Is there any way to tame down the cruise control? Now that the car is making good power and the tune is good, when using cruise control the car gives too much throttle to speed up a little and takes away too much throttle to slow down a little. Car is a ratchetfoot! Is there any way to tame down the amount of throttle the cruise control gives and takes?

Car is an '89 vette running 165 ECM with 6E ARAP based tune.

 

Cruise is controlled by a separate module. You will need to hac it and find out what part of the circuit controls the feedback loop. There is nothing in the ECM for this. Except to pull some timing to reduce the power and responsiveness of the engine.

RBob.

 

I had that same problem once with a 2600 lb car and a large engine.
It would always overshoot the throttle adjustment, especially at slower speeds <65mph.
I had to re-engineer the cable connection to the throttle lever.
I had to add some slop in the connection, and limit the total throttle movement added by the cable. It fixed the problem enough to eliminate the surging at highway speed.

Some cruise control controllers have a DIP switch that can change the gain of the system. I don't know about factory GM units though.

In some cases it may be possible to swap the vacuum diaphram that controls the cable to something smaller with less power and less travel.

 

Or modulate the vac source maybe? Some sort of solenoid to prevent vacuum buildup in the diaphram and only send vac to it when the system is on, doesn't seem that hard to rig up with a 12v vacuum solenoid pocketed at the JY, some wiring diagrams and some beer.

 

Mine does have a vac diaphragm controlling the cable, I'll have a good look at it tonight and see if I can adjust the cable somehow, or add a little slop to it. Never thought of that. Probably wouldn't take much.

 

Actually, having too much slop in the cable will cause exactly what you are describing.

HTH

 

I have same problem but again only <60 mph. tI think the issue is agrivated by my 7.4 TBI unit. Sequential throttle linkage might be the ans.

 

If you're good at welding you could extend the length of the throttle lever where the cruise cable attaches. Then, same movement of cable = less throttle opening.

 

I'm having the same problem with my GTA now too. Makes tons of low end and the cruise is too aggressive. RBob, has anyone done what you describe before?

I've also thought of purposely adding a vacuum leak at the vacuum servo to tame it down a bit.

 

> RBob, has anyone done what you describe before?

Not that I know of.

I think that the idea 305sbc has with extending the lever arm has merit. It will also reduce the maximum amount of throttle the CC will provide, but all-in-all, that isn't a bad thing. As it won't be needed.

And extending the throttle arm (lever arm) will reduce the amount of correction.

RBob.

 

I have the same problem with a few cars, one is modded to beat the band and on is stock with gears. Well both have 3.73 gears (with proper speedo gears) and both cars surge badly at highway speeds with the cruise control on.
Maybe GM techs would have the answer???

 

When I went from a 160 HP 305 with a Q-Jet to a 454 TBI and later a TPI setup I had the same issue in my van. Just a little hill would overshoot 5-10 mph! Cruising along at 75 you were suddenly at 85 mph going up hills. What I did was move the pivot point on the throttle body further away from the centerline. Now instead of being able to give full throttle or close to it, the cruise control can only give a little more than 1/2 throttle. With close to 500 ft/lbs of torque on tap, compared to my stock 235, its not a problem. Even half throttle is enough to downshift to 3rd and move it right on up the hill or past the car. Pretty funny when people that won't let you around them, see you push the button on the cruise stalk and burn past them.

 

This is what I did too....My van actually is a mix of GM cruise control parts. I think the brain was from a 92 G20 and the module an 87 2.8 S10, controlling a TPI throttle body with a revised cruise control linkage mounting point.

 

That makes sense. I was thinking about upgrading to the newer "eletronic box" type and going from there buuuuut this gives me a idea to work with.
How far out did you move the piviot ? I have atleast doubled the power an then some with my setup..

 

I looked at my TB last night and it does look like lengthening the lever will be the easiest route. I was going to add about 3/16" or so. With over 500ftlbs and a T56 I certainly don't need much more than 1/2 throttle actuation either, even in a chubby GTA.

 

I think I moved mine 3/8" up from the centerline and slightly rear-ward. Too much and you will get the cable binding on you.

Even towing a trailer behind my un-aerodynamic G-van, I never need more than 1/2 throttle to maintain speed. I can do 70 mph, pulling 5,000 lbs on a dual axle trailer up a 6-8% grade with no more than 1/2 throttle. Pretty amazing what torque will do.

 

Is there not multiple attachment holes for the cable @ servo? Would this not help?

 

I don't think so. thats for a different type of adjustment. (cable length?)

 

I just extended my throttle bracket straight down 3/4" and you'd never know it wasnt stock that way. I haven't driven the car to try it yet but will later today.

You say you moved the bracket up? Must be talking about a TBI throttle body? I just want to be clear on that so folks don't get confused.

 

Yea that was on a TBI throttle body. On a TPI throttle body it would be down. The throttle linkage needs to move OUT or AWAY from the centerline so that the same pull give less rotation of the throttle plate. Thats the easiest way to say it to confuse less people.

 

OK so my trick of adding .750" to the arm on my throttle linkage where the cruise servo attches seems to have worked very well. Smooth engagement and steady speed up and down hills and all. Keeps the big stroker nice and tame....

 

Very cool. I guess I'll give it a go then!