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 Post subject: 944 Smoke, battery light and terrible idling all of a sudden
PostPosted: Sat Mar 02, 2019 9:43 pm 
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Hi Folks, I am reasonably new to the 944 owners world and still learning. I am not that mechanically minded (not yet with 944's anyway) so I use an independent Porsche specialist for all work on my car, I am keen to learn though.

I have an '84 944 that has recently had some work done to it, 48k service, new belts, new water pump, ignition leads, new battery etc. This was due to bad idle and this was sorted after a leak was found under the manifold and sorted and the car seemed good to go. The car is stored in my garage.

I have an isolation switch next to the battery and I usually switch it off and leave the battery on a trickle charger when not in use as I was having battery drain issues when not driven. (I have had a new battery fitted recently)
I decided to go for a drive, after switching on the battery isolator switch I heard a weird hissing sound coming from underneath the car for a few seconds, I didn't think much of it as it stopped again and I thought it's something I just hadn't noticed before, the car seemed fine and started up and drove fine.

A few days later after not using the car since I decided to go for a spin and turned on the battery isolator switch and heard the same noise and car started fine, I rolled out the garage and left it idling on my sloped drive for 5 minutes while I put some bits back in the garage and then got in it and as I rolled down my drive I realised I still had the handbrake on so as I was stopping at the bottom of the drive to release it, I suddenly heard a loud continuous high pitched whirring motor noise and after quickly turning off the engine it continued at a high pitch, so I quickly lifted the bonnet and noticed smoke coming from around the rear right side of the engine bay, I immediately isolated the battery and the sound stopped but in my panic I couldn't pinpoint where it had come from, I left it a few minutes and started the car back up and everything was fine. (Edit: In hindsight I realise it was the heater fan making that loud noise I think and where the smoke was coming from as the cover is melted above the resitor.) I took the car out, no problems at all, drove fine, temp fine. I thought maybe something was maybe just sticking and it needed a drive or maybe the hand brake had something to do with it. Drove home parked up, isolated the battery put it on trickle. Thought it was just a weird thing that had happened.

Which leads me to today, the next time I planned to take it out for a drive a few days after the last whirring incident. Removed trickle charger, switched on the battery, heard a louder hissing weird almost sparking sound from underneath to the rear of the engine bay, louder than last time, a, saw a small puff of smoke rise up from rear of the engine bay. Left it a few minutes, nothing else happened. Weird. Started up the car and it struggled to idle and cut out. Started it again and the idle was all over the show with the battery light flashing as it tried to regulate the idle, it just would not stay running, turned it off, got out and went to investigate the engine bay for smoke but didn't see any but noticed a melted area on the plastic above the resistor of the heater fan. The resistor was warm/hot to the touch. I cannot remember seeing this melted area before but I may be mistaken. I isolated the battery and that's where I am now.

A guess from my extremely limited knowledge is there is a loose/worn out wire somewhere causing an intermittent ground problem. Any ideas or tips would be greatly appreciated?

Again, I am still learning so be gentle, I realise now I probably could have set the car alight with my actions. :roll:

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- '89 Porsche 944 Turbo (Guards Red)


Last edited by jjadamsart on Sun Mar 03, 2019 10:44 pm, edited 2 times in total.

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 Post subject: Re: 944 Smoke, battery light and terrible idling all of a su
PostPosted: Sun Mar 03, 2019 12:20 pm 
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That’s either the alternator cable or the starter cable
I would not turn the battery on again or you may well have a fire in the garage

I would get the car up in the air and have a very close look at all the power cables to and from the starter motor.

The live from the battery goes through the starter before it reaches the rest of the car, the alternator also connects to the starter to charge the battery there is nothing else in that rear RH area

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 Post subject: Re: 944 Smoke, battery light and terrible idling all of a su
PostPosted: Sun Mar 03, 2019 4:21 pm 
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Thanks Waylander for the response, that makes sense.

I traced the wiring from the battery but didn't see anything, I haven't jacked the car up yet so couldn't see all of it but I decided to take some photos of the starter anyway while lying down next to the car and realised the state the starter is in, first thing I spotted was a single small droplet of water dangling off it, no water underneath on the floor but it's in a dry garage so no idea where that droplet is coming from, condensation or a water leak somewhere?, I ruled out condensation as everything else on the car is dry.

The starter hasn't been a problem, but if there is water on it or on the wiring connectors, I assume this would cause a short when switching on the battery? See the pics I took.


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- '89 Porsche 944 Turbo (Guards Red)
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 Post subject: Re: 944 Smoke, battery light and terrible idling all of a su
PostPosted: Sun Mar 03, 2019 10:00 pm 
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You have a problem with the heater fan resistor overheating.hence the melted cover.

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 Post subject: Re: 944 Smoke, battery light and terrible idling all of a su
PostPosted: Sun Mar 03, 2019 10:54 pm 
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Thanks, that explains the melted plastic and smoke on my 2nd to last drive, and maybe also the puff of smoke on starting it up last time, the resistor was warm/hot within a minute or so. What would cause this? A bad ground or burned out wire? What would explain the single droplet of water on the starter I noticed today or the inability to idle suddenly as well with the battery light flickering? I am scared to touch it for fear of setting the engine bay alight and I need to somehow sort it to get it to someone to look at it. I plan to get it up on axle stands and get the starter motor out, clean the contacts and trace the wiring and check the grounds but I am learning as I go, so really lacking experience, any further advice would be greatly appreciated.

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- '89 Porsche 944 Turbo (Guards Red)


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 Post subject: Re: 944 Smoke, battery light and terrible idling all of a su
PostPosted: Sun Mar 03, 2019 11:18 pm 
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The heater fan is on low constantly with the ignition on, the resistor controls the speed, could be a faulty control switch.

The fact that the starter sounded to be running when you stopped does sound like a wiring short, but the ignition switch can also fail causing the motor to keep running. I'm not aware of any particular starter wiring issues on the early 944 (it's the same as the 924S) but the 2 litre 924 is prone to the starter wiring melting and shorting out where it runs under the exhaust manifold, not sure that is helpful though!

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1984 924 N/A Ruby Red Metallic
1986 924S Guards Red - sold
1988 924S Guards Red - sold
1984 924 N/A Black - sold
1980 924 N/A Le Mans#1 - sold
1980 924 N/A Le Mans#2 - sold
1977 924 N/A Martini - sold


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