Reluctor wheel shift
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14th tooth right here.
Any comments about that positioning and why it’s not correct? I have fought a random misfire code paired with a rich condition only at idle for a long time. I’m starting to believe this has something to do with it. It was never a real misfire and car ran good otherwise.
With the notch centered in the crankshaft position sensor bore, the cylinder *BEFORE* #1 was at TDC.
When #1 was at TDC, the 14th tooth was centered in the crankshaft position sensor bore.
The NorthStar crank has the trigger wheel in the middle of the crank. As such, it is machined into the crank. It is therefore impossible for a NorthStar trigger wheel to shift, and its is guaranteed to be accurate with CNC precision.
I have also found interesting tidbits elsewhere (copied from my post on EFILive forums):
Originally Posted by In-Tech
TDC is leading edge of 14th tooth CCW from the missing teeth on a 58x crank.
https://www.youtube.com/watch?v=Vg622WZe3oI In which the creator notes that the gap in the 58x wheel aligns to the crank sensor bore at TDC of the cylinder *BEFORE* number 1... Which is #3 on an LS.
Also this:
post I found while researching this, claimed the 14th tooth should be in the middle of the sensor hole/window, at TDC. To verify this I mocked up a crank in a block with degree wheel. With the reluctor triangles at 3 and 9 o'clock, I also found the 14th tooth was centered in the window.
...
So now i've heard of the 11th, 13th and 14th tooth past the space being used for the LS.
...
So now i've heard of the 11th, 13th and 14th tooth past the space being used for the LS.
Last weekend I pulled the balancer and front cover off the NorthStar to evaluate this relationship. I had to remove the front cover and oil pump to access the index marks on the timing set. I had to pull the intake manifold to access the crank sensor. When I turned the engine so that the gap was centered in the crank sensor bore, the index mark on the crank sprocket pointed to the case-half split. This is 90 degrees before TDC, at which point the index mark is vertical. The matched the YouTube video I linked above. I turned the crank, using a sharpie through the crank sensor bore to mark each successive tooth. The indexing marks on the timing set aligned, with the crank sprocket vertical, on the 14th tooth after the gap.
14 sounds like a weird number, until you realize that the gap contains tooth #60 and tooth #1, both missing. The 14th tooth is really tooth #15. 15 is 1/4 of 60, which coincides with the 90 degree firing interval of a V8.
This actually works reasonably well with this:
Originally Posted by gmh308
The GM 58X reluctor commences the indexing notch at 30 deg ATDC on #1 cylinder.
Anyway, the NorthStar also satisfies the "14th tooth" criteria for LS engines, so I feel pretty safe using a Corvette ECM. I'll still implement a timing mark to verify, but I feel good about it now.
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Kudos on the effort!
Clearly a lot of nuance. Not a simple subject judging by the posted enlightenment.
When I checked this out with crank in block 15 years ago & posted, I now can't recall whether I used from the rear or front perspective LOL. Should've stated for clarity & posterity!
Originally Posted by gmh308
The GM 58X reluctor commences the indexing notch at 30 deg ATDC on #1 cylinder.
Clearly a lot of nuance. Not a simple subject judging by the posted enlightenment.
When I checked this out with crank in block 15 years ago & posted, I now can't recall whether I used from the rear or front perspective LOL. Should've stated for clarity & posterity!
Originally Posted by gmh308
The GM 58X reluctor commences the indexing notch at 30 deg ATDC on #1 cylinder.
In working on my 2006 Cadillac Northstar in my Fiero to see if I could run it with a 2007 C6 Corvette ECM, I undertook the same investigation.
Also this:
Last weekend I pulled the balancer and front cover off the NorthStar to evaluate this relationship. I had to remove the front cover and oil pump to access the index marks on the timing set. I had to pull the intake manifold to access the crank sensor. When I turned the engine so that the gap was centered in the crank sensor bore, the index mark on the crank sprocket pointed to the case-half split. This is 90 degrees before TDC, at which point the index mark is vertical. The matched the YouTube video I linked above. I turned the crank, using a sharpie through the crank sensor bore to mark each successive tooth. The indexing marks on the timing set aligned, with the crank sprocket vertical, on the 14th tooth after the gap.
14 sounds like a weird number, until you realize that the gap contains tooth #60 and tooth #1, both missing. The 14th tooth is really tooth #15. 15 is 1/4 of 60, which coincides with the 90 degree firing interval of a V8.
This actually works reasonably well with this:
Originally Posted by gmh308
The GM 58X reluctor commences the indexing notch at 30 deg ATDC on #1 cylinder.
*IF* one considers that ATDC is actually BTDC. The gap is 15 degrees wide. 30 + 15 = 45. At TDC #3, the gap should be centered in the crank sensor bore. TDC for the right bank is 45 degrees beyond the center of the crank sensor bore. So the leading edge of the gap should be 37.5 degrees ATDC #3, and the trailing edge of the gap should be 37.5 degrees BTDC #1, when inspecting a bare crankshaft.
Anyway, the NorthStar also satisfies the "14th tooth" criteria for LS engines, so I feel pretty safe using a Corvette ECM. I'll still implement a timing mark to verify, but I feel good about it now.
Also this:
Last weekend I pulled the balancer and front cover off the NorthStar to evaluate this relationship. I had to remove the front cover and oil pump to access the index marks on the timing set. I had to pull the intake manifold to access the crank sensor. When I turned the engine so that the gap was centered in the crank sensor bore, the index mark on the crank sprocket pointed to the case-half split. This is 90 degrees before TDC, at which point the index mark is vertical. The matched the YouTube video I linked above. I turned the crank, using a sharpie through the crank sensor bore to mark each successive tooth. The indexing marks on the timing set aligned, with the crank sprocket vertical, on the 14th tooth after the gap.
14 sounds like a weird number, until you realize that the gap contains tooth #60 and tooth #1, both missing. The 14th tooth is really tooth #15. 15 is 1/4 of 60, which coincides with the 90 degree firing interval of a V8.
This actually works reasonably well with this:
Originally Posted by gmh308
The GM 58X reluctor commences the indexing notch at 30 deg ATDC on #1 cylinder.
*IF* one considers that ATDC is actually BTDC. The gap is 15 degrees wide. 30 + 15 = 45. At TDC #3, the gap should be centered in the crank sensor bore. TDC for the right bank is 45 degrees beyond the center of the crank sensor bore. So the leading edge of the gap should be 37.5 degrees ATDC #3, and the trailing edge of the gap should be 37.5 degrees BTDC #1, when inspecting a bare crankshaft.
Anyway, the NorthStar also satisfies the "14th tooth" criteria for LS engines, so I feel pretty safe using a Corvette ECM. I'll still implement a timing mark to verify, but I feel good about it now.
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Joined: Apr 2008
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On The Tree
Joined: Jan 2008
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My ECM guy ( https://gmtuners.com/ ) sent this service manual info:
I was wondering how people were installing the trigger wheel on-- or simply seeing-- the 13th tooth, or any tooth other than the 14th tooth, *WITHOUT* the ECM setting a P0016. The answer is that the tolerances for P0016 are wide enough that the crank trigger wheel can be off almost two whole teeth in one direction, and more than two whole teeth in the other direction before the ECM will set P0016.
A less obvious consequence is that the ECM still triggers spark based on the 14th tooth. So someone who installs the crank trigger wheel on the 13th tooth has BUILT THEIR ENGINE such that it will inherently have a SIX DEGREE TIMING RETARD vs the values in the tuning software.
That is, base timing is 6 degrees retarded vs where they think it is.
Circuit/System Description
The engine control module (ECM) uses the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor pulses to monitor the correlation between the crankshaft and the camshaft position. The crankshaft reluctor wheel consists of a 60-tooth pattern with 2 teeth missing for the reference gap. Each tooth is evenly spaced 6 degrees apart, except for the reference gap. The camshaft reluctor wheel has 4 teeth, 2 narrow, and 2 wide. The 4 trailing edges of each tooth are evenly spaced at 90 degrees apart around the circumference of the camshaft sprocket. With the engine running, and the CMP actuator in the parked position, the ECM expects the camshaft signal pulses to occur 36 crankshaft degrees before top dead center (BTDC) for cylinder number 1, and every 90 degrees thereafter.
Conditions for Setting the DTC
The cam signal falling edge is more than minus 11 degrees or more than plus 14 degrees from the corresponding crank signal falling edge. This condition is equal to the camshaft gear being either advanced or retarded by 1 tooth.
The engine control module (ECM) uses the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor pulses to monitor the correlation between the crankshaft and the camshaft position. The crankshaft reluctor wheel consists of a 60-tooth pattern with 2 teeth missing for the reference gap. Each tooth is evenly spaced 6 degrees apart, except for the reference gap. The camshaft reluctor wheel has 4 teeth, 2 narrow, and 2 wide. The 4 trailing edges of each tooth are evenly spaced at 90 degrees apart around the circumference of the camshaft sprocket. With the engine running, and the CMP actuator in the parked position, the ECM expects the camshaft signal pulses to occur 36 crankshaft degrees before top dead center (BTDC) for cylinder number 1, and every 90 degrees thereafter.
Conditions for Setting the DTC
The cam signal falling edge is more than minus 11 degrees or more than plus 14 degrees from the corresponding crank signal falling edge. This condition is equal to the camshaft gear being either advanced or retarded by 1 tooth.
A less obvious consequence is that the ECM still triggers spark based on the 14th tooth. So someone who installs the crank trigger wheel on the 13th tooth has BUILT THEIR ENGINE such that it will inherently have a SIX DEGREE TIMING RETARD vs the values in the tuning software.
That is, base timing is 6 degrees retarded vs where they think it is.
Last edited by The Dark Side of Wil; Dec 6, 2025 at 09:28 AM.
