Retrofit 24x reluctor to early V8

[Jim Blackwood]

As much as I appreciate the suggestions, you are avoiding the question.

Until this sensor/tone ring alignment question is answered it's nothing but recycling old web info that isn't on point. Simply assuming that the sensor lines up with the zero reference hole at TDC just isn't enough. Maybe it does, but maybe it doesn't. So far I have not heard from anyone who can actually confirm that it does. Based on my own testing results I'm inclined to think that maybe it does not, but again that is not definitive because failure to achieve an expected result does not disprove the existence of a relationship.

So, we are still at square one. Just so you know, I did align the sensor with the reference hole and there was no spark. This could be from other causes but the first step is to eliminate the obvious. Make sure the sensor is aligned properly so the ECM gets the right signal. At this point it is still not possible to do that.

Perchance in the next few weeks I can visit my machinist and he might have a LS block and crank and be willing to let me visually confirm the relationship. A few moments with a sharpie are all that are required. However, that again delays the operation. I was hoping someone here might be able to help.

Jim

[kur4o]

Make a drawing what exact measurements you need and I will try to get them in a day or two.

[kur4o]

I did align the sensor with the reference hole and there was no spark.

If the pcm gets the signal from the crank sensor, you will get spark but it will be at the wrong time. What is the distance from top of the sensor to the wheel. It must be really close. I have seen scored sensors by the wheel. Monitoring the pcm for rpm signal will show if it gets the signal. Troubleshooting the problem with timing light will not work. Get some logging device and monitor the PCM. If it sees rpm than you are good, if not the problem is within the sensor position.

[Jim Blackwood]

Good suggestions but one step at a time is best I think. I will measure the sensor gap tomorrow. It's pretty close but I can close it up further if needed.

I agree with your thought that out of phase timing should not result in no spark. But as you say, a lack of a proper sensor signal would. I should be able to put a scope on the sensor and at least get a pulse train while cranking. Provided that looks usable I can move on to the low level coil output trigger signals. Those should be there as well.

As for a drawing as you asked, Here is how I propose to check the tone wheel and sensor alignment. It requires a block and crank with the pan off:

1) remove the CKS from the side of the block
2) rotate the crank to the zero timing mark, TDC
3) using a sharpie, mark the edge of the tone wheel by going in through the sensor hole in the block. This may require a shot of carb cleaner and an air blast first.
4) rotate the crank so that the timing hole is visible (pan removed)
5) locate the sharpie mark and note it's location relative to the timing mark. The accuracy with which the mark is made will affect this result.

That's it. A simple matter if a block is available, and it puts this discussion to bed. Once we know that is right I can get serious about the rest of the troubleshooting process. But for the sake of anyone working up a crank trigger for the 0411 controller this needs to be a known quantity. I actually hope it turns out to be zero as that means I have it right. But I really do have to know for sure.

Jim

[lionelhutz]

I'll suggest it again. Try the forward/backwards alignment of the sensor. The 24X sensor and wheel is a dual track system. The sensor reads each half of the wheel as a separate track. Hence, it must be aligned forwards/backwards correctly. Sensor rotation and direction are very important too.

The documents and the posted scope waveform provide more than enough info to get the sensor aligned with the wheel at TDC correctly.

[lionelhutz]

Post a picture if you can too.

[Jim Blackwood]

If it worked I'll have a shot of the damper below with a mirror showing the back side. If not I'll just have to try again.

Pretty sure the pickup is adequately located on-center. I'll measure the gap in a bit. I believe the pickup to be oriented the same way it is in the block, that is to say with the opening and pins facing the front of the car, despite it being on the other side. And perhaps with this visual it will make more sense what I am getting at here. Unless you have access to GM engineering drawings there is nothing in any chart or graph that is going to show the position of that pickup relative to the engine centerline, the crankshaft keyway, or the timing mark on the damper and even if there were it would be useless without the offset from the tone wheel timing hole and the pickup. But if anyone has access to those drawings by all means break 'em out and we'll get the inside scoop. Yeah, I didn't think so.

Well, let's see if this works. I've got email and such to catch up on and then I can get out to the shop.

I do appreciate the efforts to help, don't get me wrong about that. If any thing I post comes off harsh it's only because I've been around this kinda stuff for decades now and it's aggravating when it requires this kind of a roll-in-the-dirt brawl to make it behave. It was easier when I was younger. In the end I know it will be something simple but in the meantime I need to make sure everything I touch on while sorting it out is correct. We aren't past the tone wheel orientation yet. The rest comes after that.

Jim

OK, no photo yet. I'm working on it.

[brian617]

Unless you have access to GM engineering drawings there is nothing in any chart or graph that is going to show the position of that pickup relative to the engine centerline, the crankshaft keyway, or the timing mark on the damper

LS engines don't have keyways or timing marks on the balancer.

[dave w]

I have not tried using a factory 24x trigger wheel. I doubt it maters if the trigger wheel is factory or aftermaket. In my previous pictures, I hoped to show when the #1 cylinder is TDC of the compression stroke, the aftermarket trigger wheel is "Half Way" across the crank position sensor face. I adjust the sensor to 0.030" from the trigger wheel. The "pickup" inside the sensor is approximately 2mm, which is a tight tolerance to "center" the trigger wheel on.

A multimeter connected to the output of the crank sensor should show 12 volts to 0 volts as the trigger wheel is rotated by hand past the sensor.

dave w

[Jim Blackwood]

OK here's the trace below. If you look close enough you might be able to tell where the zero reference is on the pulse train but like I've been saying, without some way to compare that to TDC it's only helpful in showing that there is a usable signal going in at C1 pin 12 on the ECM. Anyone should be able to understand that zero on the pulse train does not mean zero on the crankshaft unless you match them up. They could be up to 180 degrees apart.

No key on the LS crank snout huh? Then how is the timing chain indexed? Maybe they deleted the mark on the balancer and the keyway in that as well, but you aren't normally going to mount an indicator to the #1 piston to find TDC on a serviceable engine so I suspect the aftermarket has corrected that little oversight.

Anyway as you can clearly see the signal is good, provided it starts and stops in the right place. Gap is .040" and centering is also within 1mm or less. I don't see a problem with any of that.

I can proceed to the outputs and check them and perhaps that will reveal the problem. BUT Until I can confirm that there is no offset between the index hole on the tone ring and the VR pickup (CKP) with the crank at TDC. this question has not been answered.

I do appreciate all the attempts to help. Dave, maybe I'm just too dense to see what you are trying to say. But your photos looked to me like what I've already seen on the web and I've not spotted the critical information yet. Just matching the pulse train zero to the indicator hole in the tone ring is not enough. We have that and have had it from the very start. What we do not have is the position of the VR sensor relative to the indicator hole when the crank is at TDC.

We keep going around and around the same old circle and we're not getting anywhere.

Jim

[lionelhutz]

No spark at all means you've got something else wrong.

Match the pulses on the diagram to the notches in the wheel and you will find that the alignment hole matches with the TDC #1 pulse which means that is the TDC #1 position on the wheel. So, that's where the sensor MUST be when the #1 piston is also at TDC.

The scope traces also confirm that's exactly how it works because the cam signal switches at the same time the crank sensor picks up the #1 TDC notch beside the alignment hole. The alignment hole and corresponding notch must be passing in front of the sensor at #1 TDC for the sensor to be capable of picking it up.

When you hold a LS1 crank so the alignment hole is to the right, the #1 crank throw is facing where it'd be at TDC.

The crank sensor goes into the block with the plug facing forwards.

Tons of people have done this before and got it to work without the need to pursue the question you are so concerned about.

Centering the sensor at the alignment hole is plenty close enough to get your engine running. If you need it to be exactly accurate then tune it with no spark advance and fine adjust the crank sensor to get the spark at exactly TDC. That's assuming your crank sensor bracket is very solid yet has some adjustment and you also have TDC marked on the balancer with a pointer that has been verified with a piston stop.

Assuming you have the sensor clearance minimized, I would try moving the sensor forwards or backwards a little with respect to the wheel.