I'm fighting a resonant vibration, and today tracked it down to the plenum!! Put your hand on the plenum and rev to certain RPM's, and you can feel ( and almost hear) the vibration in the plenum. Vibration comes on at 1700 rpm, fades as you get to 1750, and then comes back at 2200 rpm's, then fades as you get higher. This is with the car sitting still in park, or when driving. Did the same check to the Valve covers- no vibration. Unplugged the EGR, same. Put a screwdriver to the EGR and Fuel regulator- No vibration from those devices. I'm stumped

To date, I have had the driveshaft balanced, replaced all plugs and plug wires, checked injectors, Checked Valvetrain with vacuum gauge, removed the Air Cleaner ( just to check). I also disconnected the Exhaust at the converter, and if felt like the vibrations went away. A little hard to tell- boy is the exhaust loud in the garage! I Had flex pipes installed in the exhaust- supposed to cancel out resonant vibrations, but no help.

Engine is a stock '87 L69, with an LT1 cam, new valve springs, TES headers, stock MCSS high flow cat back. I have Bosch Injectors with a Holley AFPR. The only part I am not real sure of is the cam. The cam, Lifters and pushrods were all used when installed. I've been running them for more than 2 years now with no issues known.

Any thoughts would be appreciated!!!

 

Any chance the Spider might have come loose?