?

Fuel gauge randomly dropping to empty indicates the PCM thinks something is wrong with the sender, that's default behavior when it throws a fuel tank level sender code. Lots of C5/C6 corvettes have this problem with their age now.