944 Geek Posted 12December, 2016 Report Share Posted 12December, 2016 G'day all I have a slight miss occasionally and today I checked my coil. The primary resistance was 1.7 Ohms and it is supposed to be 0.4-0.6.1.7 is pretty normal for an off the shelf coil but clearly Porsche does something else. Does anyone know where (apart from Porsche) to get a new coil in Aus? Link to comment Share on other sites More sharing options...
Redracn Posted 12December, 2016 Report Share Posted 12December, 2016 Try connecting you meters test leads together and rembering the reading and then subtract this from the coils reading. If the calculated reading is closer to speck you probably do not have a coil primary issue. Coil secondary's (high voltage side) fail far more often due to internal insulation breakdown. Link to comment Share on other sites More sharing options...
944 Geek Posted 12December, 2016 Author Report Share Posted 12December, 2016 Try connecting you meters test leads together and rembering the reading and then subtract this from the coils reading. If the calculated reading is closer to speck you probably do not have a coil primary issue. Coil secondary's (high voltage side) fail far more often due to internal insulation breakdown. Quite correct they read 1.2. I'll be damned. I have been working on car electrics for quite a few years and assumed that the meter's internal resistance would be filtered before the display. Thanks for the tip! Link to comment Share on other sites More sharing options...
Redracn Posted 12December, 2016 Report Share Posted 12December, 2016 Quite correct they read 1.2. I'll be damned. I have been working on car electrics for quite a few years and assumed that the meter's internal resistance would be filtered before the display. Thanks for the tip!A lot of meters come with a null or delta button that can be used to zero out the test lead resistance and any meter errors which is a must at these low resistance values. Accurate meters for low resistance usually employ a 4wire technique. Link to comment Share on other sites More sharing options...
Airhead Posted 12December, 2016 Report Share Posted 12December, 2016 . Coil secondary's (high voltage side) fail far more often due to internal insulation breakdown. What happens then? Link to comment Share on other sites More sharing options...
tazzieman Posted 12December, 2016 Report Share Posted 12December, 2016 What happens then?Little Miss becomes Big Miss I had a little miss in my 944 that ended up being a split vac pipe under the manifold. After 30 years stuff starts to deteriorate in that festy environment. Also had to redjust the MAF tracking for a similar stutter another time. Wonder what 944Geek's issue will be? Link to comment Share on other sites More sharing options...
Pauly Posted 12December, 2016 Report Share Posted 12December, 2016 If you need a new coil, Get a MSD Blaster 2. I run one in mine for many years now. Link to comment Share on other sites More sharing options...
Redracn Posted 12December, 2016 Report Share Posted 12December, 2016 What happens then?Not if but when the internal insulation of the coil breaks down you will get a short between the windings which will result in a reduction af the avaliable voltage to make get the spark to jump the plug gap. The shorted windings will also absorbs a lot of the stored energy. Bottom line is a weak spark. Most coil related issues are first noticed at full throttle and peak torque rpm when the cylinder pressure is the highest. As a general rule if your spark can not jump >20mm you have a problem. Also lots of other reasons for a miss. Fuel, spark and mechanical. Link to comment Share on other sites More sharing options...
Airhead Posted 13December, 2016 Report Share Posted 13December, 2016 Not if but when the internal insulation of the coil breaks down you will get a short between the windings which will result in a reduction af the avaliable voltage to make get the spark to jump the plug gap. The shorted windings will also absorbs a lot of the stored energy. Bottom line is a weak spark. Most coil related issues are first noticed at full throttle and peak torque rpm when the cylinder pressure is the highest. As a general rule if your spark can not jump >20mm you have a problem. Also lots of other reasons for a miss. Fuel, spark and mechanical.Having an issue with the 944 track car. Get 2 laps in and it starts to miss then cuts out and really struggles to run with any load. Car will still start and idle and can drive it onto trailer. Better try a coil change me thinks. Link to comment Share on other sites More sharing options...
Redracn Posted 13December, 2016 Report Share Posted 13December, 2016 Plugs, leads, cap, button, coil are all consumable items. Link to comment Share on other sites More sharing options...
Airhead Posted 13December, 2016 Report Share Posted 13December, 2016 Plugs, leads, cap, button, coil are all consumable items. So are tyres. Plugs, leads, cap, button - all have been replaced. coil was supposedly new. Link to comment Share on other sites More sharing options...
Redracn Posted 13December, 2016 Report Share Posted 13December, 2016 Could be the dreaded bathtub curve strikes again or perhaps Murphy is just messing with you. Link to comment Share on other sites More sharing options...
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