Spiking tach followed by actual misses
 

Last nite, AFTER I installed a racing beat FCD went for a ride. put about 30ish miles on the car, and on the way home, the tach started to jump from about 2.2kish RPMS down to about 1.5K. I was in 3rd about 30ish MPH, and then she felt like a miss was happening.

Sound like a coil pack going out? I have not looked at her yet, Will do that later.

When and where was the last time you filled up? Any other symptoms? Any other reason to believe your coil pack is going out?

I filled up that nite. Sunoco 93. I use the same station every time I put gas in the car. Never had an issue. The chances of getting bad gas in todays day is very slim. I have seen MAYBE 2 cars in my years as a tech that had a bad gas issue.

Reason Im thinkin oil pack, is because TACH was acting funny before it had the slight miss. The Tach is driven off the trailing coil.

true. Unfortunatly it's been my personal experience that bad gas has hit my car mulitple times from trusted locations. But if your getting symptoms from your tach prior to any real symptoms present itself it very well could be the pack or any of the wires leading to it. Are you throwing any CELS?

Have you tried removing the FCD and driving it again? Anytime I change a part and start having a problem, first thing I do is remove the most recent change.

No. It has sat since Sat nite. Just no time. Im gonna go drive it tonite. My thinking that its NOT the FCD is becasue I drove a good 50ish miles with it on and no probs. Ill report after. :D

The FCD's install won't effect the wiring for the tach or coils in any way.

I'd be looking at the CAS wiring and the gears and teeth inside it. Then I'd be checking the coil packs. Your tach drop symptoms sound similar to an issue I had with cracekd insualtion on the CAS wires where they the CAS body through the rubber grommet.

I drove it for about 20 miles last nite and no issues. Ugg, I hate trying to track down intermittent driveability issues. I wont have time till tomorrow to get a good look at the wiring. I hope I can get her fixed by the weekend cus we got an event sunday at our track.

Thx classic. My old CAS was that way and I will look at this one to see if my issue is there.

So I didnt get a chance to look at my wiring, but I did drive the car. No actual driveability issues, but my tach would jump 4-500 RPMS while at idle. Im thinkin It is the cas giving screwy signals.

UPDATE: Swapped out with my CAS that I had to repair wiring in, and all is well. :D