From: gt7096a@prism.gatech.edu (Adam Lotz) Subject: [z-car] [zx] Cruise Control To: z-car@CS.Princeton.EDU Date sent: Thu, 1 Jun 1995 00:56:05 -0400 (EDT) Here are ALL my notes on how the cruise control (Automatic Speed Control Device) works in my 280ZX. Er...doesn't work in my 280ZX. >my cruise is acting up too. With mine it shuts off when I hit any largish >bump. I think the brake switch (that shuts it off when you hit the >brakes) is set wrong and is too sensitive, you might see if that is >waht's wrong with yours. It may just be on all the time making the cruise >think you have your foot on the brakes. Hey Mark, Went home this weekend, and found out that a local junkyard was having their $30 for all you can carry day... got everything that looked cruise-related off a burnt 280ZX, and brought it home to compare to mine.. Here are my notes on the cruise control, in general, in case any one else is having problems: 1) It's a REALLY simple system. None of the manuals that I've seen will tell you how to work on it, presumably for insurance/safety reasons, but for people who change their own brakes, it's not too bad to look at. Okay, first, there is a switch module in the dash. Turn that on, and a relay under the passenger seat audibly clicks to the on position. This relay supplies power to the cruise brain, which is the largest (4" square) metal box under the seat. The brake pedal and clutch pedal each have plastic-tab operated switches, which are wired in series: This means that if either the brake or clutch pedal is pushed in (or both) the circuit is broken, and the cruise will disengage. The above switches can be checked by running a voltmeter to various points on the cruise brain wiring harness -- you will see 12v on 2 of them, then when you push in the clutch, 0v... push in brake, 0v... etc. As you mentioned, it's a very good idea to make sure there isn't a lot of extra play in the pedal so that it doesn't bounce off and break the circuit accidentally. The set switch on the turn signal lever can be tested WITHOUT taking apart the steering column area. Again, a voltmeter and some poking around in the wiring harness will find a closed circuit when the button is pushed in, an open circuit normally. That's all there is to the electronics. UNDER the hood, there are 3 main components. First, there is the big round thing next to the battery, which has a cable going to the throttle linkage. With the car off, you should be able to manually press the throttle to the floor, and then wiggle this cable in and out (it takes a BIT of effort.) Making sure this cable isn't frozen up would probably be a good idea. The big rubber 'nipple' on the round thing (which I'll try to call vacuum actuator from now on) is held on with a bit of adhesive which seems only moderately important. If you're adventurous, feel free to push in on it, to seperate it from the metal, then pull out gently and slide it an inch or two down the throttle cable. Looking into the big round thing, you'll see that the cable is attached to a strange rubber bag, which lo and behold can be filled with air. (the inflation/deflation tube is on the bottom) If you try to push on this bladder now, it should NOT budge, if all of your hoses are in good shape. If it moves easily, you probably have a leak somewhere. Now onto the other 2 big components of the ASCD under the hood -- two electric vacuum switches. These are hooked up via thin rubber hose to either your vacuum pump or the intake manifold (if your car doesn't have the pump) As I experimented, I gathered that these switches can be actuated with somewhere between 3 and 12v, and will open according to the amount of voltage they get. IE open a little at 3v, a lot at 12v) That MIGHT be wrong, I don't know. All I know is, I took a battery charger (14v) to the contacts and they made a nice buzzing sound, which I took as a sign that they were WORKING. Again, if you supply 12v to them, they'll make a loud doing-something noise -- if yours don't make any noise, something is probably wrong. I would NOT recommend supplying them with more than 10v for any extended length of time, as I have no idea what their normal operating voltage is. Basically, what I gathered from experimentation/reading was this: When you turn the "ON" switch on, the relay under the seat flops and the system gets 12v. This illuminates the "ON" light. When you hit the button on the end of the turn signal stalk, SOME MAGIC THING INSIDE THE DASH (this is the one part I really don't know ANYTHING about) determines your speed (from the speedometer) and stores it in some form of memory. As you *RELEASE* the button, the computer does some quick calculations and tries to decide how this compared to your last preset speed. If you didn't have a previous speed, it sets it to the new one. If you HAD a previous speed, it resets it to the new one. (this redundant logic becomes important when they add things like the accel/decelerate button in later years) So now the magic speed computer knows how fast you were going. As soon as it figures this out, it sends some electrical signal (again, don't know what) to the two vacuum relays (as I understand it, one is an emergency cutoff) that allows a specific amount of vacuum to be sucked into the bladder. As the bladder gets smaller, it will start to pull on the accelerator linkage, eventually matching speed and then going a LITTLE BIT FASTER. **THEORY --> I think at this point, the computer is still watching the 'current speed' indicator, and when it sees the cruise has sped up it thinks to itself "gosh, that must be just a LITTLE bit too much vacuum" and it adjusts itself to get you your preset speed. The computer then monitors the current speed x times per minutes (probably quite a few for safety reasons/hills/etc) and tries to compensate for any speed differences by opening/closing one of the vacuum valves slightly. So, here's a brief list of the parts I know of, and my own (not necessarily recommended) testing procedures to see if it's good: 1) Switch in dash - lights come on? probably good otherwise, swap from a parts car 2) Relay under seat - makes "ping" noise when you hit ON button - good also, 12v is being supplied to ASCD brain else replace/parts car 3) Brain box - check to make sure power is going to it. If in serious doubt, the top can be carefully pried off with a screwdriver - there is a gasket, but can be re-sealed with permatex. Metal case is VERY durable, even if it looks rusted on outside may be perfect inside. If you decide to get inside, look for traces (smell?) of smoke/fire. Best bet is to swap from a parts car / grab a friend's. (Incidentally, when I say swap from a parts car, I typically mean go to the local u-pull-it junkyard and grab one. While against the law, many people find it acceptable to pocket small electronic parts, and/or explain to the clerk that you think the mystery metal box in your hand is part of the intermittent-wiper and/or hazard light system. If they come back with "What?! Heck no, that's a 280ZX cruise control module!!" the correct response is "Oh my gosh! I needed one of THOSE, too! I'll take it!" -- either way, most electrical parts seem to run US $7.99-$29.99 around here at junk yards) 4) Pushbutton on turn stalk - check with voltmeter at brain box possibly check on stalk with steering cover removed if it doesn't work, good luck to ya. (real easy to hotwire one with a momentary contact 12v switch from radio shack) 5) The two vacuum solenoids under the hood -- *danger - haphazard idea * disconnect the wires to them, then use a 9-14v dc power supply to test. DO IT QUICKLY. My 2 made slightly different noises, but both hummed and vibrated slightly = prob OK 6) The vacuum bladder -- have an assistant hold the throttle down (car OFF) which will get some slack in the cable. disconnect the vacuum line that runs out of the bottom of the bladder from the solenoid (at the solenoid end) which will give you a few inches of vacuum tube to work with. Suck on it. (or get attractive volunteer to do it) If the cable tightens, the bladder is in ok shape. Now lick your finger and close the end of the vacuum line with it. This should MAINTAIN the vacuum in there, and keep the cable at it's present place. (have assistant stop pushing down on throttle) If this fails to keep a good vacuum, the bladder could be punctured, or just as likely, your finger isn't a good seal. If the bladder is punctured, again, find a parts car. I got a replacement by just snipping the throttle cable with wire cutters (in a hurry) The cable can be reattached at either the point inside the bladder, or on the driver's side. (driver's side is preferable, but either will work.) **** NEVER, NEVER use manifold vacuum to test the bladder. In a split-second of stupidity, I tried to save time by hooking up a vacuum line to the bladder. Immediately, the bladder started sucking in, which made the engine idle faster, which made the bladder suck in farther, which made the engine hit 5000 rpm before I knew what was happeneing. EXTREMELY important to remember that you *are* dealing with an extention of the throttle cable when fooling around with the ASCD **** 7) Rotten mystery part -- somewhere, attached/combined with the speedometer, is a speed sensor. As I've taken my dash completely off once before (in no mood to to it again) I haven't had time to fool with this. If ANYONE can shed some light as to what this is or where it hooks up, I'd appreciate it! Other than that ^^^ though, the ASCD was a remarkably simple system. The mostly on/off controls made diagnosing the brain easy, and the rest of it is a simple vacuum system with only 3 major mechanical components that could fail. Ah yes -- one last tip -- ALWAYS make sure the vacuum lines are clean by disconnecting one at a time and blowing through it... something could be lodged in one, and checking in advance will save you a lot of time. Adam