Hi all,

I have been a long time "watcher" of all the threads here and they have come in very handy though the adventure of my DI. About two months ago I thought my VSS was going bad as the truck would cut out @ about 50mph for 2 second intervals. Very intermittent. We had a spare VSS (used) that I piece-mealed together and installed it. Seemed to work OK and then the issue reappeared. Very intermittent cutout around 50Mph. A few times (very cold days) the truck would not want to accelerate over 35 and seemed fuel was cutting out. Got warm and seemed to go away.

So here comes the meat and potatoes:
Cruise was not operable when I got the truck. I have completed the "detailed" cruise control checklist and everything checked ok (Pump, vacuum lines, brake switch, cruise switch, relays etc). Also tried a spare cruise ECU with no luck. When I got to the point of testing the voltage of the VSS at the cruise ECU, I was told it should be between 2 and 5 volts? It looks like I am receiving a full 12 volts with brake applied and motionless and goes down to about 8 volts while rolling fluctuating.

The weird part- the speedo seems to be working fine and I have a scangauge II plugged in and looks like it is close ready +/- 5mph from the speedo. I figured with all that showing OK that the VSS would be ok?

Anyone have any experience with the above?

 

Between the VSS and the ECU, cruise control, and milage reminder module; there is this circuit board in the speedo cluster. It processes the pulses from the sensor, drives the speedo (electronic) and other modules. So it could be this board, or the connectors in cables to it. Might be heat related (corrosion on contacts has a mind of its own).

 

The "good tick" in your sig line comes from worn short pushrods and oval I.D. rockers now undercutting the rocker shafts...... Give a look sometime.....

Who told you that you'd get between 2 and 5 volts? WRONG, smack em in the head for me. It's a 12V device and fluctuates between Vbatt - 12 and 0 Volts 6 times per wheel revolution. Your half there with the 12V reading. I'm sure the buffer board can handle the 8V, it's less than 12. The board SB refers to by the way is the Vehicle Speed Sensor Buffer....... What you get at the cruise ECU connector should match what you'd receive before the VSSB.

Your speedo working within spec is a sign the VSS is working but I wouldn't rely on a cobbled VSS to tell me it's a perfect world..... Snag another known good and then go from there.

 

Thanks for the advice! I was (once) a good mechanic and it wasn't adding up. I did pull the cluster today as well as the board to give it a good eyeball. Going to double check the cluster ribbon as well as any bad joints on the board. Going to double check the rotary coupler while I am at it.. but last I checked all voltage was correct at the cruise ECU when buttons were pushed. I got to the point of reading the VSS voltage while moving slowly and it looked wrong according to the bad information I had. Thanks for the confirmation on the correct voltage. Looks like it may be reading correctly then. (Now I have run out of every possible thing though on the cruise not working!).. I will follow up when I figure out what the culprit is..

This is the last of my current electrical issues... then will move on to engine fun!