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Over the past 2 months or so my Viper has developed a very odd problem.

When going WOT, the car will often buck and misfire very violently. It feels exactly like the fuel cutoff when you hit the rev limiter...but it happens at 3K and will almost break your neck as the car stalls under WOT acceleration.

When this behavior occurs, the tach is going nuts. Or rather, the tach goes nuts and this is happening...? The tach needle doesn't just bounce around a little bit - it jumps around erratically from 2K to 4K regardless of what the actual engine rpm is. The engine bucks and chuggles when this happens during crusing conditions too but mostly this occurs under WOT.

I have my VEC1 meter hooked up still and when this strange behavior happens I have noted that it's indicating a 100% full lean condition (yikes!) so of course I lift as fast as humanly possible and cruise home to park it.

This has happened a few times now but it is not consistent. Some trips are completely trouble free. The other night it did it right away when I started it up - tach dancing all the way to 4K at idle and back. Today it was fine and after an hour drive, it did the bucking/crazy tach thing one single time right before I got back to the house - then it settled down.

This is probably a crazy assessment....but does the tach position actually trigger the redline fuel cut off? Is it possible that my crazy tach is triggering the fuel cut off at 3K because it is going nuts and swinging up to redline and triggering the cutoff? I have not watched to see where the needle is at when it bucks to a stop when flooring it - usually my eyeballs are flying out of my head when this happens so I don't think to look at it but I will track this from now on to see if perhaps the tach is somehow registering 6K+ instead of the actual rpm.

I know it's not the PCM that I suspected at first - I've replaced it back and forth and as of today it does it on the custom tune PCM and the stock unit.

/images/graemlins/sad /images/graemlins/sad /images/graemlins/sad

Any ideas guys?
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