Daxmanian

@MarkD: I guess you were right a year ago

I really hope this finally solves this issue, not much left to change.
Maybe I'll try to change it myself. I'll have a look at it and then decide what I shall do.
The screws haven't been loosened in 21 years so I sure hope they don't snap. That's one of the reasons I'm not sure if I should try this myself.

MarkD

We've never had a problem with these bolts
Relatively risk free replacement

Best of luck

Daxmanian

@vcnvbn : This item has NOT been changed. In post #39 I stated that the flywheel sensor was not changed yet.

Daxmanian

Finally tried to remove sensor and.......success!!








Problem now is that sensor is really stuck in its holder.
Does anybody know the Porsche nr for ordering this holder? I don't find it in PET.

edit : never mind, found it 964-101-187-01

BesideTheBox

Since I have the rear cross member and heat ducts out for replacing the rear shocks, I decided to look at my speed reference sensor (slippery slope as you all know).
The allen head bolt holding the sensor into the holder came out easily.
Then I was able to poke a flat blade screwdriver between the sensor and the holder to remove the sensor.
My sensor is made out of plastic, whereas yours appears metal.
I doubt that my gap was set correctly because there are grooves etched into the sensor magnet and plastic housing.
Now to set the gap and see if it makes any difference.




993 speed reference sensor with grooves

Daxmanian

I think you have the newer type of sensor which is made of plastic.
Better since it cannot bind with the holder due to corrosion.

I will try to replace mine in two weeks with the newer type. Off on holiday now

jstyer

Hell ya man. Here's hoping this solves it!

Daxmanian

Back from holiday and made some time to change the sensor, even made some time to fabricate an adapter lead between the old and new connector so I didn't have to cut off the original connector from the car.

Swapping the sensor wasn't that difficult just a bit difficult to reach.
After changing the sensor started the car and after about 40 seconds............rough running

I made sure the gap between sensor and flywheel was correct so I guess the sensor wasn't the problem

So I know what the car does (change injection timing) but I don't know why.
I even tried disconnecting the oxygen sensor and start the car but that does the same, rough running after about 30 seconds for a small time and then running normal again.
I don't think there is a vacuum leak because the oxygen sensor would have sensed this and it behaves the same without.

Anyone know what influences injection timing? MAF sensor showes correct values, engine and air temp have normal values. Oxygen sensor was taken out of the loop so that couldn't be it.

Anymore suggestions?

geolab

the problem communicating with the problem, is somtimes the different testers used. Because of this, my questions should sound silly, and we will answer your questions.
Which air temperatures are normal ?
Just to note, the DME electronic ignition map is subdivided up into 8 engine
speeds and 4 load ranges. Are your knock sensors loose?
A little history on the car?

Daxmanian

Hi Geolab,

I mean the temp for the intake air which is in one of the previous pics is around 26°C which is about right at that time.

What I meant to say is that when the problem occurs I see no jumps or spikes in the temps measured. None of the values I can measure shows funny stuff when the rough running occurs, only the injection timing changes.
Very weird I think.

Can it harm the engine if I unplug the knock sensors?

geolab

zero harm

but both knock sensors through the hall sender in distributor, dictate the ignition spark in cylinder 1

geolab

I slept last night on the idea, and was thinking (happens rarely)

Something is puzzling me with your pictures.

The DME 'adaptive' retard function for ignition timing, has a learning function.
This learning function interprets 3 (THREE) givens from knock sensors, into 3 (THREE) ignition Angles from HALL SENSOR.
the Angles are 3° , 6° and 9° for any designated cylinder(s)

In your pictures, we see 3.9° , 9.9° and 4°

Who , where and when did you rebuild your dual distributor ?

Daxmanian

My dual distributor was rebuild in may 2014 by an independant Porsche workshop, someone I know for a long time.

The 9.9° in the second pic is at 2000rpm, probably why it is different in the other two pics because they are at idle.

I just tried to disconnect the two knock sensors to see what happens.
First start engine behaved normal, looking good. Let it cool off for an hour and tried again because the rough running is most of the time and not always.
Second start rough running after 2 mins or so for about 20 sec with knock sensors disconnected.
Very discouraging

Daxmanian

Made short movie again with the rough running with better audio this time.
Video starts with rough running, at 30s rough running ends with slight jump in rpm's.
Opinions?

geolab

what I mean is first and third picture has same retard angle
one with rough running, one running normal