I still have the 14b and it does this.

As far as what I do about this: I don't use cruise.

 

I actually had the cruise control stick at wot back when my car was n/t, cause it over compensated going up a sudden hill.... I dont use cruise anymore. If it did that now i'd probably be toast.

 

Just wondering if anyone has played with adjusting their cruise control setup to compensate for a bigger turbo.

The stock cruise unit (at least in the 1G) appears to use a PID algorithm to try to settle on a suitable throttle setting, but the gain term (how hard it applies the throttle proportional to how far off the desired speed it is) is too high, and so it overshoots.

The net result is that if you're going up a hill, you're constantly boosting and coasting in a cycle, which wastes gas and makes people think you're trying to race them (not always amusing).

I took a quick look at the innards of the controller; it's based on a 68HC11 and so it might be possible to reprogram, but that'd be a bunch of hard work wheras it might be easier to, say, bleed some vacuum from the actuator or adjust the reservoir regulator or reduce the radius of the crank that it uses to pull the throttle cable.

Anyone been down this path yet? What do those of you with cruise, big turbos and not-flat commutes do?

I haven't been down that path (Yet) but will be soon. Once I get my turbo in, maybe we could bounce some ideas off of each other. PM me sometime

 

I don't have much of an answer, or experience with any serious
level of performance mods, but I do have a question or two, along
with a theory that may or may not be worth anything.

What does your boost gauge show when this is happening?
How does that compare with the range of boost levels using
cruise on a stock car? (sorry, I only have the factory gauge so far,
so I'm not of much help on the latter question)

The first thing I wondered about was - how is your boost controller
hooked up? A lot of people hook them to the BOV control line.
I tend to believe that if it's done that way, then under part throttle,
the wastegate stays closed more, and the turbo is working as hard
as it can (given sufficient exhaust flow) to squeeze intake air through
the throttle and pressurize the intake manifold enough to try to open
the wastegate. Thus you get more of a switched on/off throttle
response, less gradual, which could maybe cause the cruise to
oscillate like that.

A likely hole in this theory is that at normal cruise throttle settings,
and on moderate terrain, you're nowhere close to opening the wastegate
on a stock car (at least based on looking at the stock gauge), and even
less so with a big turbo and MBC. So the throttle is probably not anywhere
near the point where that on/off effect would happen. However, you did
mention that the problem is when going up hills. Steep enough hills to
ever boost beyond 11 PSI with that oscillation? (yeah, that does sound
far-fetched to me, too...)
If the boost does ever swing above 11 PSI during uphill cruise, then maybe
an easy solution would be some combination of
(a) locate the source for the boost control system before the throttle, and
(b) a two-level boost controller, hooked up so as to limit the boost to stock
levels (or less) whenever the green "cruise" light is on.

If the oscillation stays entirely below stock boost level, then this is a harder
problem, and I'm not sure what to do. I think you'd want the actuator to
just move more slowly, but I don't know of a safe & reliable way to do that.
You could try "chopping" the electrical signal to the vacuum motor, and leave
the drop-throttle solenoid as-is, but then the motor might not have enough
power to open the throttle, and the quick throttle drop might still be enough
to induce the oscillation.

BTW, what's PID stand for?

 

I don't think I've ever boosted past 11 psi with the cruise control on. But then again, I live in Iowa where we don't have too many steep hills.