MEAN LT1

It seems the higher the motor spins up my tach gets jumpy. It usally happends in the higher rpms bands like 5700 and up. I went tot he track recently and when Ithought I was shifting at 6500 I was only shifting at 5800-6100. Anyone else experience this?. I guess the only way to prevent this is to get a shift light or aftermarket tach.

Injuneer

What year is your car? The 93's have a tach filter, and are fed directly from the coil. 94 and up read from the PCM, obtained from the Opti low res pulse signal.

Why not add a "signature" with basic info about your car.... year, model, engine, tranny and any major mods.

MEAN LT1

Sorry, I usually have that box checked. Being that I know its a low percentage that my pcm is causing the problem. What are the chances my opti could be doing this?. I have no high rpm hiccups and honestly motor wise the car runs great. Could it be the cluster of wires that are grounded on the head?.

93DGTA

My tach a Auto meter pro comp started acting weird awhile back.At high rpm 5500 for me and once in awhile at lower rpm.To make a long story short Opti Spark.Finally went out.about 2 months later.Installed it and all was well. I tryed sevral differnt coils a ecm.Plug wires trying to track it down.

Injuneer

Could be the grounds, could be low system voltage, could be corrosion or damaged pins in the Opti harness connectors...... or the Opti optical sensor.

MEAN LT1

Hmm...funny you should mention that. I do havea low voltage situation at wot. As soon I go wot my voltage goes from mid 13's down to 11.0-10.9 area. Im assuming this could be casuing the tach to jump ?

applecorn37

I had a similar problem before. There is a cluster of fusable links near the battery. One of mine was damaged and cause the tach to freak out every now and then. I replaced that and all is well.

Mr_Bond

Mine did the same thing once. It turned out to be the ground on the passenger side of the block. Might want to make sure that bolt is tight.