how quickly will ECU stop retarding once gas is switched from regular to premium?

Whaler17 · Oct 17, 2018

I've read a lot of regular vs premium gas threads, and think I understand correctly that the ECU will retard the ignition if it senses pinging. So many drivers are quite happy using regular 87 octane fuel.

Some have mentioned using a tank of 91 premium every 3 or 4 tanks, while some suggest using premium for towing, high-speed trips, etc.
Some mention being able to feel the engine has more pep after a couple of tanks of premium.
One post said a mechanic who knew how to "reset the ECU" did some A/B testing between regular and premium.

Leading me to ask: once the ECU has retarded ignition to live with regular, how long will it take the ECU to sense it's now running on premium and advance the timing to take advantage of the higher octane?

Right away? 1-tank? 2-tanks? Let's assume the tank is run to near empty before the switch.

In my case, it's a 2003 V8 Limited, and I'm leaning towards using premium for towing. But it would be helpful to know how long ECU retraining takes.

Thanks....

Tmac2010 · Oct 17, 2018

Has your CEL come on and code been read indicating that your engine is pinging too much? You can always go to an auto store and have the code erased. Personally, I use Premium. All together your only paying $6 more a tank... saving $0.30 a gallon is not that big of a savings on our tanks.

blackoutt · Oct 17, 2018

ECU learning process is constant/ongoing, it never stops. So there's no way to say how long it takes if there's no conclusive end. Realistically - try it and see if you can tell the difference first tank or over time, as mentioned it doesn't cost that much more to try it.

Whaler17 · Oct 18, 2018

Sure, "try it and see" is clearly what I should do.

I have an ODB2 Auto Scanner from ieGeek (GXG-1987) for my Prius.
And I notice that in the description it includes "Timing Advance".
I'll plug it in and see what I can see.

Morphyne · Oct 18, 2018

Unhook the battery and let the ECU start fresh. I just started using premium and I might do that myself.

tom4416 · Oct 18, 2018

I don't believe the ECU learns anything where fuel is concerned. There is a knock sensor, when it detects ping, it retards the ignition. If it doesn't detect knock, it leaves the advance alone, in the default state. Switching to an almost full tank of premium should have an immediate impact on performance although I seriously doubt anyone will notice it. I would never tow on anything other than premium, wouldn't go offroading without it but I've put 130K miles on my 03 on regular without an issue. I've run back to back tanks of regular versus premium and then monitored timing, HP at various speeds and other factors available through my Scangauge and I see almost zero difference in steady state highway driving. In town acceleration might be very slightly improved but that's butt dyno talking and trying to justify spending $5 more for a fillup.

MSRP. · Oct 18, 2018

Silly question, but there are there codes that pop up if it starts to retard ignition in the case of knock sensor detecting ping?

If not, is there a parameter on Torque to monitor ping?

I didn't experience the MPG increase over that many claim to see when they pump midgrade or 91 on the v8. Did this over my drive from Toronto to Florida. Went through the Carolinas with elevation change on the way down on 87, and came up through flatter states like Tennessee and Kentucky going up on 89/91 (avoiding Hurrican Florence). Same gas mileage despite less elevation. 4-6 fillups in both directions. Yes, 90% steady state highways going 70-75mph except through the elevation near Ashville/Blue Ridge Pkwy.

I would suggest sticking to 87 unless you're "operating under severe use" aka towing, ripping it on rocks on the trail. All the above for a 2003 v8, so I don't have the higher performing vvti v8 of the later years.

tom4416 · Oct 19, 2018

MSRP. said:
Silly question, but there are there codes that pop up if it starts to retard ignition in the case of knock sensor detecting ping?

If not, is there a parameter on Torque to monitor ping?

It wouldn't set a code unless it resulted in a misfire which it should not. I can follow ignition timing on my Scangauge and see the difference in timing settings but it cannot "listen in" on the knock sensor, don't know if any code reader or OBD device can do that but it would be interesting. I do know that at steady 60-65mph on the freeway, over a couple hundred miles, the timing is exactly the same with regular as with premium. It does start to retard going up hills but only by 2 degrees. Now, put a loaded trailer behind it and start driving in the mountains and it will pull significant timing (12-14 degrees) so that's when I would always run premium (93 octane back on the east coast).

Whaler17 · Oct 19, 2018

tom4416 said:
I can follow ignition timing on my Scangauge and see the difference in timing settings but it cannot "listen in" on the knock sensor, don't know if any code reader or OBD device can do that but it would be interesting. I do know that at steady 60-65mph on the freeway, over a couple hundred miles, the timing is exactly the same with regular as with premium. It does start to retard going up hills but only by 2 degrees. Now, put a loaded trailer behind it and start driving in the mountains and it will pull significant timing (12-14 degrees) so that's when I would always run premium (93 octane back on the east coast).

Now *that's* really interesting. First time I'd heard about a Scangauge, and now I have one on order hahaha...
After reading your experience with timing and fuel quality, I figured I'd just use premium when I towed and leave it at that. But being able to monitor trans temperature while towing etc made me want to try a Scangauge.
Thanks....

MSRP. · Oct 19, 2018

Whaler17 said:
Now *that's* really interesting. First time I'd heard about a Scangauge, and now I have one on order hahaha...
After reading your experience with timing and fuel quality, I figured I'd just use premium when I towed and leave it at that. But being able to monitor trans temperature while towing etc made me want to try a Scangauge.
Thanks....

If the only reason you want the scangauge is to monitor tranny temps, then you'd be just as satisfied with the Pro version of Torque (android only).. it's what.. $15?

Legender · Oct 19, 2018

I've got a lexus that is designed to run premium and does well on it. When I use regular it does OK, but has to 'retard' the engine to align the timing with a gas that burns at a lower temperature than the engine was designed to run at. Premium gas is intended to run in higher performance engines and requires hotter spark to ignite.
You're not doing yourself any favors by putting premium in a vehicle that is designed to run on regular gas. You're only causing the engine to work hotter to burn the gas in the chamber. I wouldn't do this as there is no proven benefit.
If you're engine is knocking (pre-ignition or combustion, prior to the spark) then you probably have a problem somewhere else. Premium gas will help this possibly but you're only masking the real problem.
Just my 1.5 cents....

how quickly will ECU stop retarding once gas is switched from regular to premium?

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