FN725A high temp above 254F will it wrap to -256F

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A6intruder
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FN725A high temp above 254F will it wrap to -256F

Post by A6intruder » Thu Oct 11, 2018 10:16 pm

single turbo 331 CID, NO intercooler, 12 psi boost

When ACT exceeds 254 F will FN725A Spark - Borderline ACT Multiplier wrap from the EEC registering 254F to -256. As real temp continues to climb to say 264F will the EEC register -246F in the FN725A function.

For some reason I remember Sailorbob mentioning this as we were helping Dr. Mayf on his twin turbo (later single turbo) Sunbeam Alpine salt flat racer (used Mustang powertrain).

Trying to set up me new tune to make sure I handle any ACT temps past 254F.

thanks!
Dan Nicoson
1994 Mustang GT, CHP 331 forged crank bottom end, single Holset HX35W turbo, AFR 165 heads, TF Intake, "Baby" Crower cam with Beehive springs, TwEECer using BE and DataQ data logger

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Re: FN725A high temp above 254F will it wrap to -256F

Post by A6intruder » Fri Oct 12, 2018 8:15 pm

OK, maybe Sailorbob isn't on the list much these days. That was 8-10 years ago when we discussed that issue.

I did get an old file to run well tonight. One 4th gear pull at 12 psi gave me some good data. My inlet tract temps just hit 200 F at the end of that run. My ACT sensor is mounted on the charge pipe down in the right fender well between the turbo and the throttle body. 85F ambient tonight, running around at normal street speeds I was only seeing 100-115F ACT. So at least no heat soak of major significance...And at least tonight I didn't get anywhere near the 254F witching point for ACT.(what happens to spark above that temp?)

I have thought about FN725A and its compliment FN2220. They are used by Ford to pull spark as ACT goes up. So they are pulling advance away from the table values to "save" the engine from going into detonation. My thought, what if I set the Boarderline table to low values that are safe at high ACT temperatures and then ADD spark advance with FN725A/FN2220 below ACT=254F. That way if the ACT loop ever fails then as FN725A/FN2220 effect drops out the total spark value goes to a "safe" level, even at high boost/ACT.

Thoughts?
Dan Nicoson
1994 Mustang GT, CHP 331 forged crank bottom end, single Holset HX35W turbo, AFR 165 heads, TF Intake, "Baby" Crower cam with Beehive springs, TwEECer using BE and DataQ data logger

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Re: FN725A high temp above 254F will it wrap to -256F

Post by jsa » Fri Oct 12, 2018 8:33 pm

Spark is low selected.
Cheers

John

95 Escort RS Cosworth - GHAJ0 / ANTI on a COSY box code
Moates QH & BE
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A6intruder
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Re: FN725A high temp above 254F will it wrap to -256F

Post by A6intruder » Fri Oct 12, 2018 8:52 pm

John,

I'm not sure what you mean? "Low Selected"

I have everything set so EEC should only use the Boarderline table (Sea level, MBT, Alt set at max values)

What happens to FN725A if ACT exceeds 254F limit?

Thanks
Dan Nicoson
1994 Mustang GT, CHP 331 forged crank bottom end, single Holset HX35W turbo, AFR 165 heads, TF Intake, "Baby" Crower cam with Beehive springs, TwEECer using BE and DataQ data logger

jsa
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Re: FN725A high temp above 254F will it wrap to -256F

Post by jsa » Sat Oct 13, 2018 12:14 am

The lowest advance calculated from the available tables is calculated.

T > 254ºF would depend on how the strategy is programmed to deal with it.

Allowing temperatures to exceed 254 is not a good choice in any case.
Cheers

John

95 Escort RS Cosworth - GHAJ0 / ANTI on a COSY box code
Moates QH & BE
ForDiag

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Re: FN725A high temp above 254F will it wrap to -256F

Post by A6intruder » Sat Oct 13, 2018 11:35 am

John,

OK, we are on the same track. I had the same understanding of which calculated advance gets used. I was surprised by my recent datalog. I assumed the temps would be closer to 254F. I will have to watch as I get more driving time to see the variability. Also, as I refine my tune I might see other changes in the ACT.

Dan
Dan Nicoson
1994 Mustang GT, CHP 331 forged crank bottom end, single Holset HX35W turbo, AFR 165 heads, TF Intake, "Baby" Crower cam with Beehive springs, TwEECer using BE and DataQ data logger

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Re: FN725A high temp above 254F will it wrap to -256F

Post by sailorbob » Mon Oct 15, 2018 3:00 pm

Providing the first and last input (Y axis) values for the function are set to the maximum and minimum limits of the input variable then there is not going to be a problem as the function's interpolated output value will be limited to be within those values in the function. Problems which occurs in some stock calibrations (very, very few) is that the function input values are not set to the allow for the possible input range or when a function with a signed input value is being incorrectly looked up as if it's an unsigned value.

FN725A is fine in CBAZA.

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Re: FN725A high temp above 254F will it wrap to -256F

Post by A6intruder » Mon Oct 15, 2018 3:24 pm

So do you know what happens to the Boarderline timing solution when the sensor sees higher than 254F?

Thanks,

Dan
Dan Nicoson
1994 Mustang GT, CHP 331 forged crank bottom end, single Holset HX35W turbo, AFR 165 heads, TF Intake, "Baby" Crower cam with Beehive springs, TwEECer using BE and DataQ data logger

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Re: FN725A high temp above 254F will it wrap to -256F

Post by sailorbob » Mon Oct 15, 2018 4:10 pm

Even if the temperature at the sensor is greater than 254 deg F the ACT value is limited in the code to a maximum of 254 deg F.

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Re: FN725A high temp above 254F will it wrap to -256F

Post by A6intruder » Mon Oct 15, 2018 4:12 pm

Thanks.
Dan Nicoson
1994 Mustang GT, CHP 331 forged crank bottom end, single Holset HX35W turbo, AFR 165 heads, TF Intake, "Baby" Crower cam with Beehive springs, TwEECer using BE and DataQ data logger

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