86' Carrera no start question

[Cevan]

I’ve got a no start issue with my ‘86 coupe. It cranks over but no start.

Here’s what I’ve checked so far and I’m thinking my speed sensor is bad. I don't have an oscilloscope which is what the factory manual says to use to test them.

All fuses good.
Coil measured good.
No spark
No voltage at injector using noid light.
I have a Focus9 DME and can hear the fuel pump prime. I swapped it out with another good DME.
Checked pins 1, 18, 35 at the ECU for 12 volts
Checked pins 5, 16, 17 for ground
The reference sensor measured 1000 ohms at pins 1 and 2.
Speed sensor measured zero at pins 1 and 2.

No evidence they’ve ever been replaced. The cables have the BG and DG yellow bands on them.

Before I get a couple sensors, anything else I should check?

Thanks.

[wazzz]

From what you describe, if you double checked your measurements and still find a short for speed sensor, this is consistent with your no spark / no fuel issue. You can certainly get a couple of sensors.

[Matt at Pelican Parts]

I tried to do some searching and it seems this topic has been brought up a bit in the past. I would recommend checking some of the older threads like this one here which gives a pretty good list of systems and wires to check to help diagnose the problem:
https://forums.pelicanparts.com/porsche-911-technical-forum/1118606-good-crank-no-spark-anything-left-but-ecm.html

[Cevan]

Quick follow up. Replaced the two sensors (reference and speed) and problem is solved.

I found removing the rear shock gave me more room to work. Sensors were stuck in the bracket which was not difficult to remove. Used the old speed sensor with a .8mm spacer super glued on to set the gap.

[911obgyn]

I have a set in my 85 not installed yet, i have been meaning to do it.
I better get to it!!
I think mine are original

[GH85Carrera]

Originally Posted by 911obgyn

I have a set in my 85 not installed yet, i have been meaning to do it.
I better get to it!!
I think mine are original

Those need to be replaced as a matter of course. Like driving on 20 year old tires. Past time to replace.

[wazzz]

Originally Posted by GH85Carrera

Those need to be replaced as a matter of course. Like driving on 20 year old tires. Past time to replace.

That's what I did with mine when they were over 30, but still wonder if I should have done so. They were still good and measured ok. I hope the new parts will last another 30 years.

Wonder what makes these sensors age. Repeated cold-hot cycles?