I have a very mild SBC 383 in a Jeep using a 7427 ECU. It has been used primarily off-road all over Texas, Oklahoma and Arkansas without issue. We just returned from a trip to the San Juan Mountains in Colorado ranging from 9,500 ft to 12,500 ft and experienced severe overheating issues not related to the radiator, fan or thermostat. The exhaust and floor boards seemed to be much hotter than normal while leisurely cruising down dirt roads at 20 mph. All over heating problems went away after we returned to Texas.
In a 7427 ECU, how does “Altitude Spark Bias” and “Altitude Spark Advance Correction vs. Baro vs. Vacuum” affect the timing advance with increasing elevation? If I change the Altitude Spark Bias value, the values in the corresponding “Altitude Spark Advance Correction vs. Baro vs. Vacuum” also change.
Early in my tuning I was chasing down a spark retard issue and discovered my actual spark, as measured on the distributor, did not match my LT1 timing table in the ECU. I was missing 10 degrees everywhere even with the base timing set correctly. Once I set Altitude Spark Bias to 0, my missing ten degrees instantly returned. I suspect this may have been related to me, unknowingly at the time, zero-ing out the values in the table “Altitude Spark Advance Correction vs. Baro vs. Vacuum” but leaving the Altitude Spark Bias set to 9.8. However, in Colorado I had both, the Altitude Spark Bias and the “Altitude Spark Advance Correction vs. Baro vs. Vacuum”, all set to zero. Could this have retarded the timing at high elevations? Enough to cause hot exhaust and severe overheating?
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