Odd Surging Issue
 

I'm going to break my own rules and post a desperate plea for help without a lot of data. I've got a track event booked for next weekend and went to the dyno today. I thought the car felt weak and noticed it surging a bit at WOT. I replaced the plugs and COP coils thinking that was it and hit the the road this morning. On the dyno the car was a hot mess, surging and generally not pulling smoothly and sure enough the dyno graph looked like a seismic readout and only 200whp at 15psi. AFR'S are rock solid at 11.6ish and 15 degrees of timing.

Question is this, could a bad crank or cam sensor cause spark issues without showing up as missed sync counts? I grabbed some logs so I'll post those soon.

I've ordered the sensors and they'll be here Tuesday but I'm running out of time to order parts ahead of traveling Friday, anything else you can think of to try? Just throwing money at it at this point.

BP4W stock long block
2560 turbo, on cast manifold
3" exhaust
Sheet metal intake
Ms3x
650cc injectors at 80% duty cycle

What is a sheet metal intake?

What are you defining as "surging"?

https://cimg2.ibsrv.net/gimg/www.mia...f565f091e6.jpg

The surge is nearly a miss, but it isn't actually missing. Power is just coming and going at a very rapid pace.

Log and trigger logger

Tune

I've had my crank sensor fail once on my car. It feels exactly as you describe as a surging. I never logged it though so I'm not gonna be much help in that respect. Im assuming you've checked the crank sensor Gap already. Is the timing wheel and crank pulley tight? Those 4 m6 bolts that hold it on have been known to shear.

You're making me feel better. I have both sensors on the way, just odd not to see ant sync errors.

Yea I mean you would think it would manifest itself as sync errors. Hopefully the new sensors fix it.

Found the problem! Ended up being a pinched sensor ground wire. Evidently it set up a ground loop that was bad enough to affect power. Car pulls cleanly now, so we'll see how it does at the track this weekend.

Crank trigger sensor?

Technically it was on the coolant temp sensor wire but all the sensor grounds are tied together at the ecm so any sensor that uses that ground plane would be affected, my guess is it was affecting crank and cam sensor signals as well as others.

Glad you found it, redyno it?