Rev limit 3.2L - adjusting sensor???
 

Been chasing a "rev limit" of 5400 on my 3.2L 87 911.
I've read where people are finding that the sensor v the flywheel are not gapped correctly and this is leading to the limit.
What is the best way (short of pulling the engine) to adjust the distance of the crankshaft (reference mark) sensor against the flywheel to .40mm?
(Both sensors have been replaced within the past 2 years)

I've been told the way the system works is the ref sensor is used one time at startup to establish Top Dead Center and from then on the DME keeps track of when to fire the plugs and RPM by counting teeth on the flywheel. If the rpm was low due to a slipping count of flywheel teeth the spark timing would be all over the place and I'd think you would see other problems. The RPM limit is set in the firmware code for the DME.

As you may know, both the speed and the reference sensors are identical. You may want to just try interchanging them.

It's the speed sensor that has to be gauged properly. If the sensor bracket was originally removed to take the sensors off, a 08mm washer, glued to the end of the sensor, is used to set the correct gap.

The air gap is only 0.8mm between it and the flywheel gear ring. When it is correctly set, this setting automatically provides the correct amount of distance for the reference sensor to a small allen head screw, also situated on the flywheel

The issue with Porsche's design, is that the bracket that they go into, should have been made so that, like other vehicles, the sensor could only go into a preset distance. They chose to let each one be set manually when installing them.

A #5 allen head bolt holds them on to the bracket. The setting is made by moving the bracket. It has two 10 bolts holding it to the bell housing. One is fixed and the other one is pear shaped so as to be able to move it in or out.

I would first, only pull the speed sensor out; not take the bracket off. The easiest way to do it would be to have the left wheel off with the car on a hoist. They are located straight in and up from the headers pipe's for the CAT. You can clearly see them with a flashlight.

Here's an excellent link that was given to me that will provide you with all the info and pictures that you will need to know.

http://forums.pelicanparts.com/porsche-911-technical-forum/552276-no-spark-problem-finally-resolved.html

*I used the Bosch BMW sensors, as they are exactly the same sensor, with the exception of their wiring being a couple inches longer. They cost $60.00 vs $125.00 for a Porsche sensor.

BMW - Bosch # 0261210002

Before going down that path try this: with the engine off have an assistant push the gas pedal to the floor while you manually check in the engine compartment if the throttle can be further opened.

- What happens at 5400 RPM? (100% hard cut?)
- Does the needle on the tach drop?
- Is it always at the same exact RPM when the 'limit' happens? (And I mean EXACT...)
- Is there any variation if you are at part throttle or full throttle?
- Does it run hard up to 5400 or does it start to "sneak up on it"?
- What speed are you going in 2nd when it hits 5400? (Is the tach accurate?) Does it run up to a different speed when you are in different gears?
There are a bunch of clues in the details of this failure.

Beyond that: Test, Test, Test.
Right up front I would hook up a mechanical fuel gauge to a long hose (just run the hose out the gap of the engine lid and into the driver's window) so you can hold the gauge while you are driving and see what the fuel pressure does. I would hook up an inductive timing light (just tape it to the back window so you can see it in the rear view mirror) so you can see what the spark does. Don't guess or infer what is happening. SEE what is happening.