Folks-
Just ran into a thread by HBH in "Terminator Talk" which is very interesting. I'm no engineer, but it seems that voltage dropoff occurs at about 5600 from the alternator, which affects the BAP, which affects the quantity of fuel supplied.
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I came across a car i was tuning today that was perfect up to 5,200 rpm's then drifted lean very quickly. I tried everything to get fuel in it, then looking at the logs i noticed the maf counts were dropping from a point about 880 counts, (sct-2400 maf, ported eaton car)down to 850-860 while the rpm's were still going up!! That is making no sense unless un-metered air is getting into the intake tract pre-blower but post maf....check everything, all perfect with no leaks.... this car was making me pull out my hair!! Then i started to think about it, I thought maybe the blower was having reversion at that rpm point, which it wasn't. The car also has a 4 lb lower drive on it, I started wondering if it was possibly a voltage issue of some sort, i called my buddy ryan @ sct and he backed up my thoughts, thinking as the voltage decreased so did the power to the fuel system even though this car has a wiring upgrade and a Bap. I had never logged the voltage pid, but after doing so i found some great info....even with a metco 3.20 alternator pulley on the alternator the car the voltage stated to fall off... at 5,273 rpm's it had 12.68 volts, at 5,478 it had 12.50, at 5,587 12.25, 5,670 12.18..., 5,992 it had 12.06..., 6,078 11.87...,6,296 it had 11.81..., 6,460 it had 11.50...,6,440 11.37....and as it got over 6,200 it started to drift leaner than I would like to see so we lifted. The point of all of this is simple....as the rpm's increase on a car with a lower drive on it the voltage starts to drop off quickly, so all of you data loggers with raptor or x-cal-2's better start to log the voltage pid, it just may save your engine's life!! I am going to do a ton of datalogging with larger alternator pulleys even if we have to get some custom sizes fabbed up. EVERYTHING I FIND WILL BE POSTED AS I FIND IT! I would say this is in fact the cause of alot of the engine failures we have seen, not due to the tunes but due to the drop of voltage......this is one of the big advantages I get due to the fact I tune on the street in real world conditions....one more thing....as soon as we lifted off and the rpm's fell, the voltage returned This is going to HELP US ALL and i'm glad i could share this super important find!! Thanks to ryan @ sct for his input in solving a HUGE PROBLEM!!! Hermann
Micksnip
Just ran into a thread by HBH in "Terminator Talk" which is very interesting. I'm no engineer, but it seems that voltage dropoff occurs at about 5600 from the alternator, which affects the BAP, which affects the quantity of fuel supplied.
--------------------------------------------------------------------------------
I came across a car i was tuning today that was perfect up to 5,200 rpm's then drifted lean very quickly. I tried everything to get fuel in it, then looking at the logs i noticed the maf counts were dropping from a point about 880 counts, (sct-2400 maf, ported eaton car)down to 850-860 while the rpm's were still going up!! That is making no sense unless un-metered air is getting into the intake tract pre-blower but post maf....check everything, all perfect with no leaks.... this car was making me pull out my hair!! Then i started to think about it, I thought maybe the blower was having reversion at that rpm point, which it wasn't. The car also has a 4 lb lower drive on it, I started wondering if it was possibly a voltage issue of some sort, i called my buddy ryan @ sct and he backed up my thoughts, thinking as the voltage decreased so did the power to the fuel system even though this car has a wiring upgrade and a Bap. I had never logged the voltage pid, but after doing so i found some great info....even with a metco 3.20 alternator pulley on the alternator the car the voltage stated to fall off... at 5,273 rpm's it had 12.68 volts, at 5,478 it had 12.50, at 5,587 12.25, 5,670 12.18..., 5,992 it had 12.06..., 6,078 11.87...,6,296 it had 11.81..., 6,460 it had 11.50...,6,440 11.37....and as it got over 6,200 it started to drift leaner than I would like to see so we lifted. The point of all of this is simple....as the rpm's increase on a car with a lower drive on it the voltage starts to drop off quickly, so all of you data loggers with raptor or x-cal-2's better start to log the voltage pid, it just may save your engine's life!! I am going to do a ton of datalogging with larger alternator pulleys even if we have to get some custom sizes fabbed up. EVERYTHING I FIND WILL BE POSTED AS I FIND IT! I would say this is in fact the cause of alot of the engine failures we have seen, not due to the tunes but due to the drop of voltage......this is one of the big advantages I get due to the fact I tune on the street in real world conditions....one more thing....as soon as we lifted off and the rpm's fell, the voltage returned This is going to HELP US ALL and i'm glad i could share this super important find!! Thanks to ryan @ sct for his input in solving a HUGE PROBLEM!!! Hermann
Micksnip
