Paul Bakker

Hi.
So if I measure pin 1 & 4 and get a solid 12V (which I did) this means the whole path from there to the main battery is good ?
Cleaning the poles then won't solve my problem. The problem then only can be in the controller itself OR the wireing. Right ?
I will clean the main battery connections because I read about it so many times I'm just gonna do it to eliminate this potential cause of trouble.

Thanks, Paul

Paul Bakker

I saw a remark from Dr. Bob somewhere stating:
"A weak connection at a meted fuseholder may not show up without the load on the circiut."
That answers my question. I'll start cleaning the batteryconnections today.

SeanR

Timely thread, Chuck S's 'charlie car' is having this same issue. Didn't investigate it much yesterday but we know the fuses are good. Should be able to get a closer look at it this next week. This one fan being in/op is causing the car to run a bit hotter than it should.

If/when we figure it out I'll post an update to assist everyone here.

Imo000

Measure the voltage at the fan plug when they are on. I had power until the fan vas plugged in, then under load it dissapeared. The problem was the fuse holder and not the fuse. Check this and report back.

DanielD

I swapped 6 & 8 at the controller by the passenger seat. It was easier to get to and you don't have to bust open a plug to swap them. The plug cap pops right off. On the controller, 6 & 8 are the PWM signals to the Fan Amp pins 6 & 7.
When I swapped 6 & 8 at the controller, the problem stays on the driver's side.

Concerning the power to the fans from the fuses, I unplugged the fan amp plug and then jumpered pins 1 & 5 together. The fan ran fine. That tests out the power from the battery through the fuses to the fan. Then I jumpered 4 & 8 and again, the other fan ran fine. These tests check out the power, under full load, from the battery directly to the fans. If the fans run under these conditions, they, the 12 volts and associated wiring are good.

D

Bill Ball

OK, so I see that it was the other box's pins you were swapping. So, that tells you the problem is downstream, in the final stage box, right?

SQLGuy

IIUC:

1. You've replaced the output MOSFETs in the amplifier module, and that made no difference
2. You've reversed the inputs to the amplifier module, and that made no difference
3. You tried a known good final stage, and it made no difference either

Sounds like, as you surmised, that the problem pretty much has to be in the wiring from the control module to the final stage module. A (relatively) easy way to check that would be to remove the connector from the control module, and jumper 6 and 8 together, then remove the connector from the final stage and check for continuity between 6 and 7. If you don't have it you know that one of those wires is open somewhere along the way.

Chuck Schreiber

Sean,
It's on the list brutha!!

SQLGuy

P.S. While the BUZ11A's don't seem to be in current production, there are a lot of suitable substitutes that could be used in a switching application like this. For instance, the ST Micro STP40NF12, which runs about $1.75 from Mouser.

dprantl

$1.27 at Newark, my favorite electronics supply house

http://www.newark.com/jsp/search/pro...-OP&CMP=AFC-OP

Dan
'91 928GT S/C 475hp/460lb.ft

DanielD

OK folks, here's what I've found today. The driver's fan was coming on intermittently when I tugged on the wire harness so I remove the jump cover and started poking around. This is what I found at the T18 connection.

DanielD

The T18 connector is listed here on the photos. This can't be good of course so I am going to replace these wires now and hopefully correct my fan issues. However, I do have doubts about this killing just one fan. Very knowledgeable folks here stated that both fans run as a pair. Also, I have previously rung out these wires with nothing noted at the ohmmeter. Maybe these wires shorting intermittently drove the controller nuts. Who knows? I'll update when I have this harness fixed...

DanielD

OK. I've repaired the wiring harness at T18. Turns out it was causing a minor alternator needle jump on the voltmeter and it was causing a jumpy oil pressure guage. It's all cleaned up and reassembled. Several wires had very poor insulation remaining so I've replaced them with new wires.
It is nice to know that I've fixed two small issues.
However, I still have an inop cooling fan...

DanielD

I had borrowed a fan amp from a buddy's car and it was doing the same thing as my fan amp: Driver's side fan inop. Go figure. His car isn't running so he may have the same issue as I do and didn't know it.

Although I had swapped out the FET's for the driver's side control in the fan amplifier the final fix was swapping out the fan amplifier with one that I bought from Oklahoma Foreign. Everything, and I mean everything, was pointing to a bad fan amp.

End result is that I know a heck of a lot about the electrical cooling fan logic and drive circuits in a Porsche 928 S4. Next time (if there is one) will go much faster. (I hope!)

Thanks for all the input and questions, I hope this thread helps someone else out in the future.

andy-gts

I am confused....what was the problem that was fixed.???