[DblTrbl]

I had planned on conditioning the 12V cam sensor with a diode, as the 58x cam sensor is not a direct replacement for the 24x gen3 ls engines.

I was under the impression that the 12V gm hall cam/crank sensors can be operated on either 12V or 5V and that their output was always 5V pulse. You can confirm this on a bench and save the extra conditioning parts.

[PSIG]

I was under the impression that the 12V gm hall cam/crank sensors can be operated on either 12V or 5V and that their output was always 5V pulse. You can confirm this on a bench and save the extra conditioning parts.

That was my impression also but is apparently not always true, with a lot of "but if" exceptions. Earlier in this thread (a very long thread due to these issues) you can see that the OP tested his sensors, and received a full Vbat (12V+) signal voltage. When the 24x 12V sensors were powered with 5V, they output 5V, but the operation was unreliable for him and others. 58x are of course fine on 5V. Our takeaway from this is to suggest use of the design voltage and simple one-diode condition if necessary for the results, as it would be far too confusing to continuously say "but if". YMMV

David

[DblTrbl]

in that case, conditioning is the way to go.

There has been much of confusion about these sensors. Glad you've done the homework.

[knikula]

first post here, I'm also trying 5.3 Chevy...

so, does Speedy know where TDC is located, since the 24X reluctor wheel is indexed to the crankshaft?

I see in the wiki the GM24x decoder is shown as "untested". Is that still the case?

Thanks in advance for any help you can share.

Regards,

Ken

[PSIG]

As I understand the current state of affairs; the 24x decoder currently uses both the crank and cam sensors, and is identical to using the Dual Wheel decoder as a 24/1. The primary difference being that 24x has the Trigger Angle hard-coded so it already knows where TDC #1 is. You have to manually set Trigger Angle value if using Dual Wheel decoder. No biggie. I understand multiple LS engines are running 24x, but without much feedback. Hopefully that's a good sign, but there is always the DW decoder fallback that is well-proven.

David

[knikula]

thanks for the quick response, I'll play a little with it in the garage. The decoder wheel on the crank is a pretty complicated series of wide and narrow teeth.

Regards,

Ken

[PSIG]

…The decoder wheel on the crank is a pretty complicated series of wide and narrow teeth.

Ken - yes it is, however the trick used is that all of the trailing teeth edges are 15° apart, which makes the leading edges (and how they vary the tooth length) irrelevant. This is how the 24x decoder senses, and also if using Dual Wheel decoder, that you must ensure that the correct edge of the teeth are being detected. Be aware that not only is the Trigger Edge setting important for the correct edge, but also includes which type of signal conditioning (if any) you are using, which could invert the signal.

David

[knikula]

David, I have to admit I was pretty reluctant to believe you on that constant 15 degree distance between falling edges. But , I took the Jimstim board , set it up for LS1, set rpm steady, and measured time between falling edges ... on a 24 tooth cycle.... It looks so obvious now.

I could not get Speeduino to see the 24x signal generated by the Jimstim, so I'll give the dual wheel mode a shot tomorrow.

This is pretty cool stuff to play with, I appreciate your help.

Regards,

Ken

[knikula]

Update:

As soon as I added the cam signal to the board as the secondary trigger, the GM 24X decoder started working.

Turns out I can spin the crank by hand about 125 rpm ( with the heads off).

From a scope trace, the first falling edge on the crank sensor after the cam sensor falling edge occurs about 13 degrees away.

The cam sensor falling edge occurs at exactly at compression stroke TDC for cylinder number one.

Pretty cool to see all the ignition and injection leds flashing during hand cranking...

I have a diode blocking the 12v from each of the cam and crank sensors.

Regards,

Ken

[PSIG]

Nice! Good to hear, and thanks for reporting as you go along.

David

[EDIT] While the first tooth should be at 15° from cam signal by assumptions and calculation , this is within reasonable error to proceed, especially at only 125 rpm by hand and including production tolerances and any wear. I'm curious to see how timing settles at running rpm, and any angle offsets required (or not).