ABS is shorting out......advice?

Tishabet · 10-09-2003, 12:04 AM

Hello All,
I recently aquired an '89 944na from a collector in Detroit. He had stored the car since '92, and when I recieved it the idiot light was on as was the "antilock brakes" light on the dash. I discovered that the fuse for the ABS system was blown, so I bought a new one. With the engine off, key out of the ignition, I put in the new fuse and immediately it blew. I was pretty surprised by that, and decided to pop in another higher amperage fuse to see if that one would at least hold a few seconds longer, but that one blew immediately as well. I know a fair amount about cars and electrical stuff in general, but almost nothing about ABS. Anyway, I figure something somewhere must be shorting, but:
A) I can't find a wiring diagram of the ABS system anywhere
B) I can't imagine why the system would be hot when the ignition isn't.
So tomorrow I'm going to spend all day working on the car....I think I know how to get to the ABS pumps and all of that behind the right front wheel, but does anyone have any suggestions what I should look for?

Manute · 10-09-2003, 03:01 AM

Do you have the worshop manuals? The ABS wiring diagram is not there?
I think i have it on my manual,not sure...if you need it and i have it,i´ll send you.

Sorry cannot help you more.

Britwrench · 10-09-2003, 07:24 AM

At a guess it sounds like this 944 was badly stored. You should replace the brake master cylinder to repair the brake pedal problem. The brake pins; get a Dremel or similar and cut them in half, it's easier to drift them out then. The ABS problem; you need to have a wiring diagram before even thinking about repairing this system.
I hope you have replaced the timign abd balance shaft belts, after ten years in storage they will be in poor condition and WILL break.

Tishabet · 10-09-2003, 08:01 AM

Hi guys,
Yep, I replaced the belts right off the top, my uncle owns a 944 and basically gave me the lowdown on how important they are.
Manute-do you have the ABS manual in an electronic format? If so, I would really appreciate an attachment. My email is grantbrown@thedeuce.biz
Britwrench- I considered cutting the pins (I have a compressor and a pneumatic cutoff tool) but if I have to buy new ones I'm looking at over $100 to replace them (see the pelicanparts catalog). As to the ABS, I was thinking that maybe at the computer there would be the ability to unplug parts of the system so I can see which one is causing the short....is that good logic?

Britwrench · 10-09-2003, 10:04 AM

The 944 ABS system can be tested with the Bosch ABS2 tester. This was used by BMW, Volvo etc, so you might be able to find a Bosch shop with one. Yes, certain Porsche parts are more than you would think.
You still need a wiring diagram before touching the electrics, I', thinking that you ahve a problem with the central electric board (where the fuses and relays are) because the ABS system should not be powered up with the ignition off. Unless the ignition switch is faulty.

Manute · 10-09-2003, 10:58 PM

Tshabet,i just have the 6 vol worshop manual,one is electrical,your 2.7 engine is not common,but i suppose is there,however,abs wiring i expect it to be the same as another 89 944.

The volumes are very extensive,about 70-80 mb long, pdf format, so better i´ll take only the abs pages...This evening i´ll check it and send it to you.

I advise you to download the entire manuals when you have time,they are very useful.If you need help or something,contact me at manutillo@eresmas.com

Tishabet · 10-10-2003, 04:55 AM

Hi Manute,
That sounds great! Where can I donload the entire manual? That would be a really handy thing to have in general!

Manute · 10-11-2003, 07:21 AM

i´ve sent you an email,had you received it?

Tishabet · 10-12-2003, 05:45 PM

Hi Manute,
Got it, thanks so much! I was gone all weekend with no internet :-P