ABS VSS Reluctor Rings and ECU

Dan Carter

Bronze Supporter
#1
Much confused.

After a lot of reading about the GM ECU, seems it does use speed info to help control the idle speed and throttle positioning (so says GM).

Anyway, I'm currently using the Dakota Digital to send the ECU a speed signal (it works, however mechanical is recommended). There is a school of thought that a mechanical pulse generator (ring and magnetic sensor) is more responsive to speed, hence the ECU is more responsive in what it does.

Questions;
1. Does the number of teeth on the ring make a difference, if so how many are needed by the LS3?
2. Does the ECU differentiate between a speed signal from an axle sensor versus a wheel sensor if no ABS is present?
3. Does it mater where the ring is set up (target is the rear axle)?
4. Has anyone set up a mechanical system to the ECU (like to read your blog)?
5. Will the Graz speed sensor work for the GM ECU (I presume not, since its never been discussed that I am aware of)?
6. What's a good source for a ring and what senor should be used?
 
#2
The calculations can be adjusted in the tune. It's looking for pulse per mile I believe. You can count the pulses per tire revolution and then revolutions of tire per mile based on your tire diameter to arrive at the correct pulses per mile. It can then be added in the tune with HP Tuners or EFI live.

You could probably add the tone ring sold by Fran to the rear axle. I believe it's 47 pulses. I didn't think the Graz had a sensor.

The biggest problem with a GPS speed sensor is the delay/resolution. Cheaper GPS devices only take a one reading per second (like your cell phones built in GPS) or something like that while more expensive ones take 10 readings per second.

I think Will mentions a bit about the reluctor wheels and sensors in the Wiki.

Bottom of the page Transaxle — SL-C Wiki
 
Last edited:

Dan Carter

Bronze Supporter
#5
Ken

Good find from LS Man. That all makes sense. I never understood the pulse business until you tied the tuner and Reluctor ring together.

It seems we would gain more accuracy with faster input to the ECU via a mechanical system vice GPS. :thumbsup:
 
#7
FYI - The Dakota Digital GPS unit update rate is 10Hz (10 per second)
That's a good quality GPS signal rate. Perhaps there is a delay in the conversion to pulses. Pete, do you see any kind of delay at all with the speedo in regards to slowing down or accelerating?

I think the problem lies in not updating the pulse per mile settings in the ECM. If the Dakota Digital is set to output 4000 pulses per mile and the ECM is factory set to 33000 pulses per mile then the ECM will think the car is going at a different speed than it really is. The settings need to be updated with either HP Tuners or EFI Live. You can see my post #3 where I took a picture of the section in HP Tuners for changing the pulse count. The same thing would be true if you changed your tire size (diameter). The pulse count (in a measured mile) has changed now. The speedo will be off in OEM cars if you deviate from the factory size that is input in the ECM. Your tuner needs to update the settings if you don't have either HP Tuners or EFI Live.
 
Last edited:
#8
The pulse counts available in the Dakota Digital are 4000, 8000, 16000, 54400 and 128000. Dan, you said yours is set to 128000. You could simply try a different setting in the Dakota Digital to more closely match what is already in your ECM. I would recommend either the 16000 or 54400. Take it for a drive with either of those settings.

I'll do a online search to see if I can find out what the GMPP engine controllers have set for PPM in the stock tune. Perhaps someone else reading this thread has HP Tuners and can tell us.

I know in the past the older GMPP controllers used a CTS-V from 2007 as the operating system.
 
Last edited:

PeteB

Gold Supporter
#9
Ken,


The DD GPS has a test mode that sends out a 60mph signal. At the 128000 pulse setting, the ECU senses 75 mph. At the 54400 setting, it senses 32 mph. I didn't try anything lower.
 
#10
Ken,


The DD GPS has a test mode that sends out a 60mph signal. At the 128000 pulse setting, the ECU senses 75 mph. At the 54400 setting, it senses 32 mph. I didn't try anything lower.
So I guess leaving it at 128000 is the best setting until the value can be adjusted in the ECMs software to get it spot on.
 
Last edited:
#11
From what I can gather so far. The GMPP crate motor tune is taken from a CTS-V car from 2009. They use this as a base. It's mentioned in the manual that comes with the harness kit. It uses a 40 pulse per revolution signal (tone ring) and a final drive of 3.42:1.
 
Last edited:

Dan Carter

Bronze Supporter
#12
Ken

Tons of good data. I'm going to remove the Graz next week for a gear change, then get back on the tune to finish it up. In the mean time, I'm going to find a tone ring and sensor, and determine how its wired to the VSS in the GM harness.

The many articles you pointed me to all suggest while the DD system is pretty good, a hard wire via a ring is faster. How much faster and its true benefit remains to be seen.

Once I continue the tune, I will adjust the tables as you pointed out (thanks). Note: my speedometer is based on its own GPS receiver, so the DD is only feeding the ECU.


Sometimes its the easiest of things that create the most difficulty....
 

Dan Carter

Bronze Supporter
#14
Ken

The description says slip on....is that a press fit or literally slip on? I assume it must be tight enough to not slip as there are no visible attachment points.

What sensor did you use, or does it matter?
 
#15
Ken

The description says slip on....is that a press fit or literally slip on? I assume it must be tight enough to not slip as there are no visible attachment points.

What sensor did you use, or does it matter?
I heat it in the oven for twenty minutes (to slightly expand it) and then tapped it on carefully working my way around the diameter evenly.

Here is how Scott did it. I was lucky and just carefully tapped it on after heating it.

http://www.gt40s.com/forum/509997-post184.html

The sensor I'm using is the ones provided with the racelogic traction control.

http://www.gt40s.com/forum/447059-post415.html

Here is one on EBay. (same as mine). There are a couple of other ones listed but are more than likely fake/copies from China.

IFM EFECTOR IE5238 IEA2002-FROG PROXIMITY SWITCH *NEW NO BOX* | eBay
 
Last edited:

Dan Carter

Bronze Supporter
#17
Jared


I saw that one and it looks too challenging to mount for me. The press fit used by Ken and Scott may be easier in the long run. BTW, the CV ends are 108MM x 40MM.
 
#18
Last edited:
#19
You guys rule with all this great info! Thanks. The jags that run unit would definitely take some work to mount but I would be “delegating” that task to H.
 
Last edited:
#20
You guys rule with all this great info! Thanks. The jags that run unit would definitely take some work to mount but I would be “delegating” that task to H.
What intercooler pump are you planning to use Jared for your LT4 engine? I did a lot of research in that regard as I'm running a LS9 engine in my next build. The worst flowing one you could go with is the most popular Bosch pump.
 
Top