Hello to all. I've got a 91 L98 OBD1 car with a 700R4. It has the VSS sensor in the tale shaft housing. I changed out my diff with a lower ratio and installed an ERA, electronic ratio adapter, to correct my speedo. The speedo is working correctly but now my cruise control is surging. I have Tunerpro and can mod the chip if needed. Can anyone help me with this problem? I've searched the threads with no success.

Thanks so much

Chuck

 

The ecm is a Vss buffer and sends the signal to the cruise control. Have you tried the signal from the era directly bypassing the ecms signal.
You say it’s a 91 a 1227730 ecm has the cruise output on pin c1 2k ppm.

 

Thanks for the response. No I've not tried bypassing the ECM. Let me tell you the whole story. This is a 91 vette. I changed the 2.59 to a 3.45. I first tried to change the VSS settings in the scalars thinking I could do some math and adjust from the current 4K ppm to get the speedo reading correctly. That didn't work. I did not make any changes in the "vehicle speed sensor instrument panel pulse divisor". I did some research on that but could not find anything. I also looked for gears to go in the VSS unit in the tail shaft housing. I needed 14-40 to get it correct. I've since found some gears on line but am already into trying the ERA so I want to see if I can get this working correctly, which would be easier than changing the gears.

From the wiring diagram I have it shows the VSS feeding the ECM then from the ECM the signal goes to the CCM, Cruise, and the radio. If I bypass the ECM with the signal would that have an affect on any of the other outputs, ie miles per gallon, avg mpg etc.? If there is a way to correct this thru programming I'm all ears. If you think the gears is the best option, then I'll go thru that.

 

Best bet to correct the speedometer is to place the ERA between the VSS and the ECM. Sine wave in, and sine wave out (to ECM). This will have everything having the proper vehicle speed.

The IP divisor in the code won't be helpful. It can divide by 1 (default for a 4K PPM VSS), then divide from 6 through 11.

As for the cruise control surging, this is likely the cruise control (CC) module itself. They are tuned to the drivetrain. So now with the higher ratio gear out back the vehicle will accelerate faster. Which throws the CC module for a loop.

If a '90 - '91 Corvette was available with a ratio close to the 3.45s you installed. Try to get a CC module from that vehicle and install it.

RBob.

 

Thanks RBob. I have the ERA between the VSS and the ECM. Looked on line and didn't see any different CC module based on rear end ratio. This is a factory ratio that came as an option in the stick cars. I disconnected the battery while doing all this do you think the car needs to "learn" how to deal with the change? I know they say the computer has to re learn after you burn a chip.

 

Is the reported speed steady? If not the CC module may be getting confused.

I don't believe that this is something that needs to be re-learned.

RBob.

 

Yes the reported speed is steady. So the ERA basically converts the pulse to the new pulse necessary to compensate for the new ratio. So then the system is seeing this new pulse and acting accordingly. I would think that the computer/tune, would need to be adjusted for this. Currently the vss pulse is set at 4K in the tune and the divisor is at O. This is what it was set at for the 2.59 ratio. Do you think, or know, that if the vss is set to a different pulse it will have any affect? I downloaded some BIN files for ARAP, APYP, and they show a different setting for the VSS, 230400.00. I don't know what these BINS were for, stick or auto, but it would appear if these are stock BINS the change was for something. Any thoughts on that?

Also I wonder if I can't find a solution if I restrict the vacumn line feeding the cruise, so it reacts slower, if that would help. I tried a 58MM throttle body one time and that basically caused the same problem. When I went back to the 52mm one it cleared it up. The tip in with the bigger blades more than likely moved the vacuum so much it made the cruise hunt. As you stated earlier the ratio change could have the same affect.

Thoughts on that?

 

Are you opening $6e mask with $8d ?

 

No, using an 8D XDF. Not sure I understand.

 

The data from the arap automatic, and apyp 6 speed is $6e and 16k in size.
To view this data you need to look at it with a $6e xdf.
If you try viewing this in $8d all the information will look messed up.

 

I opened the apyp in 6e and I don't see the VSS settings. Are they in the Scalars?

 

$6E: it is hard coded for a 2K PPM input.

RBob.