Dynamometer Test Confusion and Frustration
 

In connection with my chip tuning, I wanted to do before and after tests on a dynamometer. (I should say that, a couple of months ago, I knew ABSOLUTELY nothing about dyno tests...now I know just a wee bit more! :)) As I looked into the matter, I learned about needing to put the car in dyno mode to completely disable the traction control and that simply turning ESP off would not accomplish that. The issue arises because of the wheel speed differential on some dynos.

However, the dyno shop that I used has a dyno (it's a Mustang AWD 500) where the front and rear rollers spin at exactly the same speed; so that, as far as the car is concerned, it's as if it's driving on the road. So, based on my conversation with the proprietor, I concluded that putting the car in dyno mode was a non issue.

When I took the car for the first test, the tech put the car facing forward on the dyno and the car wouldn't move....he couldn't explain why. So, he then put the car on facing backward and it ran fine. He was able to do three pulls without incident.

Then I brought the car back after the chip tune. Still not knowing why the test wouldn't work with the car facing forward, he put the car on facing backward and it wouldn't work. Then he tried facing forward and it still wouldn't work. At that point he concluded that he wouldn't be able to do the test.

He explained to me that he's done tests on all sorts of cars, including Mercedes newer than mine, and he's never had this sort of a problem. So, he's frustrated that he's wasted an hour of his time with my car with its inexplicable quirk....and I'm of course frustrated that I can't get a second test done on the same dyno.

While I'm quite certain that I'm not exactly his favorite customer, he is willing to try the test again provided that I (a) pay up front and (b) figure out what needs to be done differently with my car. It makes no sense for me to go to another shop because it would be a different dyno with a different set of variables.

Does anyone have any insights or suggestions? Thanks so much!

David, as I sent via email previously... you gotta disable ASR/ESP manually in order to properly dyno the car. I don't know why it worked backwards the first time.

:scooter:

What do you mean the car wouldn't move? If your car was on the dyno, it better not move. If it moved, it would have gone through the walls or the door.:D

Did you mean your wheels did not spin?

Yes, but that was my point about this particular dyno....if the rollers are moving at EXACTLY the same speed, then the traction control issue should be moot. What am I missing?

That SHOULD be a moot point, if front & rear are moving at identical speeds. My guess is, they are not, although they may look like it. If the computer senses X% deviation, it spoils the party. Best way is to disable traction control and then it won't matter. Should be a 2 minute job to jumper pin 1+6, but please verify that elsewhere before attempting... it's been a while since I did this and I don't recall the details.

:batman:

I don't have much AWD dyno experience though I did dyno testing for a living for over 31 years. However, my sister-in-law is really up to speed on this stuff so I'll send her a note - she likely has an answer or can contact her connections at Mustang and see what the issue is. She is still working in the field and pretty much knows everyone who works with this stuff in industrial settings.

Dan

Yes, wheels would not spin.

Thanks, Dan....would be glad to hear any insights she has.

While I was at the shop, the tech called Mustang tech support to see if they could resolve the problem and they were stumped.

That sounds like a logical next step. I'm still confused by (a) why the test worked the first time (again, three pulls without incident) and (b) why he has not had a problem with other and nertw MBs (I take him at his word on this).

I think I'm missing something here... Is the dyno pulling data from the car's computer and somehow that is causing the car to not move? or does the dyno pull data from electronics attached to the rollers?

If the latter then...how does the car not move?

:confused: lol

WIS says to connect pin 1+6 at the 38-pin diagnostic port under the hood. See attached PDF.

:chinese2:

The dyno pulls data from electronics attached to the rollers (I think). BUT my working assumption is that the reason that the car's wheels won't turn is something the CAR is sensing about its environment. Hence GSXR's point that what I needed to do was manually disable traction control. Still leaves unanswered questions, though.

Wonder if the car's data banks can be read at the time the car won't respond? The Germans are always thinking when they design these machines, I can tell you that.

Talked to another dyno shop. It sounds like, rollers working in tandem notwithstanding, what would need to be done is is just what GSXR says: manually disable the ABS and traction control. Apparently the system used on the W210 is early and somewhat finicky...which may explain why newer MBs have no problem on the Mustang dyno. As to why I was able to have the test work the first time, he said it had nothing to do with which direction the car was facing...he said the tech just got lucky in somehow throwing codes, disabling the system, and thus being able to do the pulls.

We need very specific information to solve this.

From your description, when the wheels were lowered onto the rollers the wheels remained at Zero RPM regardless of throttle opening. ( car would not move. . ) Is this the case?

For the ESP to take control, there has to be some rotation of the wheels.

Was each tire centered in the dyno rollers? ( RE This dyno uses a pair of rollers for each tire, one end might be trying to climb a roller causing a ratio issue. ) Adjusting dyno wheel base solves this.

Is there clutch between the two ends of dyno? Leaving it open would cause the problem.

Are the front and rear tires different sizes ( They might be the same sidewall size but different actual dimensions, something that is pretty common. )