MSD ignition / tach issue

[STEVE-O]

Have an MSD 6AL and Roush 402 / Holley carb installed in a superformance built in 2008. MSD rev limiter is 7000.
Weird issue I've noticed recently with the tach.
As the engine revs to 4000 rpms, the tach seems to lose its reading and the needle begine to drop. Even though the engine is running OK.. no stumble / miss etc..
As the engine goes back under 4000, the tach starts reading again.

Sounds like some kind of lost signal issue. Anyone else notice anything like this?
Symptom of MSD going bad?
Any other ideas?


Thanks

[jhv48]

Where is the needle pointing on your ammeter?

[vatdevil]

Need to install an MSD tach adapter .....

[Rick Parker]

What brand of tachometer. Have you been doing any other rerouting of wires under the dash or hood? Sometimes misleading signals can be induced or picked up by the trigger wire.

[STEVE-O]

Originally Posted by vatdevil

Need to install an MSD tach adapter .....

I've seen the 8920 adapter mentioned on the MSD site and was wondering if that would fix the issue.
What tach symptoms indicate the need for the adapter? Do you have Smiths guages and use one?
Thanks

[user509035]

I got the same problem