algie928s4

Hi All,
I finished my Plenum overhaul today with only one issue and jeeze it's weird!- when I turn on the ignition the blowers for cooling the radiator are constantly on-however if I open then close the passenger side door they turn off, when I close the hood they turn back on and when I open the rear hatch -and this is the best one- the fans increase to full power!
Once I have turned on the ignition the sympton persists- the only way to stop them is to disconnect the battery earth-they do not switch off once the radiator cools, and once I turn on the ignition again I'm back to square one.
Now it's been a long day and the full extent of my investigation was to laugh, and to be honest that's all I could do as I have no idea at all where to start on this one- any ideas?
It's an 88 S4 auto, and the car starts and runs sweet after the Plenum overhaul and at no point did I touch the radiator or any wiring going to the radiator, all symptons can be repeated over and over with the same result.

Bill Ball

Alan!!!


Did you mess with the wires on the harness connector next to the charge post under the hood?

dr bob

Try disconnecting the thermo switch on top of the intake manifold. Do they stop then?

Alan

Check the plugs to the fan controller (under the amplifier cover at the passenger sill), check the connections to the final fan drive stage - in front of the AC drier. Check the fuses for the fan controller.

You don't have an aftermarket alarm installed do you? some o fthese symptoms sound like there is some feedback between the alarm triggers (hatch, doors, hood) and the fan controller (which does use the hood switch). Did you connect the plenum top temp sensor correctly ? you sure? really sure? this controls the fan running after the power is off due to over temp heat soak...

Alan

Bill Ball

Alan: Glad you heard me yelling for you!

ew928

When the temp sender on top of the plenum failed earlier this year, it would think engine cold was engine very hot and turn the cooling fans on.
Till it nearly drained the battery.

I thought the default operation was the cooling fans would stop if the hood was open. Press down on the hood switch and presto, fans would come back on.

I pulled off one of the leads on the temp sender and taped it off till I could get a new one on. Easiest thing to replace. It just screws into top of the S4 plenum.

algie928s4

Thanks for the replies, I'd guess that EW928 is on the money-I'll work through the suggestions on Thursday, for now the electrical issues multiply- today was the maiden voyage to work and back, only problem was I finished at 4am and had no headlights or side lights however when I put full beam on the nearside front fog (UK car) came on so that's what got me home lol!
The after market alarm was installed solely for remote central locking and has been installed for 2 years now with no issues, I don't touch electrics- I have been banned by fellow 928 mates due to my dodgy repairs on past cars and acute colour blindness-the threat of having my hands cut off if I touched electrics on my 928 didn't feel like an empty threat!
I was really quite **** with the Plenum overhaul and documented each nut and bolt and each step one by one- at no point did I touch any electrics other than knock sensors etc, which although tediouse meant I had not as much as an unaccounted washer left over at the end!

Alan

I think there are still problems with the way your alarm is wired. Seems like someone just connected together all the door & hood/hatch triggers... This is not really good...

Do your your interior lights come on with the hood open?

the fan problem is almost certainly the plenum switch - initially just disconnect it - but get a replacement - it serves a purpose.

Alan

algie928s4

Bravo gents-disconnected temp sender and fans stopped the weird stuff- with the headlights I removed the double relay, looked at it-replaced-lights worked!
Maybe this electrical stuff is easy!

Bill Ball

No it isn't. You just got very lucky.