Calling all cruise control experts!

[Pyro15D]

Hey, I have a 1987 Turbo and my cruise control has never worked. I press the button, light on the switch comes on, press the set switch...nothing. At first I thought it might be a switch problem, so I whipped out the factory service manual (a necessity for these cars) and went through the diagnostics. Everything checks out. All three switches are functioning correctly because I'm getting the correct flashes on the LED. When I go to the speed portion (step 5&6 for type A codes) that is when things get weird. It stays lit when driving below 21 mph, but when I travel over 21 mph, there is no change. According to the diagnostics, it should start regularly blinking. The thing is, I know the speed sensor is working because TEMS automatically goes into medium mode around 70mph like it is supposed to. I thought maybe it is a problem with the wiring to the cruise control unit itself, so I jacked the rear end up, disconnected the speed control connector and rang out pin 7 to ground. It pulses like it should as I rotate the rear wheel. I don't have another computer to swap out and test, but everything on the troubleshooting trees seem to tell me to shitcan the computer. I pulled the board out of the plastic case (at an ESD-safe area) and I can't see anything that looks like a failed component. Does anyone have a publication that deals with more in-depth troubleshooting on this? The factory service manual (and the TSRM online) seem to be woefully inadequate for troubleshooting.

 

[Pyro15D]

Anyone? I was hoping someone would know something about this system.

 

[suprajztwenty]

id imagine the turbo vs non turbo stuff would be the same...are there no junk yards near you to see if they might have a mk3 and how much the ecu would be?

 

[suprasick]

Hey Dane it's Derek. After looking through both the 87 and 90+ TEWD the only connection I can see that is coming from the TCCS is NSW as you can see here: http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=49

That is connected on the CCC to ST as you can see here:
http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=100

Knowing that your using the AEM system, that is all that I see that the CCC uses from the TCCS. Do you have it properly connected?

Hopefully someone else knowledgeable in the CC system chimes in, I know Jetjock helped me with my CC issue, I believe he might even have the training manual...

 

[supraguy@aol]

did you verify that you vac lines are connected properly to it, and there are no leaks?

 

[Pyro15D]

Thanks for the suggestions guys. I tried them and I'm still not getting my speed indication. I checked at the CC computer for the speed sensor pulses and I'm getting them there. It is quite frustrating. Seriously debating on ditching this setup for a dakota digital cruise control. Pride will not let this car get the better of me though. I must persevere!

 

[Poodles]

I'm sure you know where to start, but going to link anyway.

TEWD: http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=100
TSRM: http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=BE&P=58

Going off the other posts, it appears you're running an AEM which could be the issue here as there is a signal to the CC computer from the ECU. It could also be any number of sensors or switches.

If it's a manual and you have the clutch switch bypassed for instance will cause it to not work.

 

[Pyro15D]

I'll take a look at the clutch switch. I may have misunderstood the tewd but I thought the clutch switch for cruise was at the top of the pedal travel, so if you barely touched it, it would shut off cruise. I did bypass the clutch switch, but the one at the bottom of the pedal travel that inhibited the starter. I'll look there next.

 

[supraguy@aol]

And here I thought that there was only one clutch switch...

 

[Pyro15D]

I guess there is one at the bottom of the stroke to make sure that the engine is thoroughly disconnected from the transmission to start the car. The one at the top of pedal travel is probably there to disengage thecruise control if somewhere where to maybe rest their foot on the clutch or something. Anyway, I undid the clutch bypass wiring and it still isn't picking up the speed inputs.

 

[jetjock]

Any B codes? Fwiw no indication of speed sensor in diag mode can be caused by any cancel input being true. Course, it'll also prevent CC operation. Make sure none are.

 

[Pyro15D]

JJ, I checked the type A codes and if I push the clutch, brake, or cancel switch, the led goes out, then when I release them, the light goes back on solid, even if I am driving over 19mph. As for type b codes, it just steadily blinks, which indicates normal. Any thoughts?

 

[jetjock]

Yeah, I read that. Did you read what I wrote?

 

[Pyro15D]

Yeah, I read that. What cancel inputs are there though? All the switches work the way they are supposed to work. If I'm driving at a steady speed of 40 mph without pressing the brake, clutch, or cancel switch, that should satisfy the cancel reasons, right? The parking brake switch is not activated, neither is the brake fluid level warning switch. It is a manual, so no ect ecu to worry about. I've also followed all the instructions on page be-72 for inspection of voltages and continuity on the 18-pin connector for the cc computer. I even checked the vacuum switch for continuity with no vacuum and no continuity with vacuum (engine idling). I'm at my wits end with this thing. I was about to swap in a cruise control computer from an 80's toyota pickup till I compared the two boards. They look nothing alike. What now?

 

[Dan_Gyoba]

Cancel inputs are:

Park Brake Switch,
Brake fluid level low switch (Implied by Park Brake Switch)
Brake light switch
Clutch Cruise Switch
Neutral Start Switch/Clutch Start Switch
Cancel Switch

I would investigate the Neutral Start Switch possibility, since that could be affected by your stand-alone, a bypass of the clutch start switch (Which would be wired differently for USA models than mine) or other, without having anything light up anywhere.

 

[Pyro15D]

All right, I just tried reading these out for continuity. Still the same issue. This is so frustrating! Who woulda thought cruise control would be such an issue? Would anyone be willing to send me the manual dealing with cruise control?

 

[jetjock]

Continuity? Dummy the inputs. If it doesn't work the box is tango uniform. Simple as that. As pointed out I do have factory CC documentation but even though it describes in depth how the system works it's not going to be of any help.

 

[Pyro15D]

Sorry, I meant continuity to ground. I followed the procedures listed here http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=BE&P=80 and everything is indicating correct. Jetjock, what do you mean by dummy inputs? Like manually disabling them? I'm debating on pulling out all the pins that cancel the inputs just to see if that is the problem, but that shouldn't be it if they rang out good. I'd like to think of myself as not a moron, especially since I do this for the Navy, but this is really leaving me scratching my head.

 

[jetjock]

Have you done all the flowcharts? Yes, hardwire configure the inputs the box needs to operate. Do it in the car or on the bench. All the switches come off easy enough. Rig something up for SPD or use a signal generator. Have you scoped SPD in the car? Just because the waveform is good at the TEM module doesn't mean it is at the CC. Check the connector and pins. Signal trace everything to the PCB. You have to dig. All that said if you're so sure the wiring is good why not just get another box?

 

[Pyro15D]

Okay, sounds easy enough. I don't have a sig gen so can I just use a simple 555 timer circuit set to like 20hz then? If not, I guess I could just jack up the rear with the engine running in 5th gear, but that seems a bit unsafe (Ferris Bueller's Day Off comes to mind). I checked voltages and grounds to the CC and those appear to be fine. I would get another box, but nobody really has supras around here, and the ones that do have them have long tossed that piece of "useless junk" in an effort to shave a few ounces on a car that was originally designed to be a Grand Tourer. I dunno. Call me crazy, but I can't stand things being in my car that don't work. I'll dig deep and see what I find. Thanks jetjock.