TDC Reference Angle for LS vs Northstar

[The Dark Side of Will]

I'm trying to run a 2006-2011 Cadillac Northstar with 58x crank trigger and 4x cam trigger using the E38 ECM from a 2007 Corvette.
Do those two applications have the same TDC reference angles?

I've found the following on this forum:

The GM 58X reluctor commences the indexing notch at 30 deg ATDC on #1 cylinder. You could call GMPP and check with them too. Or confirm with EFI Connection if you are buying a 4X dist reluctor from them.

So I'll be looking at my spare NorthStar crank over the weekend to see if it looks like the Northstar is similar or radically different.
It would be great to put some actual numbers on it.

I've used HPT before and it can't show the TDC reference angle. Can EFILive do that?


Thanks!

[gmh308]

The angle was measured on an actual LS crank, no idea if there is a PID for it or whether Northstar is the same - interesting question though

[The Dark Side of Will]

The angle was measured on an actual LS crank, no idea if there is a PID for it or whether Northstar is the same - interesting question though

Thanks for getting back to me!

I didn't get to my spare crank over last weekend, but I'll put it higher on the list next weekend.

Of course there's no way for the ECM to know the physical relationship between the engine and the trigger wheel. The only thing it can see is whether the crank and cam sensors have the correct relationship.

I assumed you had looked at the crank and counted teeth. I can do the same... maybe even have the gap located by a CMM. The Northstar is right bank forward and the crank sensor is in the valley, so the relationship definitely will not be the same. The question is how much of the difference is in hardware and how much is in software?



Of course the real question is: Can EFI Live change the TDC reference angle in an E38 ECM?

[The Dark Side of Will]

The angle was measured on an actual LS crank, no idea if there is a PID for it or whether Northstar is the same - interesting question though

Ok, I see what you mean by that.

https://ls1tech.com/forums/carburete...ationship.html

This says that TDC #1 happens when the falling edge of the 15th tooth after the gap passes the crank sensor location.

The LS series is left bank forward, so TDC #1 is 135 degrees ahead of the crank sensor location. 15 teeth is 90 degrees. The gap is 15 degrees. This means that the last falling edge before the gap is 105 degrees ahead of the crank sensor location... which puts it 30 degrees behind TDC #1 on the crankshaft.

[ScarabEpic22]

Why do you not want to use the E67 that was used on the Northstars?

Do you have a spare E38 lying around instead of grabbing an E67?

[joecar]

Post pic of your Northstar crank showing the reluctor wheel.

[The Dark Side of Will]

Why do you not want to use the E67 that was used on the Northstars?

Do you have a spare E38 lying around instead of grabbing an E67?

The Corvette calibration or OS is already set up for a manual transmission, while the Cadillac was never offered with a manual transmission.

Post pic of your Northstar crank showing the reluctor wheel.

That's the next step... evaluate the relationship on the crankshaft. The Northstar is *RIGHT* bank forward and has the crank sensor in the valley, so both sides of the TDC vs trigger wheel relationship are different.

[ScarabEpic22]

Any chance the N* E67 OS shares a common OS with like a CTSV where you could grab the segments to do a manual swap? You can definitely run an E67 auto OS with a manual, some things wont work as if it was 100% factory.

I havent seen a "Platform Options" type of parameter in the E67s like the LS1Bs have unfortunately.

[The Dark Side of Will]

I've found a few interesting tidbits.

TDC is leading edge of 14th tooth CCW from the missing teeth on a 58x crank.

and:



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.

https://engineprofessional.com/2015EPQ4/

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.

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:

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.

[The Dark Side of Will]

My ECM guy ( https://gmtuners.com/ ) sent this service manual info:

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.

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.