Voltage

So im still having voltage issues even w the j2fab alternator. Thinking this battery relocation the previous owner did is the problem. Still drops to 12-12.5v under wot. Or any aggressive acceleration. I did a datalog at idle of the battery voltage and its all over the place. Is this normal?

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That definitely doesn't look good. My alternator is pretty stable even when hot. If the battery was relocated I would make sure the cables used are large enough. Also make sure the grounds are clean and tight. Is there a separate cable ran for ground or was the body used as the main ground?

Just did a wot pull about 90° here in Texas. Battery voltage dropped to around 11.8. I just hate that it fluctuates about 1 volt just at idle

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01yellercobra said:

That definitely doesn't look good. My alternator is pretty stable even when hot. If the battery was relocated I would make sure the cables used are large enough. Also make sure the grounds are clean and tight. Is there a separate cable ran for ground or was the body used as the main ground?

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Im just going to relocate it back to stock location because they didnt do a good job. Thanks for the tips

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Let us know how that goes

First-on-race-day said:

Just did a wot pull about 90° here in Texas. Battery voltage dropped to around 11.8. I just hate that it fluctuates about 1 volt just at idleView attachment 1649322

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11.8 is WAY too low.....do not go WOT until you figure this out. She gonna go lean and eat a piston.....

Well the thing is i got it dyno tuned about 1 year ago. Same issues and my tuner tuned it to the low voltage. He just added more fuel up top and told me to fix the issue and he would send me a revised tune to lean it out. I monitored my fuel pressure and it seems to stay around 38-39psi under wot even during low voltage conditions. And my afr is actually rich 10.8-11.0 afr at 5000-6200rpm

c6zhombre said:

11.8 is WAY too low.....do not go WOT until you figure this out. She gonna go lean and eat a piston.....

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A lot of alternators dip down to 12.xx at wot. If it gets into the 11's at wot that is too low. You can account for voltage loss in the tune (using correct injector data not adding fuel using the maf curve) so that even if your alternator dies you can maintain af throughout the pull.

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Does that look acceptable? Spiked for a small bit to 12.44 other than that averaged about 12.7-13v at wot under this hot hot texas weather

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First-on-race-day said:

Does that look acceptable? Spiked for a small bit to 12.44 other than that averaged about 12.7-13v at wot under this hot hot texas weatherView attachment 1649614View attachment 1649615

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Looks pretty normal. Are you logging af with a wideband?

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03cobra#2 said:

Looks pretty normal. Are you logging af with a wideband?

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Not logging my afr but am keeping a close eye on it. Its actually running a bit rich at 10.8-11.0afr

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Dataloged a couple wot pulls today. I have a El cheapo alternator I bought just to get the car going. I have a better one ready to go.

Any who my logs say around 13.3 or so cruising around all warmed up. Warmed up idle is around 13.4.

During wot it dipped down to 12.5 for a brief moment but was at about 12.6-12.8 during the pull. No issues at all with AF or fuel pressure.

I know it's a cheap $50 piece but I may run with this alternator for a bit longer before swapping to my other one.

And again..
The ecu will compensate for a drop in voltage (as long as you have either the stock tune or a solid custom tune) so you don't go lean during voltage drops.

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