At WOT my factory tachometer immediately pegs out to 7000. You can ease into it and it will come up ok with the RPM's but once the foot is on the floor, it jumps to 7000. Anyone know what's going on? Thanks.

 

Do you have a scanner? If so, does the scanner show the same RPM as the gauge?

 

I have data logging capabilities with my LT1 Edit. I'll do a run and see.

 

Finally got around to logging a run. Log shows rpm coming up normally. No abnormal jumping to max like shown on dash tach.

 

 

Yes, that is correct. If you just ease into it, the dash tach will go up normally. But once you mat the throttle, it jumps up. Log showed TPS at 100% but rpm's looked normal--just climbing gradually. Now my speedometer is doing the same thing. I guess it's just the wiring going to the dash gauges. Very odd though. Tracking down that wiring would be a pain, so I guess as long as it isn't affecting anything performance wise, I'll leave it alone. Don't really watch the gauges at WOT anyway. It would be interesting to know where that voltage/signal is coming from, though. I was just wondering if anyone else had experienced this and knew what it was.

 

I notice that the speedometer and tach have a separate power input to the cluster. If nothing else is being affected, perhaps that connector is intermittent.

 

Are they both “pulse” driven? Where could extra pulses come from? Wild guesses.

 

They appear to be but I really don't know much about the internals of the gauge cluster. If the power to the cluster is intermittent, that might cause the electronics to make extra pulses. But I doubt that is the case. I suspect the problem is internal to the cluster and those gauges are losing whichever voltage (12v or ground) keeps the needles down. The natural tendency is to think that the ground keeps the needles from pegging positive, but I have assumed wrong before. Electrical engineers are crazy bastards, don't assume they did the logical thing ;-)