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Username Post: Electric Speedometer Issue        (Topic#343523)
roger55 
Contributor
Posts: 606

Reg: 08-07-09
03-23-17 06:27 PM - Post#2683034    


I have an El Camino with a '96 4L60E.

A while back the speedometer started acting up. It's a VDO electric connected to the VSS on the transmission.

When accelerating normally, it seems to work fine. If accelerating fast, it lags and catches up when a constant speed is reached.

On the highway, if you stab the pedal to downshift and pass a car, the speedometer will not increase and will even decrease some for a moment. Again when a constant speed is reached, it quickly comes back up and returns to the correct speed.

Bad VSS or could it be the VDO speedometer? Or something else?



 




raycow 
Honored Member
Posts: 27079
raycow
Loc: San Francisco, CA
Reg: 11-26-02
03-24-17 06:22 AM - Post#2683062    
    In response to roger55

Are you using any kind of electronic interface or calibration device between the VSS and the VDO?

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
roger55 
Contributor
Posts: 606

Reg: 08-07-09
03-24-17 06:58 AM - Post#2683068    
    In response to raycow

Hi. Thanks for responding.
No extra device. The calibration is done at the VDO head.

Someone else told me that they thought that the reluctor is probably spinning on the shaft. That makes sense to me as explanation of the symptoms.

I'm headed out to my garage right now and see if I can determine if that is the problem. Sounds like I need to remove the tail section of the case and inspect it.

Do you agree?



 
raycow 
Honored Member
Posts: 27079
raycow
Loc: San Francisco, CA
Reg: 11-26-02
03-24-17 10:26 AM - Post#2683090    
    In response to roger55

Well, I was originally thinking some kind of processing delay until you answered no additional device, but I suppose a mechanical issue may be possible.

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
roger55 
Contributor
Posts: 606

Reg: 08-07-09
03-24-17 10:31 AM - Post#2683091    
    In response to raycow

I took the tail shaft cover off and the reluctor looks fine and doesn't rotate on the shaft. I even used a heat gun on it but still couldn't budge it.

Got to be the VSS or the VDO head unit. Sure is weird symptoms though.
If I'm going 60, stab the pedal to downshift and pass a car, the car goes just fine but the speedo drops and corrects quickly once my speed steadies.



 
roger55 
Contributor
Posts: 606

Reg: 08-07-09
03-24-17 01:24 PM - Post#2683111    
    In response to roger55

It looks like the VDO speedometer is bad.

This LT1 engine is ODB1 and I have the old Diacom software that will only work on older laptops with a parallel port.
After an hour of fiddling around with an old laptop I kept, I was able to get it to boot off an MSDOS floppy.
I hooked it up to the car (with it up on jackstands) and read the speed the ECM reported to the Diacom program. No lag. It responded with acceleration just like it should while I could see the VDO lagging well behind.
Since the ECM is connected to the same VSS as the VDO speedometer, this pretty much verifies the VSS is good and the speedometer is bad.
The VDO speedometer is 18 years old but I've only driven the car 26K miles with it.



 
65_Impala 
Very Senior Member
Posts: 3920

Reg: 12-29-02
03-25-17 07:22 AM - Post#2683206    
    In response to roger55

I use pin B8 from the PCM to drive my speedometer. It's a PWM signal so check if the speedometer can accept that signal type. It's also 4000ppm so when I put my speedometer into learning mode where it counts the pulses I just ran the car with the rear wheels on stands until it displayed 4000.

There are better scanning tool options if you want to get a USB cable for the car.



 
roger55 
Contributor
Posts: 606

Reg: 08-07-09
03-25-17 07:50 AM - Post#2683213    
    In response to 65_Impala

  • 65_Impala Said:
I use pin B8 from the PCM to drive my speedometer. It's a PWM signal so check if the speedometer can accept that signal type. It's also 4000ppm so when I put my speedometer into learning mode where it counts the pulses I just ran the car with the rear wheels on stands until it displayed 4000.

There are better scanning tool options if you want to get a USB cable for the car.


To be honest with you, I don't remember where I hooked the speedometer up. It's been 18 years since I installed it. I might have hooked it up to the PCM pin. But, it worked perfectly for the first 17 years and 25K miles so I didn't bother to take a look to where I actually had it hooked up. I said it was the VSS directly but that may have been wrong. Either case, the speedo must be going bad.

Yes, the Diacom is ancient and I spent some time last night researching some better ODB1 options.
I see a bluetooth adapter from 1320 Electronics ($90) that works with their Android App as well as the $18 ALDLDroid App that appears to be quite popular. I'm an Android versus Apple guy and have both a phone and a tablet. I've got a newish Dell laptop too.

I'd like to rid myself of that old laptop computer that's failing (hard drive acting up, dead CD drive and a battery that wont hold a charge) as well as all my floppies. The Diacom floppies have been the only ones I've had left for several years now.

I also own a 1957 Chevy pickup with a '91 TPI engine in it. So another there's second reason for me to get updated for ODB1 scanning capability.



Edited by roger55 on 03-25-17 07:52 AM. Reason for edit: No reason given.

 




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