My RPM tach and the signal to the EBL ECU that I'm running bounce while I'm driving. I think they also bounce at idle but it's hard for me to tell at low RPM. RBob, the EBL guru, caught the problem based on a datalog I sent him. I've tried the following based on his recommendation:

• Checked magnetic star (reluctor) for looseness, it's good.
• Swapped ignition control module (the black box on the distributor)
• Swapped the small external coil. (I did this since I had a spare)

No change. There's one thing I haven't check that he suggested and that's the pick up coil in the distributor. Is it also possible that my Taylor plug wires are creating an electro-magnetic interference problem? I read that somewhere but don't know if that is possible since I'm not running a MSD 6AL box or anything like that.

Any help, suggestions with my problem is appreciated. The attached jpg shows my RPMs bouncing (blue line)

 

Anyone?

 

Bump (last attempt)

 

I did another rev session in neutral and my RPMs bounced between 2500 and 4000 as shown in the attached datalog. It doesn't sound like the motor is actually bouncing, just the tach and the signal to the ECU. I've done the following:
- Replaced the external coil with a used one I had laying around.
- Ignition control module (ICU) with a used one I had laying around (used dielectric grease on bottom of ICU and on terminals to ICU.
- Ohmed out the magnetic pick up. MSD says it should be between 500-700, I got 680.
- Re-routed the wires to see if electro-magnetic interference (EMI), no change.
- I have Taylor SpiroPro wires which are supposed to be good for EMI.

Does anyone have suggestions on what to check next?

 

Try shielding the tach signal wire with aluminum tape and ground it on one side of the tape just like we did in the below video..somewhere on the routing of the tach signal wire its picking up interference..

 

I will definitely try that aluminum shielded trick out....good video too. I have an SGI box with wiring that I haven't shielded so that'll be next.

 

Change the dizzy or the coil inside.