Help with Dyno Chart - torque spikes

#1

I was at Roebling Road last weekend and put the car on a mobile dyno (Dynojet). The car was running well, but the dyno chart (attached) showed an odd data curve for the torque. The torque line shows numerous spikes.

We ran the car two separate times, 2 hours apart, on the same day, and the same odd spikes in the torque curve were present. This was the only one of 10+ cars that showed this pattern. (eliminating the idea of a bad connection on my runs or faulty pickup line.)

The chart vs. speed:
[attachment=2109]JSDynographBMW3251.24.16.jpg[/attachment]

Also, when the charts were run for Torque and HP vs. RPM the curves were ‘broken’.
[attachment=2110]JSDynoBMW325rpm01.24.16.pdf[/attachment]

Any suggestions as to the cause of the odd charts and/or remedy for this?

Thanks,
Jon

#2

Looks like an issue with the dyno to me. Have Lako hit it with is car. It’s not part of Group 3 until another Group 3 driver hits it.

#3

Additionally, it needs to be SAE 5.

SAE J1349 Rev JUN901 and the dyno’s smoothing function set to 5

#4

Since the only thing the dyno knows about from your car is the RPM signal, I would guess that it is an intermittent ignition issue.

#5

I agree. That can be caused by other outside influences, though. Check out the thread on the AFM…there is a lot of good information there and this case might warrant a new unit, or at least trying a known good one.

#6

LOL. Didn’t think of that. Lako hit my car, but not the dyno. Thanks for the comments. At the track some suggested it might be a bad coil. I will do more research.

#7

Based on the suggestions the plan to fix is: 1)swap in a good AFM and test on dyno; and/or 2) swap in a good coil and test on dyno. Other ideas?
Is there any way to test whether the issue is resolved without using a dyno?

Any other suggestions welcome.

Thanks,
Jon

#8

the hp curve looks fine, it looks like the dyno’s pickup wasn’t working properly so when the dyno software did the calculation for derived torque it cause a spikey result. im not convinced you need to do anything certainly not the AFM that causing the spikiness. if you had an major ignition or some other issue it should also manifest in the hp curve as that is the thing being measured the spikey result is a calculation using a bad signal.

in theory it could be that there is some electrical interference going on but its odd it doesn’t seem to affect anything on your car but the dyno pickup wasnt happy with something.

what plug and wires are you using?

#9

I agree with those that think is is a dyno artifact. If it were a real condition I’d expect engine performance to be affected to the point that you’d notice it.

I’d consider another dyno run on a different dyno. If the spikes are still there I’d change the distributor cap, rotor, ignition wires, and plugs. And maybe the coil.

The only other possibilities I can think of would be a flaky CPS, engine harness, or DME. But again you ought to notice problems there in the engine’s performance.

#10

My car does the same thing on the track dyno more often than not. works fine on the hometown dyno shrug

#11

[quote=“jlevie” post=82816]I agree with those that think is is a dyno artifact. If it were a real condition I’d expect engine performance to be affected to the point that you’d notice it.

I’d consider another dyno run on a different dyno. If the spikes are still there I’d change the distributor cap, rotor, ignition wires, and plugs. And maybe the coil.

The only other possibilities I can think of would be a flaky CPS, engine harness, or DME. But again you ought to notice problems there in the engine’s performance.[/quote]

Nice to see you back on the forum Jim.