How does k-pro determine what gear you are in?

chunky · Post by **chunky** » Sun Jan 13, 2008 10:39 pm

I was looking at some datalogs tonight and I noticed that my VSS reads all out of whack at times. K-pro sees the wrong gear as well - seeing 6th gear when I'm in 3rd and then 4th. The VSS seems to read correctly during normal driving. I only observe issues during wide open throttle. I have never noticed my actual speedometer jumping around during a pull.

I have a PRB ecu in a 2002 civic si. The VSS was replaced a few thousand miles ago (corroded contacts old one, speedo on cluster showed zero at all times, new sensor fixed problem). The transmission is a rsx-s + ep3 final drive (2005 RSX gear ratios). The diff from my EP3 was retained, so the speedo gear matches the speedo sensor.

I've included two datalogs. One of a 3-4 gear pull, and another of random driving around.

Post by **Hondata** » Mon Jan 14, 2008 11:25 am

It's from electrical noise. Go through the engine swap checklist http://www.hondata.com/techk20swaps.html, particlarly the spark plugs and number of engine grounds.

Post by **Spunkster** » Mon Jan 14, 2008 12:03 pm

I would check your grounds and possibly faulty wiring. It appears to be correlated to the vtec pressure activating.

chunky · Post by **chunky** » Mon Jan 14, 2008 12:04 pm

Hondata wrote:It's from electrical noise. Go through the engine swap checklist http://www.hondata.com/techk20swaps.html, particlarly the spark plugs and number of engine grounds.

I have a 100% stock engine harness. Never had to change it. I'll double check all of my ground points, the terminals on the VSS itself, and the harness plug.

Thanks for the advice.

chunky · Post by **chunky** » Mon Jan 14, 2008 12:08 pm

Spunkster wrote:I would check your grounds and possibly faulty wiring. It appears to be correlated to the vtec pressure activating.

Good obesrvation. When VTP & VTS go on, things go nuts. Thanks for the advice.

For my own benefit, I'm still curious as to how k-pro knows what gear you're in. I'm assuming it's calculating it based on speed & rpm?

thesilverbullet · Post by **thesilverbullet** » Mon Jan 14, 2008 3:56 pm

you're right its a calculation based on speed, rpm and the gear ratios loaded into the gear tab of kmanger. lookup gear ratios in help files of Kmanger for details...

chunky · Post by **chunky** » Mon Jan 21, 2008 10:22 pm

I got a chance to mess with the car tonight. All of my grounds were properly connected. I went ahead and cleaned up all the ground connection points with some light grit sandpaper to make sure that they were 100% clean. I removed the passenger side motor mount and bracket from the block. It had significant oxidation on the contact surface between the block and the side motor mount. I cleaned that up with sandpaper & cleaning solvent. I bolted everything back together and took her for a spin. The problem is not 100% gone, but the condition has improved.

The passenger side motor mount, valve cover, and transmission grounds are all cleaned up. I may remove the transmission ground bracket from the transmission housing and clean up any oxidation at that interface. I also plan to remove the alternator and clean up any oxidation at its contact points with the water housing.

I will also try out a couple of different ground locations for my battery (deka etx14) which has been relocated to the rear of the car. I used to have it grounded to the seat belt bolt in back seat, but when I removed the 0 gauge wire in favor of 4 gauge, I put the ground strap on one of the bolts that is for the safety tether hook points. I looked through some of my old datalogs, and I had no issues with the speed seen by k-pro prior to last year. So I know that things used to work even with a relocated battery.

If things do not improve, I may try adding a few additional grounding straps to improve the grounding between the VTEC switch and the chassis.

Either way, I'm sure it's a grounding/electrical issue at this point, so thanks for pointing me in the right direction. :)

chunky · Post by **chunky** » Mon Feb 04, 2008 9:11 pm

Just thought I'd update with the happy ending. I finally found my electrical gremlin. After checking continuity between all the grounds, checking continuity between each sensor's ground and the chassis, I ruled out the grounding system. I then checked voltage at the battery and at the fusebox. I read the exact same voltage at my battery (in the trunk) and the terminals (under hood).

Eventually, I pulled my speed sensor. Looking at the pins of the connector on the wire harness, I thought they looked like they could use some cleaning. I sprayed them down with WD-40 to loosen up any corrosion. I let it soak, then sprayed it out with non-chlorinated brake cleaner. I bent the pins in the sensor slightly to increase the contact pressure between the sensor pins & the harness pins. I plugged it back up and the VSS is smooth again. :)

I'm guessing the problem started from when coolant spilled into my old VSS at some point during a head swap or other occasion when the rear heater hoses were removed. The corrosion killed my factory VSS, so I got a new one and everything seemed to be fine. However, I never properly cleaned out the harness plug until now.

I will say that cleaning up all the grounds seems to have made a positive impact on the engine's overall smoothness as well as knock counts observed.