Cruise Control Problem

Lug Nut · Jan 17, 2018

When using my cruise control it surges. In other words if I set the cruise on 75, it will drop down to about 72 then speed back up to 75, then drop back down to 72. This is on flat ground. It feels like someone is pressing the accelerator then letting off, then pressing it again then letting off, over and over again. What would cause this ? Truck info in email sig.

DrCharles · Jan 17, 2018

Not sure... Too much slack in the connection from the throttle to the servo? Or something else causing the control loop to be underdamped. So it "yanks" harder than it needs to, and overshoots...

79jasper · Jan 17, 2018

I would look at the vss.....

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Mulochico · Jan 18, 2018

Check vacuum canister and hoses for leaks. Mine had a few.

nostrokes · Jan 18, 2018

X2 on the vacuum. My 88 did the same had a cracked line.

Macrobb · Jan 18, 2018

Hang on; he's got a '93; My '93 has an all-electric cruise control, like the newer gassers. My '92 does as well...

Is the speedo surging? I'd probably be looking at the tone ring, which is what the VSS reads.
Pull off the rear diff cover and look at the ring there with all the teeth; it's mounted to the carrier and spins parallel to the wheels. Look for rust, broken teeth etc.

79jasper · Jan 18, 2018

Yeah, complete different system. If it was a vacuum problem, cruise would be disabled.
It's common for the vss to get dirty.

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Lug Nut · Jan 18, 2018

Macrobb said:
Hang on; he's got a '93; My '93 has an all-electric cruise control, like the newer gassers. My '92 does as well...

Is the speedo surging? I'd probably be looking at the tone ring, which is what the VSS reads.
Pull off the rear diff cover and look at the ring there with all the teeth; it's mounted to the carrier and spins parallel to the wheels. Look for rust, broken teeth etc.

Lug Nut · Jan 18, 2018

The speedo surges but with the change in speed only. It's not bouncing around like I have seen some when the VSS sensor is bad.

gandalf · Jan 19, 2018

Have you read the article in the tech section? Cruise Control Diagnostic. It may point you in the right direction.

Cruise Control Problem

Lug Nut

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DrCharles

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79jasper

Chickenhawk

Mulochico

Supporting Member

nostrokes

Full Access Member

Macrobb

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79jasper

Chickenhawk

Lug Nut

Registered User

Lug Nut

Registered User

gandalf

Senior Member

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