Positive KNOCKR when not using octane booster now

[illadvised]

I was using octane booster with a few tanks in a row, and now when I go WOT I am seeing positive knockr on my nguage. It is usually negative at anything less than wide open.

This all makes sense; but how would I go about resetting what the ecu uses to guess octane, or should I just keep driving and let it figure itself out? I am not sure how much positive knock is dangerous. Would a KAM reset fix this, or would it be better to let the car figure itself out

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[sk47]

Hello; I am far from an expert so bear that in mind. I would think the knock sensors and the programming which retards timing will work quickly, not like years ago.
I see you have a 2015. With enough miles you may have some carbon build up in the combustion chambers. A carbon build up can retain enough heat to trigger detonation.

 

[Pistol_91]

PCM should learn

 

[K4fxd]

I don't know about Ca gas but whatever chemical that is in Boostane is already in our gas here in NKY.

I was getting spark reduction even using a full bottle to a tank of gas. I seriously thought it was false knock.

I ran it down to 50 miles to empty and filled it with 100 octane race gas. Knock went away. I now add 4 gallons of E85 per tank to solve the knock issue.

 

[Grimreaper]

The ecu can learn from past KR (similar to LTFT) but the tune has to be setup for it. If it's not, it will continue to knock everytime and rely on knock sensors to react vs learn. On stock settings, 2 to 3 degrees of KR will move the learning along very quickly. And it would progressively reduce on each pull. Ideally the tune allows learning before full load situations but this requires accurate borderline tables which means R/D and real world time spent verifying under different weather conditions etc..

Who tuned it? Got a log?

 

[Grimreaper]

I don't know about Ca gas but whatever chemical that is in Boostane is already in our gas here in NKY.

I was getting spark reduction even using a full bottle to a tank of gas. I seriously thought it was false knock.

I ran it down to 50 miles to empty and filled it with 100 octane race gas. Knock went away. I now add 4 gallons of E85 per tank to solve the knock issue.

How much timing change?

I only ever saw 24 degrees na on 93 and what ever I wanted on e85. Never ran boostane until boost. No issues with 18.5 to 19.5 at 10psi with 4 oz or so per tank. I suspect I could get away with another degree but meh. It's already fast and no issues with this timing for 2 years now. I'm shocked a full can didn't get you to mbt na though.

 

[ZXMustang]

The ECU doesnt guess octane. It just uses all of the tables and values in the PCM for air, spark and fuel delivery plus information from the knock sensors and fuel trims to decide how much spark you get at any given RPM/throttle and so on. The less octane you have, the quicker you will hit those knock limits set out in the tune. The car is literally measuring knock via sensors and will pull back timing based on that.

Now if you want to stop using octane boosters, you can just run a splash of E85 in the tank with your 91/93 and that will do the same or similar at least in getting you a bit of octane headroom. I run e20 on my 93 tune. My third gen has more than enough fuel system headroom to compensate for the added ethanol it will see. The fuel trims add a bit of fuel to keep the car running at e10 stoich, but it will have the added benefit of e20 octane. I'd much rather do this than run any octane booster brand. I've been running 2 gallons of E85 and topping the rest off with 93. Now if you keep doing this, you will need to calculate down the E since whatever level you add more fuel at, there will be residual e20 in there. I use the ecal app that allows me to do the calculation based off of all the factors including fuel left in the tank. It tells me how much E to put in to maintain that e20 blend. And when I run e20, I get no knock. When let that run all the way out and go back to straight 93, I will get knock here and there with WOT pulls.

 

[waulypaul]

The ECU doesnt guess octane. It just uses all of the tables and values in the PCM for air, spark and fuel delivery plus information from the knock sensors and fuel trims to decide how much spark you get at any given RPM/throttle and so on. The less octane you have, the quicker you will hit those knock limits set out in the tune. The car is literally measuring knock via sensors and will pull back timing based on that.

Now if you want to stop using octane boosters, you can just run a splash of E85 in the tank with your 91/93 and that will do the same or similar at least in getting you a bit of octane headroom. I run e20 on my 93 tune. My third gen has more than enough fuel system headroom to compensate for the added ethanol it will see. The fuel trims add a bit of fuel to keep the car running at e10 stoich, but it will have the added benefit of e20 octane. I'd much rather do this than run any octane booster brand. I've been running 2 gallons of E85 and topping the rest off with 93. Now if you keep doing this, you will need to calculate down the E since whatever level you add more fuel at, there will be residual e20 in there. I use the ecal app that allows me to do the calculation based off of all the factors including fuel left in the tank. It tells me how much E to put in to maintain that e20 blend. And when I run e20, I get no knock. When let that run all the way out and go back to straight 93, I will get knock here and there with WOT pulls.

Does that splash of e85 require a retune or something you can benefit from without it?

 

[K4fxd]

How much timing change?

I'll get 25 on 93 and 29 with 4 gallons of E Which is where my MBT tables are set.

Does that splash of e85 require a retune or something you can benefit from without it?

You can easily run up to E30 without a tune assuming stock or better MAF tuning. If you have an after market CAI I would run logs to make sure the MAF is 5% or better on straight 93.

 

[illadvised]

Who tuned it? Got a log?

It's currently an old lund tune for straight 91, but I was adding octane booster for a while. Now that I am back on straight 91, I was seeing +2 (I believe) on WOT but I tried not to beat on it after seeing that. I will try to do a wot pull next time I am on the freeway and get a log if that would help

When let that run all the way out and go back to straight 93, I will get knock here and there with WOT pulls.

Is your tune for straight 93, or is it tuned for that mixture? I just wanted to know if it will eventually level out and stop knocking on WOT at 93 (unless some knock is normal??)

I am not sure how much knock is bad or how often is bad. I only saw positive a few times and let off pretty quickly and haven't gone WOT much since then just in case. I wasn't even sure if it would go above +2 if I kept on it

I just wanted the ability to run straight 91 octane without hurting the motor, in case I have my gf drive the car for long periods of time. I didn't want to make things difficult with adding octane booster all the time.

 

[ZXMustang]

It's currently an old lund tune for straight 91, but I was adding octane booster for a while. Now that I am back on straight 91, I was seeing +2 (I believe) on WOT but I tried not to beat on it after seeing that. I will try to do a wot pull next time I am on the freeway and get a log if that would help


Is your tune for straight 93, or is it tuned for that mixture? I just wanted to know if it will eventually level out and stop knocking on WOT at 93 (unless some knock is normal??)

I am not sure how much knock is bad or how often is bad. I only saw positive a few times and let off pretty quickly and haven't gone WOT much since then just in case. I wasn't even sure if it would go above +2 if I kept on it

I just wanted the ability to run straight 91 octane without hurting the motor, in case I have my gf drive the car for long periods of time. I didn't want to make things difficult with adding octane booster all the time.

Mine is tuned for 93. And it will get small knock here and there depending on temps and DA. When I add the E, no knock at all in any weather. Just clean runs with all the timing the 93 tune is set to give in optimal conditions.

 

[Bobby57]

I was using octane booster with a few tanks in a row, and now when I go WOT I am seeing positive knockr on my nguage. It is usually negative at anything less than wide open.

This all makes sense; but how would I go about resetting what the ecu uses to guess octane, or should I just keep driving and let it figure itself out? I am not sure how much positive knock is dangerous. Would a KAM reset fix this, or would it be better to let the car figure itself out

A mechanic who helped me with a Lund tune and associated bolt-ons warned me against the excessive use of octane boosters as he came across a number of instances of a nasty orangish deposit having formed on spark plugs that he traced to their use

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