ECU Pulling Timing / OAR Changes Under WOT | Looking for Input

Well aware this could turn into a big can of worms on the internet, but genuinely looking for useful input here, or maybe some PIDs I can start checking on the COBB AP to help diagnose before I start getting into more mechanical issues. Anyone else in CA experiencing this on their 91 octane tunes?
ECU Pulling Timing / OAR Changes Under WOT | Looking for Input
Issue:

• ECU pulling timing and adjusting OAR during WOT pulls on both 91 oct and E30 tunes
• OAR sits between -0.78 and -0.84 on 91 oct tune during WOT
• Issue only occurs under high load — smooth at idle and normal driving

Fuel:

• CA 91 octane should be ~E10, recent sample tested at E5–E6
• Adding a gallon of E85 to either the 91 or E30 tune resolves the knock and OAR changes
• Tested two different 76 stations — issue persists at both, worse at the second

Recent Changes (~1 year ago):

• Timing belt replaced - everything was dead on with double checking the timing locks and rotating the engine severals times back to TDC.
• AWR 70A durometer passenger engine mount installed... I might swap back to the stock mount just to rule this out.. but does NVM result in OAR changes?

Checks Performed/Observations

• Spark plugs — no fouling, gap correct
• Charge temps — 5–6°F above ambient during WOT pulls
• IAT — stable during pulls, not spiking
• Knock appears mostly even across all cylinders during WOT
• Compression check: All cyls hitting 180+ psi

Not California but Cali gas in Arizona, I have a Dizzy stage 2 91 and it will pull timing when boost comes on and my OAR will drop, it does recover quickly when I'm cruising. I find adding half a can of Octanium from VP fuels, to a full tank solves the issue. I think that amount added to 91 will net 94oct, which just really showed the gas quality isn't great and I've tried multiple different brands and locations 🤷🏼‍♂️

Yeah, similar. If I add a gallon of E85 while on a 91 oct tune... everything corrects. I didn't need to do that before is the issue. Someone on reddit said I should've performed the misfire correction programming with Forscan after my timing belt job so I'm gonna tackle that and see what happens.

Let's us know your findings, I'm on a stock timing belt and currently at 100k with similar issues so I'm skeptical it's that... Especially since the issue is only under high load vs all time which would be a timing issue

Totally, it could be something else like higher temps, carbon build up or other things are at play
So you've changed absolutely nothing about your car, no timing belt work... no new tunes, same fuel etc.. and you have this problem? If a large group of people in CA said "Hey... I need to add octane to make my car not knock...I've been on the same tune forever..." then I'd suspect its a pump gas fuel problem.

Correct same tune everything, I changed my mounts but no change to timing corrections, only if I use a higher octane rating...

A few questions, maybe you’ve already thought of:

- Have you contacted whoever wrote the tune you are using (Dizzy/etc)?

- Where are you buying your gas? Have you tried filling up at different stations? Try a different brand than your usual 76 - as many of the same branded stations will be getting their gas from the same source depot/trucks. If you’re getting “bad” or substandard fuel that’s supposed to be 91 octane, you’ll also have the same issue if that’s what you’re blending into your E30.

- That small difference in ethanol content shouldn’t move the needle that much, but it’s worth pointing out that in modern turbo engines, ethanol makes a bigger difference than you’d think due to higher RON - under boost conditions E10 of the same octane (AKI) actually has a higher effective “octane index” (OI) than straight E0 gasoline of the same AKI octane. But it’s only about one octane index point difference. Anyone that tells you straight gasoline is “better” has been wrong since the advent of unleaded fuel. The only reason for bringing it up is that it seems like adding another 7-8% ethanol (even mixed with 87 octane as E85 is) is making the difference.

Last point is that OAR rising briefly above -1.0 is not that much to worry about. OAR below 0 still means the ECU is adding ignition advance over the base tune. If it rises above 0, then really start to worry.

When you did the timing belt did you check your intake valves? Also, take some logs of your AFRs and also of your HP fuel rail pressures. Either of those off could point to something like running a wee bit lean of target, at which point things like a fuel pump/fuel filter or a worn HPFP cam bucket might be in play.

Harsher mounts will trigger off the knock sensors too.. just a thought.

- Have you contacted whoever wrote the tune you are using (Dizzy/etc)?

Yep. And also this is consistent with all my tunes. not just one tune from one tuner.

- Where are you buying your gas? Have you tried filling up at different stations? Try a different brand than your usual 76 - as many of the same branded stations will be getting their gas from the same source depot/trucks. If you’re getting “bad” or substandard fuel that’s supposed to be 91 octane, you’ll also have the same issue if that’s what you’re blending into your E30.

I'm currently buying from 76 stations. Tried a Chevron maybe a month ago, didn' seem to change much.

- That small difference in ethanol content shouldn’t move the needle that much, but it’s worth pointing out that in modern turbo engines, ethanol makes a bigger difference than you’d think due to higher RON - under boost conditions E10 of the same octane (AKI) actually has a higher effective “octane index” (OI) than straight E0 gasoline of the same AKI octane. But it’s only about one octane index point difference. Anyone that tells you straight gasoline is “better” has been wrong since the advent of unleaded fuel. The only reason for bringing it up is that it seems like adding another 7-8% ethanol (even mixed with 87 octane as E85 is) is making the difference.

Yeah I think that gap of perfect harmony is greater when the tunes are aggressive and on the ragged edge of knock. So if the octane is lower than needed...and the the tuner is relying on perfectly good 91/rather pushing the limits of the 91... its gonna have issues. BUT... after talks with fella on Reddit we found it could be something likely more mechanical. I'll write more below.

Last point is that OAR rising briefly above -1.0 is not that much to worry about. OAR below 0 still means the ECU is adding ignition advance over the base tune. If it rises above 0, then really start to worry.

The OAR was consistently moving further and further away from -1, even have I changed to a new fuel station... I went up to -0.76 at one point. Mind you ONLY when doing heavy load, datalog like WOT pulls. Normal driving or 50% throttle pulls it would clear up (Less load).

When you did the timing belt did you check your intake valves? Also, take some logs of your AFRs and also of your HP fuel rail pressures. Either of those off could point to something like running a wee bit lean of target, at which point things like a fuel pump/fuel filter or a worn HPFP cam bucket might be in play.

Yeah the intake valves had some gunk on the stems... but the heads of the valves themselves were smooth and not caked up at all. I'll have to double check AFR, last i checked it was on target. I AM on the original cam bucket. I replaced my LPFP maybe 2 years ago.

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(Reddit Thread - Click Here )


RE: The timing belt stuff....It's possible while the cam phasers and crank assmbly are all in time, the cams themselves COULD be out. Before we get there though, it was pointed out that I should've done a "Neutral Misfire Monitor Correction" using FORscan. At the cost of only the OBD cable and some of my time... its worth a try. It's basically a recalibration for the Crank Position Sensor any time you have removed it for service. Could it be unecessary? Maybe.