Ignition timing question

[djnolan]

Can ignition timing on an 85.5 N/A be out of adjustment and cause a knock/stumble at idle?

I am thinking that the reference sensors could be out of adjustment. The reference sensors and bracket were replaced when the flex damper was replaced.

Could this affect ignition timing? Can timing be checked with a timing light?

(or is it my old sparkplugs causing the miss/knock? see other thread)

[dgcantrell]

Yes, if the distance between the tip of the sensor and the reference tabs on the flywheel is not right (too close it can hit, too far and it won't read properly) it may cause those issues. These two links will help out there..

944online.com - The place for your 944 Porsche Stuff
944online.com - The place for your 944 Porsche Stuff

The timing is controlled entirely by the DME and there are no other markers on the flywheel other than TDC so you won't be able to really tell much about it with a timing light.

[sausagehacker]

Ignition timing is an angle, the (vertical) distance from your reference sensor to the set screw on the flywheel can cause running trouble but will not affect ignition timing. Unless you recently removed the flywheel and put it back on in the wrong orientation.

[djnolan]

So there is no possibility of horizontal misalignment of the sensors or the bracket that could affect timing?

[sausagehacker]

If you're asking if the spark could be advanced for retarded based on that sensor's reading, no. Either the DME can make sense of the pulse, or it doesn't. But it could miss if it gets a weak/fuzzy/inconsistent signal.

[dgcantrell]

Mike,

That's what I was referring to. If the offset distance is not right, the signal that the sensor gets could be weak. The second link I posted shows how to set it properly.

[Bradical]

Does it occur during start-up only or during idle? The late model cars require an aluminum sleave for the flywheel position sensor because EMF interference from the 85.5+ starter can cause pre-ignition and knock. If you have an early sensor bracket on a later car this problem will occur. The later bracket will have a larger diameter mounting hole for the reference sensor (the one closest to the front bumper) and requires the aluminum sleeve.

http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=944-101-320-00-OEM&SuperCat=Y&SVSVSI=&catalog_description=Sender%20Sleeve%2C%20%39%34%34 %2FS%2FS%32

[djnolan]

Originally Posted by Bradical

Does it occur during start-up only or during idle? The late model cars require an aluminum sleave for the flywheel position sensor because EMF interference from the 85.5+ starter can cause pre-ignition and knock. If you have an early sensor bracket on a later car this problem will occur. The later bracket will have a larger diameter mounting hole for the reference sensor (the one closest to the front bumper) and requires the aluminum sleeve.

It is an 85/2 automatic car. I only notice the [knock/stumble/misfire] during idle and not startup. The bracket shown was the broken bracket removed from the car. The replacement bracket was significantly different, but I cant recall how, and don"t have a picture of it.

Could it have been an early bracket? Is there a way to tell without dropping the bell housing? Since it mainly happens at idle, does it matter?

[Bradical]

Its easy to check- remove the front (reference) sensor and check to see if there is an aluminum sleeve there. You dont have to remove the bellhousing to take the bracket off- its the other way around. If it doesnt happen at start-up I cant imagine thats the issue at all. I agree with everyone else- adjust the bracket and see if anything changes. When it's idling, did you try unplugging any of the injectors? If the idle doesnt slow when you unplug one, its not working.

[944 Ecology]

Vacuum leak.

Do a smoke test.