944 won't start

marpos · 08-29-2002, 09:18 AM

Hi forum members;
I've got a 87 944 that will not start. I have 12 volts going to the coil but no spark comming from the coil. The car was running fine a couple of days ago. Starting has been a little strange, sometimes the starter turns fast and sometimes very slow then it starts to turn faster but always kicked over. Mechanic is dumbfounded. Clutch was recently replaced and they had problem starting the car afterwards, ground problem they think. Anyone have any suggestions.

Britwrench · 08-29-2002, 09:24 AM

If they just did the clutch, I would suspect the reference and speed sensors, probably the gap is set wrong. Go back to the shop and ask them what they are going to do about it.

There is also a modified sensor bracket and sleeve to prevent the turning fast/slow. (If you mean that is sounds like the ignition is too far advanced and the cranking speed slows - the engine will still start)
Check your VIN number with the Porsche technical bulletin

todwic · todwic's Garage

In case you don't know, and for those of you keeping score at home, Heres how the ign. system works (not so much timing, but just how spark gets from here to there.

It's important to understand that there are two ignition systems on your car, aptly named Primary, and Secondary.

Primary is your Batt/starter/alt. They provide at least 12v to whoever needs it. Your coil has two sides. Those two wires are not Hot and Ground, but Hot and Timed Hot. Hot is a happy member of the Primary ignition circuit. those 12v keep the coil windings charged, but don't supply any voltage to the plugs.

The other wire is Timed Hot, and it is controlled by the DME (who lets sensors and position guys boss it around and tell it what to do, and when to do it.) The DME tells the Timed Hot guy to kick Mr. Coilwindings in the butt, and that activates your Secondary system . That's where 12v is turned into thousands of volts, all through the magic of voodoo. That's sent to your coil wire to the dist. where it is made to Jump the gap (ever wonder why there's a space? here's why) and that creates spark. now those volts are angry at having to do tricks, and when it gets to the spark plug, spark begets spark, and it has to jump the gap at the plug igniting your Lambda mixture, blase blase you know the rest.

As you may have guessed, Timed Hot is a measured pulse and that is gaugable with a multi-meter that has an RPM mode. (and a myriad of other methods, I'm sure)

So, if you have Hot (primary) and Timed Hot (secondary), your problem HAS to be in your coil/coil wire/dist. cap/rotor/sparkplugs

Thank you, and goodnight

marpos · 08-29-2002, 11:48 PM

Thanks for the explanation. I measure 12v on both terminals of the coil with the ignition on. If I'm getting that then the problem has to be the timmed hot which comes from the electronic points/ignition module. Is this the DME? (what does that stand for)? My mechanic thinks the problem is at the starter and flywheel. I think it's something simple like an ignition module or ground wire.

Britwrench · 08-30-2002, 11:33 AM

Todwic;

Nice explanation, however the quickest way is to check for spark and fuel pressure; if none of both the DME is not getting a signal.

You will always get 12v to the coil with the ignition on; the DME is the ground and sets the time for the ignition to fire.

drew1 · 08-30-2002, 04:41 PM

Marpos,

Like Britwrench says check the sensors, make sure they are plugged in good & you might want to swap the sensor plugs & try again. Also make sure the big brown ground wire is hooked to the motor.

drew1

todwic · todwic's Garage

Crank you engine for 10 sec. Immediately pull a spark plug. Is there gas on electrode? If you shine a flashlight into your sparkplug port, is it wet inside? Gettin a buzz off of the fuel smell? Then that cylinder is getting fuel, and odds are the rest are too.
No? ok then, what I'm about to suggest is very dangerous, so dont' do it*. Take off the cover to your airfilter. take out filter, make sure area is very clean. tie a washcloth onto a bar or a ratchet or something. Drench the rag in gasoline. place at the intake hole right befor your AFM. Try to start your car. Hear that hissing noise? you forgot to put your sparkplug back in, mr. Do that. repeat process.

The rag holds the gas untill the vacuum sucks it out. you tied it to something so that you don't suck the rag into the intake valves, which is bad. There is a great risk of fire, so have a extinguisher handy.

Did your car start?
No?:Electrical/timming problem

Yes?:Fuel problems

Norm Faustino · Norm Faustino's Garage

I believe DME stands for Digital Motor Electronics!