944 Turbo Headache odd...No spark

[Frenchy]

Change the distributor cap, you are getting too deep !

 

[Sweeney2255]

Already have done. Had a couple of days away from it, shall relook at the weekend ??

 

[Sweeney2255]

Ok here is an update! The fault, is the grub screw on flywheel for signal for reference sensor is missing, looks like broken off flat! Gulp

 

[PhilKent]

Hi Sweeney,

A few obvious suggestions that I'm sure you've already covered, but depending on how long the car has not run for and what was possibly done in the meantime, have you;
Checked the timing on the camshaft markers to make sure all is well and not off by a tooth or two?
Checked condition of HT leads (I had a faulty one with no obvious signs, only noticed as car ran better after replacing!)
Rotor and cap condition
Continuity from DME plug to engine harness (I replaced the ignition wiring with a new one from LR due to possible issues)
Checked all engine ground points for condition and possibly re-fix with vaseline/conductive grease to ensure a good contact.

If you want to pm me an email I can send further details wrt wiring pins to be checked etc.
I went through a no spark issue last year, but I'm running after market ECU as well so possibly different causes to your own...

 

[Sweeney2255]

Hi yes I have found the issue, the grub screw on the flywheel has dissapeared.

 

[Waylander]

the screw is available from Porsche, no idea how it fell out with out mashing the reference sensors, in fact the gap is so small if the engine was running when it fell out it would do some serious damage,

has it had a clutch and flywheel change, and the screw not refitted?

the part is 477 105 276 @ ££5.21 and PET lists 3 for the fly wheel, cant imagine why 3 for a 4 pot engine



from pictures and posts on renlist there seems to be different sizes, but PET only lists one, what ever you do make sure its in there with Loctite and lots of it


http://www.arnnworx.com/sensors.htm

 

[Frenchy]

You should be able to fit one through the sensor opening using some ingenuity and lots of Loctite on the threads, I would tape the grub screw on to an Allen to stop it coming adrift when fittng, once fitted the tape should come away with the key leaving the screw in place, use some masking tape, if it falls into the bellhousing it should be fine.

 

[944Scott]

I'm pretty sue you could use any grub screw as long as its long enough and ferrous (Loctite it in place) I have a non genuine grub screw in my aftermarket flywheel.

Has it made contact with the sensor?

 

[Sweeney2255]

Hi we put in the new grub screw, set the gap which we believe is correct, but still no spark. Just a ghost spark when you switch on and of the ignition??????? Flippin thing!

 

[Waylander]

0.8 mm gap

and is the tachometer bouncing as you crank it

 

[944Turbo]

from the manauls
0.8m is between speed sensor and ring gear
DG on cable is speed sensor
BG reference sensor
D (speed) & B (Ref) should be marked on the housing bracket

Flywheel stud (for ref sensor) screw in with loctite 270 and adjust to 5+- 0.1mm

I can't find / remember if you can adjust reference sensor depth, or if it is fixed, did the ref sensor hit the stud?

Tony

 

[Sweeney2255]

So the ref sensor to flywheel stud top is not 0.8mm? its o.5mm?

Not sure what happened to the old one but was flush ??

 

[Waylander]

All here
http://www.arnnworx.com/sensors.htm

https://porschedocs.s3.eu-west-2.amazonaws.com/Porsche%20944%20Manuals/944%20Workshop%20Manuals/Vol1x-engine.pdf section 28-14

 

[944Turbo]

So the ref sensor to flywheel stud top is not 0.8mm? its o.5mm?

Not sure what happened to the old one but was flush ??

I read that as the protrusion from the flywheel rather than clearance to the sensor - the 5mm figure was in the engine section (flywheel assembly) rather than the ignition section
Tony

 

[Waylander]

Flywheel stud (for ref sensor) screw in with loctite 270 and adjust to 5+- 0.1mm

that means 5mm + - 0.1 does it not, or am I reading that wrong

 

[944Turbo]

Flywheel stud (for ref sensor) screw in with loctite 270 and adjust to 5+- 0.1mm

that means 5mm + - 0.1 does it not, or am I reading that wrong

it is in the section about installing it in the flywheel so screw it in until 4.9mm to 5.1mm is exposed. But do you then space the sensor 8mm from the flywheel giving 3mm clearance or 8mm from the the 5mm protruding grub screw? or is the ref sensor not adjustable anyway and setting the speed sensor 8mm sets the ref sensor?
Tony

 

[Waylander]

As far as I can work out the gap between the the sensor and the stud must be 0.8mm, It is after all a Hall Effect Sensor so it needs something to pass really close to trigger, if it was a magnet that was passing, the gap could be a lot bigger

 

[peanut]

Crank speed and hall effect sensors operate differently .

The hall effect sensor registers when a magnetic field passes the sensor , it then emits a electrical signal in the form of voltage every time a magnetic field passes the sensor .

The hall effect ( HE) sensor on the back of the distributor housing senses the position of the cam of each cylinder relative to TDC (half crank speed ) and sends a signal to the ECU which on the Motronic 2.5 tells the ECU which injector to pulse sequentially

The crank TDC sensor on the bell housing is essentially a magnet which creates a magnetic field . When the flywheel reference pin passes the sensor it varies the magnetic field sending the position of TDC to the ECU .The gap from reference pin to sensor is critical.

Later cars have a combined speed sensor and TDC position sensor and use a toothed ring attached to the flywheel.

 

[944Turbo]

Crank speed and hall effect sensors operate differently .

The hall effect sensor registers when a magnetic field passes the sensor , it then emits a electrical signal in the form of voltage every time a magnetic field passes the sensor .

The hall effect ( HE) sensor on the back of the distributor housing senses the position of the cam of each cylinder relative to TDC (half crank speed ) and sends a signal to the ECU which on the Motronic 2.5 tells the ECU which injector to pulse sequentially

The crank TDC sensor on the bell housing is essentially a magnet which creates a magnetic field . When the flywheel reference pin passes the sensor it varies the magnetic field sending the position of TDC to the ECU .The gap from reference pin to sensor is critical.

Later cars have a combined speed sensor and TDC position sensor and use a toothed ring attached to the flywheel.

I think the HE on the back of the distributor is s2 only
Tony

 

[vitesse]

When I replaced the 2 sensors on my 1987 924S,I followed Clarkes garage instructions & glued a 0.8mm clean flat washer to the cleaned up sensor to be replaced after removal ,the TDC one, inserted this initially hard against the timing stud adjusting the housing fasteners.
Then removed it & replaced with the new replacement.The speed sensor then fits inside it's shielding aluminium can which fits into the housing & doesn't then need separate adjustment.