Cruise control pulsing

[stickypoop]

Don't do a lot of highway driving so just noticed this tonight. Cruise works fine but when it's attempting to maintain speed on a decline I can feel a pulsing. It's not violent but it's enough I notice. RPM's appear steady as far as I can tell from the gauge. No codes. Throttle body removed and cleaned only a few months ago.

 

[DAlastDON]

Like engine braking?

 

[Mooseman]

Could just be the torque converter clutch disengaging and re-engaging if the throttle is being let off due to increased speed. Could just be the inability of the cruise control to maintain proper speed going downhill.

 

[Wooluf1952]

This has been discussed before. I don't remember if anything was explained, but it's not unusual.

 

[stickypoop]

Like engine braking?

Less smooth... more like someone tapping the brakes repeatedly to watch a sleeping passenger's head bob (not that I've done that )

 

[DAlastDON]

I like to scream and do a brake check when my passengers fall asleep.

 

[Tiggerr]

Less smooth... more like someone tapping the brakes repeatedly to watch a sleeping passenger's head bob (not that I've done that )

Lol! I remember seeing another tread on this. If I remember its just the way these trucks are, kinda aggressive imho. Seems the cruise will keep your speed at all cost lol. Mine does it too

 

[stickypoop]

I did a search before posting but didn't really come up with anything ... since some of you are recalling seeing this before I searched a bit harder and I think I found the previous discussion. Linked for anyone interested in the future:

http://gmtnation.com/forums/topic/7117-cruise-control-down-hill-jerk-help-needed/?hl=%2Bcruise+%2Bjerking

 

[littleblazer]

I only started noticing mine after the tune. It's engine braking basically, atleast that's what it feels like.

 

[The_Roadie]

It's a poor programming job in the cruise control part of the pcm software. If I could find the goofball who never took a test ride after writing the code, I'd rub their nose in it. Proof that GM fails to listen to customer complaints.

 

[Tiggerr]

Proof that GM fails to listen to customer complaints.

Lol! Say it ain't so!

 

[Wishbone]

It happens on mine too. It's always been there. I know exactly the few hills it happens on, and now I expect it. Only does it at highway speeds, not below 55.

 

[Robbabob]

There was a Technical Builtin for severe cases, but yours sounds typical.

 

[webdawg]

Here you go pal:

http://gmtnation.com/forums/topic/11287-buckingchugging-not-hard-on-cruise-control-downhill-around-70mph-2004-chevy-trailblazer-lt/

As you know, people have been talking about the PCM. I had mine checked and it was already updated.

I replaced the fuel regulator.

I clamped down the tube the goes from the air box to the crankshaft vent on both sides with some hose clamps and put new rubber boots on the line that ran from the airbox to the fuel regulator. The boots were completely bad. They were rock hard and loose fitting. The tube was loose fitting too.

Be careful clamping hoses to plastic, do not want to crack them.

I had the problem again last week and the boots that connect the plastic tube to the fuel regulator went bad in 1 year. I replaced them again and am looking for a better solution to replace the vacuum line between the fuel regulator and intake box now.