hderr

I'm still on the channel. After resoldering the board from the 87, trying to compare pins, I swapped my 87 board with the 85 car's board. Resoldered board didn't work. I swapped between an 85.5 and 87 and as far as I know the swap should work. I'm reluctant to put the working board from the 85 in the 87. :-(

hderr

My brain is fixed!!! 944 cruise control computer that is. OK, I finally got replacement capacitors as Mike suggested, and soldered them in and what to my surprise, the board works. Took the queen out for a cruise this morning and the cruise works great. Sweet. I have my fingers crossed that I'm not premature in this and that it is a good fix.

I tested the capacitors I pulled and they all tested 20-30% too high, hmmm... If you need more info on any of this let me know. I have part no., pics, and even capacitors left over.

I sure would like to know if others have had success with replacing these capacitors or if our situation is unique.
Hank

Mike C.

Great! How did you test the capacitors?

Red1

My '76 Mercury Cougar had cruise control. I should certainly hope a porsche of '80s build would have it. Which is kind of funny really, since I'll be yanking mine out.

Mike C.

Yea the old vacuum operated cruise has been around for quite some time...

hderr

With the caps out of the board, I used a DMM with a capacitor test function. The caps that should have been 2.2 uF were around 3.0. That's about 30 % high. New caps I tested were within 5% of specified value.

Mike C.

I didn't know some DMM's had that feature. I wouldn't have guessed that 30% off labeled value would mean much. I wonder what the typical failure mode is for an electrolytic?

jpk

There's a good explaination about how capacitors work on the wikipedia at http://en.wikipedia.org/wiki/Capacitor

At the top of that page, there's a link to Capacitor(component) which does a pretty good job explaining how they are made.

In a nutshell, electrolytic caps are made by stacking a thin foil sheet and paper soaked in electrolyte. This is then rolled up inside the can. The electrolyte is usually boric acid and water, with ethelyne glycol added to help retard evaporation, but it does eventually evaporate over time. As it evaporates, the insulative qualities change as does the capacitance.

This is the primary reason why old vacume tube radio sets stop working. The power supplies use big electrolytic caps to handle the high voltages, and after 30+ years they dry out.

Mike C.

Interesting. But it does say that age would tend to dry out the dielectric which tends to reduce, not increase capacitance.

sendarius

Guys,
I have a problem that may be with the cruise control.

Has anybody experienced the throttle going to the floor every time you use more than one third? As in, I push the throttle down to ~ one third and something sucks the pedal to the floor. I have to shut the engine down (or soemtimes hitting the brakes seems to release the throttle pedal).

Does this sound like it could be the cruise control brain?

35thSLP

unplug the servo in the engine copartment and take her for a drive. that should isolate wether it is the cc causing the problem.

Mike C.

It's hard to image anything else that could cause that to happen. Typically the cancel function does turn off the cruise but who knows? You could also unplug the brain but the muscle to move the throttle does come from the servo in the engine compartment. Imagine if that occurred whent he car was new? Think Audi nightmares....

sendarius

Mike (and others),

I tried unplugging the brain, but when I started the car it immediately went full throttle.

Next thought was pull the fuse, but in my S2 has the brake lights and cruise brain are on the same circuit according to the diagram fuse box lid, so count that out even as a temporary fix.

I'll disconnect the servo, and try again, but from the feel of the throttle pedal I am beginning to wonder if there is a failed/disconnected counter spring at the pedal end of the throttle cable.

Everything is fine at the throttle body as manually opening the throttle from under the bonnet (hood) doesn't trip the problem, but that doesn't move the throttle cable at all.

sendarius

Greetings guys,

Well, I resolved the problem. Believe it or not, but the culprit was a NUT, as in seed pod from a tree, that had lodged in the hinge area of the throttle pedal.

The bottom was jammed in the hinge and the top was exactly the right size to wedge into the recesses in the underside of the pedal, and counter the spring pressure, giving me the impression that the pedal was falling to the floor.

After an hour upside down under the dash, I managed to disconnect the pedal, clean out the hinge area, and all is now fine.

Mike C.

That is a scream! I would have been blaming ghosts at that point....