Retrofit 24x reluctor to early V8

**lionelhutz** · 02-25-2020

Proof that #1 is beside the alignment hole.
#1. The pulse pattern is known.
#2. The Holden? document is marked from 0-360 degrees, which would be one crankshaft rotation from #1TDC to #1TDC.
#3. It is well known that the 1X cam signal switches between high and low each time the #1 cylinder passes TDC and two different scope traces were posted that shows the cam and crank signals with the cam signal switch lining up with the tooth edge that everyone calls #1 TDC.
#4. One of the scope traces also shows the #1 ignition happening before the #1 tooth edge gets to the sensor which helps confirm the alignment.

It doesn't matter at all what the PCM does internally with the signals. All that matters is that the sensor sends the #1 TDC signal to the PCM at the right time, using the well established 24x pattern.

People have had their engine run with the wheel both backwards and misaligned. You are getting the signal from the sensor. If you have the crank signal but no ignition then it must be something else.

Finally, you are posting rather blunt to ignorant comments about people not reading what you are asking and having to prove the already known to you so what do you expect in return?

**Jim Blackwood** · 02-25-2020

Fair enough, I think we need to put this on hold and move on. I will revisit it once I have a chance to do a physical inspection, probably in a few weeks. I'd encourage anyone else who has the chance to also do so. As I said, I'm just as willing to see the results go either way and would in fact favor your viewpoint as it means less work for me. I just want it resolved. I know you think... well, let's not go there right now.

Anyway, the next step is to set the cam sensor pulse to match the CKP sensor. It will be a wasted effort if I have to change the position of the tone ring but I suppose it's a chance I will have to take. After that I will look at the coil logic outputs. I agree, those should be there regardless of the timing and regardless of the cam sensor for that matter. (It and the coils are presently unplugged.) This should point me to the actual problem.

How about this, if I can get it to run and the timing light either does or does not match the advance map we should be able to claim we've proven the case one way or the other. Sound reasonable? (This engine DOES have timing marks.)

Jim

**dave w** · 02-25-2020

The measurements I have for the L31 Cam Position Sensor Flag is 175 degrees "Flag in Sensor" and 185 degrees "Flag out of Sensor".

My daily driver has a L31 engine with an aftermarket 24x Coil-on-Plug Conversion, using the original L31 distributor Cam Position Sensor.

Sensors will trigger on Leading Edge / Trailing Edge of the trigger wheel or sensor flag. The center line of the sensor is the critical alignment point for the trigger wheel or sensor flag.

GEN III computers have a CASE Learn Procedure for "Timing", mostly for production tolerance reasons. GEN III computers will "Assume" near perfect alignment of the CKP / CMP sensors, because that's the methodology of mass production.

It can be a challenging question: is success re-engineering the factory mass production methodology, or reverse engineering the factory mass production methodology. Either method will yield success, with measurements, alignments, and parts fabrication as good as the factory mass production tolerances.

dave w

**Jim Blackwood** · 02-25-2020

In this case the CMP sensor is mounted to a specially built oil pump drive unit which includes the flag for the sensor. It is essentially a cut down distributor which due to space constraints is in a much smaller package. Since I did not have those measurements it is 180/180 but hopefully that will be close enough. Once I get out to the shop I will backprobe the signal lead at the ECM, run a trace, and then rotate the body of the sensor to get the right alignment, or as close as I can get it given the 5 degree difference. I could probably trim the flag to match your specs but it would require some work with a die grinder. I'll see what the trace looks like first. Given considerations like the sensor lobe pattern, target distance, and overlap, that 180 degree mechanical configuration could certainly result in either a 175 or 185 degree pulse. I'll just have to measure it.

Sorry, no photo available at the moment.

Jim

**lionelhutz** · 02-25-2020

A true 1X cam signal is 180*. Look at the posted scope probes and it's clear the cam signal transitions at each full single turn of the crank.

The distributor Dave used was not from a 24X application, but apparently the PCM can cope with the variance of that sensor.

**lionelhutz** · 02-25-2020

Don't align the cam sensor to the crank wheel. Align it to TDC. The signal should transition low to high at TDC #6 and transition high to low at TDC #1. With a meter you should be very able to set it up and test it for accuracy.

On a similar note, the engine will start without the cam sensor, just might need more cranking or a couple of tries to get it going.