SAFTOT Not Matching OBD Spark

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ShadowDrake
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Joined: Sat May 30, 2009 4:32 pm

SAFTOT Not Matching OBD Spark

Post by ShadowDrake » Thu Jun 14, 2018 12:10 pm

Couldn't find this listed anywhere though I swear at some time in all the years past I've seen this asked/answered.

My SAFTOT does not match the stated spark value over OBD.

I've been working on my timing and logged SAFTOT which should be my final delivered spark value... if I'm not mistaken.

I set up the tune and ran with it. I was using 18-20 degrees of spark at the top of the rev range. I added some boost later, blindly took out a few degrees and some time later decided to see what my spark timing was coming out as and happened to have an OBD logger available at the time so I used that to check spark and saw logged values in the single digits (7-8 degrees).

So which of these is my actual delivered spark value? I pushed the spark up a bit til SAFTOT was saying 22-23 (which should be detonating at 22 psi?) and never ran into any preignition as I inched it up but decided to put it back to be safe till I get it sorted.
2004 GT
-RKN2
-4.6 DOHC C-heads
-Precision 7275

motorhead1991
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Re: SAFTOT Not Matching OBD Spark

Post by motorhead1991 » Thu Jun 14, 2018 11:15 pm

IME, there are a couple of factors that change saftot: ECT, ACT, runtime (which affects block temperature), load
1990 Ford Ranger FLH2 conversion. Ford forged/dished pistons, Total Seal file-fit rings, Clevite rod and main bearings, Clevite cam bearings, IHI turbo, Siemens Deka 60lb/hr injectors, Ford slot MAF in custom 3" housing. Moates Quarterhorse with Binary Editor, using the PAAD6 database.

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ShadowDrake
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Posts: 79
Joined: Sat May 30, 2009 4:32 pm

Re: SAFTOT Not Matching OBD Spark

Post by ShadowDrake » Fri Jun 15, 2018 6:11 am

And this would be after SAFTOT is calculated? If that's the case then is there a payload I can log that's the actual final delivered spark value? Or do I need to add the ECT/ACT adjustments to my logging payload and calculate it manually?
2004 GT
-RKN2
-4.6 DOHC C-heads
-Precision 7275

sailorbob
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Joined: Tue Jul 12, 2005 6:10 am

Re: SAFTOT Not Matching OBD Spark

Post by sailorbob » Wed Jun 20, 2018 12:01 pm

The SAFTOT value is the foreground calculated spark advance that is used to generate the Spark Angle Pulse Width (SAPW) value sent to the EDIS module. The ODB-II spark value should track the SAFTOT value very closely as it is derived from the SAFTOT value converted to meet the requirements of the J1979-01-0E formula. There will be some minor differences at times as the SAFTOT calculation occurs more frequently that the J1979-01-0E PID calculation.

If you are seeing different values for the two during steady state conditions (i.e. when the timing advance value remains static) then I suspect you are not datalogging the SAFTOT value.

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