I just completed my cruise install last night, but i'm having a weird problem with it. Whenever I set the cruise, the car's throttle is jumpy. It feels like the cruise is pulling half throttle, then letting off totally every time to keep speed, so it's jerky.
The only thing I can think that would cause this is my vacuum wiring. I teed into the 90 degree fitting on the end of the brake booster, and split into it with a t fitting. now the only problem with this is I ran small diameter vacuum line between the t fitting and the t where it splits into the check valve going to the vacuum canister and the servo motor. The line is literally the same size that the line between the canister and the servo is (which is the same size that was provided with the kit).
Does it happen at all speeds? Mine does the same thing if I'm below about 50mph. I haven't really looked into what's causing it yet.
I have a hard time imagining the vacuum causing it. That canister should make the vacuum at the servo pretty steady. My best guess is that it's a computer issue. The CC control was probably tuned for a neon. It's got much less power, so it would require much more throttle input to accelerate. The system then doesn't expect the car to overshoot the speed so much, so it chops the throttle completely to bring it back down.
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I guess I need to go out and try mine at highway speeds this evening and see what happens. I have been trying it right around 50mph, and it's still doing it. i'll take it out and try it at 70mph this evening...
*EDIT* the only reason i was thinking vacuum is because i have a 7/64 line supplying 2 7/64" lines, whereas the stock kit had a 3/16" line supplying those 7/64" lines.
The actual flow through the vacuum lines is extremely small, so I think the size of the lines will make a negligible difference. Try it at higher speeds and tell us what happens.
Quote: Originally Posted by SoloDogg
btw..you in Evansville????
I'm not at the moment, but I was yesterday. I do live in E'ville. I go to school in Terre Haute, so that's where I am now.
ok, went out on a trip tonite...50mph flat ground, watch the vacuum gauge...up, down, up, down. 60mph smoothed it out a tad, but didn't fix it. 70mph you couldn't feel it, but you could barely watch it. 75mph fixed it. I'm still leaning towards my vacuum supply being a tad small.
I'm starting to think you're right. I'm surprised, but I don't know what else it could be. Good luck, and let me know if there's anything I can do to help.
Solodogg, got your PM, but I'll try to answer here. Travelling at any speed at high elevation seems to be no problem. I was at sea level about a month ago, and for one stretch of highway, I had this same problem. Driving the car without the cruise for a few miles, seemed to cure it. However, I think the real problem is that the cruise is calibrated for a N/A engine. Therefore, it will cause the cruise servo to pull too much, and the car just simply makes more power than the stock N/A does. So, the car quickly overshoots the speed, and so the computer 'dumps' vacuum, causing a decel. On an automatice car, this might not be so pronouced, either, btw. Anyway, too much vacuum is probably the actual problem. I thought if this reared it's ugly head up here, I might try adding a vacuum restrictor (like one in the wastegate lines of older turbo cars), and see if I could slow down the reponse of the servo a bit. Might be worth trying on yours.
I get something similar occasionally... what I can only describe as Cruise Surge... activating the cruise causes the sucker to immediately go into nearly 5psi of boost for about 2 seconds until the thing settles down. Funny part, it seemed to go away after a couple dozen activate/deactivates of the cruise system. It has however reared its ugly head as of today. Curious. I'll see if it goes away later on.
neil...what do you think about removing the check valve...and killing the constant vacuum supply that the servo has, and making it vary with the engine speed, think that might cure some of it, and work the same way you're speaking of? i don't really know what else to try...but sometimes it does work just fine.
have any of you guys checked gas mileage on a fairly long trip yet? i bet this makes the miles per gallon go way up. i used to have a 5 series bmw with a mpg gauge and when i used the cruise compared to using my foot i got around 4-5 mpg better on long hauls.
solodogg, One thing that helps mine stay steady sooner is trying to hold a very steady throttle position at the right speed when I hit the set button. This might not cure the problem, but if you're not already doing it, it might help.
cooper, I haven't gotten any chances to go on a real trip since I installed cruise control.
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