Timing

Johan

GT40s Supporter
For your information.
Many of you on this forum might already know this but I didn`t.

If you change your ECU to an aftermarket or buy an engine and ECU that doesn`t "belong" together there is a chance that they are not synchronized together. The same goes for if you for some reason change the crank reluctor.

I spoke to the Holley rep here and was recommended to "zero" my crank since I have a new Dominator ECU.
It can be as much as +/- 5* diff, which means if your data logger shows 20* your actual timing can be anything from 15* to 25*.
OEM correct this at manufacturing.
The cure is to zero the crank by eighter measure TDC if the heads are off or with a piston stop.
Mark the harmonic damper temporarily start engine and check with a stroboscope light, then correct in ECU if possible or just make a note of diff.

I had already put my engine together again so I used the piston stop method.


Here I have a temporary pointer and it shows 348* at TDC, so at start up if I want 10* at idle it will show 358* at the crank with a light, anything else I have to correct in the ECU.
 
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If that's true, that would apply to every single GM crate engine ever sold.......since you buy the engine and then the ECU/Harness/throttle pedal separately. And doesn't your engine prove that the 5* tolerance isn't true since yours is off 12*?

This really makes me wonder......I've installed and fired up a bunch of brand new LS engines here for the first time....all with very similar intake and MAF set-ups. Some start right up and run and idle like you would expect...while some won't idle and don't run worth a crap. If your engine is used as an example and the ECU is calibrated to run 12* timing at idle, it could really be anywhere from 0* to 24*. That would explain a lot.....
 

Johan

GT40s Supporter
Shane, I think you misunderstod me, it’s not 12* off. It just happen to end up at 348* with my home made temporary pointer, I didn’t want to spend too much time making a pointer that corresponded with zero at the damper.
It’s just my own index.
And the Holley rep said he had seen as much as 5* diff once, I don’t know under what circumstances.
But since I had my engine out of the car, it wasn’t too much extra work to zero it.
After startup and comfirmation between ECU and my index I’ll just take the pointer off again.
None of the LS engines have a timing pointer nor a timing scale on the damper, the only timing you see is the one that the ecu tells you, and the ecu tells what the crank sensor says, but if the reluctor is off 1,2 or 3* you will never know if you don’t zero the crank and make a mark on it and then check with a strobe light.
 
Ahhh....yes, I did misunderstand. I thought you were saying you had your pointer set up to where the reluctor indicated zero was compared to physical TDC....and therefore the reluctor on your engine was 12* off. My bad!
 
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