ljhcav

My 1986 Porsche 911 Carrera with 49,000 miles starts easily and generally runs well. Recently, after running for about 10 minutes the engine suddenly stalls without warning or sputtering. It will not restart immediately but after waiting a few minutes it will restart. Drive along a few miles and stalls again. It's like a switch turns off the engine as it happens without any other symptoms. I have replaced the DME relay but no change. This spring, I replaced fuel filter, air filter, spark plugs, distributor cap and rotor. Fuel in tank was fresh with stabilizer.

I am leaning towards an electrical problem as there is no sputtering or loss of power before stalling. If it were the fuel pump, I would think there would be some sputter as it burns off remaining fuel in lines. Would a failing ignition coil act like that when it heats up and then resets when it cools? As a side note, when I changed the plugs they looked like good combustion but gap was almost twice the recommended setting. Also, cap and rotor were pitted and worn. Would these conditions cause a failing of the coil?

Anyone with some thoughts would be appreciated!

theiceman

keep a spare plug, after it sudenly stalls .. check for spark .. lilkely the coil or DME soldering needs reflowing.

ljhcav

Good tip for checking spark when car dies. Thanks.

ron mcatee

My vote is a bad DME Relay.

theiceman

gees you Carrera guys and your relays .. you guys drive around with a shoebox full of relays in case the first 12 or so dont work ?

ron mcatee

Ice, I don't have a shoebox full of them....only two spares. If you ever had one fail, you'd know why. The original one in my Carrera failed 11 years ago. Since then, it purrs like it should.

Cheers

donnieknoxville

You might also consider the temperature head sensor and/or the reference sensor and speed sensor that insert into the casing by the flywheel by the rear left wheel.

When my temperature sensor when bad, it did so intermittently and I spend $700 in labor chasing electrical gremlins. Could have replaced almost every sensor on the car for that.

When the temp head sensor goes bad, its like the car shuts off. Since mine was failing intermittently, I would just have these little blips in the tach as the engine quit and then resumed operation. As name implies, temperature is a factor in its operation.

Donnieknoxville

Amber Gramps

DO NOT BUY The URO brand relay.

theiceman

if you think its the Cylinder head temp sensor it will run fine cold then die as it warms up . jumper it out with a paper clip . if it starts right up and purs them ur CHT has died, it will run fimne jumpered till the car cools down again though. Usually you can tell if its the CHT as it will hunt realy badly and lurch ( rich ) . if its single wire CHT i would consider changing it anyway to a two wire one.

it is the top of the three white connectors on the upper left part of the engine as you are facing it.

Dryfly57

CHT- not sure what this is.
Can somebody explain.

theiceman

CHT= cylinder head temp sensor. As it senses the engine warm up it leans out the mixture. if it has failed ususally it treats it as cold all the time and causes the engine to run too rich.

ljhcav

Thanks everyone for the tips. Pelican Parts technician also suspected the head temp sensor or crank position sensor. I'll see if I can narrow it down.

tbanasiak

Change the cht sensor. Easy DIY and it'll solve your issue. It's what was causing mine and been trouble free since.

Ed Hughes

This can be done in car, but it's a little tight. Take a socket, and cut a long groove in it from the business end, as far as you can, to accomodate the wires. When you look at it, front LH side of the #3 head, you'll see what I mean.

Lorenfb

"if you think its the Cylinder head temp sensor it will run fine cold then die as it warms up . jumper it out with a paper clip"

Follow that advice before changing parts.