1992 Jeep Wrangler with 350TPI/700R4 VSS Options

[sturgillbd]

Yes, for any normal speed. I'll give you a ten sample chart if you want. It is normally 2, 3 or 4

[lionelhutz]

Good work. I see 133kHz which is 8k ppm so the PCM is expecting 4k ppm.

If I'm interpreting that correctly, your waveform in the picture has an amplitude of about 4.5V and it has an offset that makes it go 1.5V negative. Correct?

The issue seems to be getting the PCM to recognize the 5V Jeep VSS signal.

[sturgillbd]

It is 133 HZ and yes it seems to be expecting 4K/mile. The offset doesn't change any reading in the ECM unless you go above or below the 0V reference with the whole waveform. I did try to see how the offset would affect what the ECM reads. and that was my observation. I can turn off the offset but I do not have the VSS low tied to ECM gnd. Anything over 2V P/P, the ecm is rock solid on speed reading. I think if upper voltage is an issue, a zener clamp on the vss lines will solve that. I can capacitive couple the signal into the ECM and that will do away with any offset or bias and I can tell the results of that if wanted.

[lionelhutz]

Ok, but the last tests were trying to use the PCM optical input which is C6 on the 7730 or B21 on a 7727. Can you try your tests with 0-5V signals of different types on that input.

^ Jeep VSS tests is what I was referring to.

Don't use an offset. The Jeep VSS is powered by 5V and ground so I doubt it's producing anything besides a signal that goes from around 0V to 5V.

My first idea was bad so I've been trying to think of a way to introduce an offset to the Jeep sensor so it goes -2.5V to +2.5V and can be fed to the B9 & B10 (or C2 & C8) VSS input. A simple high pass C-R filter would work except for the transition between stopped and moving where it might take a little time for the capacitor to charge to 2.5V so it's giving the correct offset.

[sturgillbd]

Yes. It will take me a few mins to move some cables. I have to make sure my V6 pigtails have B21. If not, I will have to drill a hole to put a pin in. I will post back with results in a bit. I lost track in the thread as to which input you guys were trying to use. Is the signal between B21 and ground? Also do I need to change the flag for optical? Ill have to look at the xdf I have for 8D. I just tried it and I got no vss data in TunerPro. It will be a bit before I get back. Supper is almost ready :)

[1project2many]

Yes, for any normal speed. I'll give you a ten sample chart if you want. It is normally 2, 3 or 4

A chart would be great, thanks. The code tests for a count of 4, 3,or 2 then selects a pulse divisor based on the count. As long as the count stays below 4 it looks like all I need to do is alter the divisor values.

I lost track in the thread as to which input you guys were trying to use.

Well... we've got two different tests going on. lionelhutz is working on using the a/c input on C2 with the digital sensor. The ecm should be configured for a magnetic sensor to use this pin.

I'm asking about using the optical input at pin B21. The ecm should be configured for the optical sensor.

Good work. I see 133kHz which is 8k ppm so the PCM is expecting 4k ppm.

Yep, so doubling the current divisor values looks like the correct answer for the optical input.

FWIW, I'll be away from this for a bit, too. If the table looks as I expect, I should have another .bin to try.

[JeepsAndGuns]

Does the .adx you're using allow you to see promid? If so, would you mind trying this .bin and watching the promid. If I understand the code properly then the first number displayed will be fairly low, less than 10, when the VSS is spinning. The second number will increase or decrease with speed sensor speed.

Thanks.

Yes I do have a adx that can display that. It will probably saturday afternoon or sunday afternoon before I can run the test. Not sure if sturgillbd's test gave you what your needing or not. I can still run the test though.

[JeepsAndGuns]

Yes. It will take me a few mins to move some cables. I have to make sure my V6 pigtails have B21. If not, I will have to drill a hole to put a pin in. I will post back with results in a bit. I lost track in the thread as to which input you guys were trying to use. Is the signal between B21 and ground? Also do I need to change the flag for optical? Ill have to look at the xdf I have for 8D. I just tried it and I got no vss data in TunerPro. It will be a bit before I get back. Supper is almost ready :)

I had to drill a hole in the V6 car connectors I am using to be able to input the correct pin. And yes, you will need to uncheck the box for "magnetic vss installed" before that input will work.

[sturgillbd]

Ok, Breaking it down in 15Hz increments shows as follows

0Hz Prom ID 119 Speed 0mph
15Hz Prom ID 111 Speed 13mph
30Hz Prom ID 108 Speed 27mph
45Hz Prom ID 105 Speed 40mph
60Hz Prom ID 104/208 Speed 54mph
75Hz Prom ID 103/206 Speed 67mph
90Hz Prom ID 205/308 Speed 81mph
105Hz Prom ID 204/307 Speed 94mph
120Hz Prom ID 306 Speed 108mph
135 Prom ID 305/407 Speed 122mph

The two numbered Prom ID's are because the prom ID cycles back and forth between those two numbers even though the frequency is stable and the MPH reading is stable. This is with a 5v p/p square wave signal with no DC offset.

[sturgillbd]

I'll be back on a little later. I'm heading to a buddy's and I will take some measurements on that 4.0 Jeep TPS sensor while I am there. I should be back by 10:00pm. If needed, I'll do more testing when I get back and post results then.
Brian

[lionelhutz]

1project2many - I just want to point out that all the data sturgillbd has posted so far is for the magnetic AC input. Your posted code was intended to test at the optical input, was it not?

JeepsAndGuns - I'm not convinced the Jeep hall-effect VSS is giving a signal compatible with the PCM optical input based on the way you describe turning the sensor and getting a high speed. If your feed that Jeep VSS into both the speedometer and PCM optical input and turn it at a consistent rate, you should see the PCM showing a speed that stable and a multiple of the speedometer (it'd be 4X the speedometer I think). If you hook that VSS back to power, connect a voltmeter to it's output and turn it slowly and see what the meter reads. I am expecting that it switches between 0V and 5V but who knows what it really does.

sturgillbd - See if the PCM is stable at reading the speed when feeding the different types of 0-5V signals into pin B21.

[1project2many]

The two numbered Prom ID's are because the prom ID cycles back and forth between those two numbers even though the frequency is stable and the MPH reading is stable.

I had a hunch that was going to happen.

1project2many - I just want to point out that all the data sturgillbd has posted so far is for the magnetic AC input. Your posted code was intended to test at the optical input, was it not?

It was. If I'd remembered to select optical VSS the ecm would have ignored the magnetic input anyway. The results are still valid though. The variable displayed in the high byte of promid was the main concern. It's in play with either speed sensor type. With magnetic VSS it's value is multiplied by the road speed sensor constant to create a divisor. It's still at 4006 in the test cal so displayed speed is 2x measured speed. If that test is run again supplying signal at C2, magnetic VSS selected, and the road speed constant set to approximately 8000, the displayed speed will be correct.

With optical selected the code checks this byte and determines which hard coded divisor is selected. The divisor is a multiple of 461. Since the original optical VSS is 4k then it makes sense the divisor should be doubled. We haven't tested it though.

So if this is simple as it seems on the face, the attached calibration will display correct speed if an 8 pulse square wave at about 5V is supplied to B21. The optical VSS is already selected and the Promid is still modified to show two raw speed related bytes. I am expecting problems with calculated speed when the high byte of promid shows 04 but we'll see.

It will probably saturday afternoon or sunday afternoon before I can run the test. Not sure if sturgillbd's test gave you what your needing or not. I can still run the test though.

Sturgillbd's testing with the signal generator is helping this move along well. Eventually, with either solution, actual testing with a VSS will be necessary.

Again, a I'd like to give a big thanks to guys willing to take time and run tests, especially with two different solutions being worked on. It's really great to do this.

[JeepsAndGuns]

Again, a I'd like to give a big thanks to guys willing to take time and run tests, especially with two different solutions being worked on. It's really great to do this.

Its just as much to help me as it is to help the OP. We both had the same desire. Being able to keep the stock jeep speedo and vss, but also be able to run a GM ecm.
I will try and run the tests when I get home from work today and will report back when I do.

[sturgillbd]

With signal generator on B21 and square wave set for 0-5v, the speed is way too fast. With the other bin 133 Hz would cause 120 MPH. This new bin it is maxed out at 255. At 30Hz, it shows 108MPH and at 60Hz it shows 218Mph

[1project2many]

Thanks.

How about the high byte in the promid? 2,3,4 again or higher values?