Speed & Reference signals on 'scope

[Dan Martinic]

Hello!

The 1988 951 ran fine, then I parked it in December to do a thorough clutch job and also repair the rad.

Now, it won't start.

Breaking the old, I put in new (FAE) speed & ref sensors plus a (used) bracket. The bracket has the aluminum sleeve. I gapped using a new 2mm figure 8 washer.

Here is a screenshot of my analogue scope probing the DME harness pins 25&26 and pins 8&27 while cranking -- speed on top, ref on bottom:




The signals are above factory minimums.. however, the ref signal only reads as top half of the sine wave. Is this normal?

An LED attached to the coil does not flash nor does a noid light on an injector.

[kdjones2000]

Does the tach bounce while cranking?

As I mentioned in your other post, try bypassing the KLR and see if the car will start. If the KLR is bad it can prevent your car from running.

[Dan Martinic]

No, there is no tach bounce. I also tried to bypass the KLR, among many other things. UPDATE: I have discovered similar symptoms from an older thread on a different forum; the solution was to replace the FAE sensors with Bosch.

One of my FAE sensors has continuity between its pin #1 (25--an outer signal pin) and its metal shield. Apparently, this could cause the DME to ground the signal.

Have ordered new Bosch sensors

[soxnail]

Yup you should get full wave AC signal...
Sox
Sorry ignore this pic its for the knock sensor

[DannoXYZ]

Here's minimum voltages for speed/ref signals:



Ref signal should also start on a positive slope.

[pmar911]

Not sure how you gapped the sensors, but Bosch / factory gap should be be 0.8mm.

[soxnail]

The old use a washer glued to the end of the (old) sensor trick ?
Sox

[C2951]

Here are the 2 sensors from my '88 951 with the waveforms captured while the engine was idling: