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The importance of good fuel:

Updated: Sep 5, 2022



Boosted cars are much more susceptible to engine failure from bad gas than NA cars because of the extreme pressures/heat the cylinders are under when compared to a stock compression NA car. When I(or any good tuner) send a customer a basemap for a VR30, regardless of mods, the first pull is done on significantly less boost and timing from where we will end up. The reason this is done is to do an overall wellness check on the current condition of the engine. The margin of error is much bigger when the car is running a little more than stock power/timing on the first map. This way, if a problem does occur(like a belt flying off, or bad gas) the likely hood of catastrophic failure is reduced(not eliminated). Unfortunately, even the safest tune can push an engine to the point of failure that was already close to the edge.


When it comes to fuel, where you get it is just as important as who you allow to tune your car. It doesn't matter if its from Costco, Mobile, BP, Shell, Sunoco, or the supermarket. It also doesn't matter if you have the best tuner in the world. If the quality of gas at that specific station is bad, it could lead to engine failure. This can be due to bad/old/leaking fuel storage tanks that seriously degrade the quality of fuel being pumped into your car.


Now, 1-2° of knock is completely acceptable and can happen randomly even with good fuel. There are too many factors to list as to what can be the actual cause, but something as simple as hitting a bump in the road and momentarily changing load can do this. The ECU constantly transitions between a BASE TIMING MAP and A MAX TIMING MAP. If the car detects knock, it will move away from the max timing map back toward the base timing map. It also has the ability to go even further(whatever your tuner sets in the KNOCK RETARD LIMITER MAP) which can be up to an additional 10°(or more) of timing pulled out from the BASE TIMING MAP to try and save the engine. This doesn't guarantee a save, but aids in a reduction of potential failure. When you see things like 5° of knock or more, that is usually a sign of a potentially major issue. Ignoring it can and will usually lead to an engine failure.


When a customer past or present comes to me saying their car is knocking out of nowhere(or the basemap shows a ton of knock) the first thing I tell them to do is STOP beating on the car, get the gas down to the light, and fill up at a different station(preferably a name brand) and get me another log. 997/1000 times, this fixes the issue. With no other changes to the map and the total absence knock, the problem was the fuel. I had one customer spend 2 weeks in the dealership due to the car breaking up, plugs, injectors, and coils were replaced only to find out that the fuel was not only bad, but horrible. If you smell "rotten" gas, its a smell you will never forget.


If you see a massive amount of knock come out of nowhere and cannot get ahold of your tuner right away, don't panic. Drive the car like normal to exhaust all of the fuel in the tank and fill up somewhere else and monitor it. It may take up to two refills to completely get rid of whatever was in the tank. If the issue disappears, you solved the issue on your own and there is no need for any further action other than never going back to the place that caused the issue. If it doesn't go away, there may be other issues that you will need a mechanic and/or your tuner to try and help diagnose. Many engine failures have gone misdiagnosed as a bad tune or something else when the only thing wrong was the gas they put in their car and the massive amount of detonation broke a piston/ring land or something else.


I have attached a datalog comparison below of a customer who has been having heavy knock issues. Despite turning down the timing to try and accommodate fuel quality, the knock remained and even got worse. The top log shows the customer doing an extended pull and the knock getting up to 6° which is considered heavy knock and as you can see, it would have kept going up as the run continued. The log below it is the exact same run showing zero knock. Both runs were done on the same map with the ONLY changes being made were from getting fuel at a different gas station. As you can see, by simply changing stations, a tune that someone could have seen as "dangerous" was nothing more than poor fuel and it would have been enough to eventually take the engine out.





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