Vehicle speed sensor erratic

[Bruce Hislop]

My vehicle speed on the WUD is very erratic lately. if driving at 60mph it will jump to 80 or 90 even as high as 120mph randomly. It always jumps to a higher than actual reading, not a lower reading.  Speedometer reads fine and is steady. Speedo cable spins easy and OEM cruise has been removed.

Along with the eratic speed reading, the engine will stumble randomly.  I though maybe it was the Deceleration fuel Cutoff due to the speed sensor issue so I set the DFCO Enable temperature to 150 (maximum setting) so it would not come ON but it still stumbled.  When the WUD shows a steady ready the engine runs fine.

I tested the VSS using my battery drill and it was stable the entire time I was testing it.

I disconnected the VSS for a 4 hour trip home yesterday and the engine worked fine.  This is the second time I've disconnected it and each time the engine ran fine.

Wiring looks fine, so I'm guessing its the VSS.  Does anyone have a good part number for a VSS sensor to fit our application?

Thanks

-- 
Bruce Hislop
Perth Communications is now merged with MRC Wireless.
Office and phone numbers remain the same.
519-273-3307    800-565-9983

[Johnny Bridges]

Sounds as if your VSS is noisy (Electrically).  I'd try another if it's like mine - sealed.

--johnny

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[Randy Van Winkle]

VSS sensors are becoming quite pricey. This one from Howell https://howellefi.com/product/tpi-tbi-vehicle-speed-sensor/

The 2PRS or the 4PRS square wave senders will work from here: https://jagsthatrun.com/collections/speed-sensors/products/speed-sensor-place-holder-4pac  

The ECM is looking for 2000 pulses per miles by default. The EBL allows calibration for other # of pulses per miles.

At $120 for most VSS senders, I think I would go with Dakota Digital. You need their converter box but it takes input from the sensor and outputs multiple signals that can be used for the ECM and a Speedo and Cruise Control and any other devices looking for pulse per mile inputs. The sender and the translator box are around $130.00.

SEN-01-4160 VSS is for GM in-line cable. Used with this translator 

http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=126/category_id=287/mode=prod/prd126.htm

it will support the signal needed. All of this is about the same price as a VSS from other places and gives you future expansion - also can compensate for gear changes.  It has been awhile since I really looked at the correct p/n so you might want to verify with them that these two items will work for you. If you have a sender for your cruise control already, then just the translator might be all you would need.

Randy

--

[Bruce Hislop]

The one I had came from Howell and I see they are currently $130US, so that's about $185 Canuck bucks.

Since this one was acting erratically (I tested it with my VOM and scope), I took it apart (4 rivets). Inside there is just a magnetic wheel and a reed switch. I'm guessing the reed switch is worn out as I figure its done about 60 million cycles.

Not sure why they are so expensive since I can get a replacement reed switch from Digikey for about $1.00 for Qty 1.

So I think I will just try replacing the reed switch and see how that goes ;-)

Bruce Hislop
Perth Communications is now merged with MRC Wireless.
Office and phone numbers remain the same.
519-273-3307    800-565-9983

[kdpotato]

I'll be very interested to hear what you find. We've had this problem for quite some time, though I hadn't noticed an engine stumble.

I checked all the wiring, grounds, etc, and haven't fixed it.    I'm using the Dakota Digital converter box and speed sensor.  

I kinda recall KenH ran into something similar, and it only disappeared when he got another EBL/ECM box after talking to BobR about it. 

Not 100% sure on that though.

Karen

1975 26'

[James Hupy]

Anything that moves, be suspicious of it. Speed sensors included. Hybrid devices, like cable driven rotating discs that are counted by electronic components are specially prone to this stuff. Dollar cost has little to do with their lifespan.

Jim Hupy

Salem, Or

78 GMC ROYALE 403

[Johnny Bridges]

Optical sensors get crud in the ptotocell eventually.  Most are sealed , can't get it out.  Both optical and Hall Effect sensors are affected by noise, especially pulse noise.  Autos are notoriously noisy environs electrically.  If it used to but now it doesn't, try a new one.

--johnny

  

[Bruce Hislop]

I've ordered the 72 cent reed switch from Digi-Key.  The reed leads came out of the solder while I was removing it so it could have been a cold solder joint as well.  But for 72 cents I'll just replace it.

I'll you know how it turns out.
 

Bruce Hislop
Perth Communications is now merged with MRC Wireless.
Office and phone numbers remain the same.
519-273-3307    800-565-9983

[Randy Van Winkle]

Using TunerPro to set the VSS - Filter Filter % in Scalars will help smooth out the VSS display.  This parameter is not intuitive as higher values provide less filtering. I have mine set to 20 and the Speedo display is rock solid. Otherwise, it was jumping all over the place.

Randy

[Randy Van Winkle]

Should have mentioned that this parameter probably won't fix a bad reed switch. ha!

Randy

[Johnny Bridges]

The price is right, anyway.  If you still have problems, find a 'scope and look at the incoming and outgoing wire vs ground.  Use the fastest sweep speed on the scope and look for spikes.

--johnny

[Gordon]

Bruce won't have to look far to "find a scope."  :-D

On 2018-09-18 5:59 AM, 'Johnny Bridges' via GMCMH EFI wrote:

The price is right, anyway.  If you still have problems, find a 'scope and look at the incoming and outgoing wire vs ground.  Use the fastest sweep speed on the scope and look for spikes.

--johnny

On Monday, September 17, 2018, 8:50:47 PM EDT, Bruce Hislop <br...@perthcomm.com> wrote:

[Johnny Bridges]

I'm eyeing for a second hand Tek, I miss the ones at work.  The problem with noise spikes is, if they exceed the threshold of the input device and it's fast enough, they look like a zero crossing and the device switches.  Debouncing usually depends on a capacitor which eventually dies.  At that point, the circuit seems to go bats--t, counting noise spikes.

--johnny

[Bruce Hislop]

Randy,
Thanks for pointing out that parameter. Mine was set to 75% so I have reduced it to 20%

Waiting for my DigiKey order... says its in Memphis and still says delivery by 5pm today.

Bruce Hislop
Perth Communications is now merged with MRC Wireless.
Office and phone numbers remain the same.
519-273-3307    800-565-9983