Pfc. Parts

I know this is a ridiculously complicated subject but I figured I'd throw it out for speculation anyway; maybe some of you with god-like experience on these cars might have an epiphany and lead me towards the light.

I just completed a full scale intake refresh on my '85 and after tightening the last nut on the air box and strapping the rubber straps I re-connected my battery ground, eagerly anticipating a few more months working through the things I'd done wrong. I didn't even make it to the driver's seat before noticing my auxiliary electric fan was whirring away on the front of the engine. I chose to ignore this as a "minor peccadillo", turned the key and got nothing more than console lights and a couple of dim bulbs in the cabin. Being an optimist I decided the battery might be a bit low on juice after sitting for three months so I wasted a few minutes connecting a battery charger, which promptly told me it wasn't charging. At this point I went inside to the bar, poured myself a stiff scotch and soda, and began quietly weeping.

I have a ground fault somewhere, that much is obvious. A voltmeter between the battery ground strap and the rear hatch ground point shows 11 volts and a 2 amp current drain, which might be the fan but that seems large. With the ignition off I have no voltage at the coil, I get 5 volts with the ignition in "run".

I figure it has to be somewhere in the primary wiring but I haven't touched the primary wiring in decades (literally). I'm assuming nothing in either the right or left injector harnesses could carry 2 amps and survive? Anyone know what the injectors pull? Aside from those, the MAF and TPS cables were the only major harnesses I even moved. I did R&R the cables for the various temp sensors but I can't imagine 2 amps going through any of those without resulting in smoke.

I replaced one of the two coils last year but the car has run since then, It's possible I jogged something loose so I'll probably take it out, check and replace tomorrow. Anyone else have suggestions?

Thanks,

Landseer

85 has an intake air temp sensor on organ pipes. If the two wires leading to that sensor are bridged, say at the sensor because they inadvertantly touch each other, then the fan will run. Try inspecting them.

Purpose of sensor ---- if engine compartment were quite hot after a very hot summer run, even with key off parked, the fan will run and try to take some heat out. IIRC the fan runs in this case at a reduced speed, passing current also thru a round ceramic resistor located on passenger inner fender well near radiator.

Sensor location --- stand in front of car and look down at yellow oil fill cap. Sensor is located just below it, axially screwed into the organ pipe, just at the 1 o clock position.

MainePorsche

Did you work near / lean on / get wet or anything like this near any of the power harness lines at the 14 point connector/ jump post.

Landseer

Here's the diagram involving that sensor for 85 car, in two pieces.

The second part of diagram shows how the power is connected to the 30 bus, thru fuse 23, which means there is a wire (green one) that is energized all the time leading to the sensor. So with key off, hooking up battery would make fan run if the two wires leading to the sensor are inadvertantly touching. Easy to have happen, BTDT. (EDIT --- if this particular temp sensor itself failed in closed position, fan would run --- That turns-out to be one of the OP's situations, see later posts)

Because its got power all the time, a short anywhere along circuit, including inside 14 pin, would make fan run. Chances are its where your sensor wires plug into sensor or in 14 pin.

Fair amount of current, esp. running thru resistor.


Notice that the fan can still be actuated by high temp water, freon temp, or high temp of trans fluid at torque convertor area sensor, regardless of 23 fuse being pulled, as the fan has multiple ways of being actuated through several separate circuits. But for those circuits to actuate the aux fan, ign key must be on, relay 18 engaged thru ignition X bus, and fan power passing power thru fuse 29. None of that is your issue.

Landseer

So you may have multiple things going on

Minor wiring problem triggering the fan.
(fix wiring at intake temp sensor / or pull fuse 23)

Low battery from sitting. (Disconnect from car and top off charge)

Bad ground strap (these babies go bad internally, replace if original --- do not discount this! This has demonized at least a dozen of us here-- it corrodes).

Thats best I can give ya here at 3:30 am. Maybe Alan or Dr. Bob will happen-by soon and apply real engineering logic.

MainePorsche

Agree.
Just concerned about the 14 pin connector for OP says starter didn't even make an attempt and there is a tie in there to the fan.

Landseer

Just connecting ground strap will engage the fan as described, if sensor wires are shorted leading into sensor. He worked with that sensor to do refresh.

But it does also run thru 14 pin. Here's a 14 pin map I made a few years ago that might help if you need to go there.
Green wire at position 12 is hot all the time. Doubt this is your problem since you didn't mess with the harness/wiring otherwise.

( big wire at terminal 14, unrelated to fan, is also hot )


All good

Alan

I'm not quite sure why you say this - it certainly wouldn't explain all the symptoms - so its not so obvious to me. If there is a ground fault - it is not the only fault.

This alone suggests your battery ground straop is dead. (assuming you mean between battery neg post and battery ground point.How did you measure this? No - it seems too small This is simply not possible if you really consistently have 11v between the battery ground post and the battery ground point.

Just get a new battery ground strap - or temporarily bypass it with 1/2 a jumper cable to test further.

Pfc. Parts

I know that sensor The first thing I did was unhook the two (badly hardened/corroded) wires that connect to it on the assumption the sensor itself was bad and had bridged. That didn't work.

Now for the good news. Like a fool, I didn't bother checking to see if the disconnected wires were making contact with each other during the test (I had to go around back and re-connect the battery). What can I say, I was overwrought... I'm going to do it again (carefully this time) in a few minutes.

Honestly it seemed too simple. I didn't take it seriously. Sometimes a cool head and clear mind are needed. Thanks for lending yours. I'll report back soon.

I should mention also that I hadn't looked at the schematics. I *assumed* those wires didn't carry current (I thought they were too small to carry current) but instead went back to the brain and ended up triggering a relay that carried the real juice to the fan. After reading your post I realize that doesn't make sense since the aux fan needs to stay on as long as the engine is hot, even with the ignition off. Duh.

Thanks again.

Pfc. Parts

I connected the negative probe of a DC voltmeter to the ground strap running out of the battery box and touched the positive probe to the ground point. I measured approx. 11 volts. When switched to DC amps, the meter read approx. 2 in the same position.

I can't explain it then. It's a consistent voltage between those points, when I put the meter on the positive terminal of the driver's side coil and ground it to the engine block it reads 0V with the key off, about 4V with the key in "run" or "on". I expected it to read about 11V but it doesn't. I checked it twice.

It will take a few days to get a replacement strap so I'll try jumping it and report back.

Thanks,

Pfc. Parts

No, but the connector is badly aged and that was where I had planned to begin de-lousing today. The entire harness has aged poorly and the sheathing is cracked where the harness meets the connector. Even normal vibration could have busted it.

Thanks for confirming.

Regards,

neilh

If your 14 pin looks like this, get ready to rebuild it!

Pfc. Parts

This diagram tells the story of my folly.

I mentioned I had removed the connectors for the fan sensor, reconnected the battery and the fan came on anyway. From this I concluded I had some sort of ground fault since the only way the fan could be getting power was through the chassis.

My error was identifying the fan sensor. As you say, the sensor is just to the right and below the oil filler. There are actually two sensors in that location, one is mounted to the water bridge, the other is mounted to the intake manifold.

Without consulting the manual I assumed the fan would be controlled by coolant temperature not air temperature, so I removed the connectors from the sensor in the water bridge to perform the test. Wrong.

The fan is controlled by block temperature apparently with manifold temp being a close analog.

When I went to perform the test again after looking at your diagram I realized the mistake. Disconnecting the intake sensor caused the fan to stop. I pulled the sensor and replaced it with one from another car, problem went away.

Now the battery will charge (no drain on the charger). In a few hours I should know if the car will start.

Thanks for your help.

Alan

Assuming the battery -ve post was connected to the ground strap and the ground strap to the ground point - this tells us the ground strap is bad.

(If the battery -ve post or ground strap were not connected normally this was a meaningless test.. don't bother with it again for this purpose).

You do not measure DC Amps the same way you measure DC volts. On most DMM's you need to use different terminal sets and you need to change the configuration to break the circuit and measure using the meter to complete the circuit.

Keep the connections as normal - measure the battery post direct to ground point direct - what voltage? - Ignore current for now, it might indicate a battery drain problem - but it is not the reason your fan comes on or the reason the car won't start - so secondary focus at best.

Also measure voltage directly across the battery posts with inition turned off and with it turned on - what voltages?

Could be your battery is totally shot also.

Alan

Pfc. Parts

That's truly scary looking. I thought mine was bad!

Not that bad but bad anyway. If I get a chance I'll send a picture. What happened to mine is a story in itself. About 25 years ago my alternator failed and rather than replace it I decided to re-build it. At the time Porsche wanted about $900 for an alternator (those were the good old days weren't they

When I installed the re-built alternator I found out I'd reversed a few standoffs so when I turned on the ignition I shorted the primary wiring running through this harness to the chassis. Smoke was released, fire extinguishers were used and I spent about three weeks re-building the harness. But I was cheap, I didn't start from scratch, instead I fed new primary wire through the existing harness and re-terminated it.

It's worked for the past 25 years but it's in pretty bad shape.