Took a while to figure this one out but low voltage is hurting my power. My voltage varies from 14.5 to 12.5V all the time, which I know is an issue but maybe it's one others also have? The problem, on top of that, is under full load it drops ~1V. Not sure if this is normal or not but if it's ~14.5 and drops to 13.5 everything (boost) seems fine. If at 12.5 and drops to 11.5, I lose a good chunk of boost. It seems obvious to me the solenoid can't hold position with that voltage and bleeds vacuum... It's a pattern I see when I look at old data where the turbo DC is good but boost varies, and the only thing that coincides is voltage.
I have the default voltage compensation selected on the turbo page but my assumption is it's dropping lower than it can comp for. I assumed the voltage was 5V, but a big assumption on my part. The next most obvious voltage choice would be 12V, and clearly it can't comp for 11.5. Either way I bet $ it comps by adjusting DC, not voltage, and since it cannot adjust DC higher than the max DC, any V loss will hurt power. I adjusted the max DC from 90 to 95 and it seems to have helped, on avg, but very difficult to tell since the voltage is different each time, as are IAT etc. But on avg I think it helped. I also tried 100% DC which again seems to help a bit more. It's certainly no fix, just a clue that voltage is the issue.
Example for today: With 11.69V @ 5800 I netted 8.8psi >: |
Minutes later with 13.16V @ 5800 I net 13.3psi.
Both cases the turbo duty cycle is the same, throttle fully open and IAT was ~4F lower with the low boost.
Of course I can't say the rpm is accurate, per my post a few weeks ago on that subject; https://forum.hptuners.com/showthread.php?102508
or the boost for that matter, but the boost to voltage issue is a repeatable pattern. When everything is happy and V is good I get ~13.5 @ 5800, 12.5 @ 6k. So regardless of rpm error, 8.8 is simply not possible if the DC is maxed and throttle open etc.
It also makes me wonder about others with an M278 who have low boost @ 6k, which we discussed Aug '22 starting at post 57:
https://forum.hptuners.com/showthread.php?95688
So if you guys keep tabs on voltage, does it drop under load? If not monitoring it, please do and post what you see!