early 944 cruise control problem

go86 · 07-13-2014, 12:09 PM

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I have been trying to get the cruise control to work in my 84 944. Here is what I have done so far. tried 4 different brains all did not work 2 servo motors tested the same as the one that came with the car. Brain #5 when I turn the key on the servo motor begins to run and stays running but cruise does not work not sure where to go from here, any help or ideas would be great. Thanks!

mytrplseven · mytrplseven's Garage

Welcome to the club. These things are about as reliable as my first wife. On my '87 my CC would only work at a couple of speeds and then only on occasion. I replace the brain and opened up the servo and did some soldering and after it was all replaced and the tests were done on the connectors I took it for a drive. It worked great. Next day....inop. So we're back to that again, except when it does decide to work, it does it at all speeds. I just gave up expecting it to work and when it does, it's a pleasant surprise.

go86 · 07-13-2014, 04:10 PM

Thanks for the reply does your servo motor run all the time or does it click? I'm not sure if I have another bad cruise brain where I got it he said it was tested. This is the only thing that does not work in the car. Thanks again

guru944 · guru944's Garage

Every vehicle has multiple ground loop and stray current issues. The German cars are the worst I have ever seen. My own "S" including. Cleaning the ground contacts does help in extreme cases however adding rectifier diodes and cleaning contacts works best. I'm currently adding diodes in my lighting systems front and rear as I upgrade to HID and replacing rear bulbs.. helps to also minimize noise and response is quicker. Noticeable. Most servo and relay systems function much better as well like the cruse control solenoids. I'll post some pics in a few days as I integrate to mods.
Later...

Union944 · 07-16-2014, 01:14 PM

Does anyone have a pic of the cruise control computer in the car (early)? I know it is not an easy place to take a pic.

Slam · 07-23-2014, 11:47 AM

THe early brain lives under the console, right beside your right calf when you're in the driver's seat. Two screws and a tug and it's out. The connector may take a little wiggling to free. Sorry I don' have a pic, but maybe Google can help.

I fixed two brains this morning and it was dead easy. I can't take credit for the fix, as I read it on Rennlist, but I can say it's not blind luck.

Remove cruise brain box from car, pry up the flanges retaining the board and slide the board out of the box. Wrap aluminum foil around the board to protect the components but leave the solder points bare.

Preheat your oven to 385 degrees.

Cook the brain in the oven for 8 minutes.

Remove, invert on cooling rack and prepare icing... Oh, wait!

Once it cools, throw it back in the car and go for a drive.

In my case I had nothing to lose. I had a brain that I'd used a heat gun AND a soldering iron on, and thought it was totally dead because of my hamfistedness. The oven trick fixed it. I'd bought a 'tested good' unit here on Pelican and, of course, it was dead too. So to make sure my first success wasn't blind luck, I cooked it too.

Now I have two functioning brains. And Steve Martin nowhere in sight. (If you get that, I can tell your age... And you mine.)

THis isn't voodoo or blind luck. It works. OP, you said you have 4 brains. Why not bake a couple and see where you end up!

John_AZ · 07-23-2014, 04:30 PM

Slam,
Thanks for the tip.

I might put a toasted cheese sandwich in with the brain and have lunch while it cools.

John

Slam · 07-28-2014, 08:34 AM

Just thought I'd check in with a SITREP. Cruise control is still functioning the way it should. I'm crossing my fingers and calling it fixed. I'll pop by this thread every now and then with an update.

And perhaps some cheese...

Slam · 08-06-2014, 08:28 AM

Aug 6 update. I regret to report that the first brain I baked (yes, I welcome snide comments at this point) quit on me after the car sat in the sun all day in +33C heat. Confirms my suspicion of a cracked solder joint - obviously it didn't reflow properly in the oven. So back to the oven with it and under the broiler! Haven't tested it yet.

The SECOND brain I baked (as above, bring on the comments) started to become intermittent this morning. Tapping on it got its attention but not for long. Perhaps I'll bite the bullet and get out the soldering iron.

I really want this stupid thing to work! And I apologize to the OP for hijacking, but at least I'm on topic and tracking my progress.

mytrplseven · mytrplseven's Garage

I drove to Tampa (two hours) and because the car had sat out in 95 degree heat, it was pretty much "heat soaked". Decided to try the CC just for grins, since it hasn't worked but once, since I installed a new computer. It worked all the way to Tampa. Temp in the car moderated while I was there due mostly to thunderstorm that came by and refused to re-engage all the way home. I'm beginning to think that this is a temp issue since my car is usually in the garage full time. After I get the intake issue fixed, I'm going to let the car get hot again and see if it re-occurs.

Slam · 08-14-2014, 06:51 AM

Good plan. Temps do make a difference - the PC board heats/cools and any cracks in old solder joints will of cours expand and contract accordingly.

Mine's working again. I tossed the brain under the broiler and then after it cooled I resoldered the large joints for the input pins. I did fill the kitchen with smoke...

mytrplseven · mytrplseven's Garage

Quote:

Originally Posted by Slam

Good plan. Temps do make a difference - the PC board heats/cools and any cracks in old solder joints will of cours expand and contract accordingly.

Mine's working again. I tossed the brain under the broiler and then after it cooled I resoldered the large joints for the input pins. I did fill the kitchen with smoke...

Kinda hard to concentrate on soldering small joints with the smoke alarm going off

tomiki · 08-15-2014, 08:41 AM

I have two dead and one good brain, I mean cc brains of course, my own is probably long gone due to the beer I've drunk in my life, so I will also try the oven trick, it sounds cool, I mean hot

Otherwise a "pleasant" source of not functioning cc is the Hall sensor in the speedometer... However, this one is easy to test if you have targa: with ignition off move the targa to open ("take out") position. Then start the car and start driving. At around 3-5 mph the targa should close automatically. If not: the Hall sensor or its connections are faulty.