silvere

I am at my wits end trying to diagnose a problem with my 87 928S4 cooling fans. I've read tons of messages related to this, and the information has been more than helpful. I've learned so much from everyone, but I am still in the same boat. I know this post is long, but I wanted to supply as much info as I could so that maybe (I'm praying right now) someone would have the answer. Here's the situation.

I have an intermittent problem with both cooling fans. Sometimes they run, sometimes they don't. I never have a time when only one is running. It's either both, or neither. Sometimes I can get them to come on by switching the AC on when the car is off, and sometimes I can't. Sometimes they will trigger on when the engine temp heats up, sometimes they don't.

I can't find any pattern. Last Sunday I drove the car for about 20 minutes. Mostly the temp gauge stayed below 1/2 way. I turned the AC on, stopped for a few minutes, let the car idle, temp gauge went up, and the fans came on. I drove home, turned the car off, and the fans ran as normal for a few minutes cooling it down.

Yesterday, I drove the car to work. In the parking lot, I let the car idle, temp gauge went up, the fans did not come on.

Some history - about 6 months ago, one fan stopped working. Fuse #28 had blown, and caused charring & melting in the plastic. I cleaned the connectors, replaced the fuse, and all was well. When the current problem started about a month ago, I immediately assumed a fuse problem. But the fuses were ok. To summarize what I have done to date:

- Cleaned fuse contacts / connections and replaced fuses #3, #23, #28, & #29
- Checked relay XVIII, opened and closed fine
- Checked voltage at fuse panel (#3, #23, #28 & #29) - good
- Checked voltage at control panel - good
- Checked voltage at output stage - good
- Wired directly from battery terminal by engine to the fans - fans ran fine
- Jumper wire from temp sensor on manifold - fans did not run (not sure why this didn't work or if its related to the problem)
- Inspected the battery / terminals – looks fine (I haven’t actually cleaned them yet)

All of this was done with the hood sensor held down.

One thing I’ve noticed since I’ve been working on this, which I don’t think is normal, is that periodically I hear a clicking noise coming from somewhere in the fuse panel. One time when the click happened I had my voltmeter connected to one of the fuses, and there was a voltage spike for about 1 second during the click. Seemed like some kind of a surge or something. I don’t think it’s related to my problem, but I thought I would mention it. It’s not like the surge starts or stops the fans. Plus, I think I’ve always heard that click, even before I had this problem.

I have no other electrical problems that I know of. If anyone has any other thoughts / ideas on what to do, I would really appreciate it.

Thanks in advance.

Eric

Sab

Have you swapped the controller under the hood or the one next to the passenger seat with someone? I would try to swap with another car and see if you can get the problem to duplicate at the other car...

Alan

Check the ground connections to both fans. There is nothing on the CE panel that affects the fans - except the 2 fuses - check they are not getting hot/melted. The supplies to those fuses and their outputs don't connect to anything else on the panel.

What you heard was probably the AC clutch disengaging and possibly the suppressor on the board taking the spike... It would not cause a 1 second voltage bump but the regulator may take a while to recover full regulation - although that sounds a bit odd... if the voltage stayed in the <14V range you are OK.

The other thing to look at which I assume you have - is the fan control unit under the passenger sill cover - make sure its plugs are in OK (probably OK).

Also check and clean the seperate connections for the fans at the battery +v post - seperate ring terminals - these feed the fuses directly.

If it fails again - check the power connections to the fan output stage in front of the radiator RHS. Unplug the round plug and test for 12v+ on the main power in connectors - pins 1 & 4 - Red Wire & Red/White wire. These come direct from the fuses.

Alan

Earl Gillstrom

Eric,
I have both control units available and live 15 minutes from the Barry Bridge in PA if you want to try them.
Earl 610-358-1268

silvere

Thanks for the quick responses.

Sab - I would love to swap with someone to test, unfortunately I don't know anyone else in my area with a 928. Maybe someone reading this post is local and could help......

Alan - I have looked at the contol unit, and I tested the voltage there. Everything seemed ok. I plan on checking and cleaning the battery connections tonight. I have also already tested the output stage pins 1 & 4, and I had a good 12V.

Alan

You may also need to check them under load (this is harder) - you need the plug still in. Sometime if its a resistance build up it looks good untill you try to load it with much current - then collapses to a few millivolts. You also will need to check the output to the fans there - pins 5 & 8.

Of course it needs to be acting up when you are testing it...

Earls offer is a good one - could be the control unit - but the operation is too hard to debug easily....beyond just checking the drive signals to the final stage.

Alan

silvere

Earl - thanks for your offer. I may be giving you a call.

Just an update - I removed the battery connections and cleaned. The fan wires looked ok. Fans were running after I put everything back. We'll see what happens over the weekend.