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Whats The VSSB's function?

NoInterstates!

NoInterstates!

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Hey All,

I have a 1994 F vin K3500 that comes out of cruise control really rough. That is when I have the cruise set, and I tap the brakes throttle goes from cruise power instantly to idle. I think you might already know, but with 4:10 rear and the NV4500 up front you can feel the instant change in throttle more than just a little. It's likely plant you into the steering wheel. Any great friend has quirks so I have learned to deal with this with some fancy footwork. I add a little throttle with the right foot and tap the break with the clutch foot. I ask for your advise on this. I have a feeling it may be related to the VSSB just based on what that component is named. If anyone would like to share the fundamentals/basic function of the VSSB I would greatly appreciate it. Is it's purpose to act as a buffer to even out rapid speed/voltage changes or as a buffer like a place where information is stored for use by the ECM?

I also wanted to ask if there is anyone who owns a 1994/1995 since new or owned one when knew. I know this is the first year for the FSD/PMD/APPS.

Thanks to all!
 
Don't throw parts at it! VSSB is not the issue. There are some updated PROMS's for 1994 that may help. IMO cutting throttle to idle is normal for cruise cancel. So you feel power to full compression braking when cruise cancels. Does it feel the same if you take your foot off the accelerator quickly from power added?
 
I like the term "troubleguessing" to "throwing parts at it." Just kidding. It's only when out of cruise. It takes place in second at most, stick shifter bounces to the side and back and it even makes kind of a rough jerk. I replaced both motor and the trans mounts which helped with the noise it made, but it's still really abrupt. It cuts the throttle faster than I could ever take my foot off the pedal. You can get a close to as bad of a response by rapidly cutting throttle at high RPM in 1'st and reverse, but I can't duplicate it with my foot in the higher gears at highway speed. I guess I was just wondering if there was a way that the engine gradually cuts throttle vs. all or none. I did replace my computer for a different issue a while back, but you know the Prom remained the same. Thanks for your reply WarWagon.
 
The VSSB's function is to convert the vehicle speed sensors output into a useable signal for the ECM(4000 pulse per mile), ABS(128,000 pulse per mile), and speedo(4000 pulse per mile) to use. If your speedo and ABS is working, then the VSSB is most likely working fine. And teh VSSB is normally one of those items that either works or doesn't. Sounds like you need to look into a EPROM update like warwagon said.
 
THEFERMANATOR said:
The VSSB's function is to convert the vehicle speed sensors output into a useable signal for the ECM(4000 pulse per mile), ABS(128,000 pulse per mile), and speedo(4000 pulse per mile) to use. If your speedo and ABS is working, then the VSSB is most likely working fine. And teh VSSB is normally one of those items that either works or doesn't. Sounds like you need to look into a EPROM update like warwagon said.
Click to expand...

To add further clarity (having just gone through this on my son's '94), the vehicle speed sensors are the same for all vehicles. The VSSB is used to adjust that signal for the different rear end gear ratios and tire sizes. Supposedly there are Dip Switches on the VSSB to adjust it, but the adjustment is limited or constrained to a defined set of parameters.
 
Big T said:
To add further clarity (having just gone through this on my son's '94), the vehicle speed sensors are the same for all vehicles. The VSSB is used to adjust that signal for the different rear end gear ratios and tire sizes. Supposedly there are Dip Switches on the VSSB to adjust it, but the adjustment is limited or constrained to a defined set of parameters.
Click to expand...

many VSSB's have jumper wires, since usually its a set it up and forget it item. (Unless your changing tire diameters regularly)
 
You said that you replace the ECM before, it may be that the replacement is for Auto trans? sounds like the truck is manual?
 
Hey all,

While out on the highway I tested this again to be sure I couldn't duplicate it with my foot. I was wrong, when I pull my foot off the pedal as fast as I possibly can it's the same as when you cut the cruise. I think this might be normal system operation. I guess I just never imagined it being like this when the truck was new, such a rough departure from cruise control. Thank you all for the great info on the VSSB!
 
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