What are these spikes and dips in my dyno graph from?

[FRSFrank]

Please correct me if I am posting this in the wrong sub-forum. I recently made the switch to a OFT E85 tune and decided I want to see where my car is at performance wise.

After seeing the results of the dyno, I was confused as to why there were spikes and dips in the torque reading. The shop owner told me this could be because of "interference" in the signal cable, but the explanation seemed rather vague and I was left with a unsettled feeling that something could be wrong. Please note the shop usually dynos muscle cars and high horsepower american cars, so his knowledge of import/tuner cars might be the reason he couldn't give me a for sure answer.

Can anyone chime in to whether this is a problem with my vehicle, or is it a problem with the way my dyno was conducted? He attached the signal cable on the left side of the engine down into some hard to reach area, which took a few attempts to get connected.

Thanks in advance.

- FRSFrank

[jamesm]

Bad tach pickup. A dynojet is an inertia dyno, meaning that it doesn't measure torque directly. Rather, it measures how fast you can accelerate a known mass (ie measures power) then calculates torque from that with an rpm input. The weirdness you're seeing is due to the rpm input being less than perfect.