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Ethanol & Flex Fuel Tuning: Precautions

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Precautions

06.55

00:00 - If the power possibilities of converting to E85 or an ethanol based fuel seem too good to be true, you do need to understand that ethanol does come with some downsides too.
00:12 We've already discussed the fact that ethanol can be corrosive to some fuel system components, but the other issue is to do with its hygroscopic nature.
00:22 In plain english this means that ethanol is exceptionally good at absorbing moisture from the atmosphere.
00:29 Particularly in very humid climates this can become a problem with the fuel absorbing moisture, if the fuel is left to sit in the fuel tank for even moderate periods of time.
00:40 The result of this moisture is that it can affect components in the fuel system such as the injectors and the fuel pumps and cause corrosion.
00:49 In extreme cases this can result in these components failing completely.
00:54 However actually a worse situation is when the injector still continues to operate but with the injector flow reduced by this corrosion.
01:04 The result is that the injector's flowing less than expected which can result in a lean air fuel ratio.
01:11 We can see a similar result if the fuel pump output is reduced, resulting in lower fuel pressure, and reduced fuel flow right where we need it most.
01:21 There's no simple solution to this problem but understanding it is the first step to preventing expensive damage.
01:29 How serious the issue of moisture absorption is will depend primarily on the humidity in your area.
01:36 The key is how long the car will be left with ethanol in the fuel tank.
01:41 If the car's a daily driver or is driven regularly, then generally you'll be using the fuel fast enough that you're unliekly to see a problem.
01:50 If your car is used infrequently or stored for long periods of time, such is the case with many dedicated race cars, more care is required though.
02:00 If you have a race car that runs on ethanol fuel and doesn't run between race meetings, it's advisable to drain the ethanol fuel after a meeting and run the engine to operating temperature on gasoline to flush the fuel system.
02:13 Likewise if you have a street car that's only used occasionally, then it's recommended to run gasoline through the fuel system before it's stored.
02:22 Given the wide range of humidities seen in different parts of the world, it's hard to really put an exact timeline on what's safe and what could become a problem.
02:33 Personally if I'm not going to be using a car running on E85 for more than a week or two, I would drain the tank and run it on gasoline.
02:41 The other issue that's probably one of the biggest causes of poor reliability on ethanol based fuels is the variable nature of pump E85.
02:52 As we've discussed already, the specification for pump E85 allows the ethanol content to fluctuate anywhere from 51% through to 85%.
03:02 If you're not using a flex fuel system to account for this fluctuation in ethanol content this can be a very real problem.
03:11 For example let's say that we happen to tune on a tank of E85 with an actual measured ethanol content of 51%.
03:19 We optimise the tune and get the air fuel ratio exactly where we want it.
03:24 Once the tank is empty, we refill it with fresh fuel, and this time we get E85 with an ethanol content that actually is 85%.
03:35 With an ethanol content of 51%, we have stoichiometric air fuel ratio of 11.8:1 while with 85% it's 9.8:1 What this means is that if we tune our engine on a 51% blend of ethanol to a lambda value of 0.80 at wide open throttle, when we refill with true E85, the lambda would end up much leaner since we now need more fuel to meet our target.
04:04 Without getting too bogged down on the math here, what we'd actually find is that our measured lambda under wide open throttle, would now be approximately 0.96 With this dramatic shift in lambda, it isn't hard to see how a fluctuation in ethanol content can result in engine damage.
04:23 In fact my belief is it's only the high octane rating and the cooling effect of ethanol that prevent more engines from being damaged from this exact scenario.
04:33 While varying ethanol content at the pump is obviously an issue, we can end up with the same sort of problem if we're swapping regularly between gasoline and E85.
04:44 Unless you're running a fuel cell it can be all but impossible to completely drain all of the fuel out of a factory tank.
04:52 This may result in as much as five litres of gasoline remaining in the tank when you refill on E85, and consequently this will dilute the ethanol content.
05:03 Even if we can completely empty the fuel tank, the feed and return lines from the fuel tank to the engine as well as the fuel filters and the fuel rail may contain upwards of two litres of residual fuel.
05:16 If you're dealing with race blended E85, with a guaranteed ethanol percentage, this obviously should fix the possibility of variable ethanol content in the actual fuel.
05:26 However this still can have you in the same situation due to pump gasoline dilution from residual fuel in the tank and lines.
05:35 The same issue will also happen in reverse when you swap back from E85 to gasoline as some amount of the E85 will inevitably remain in your tank.
05:46 So what can you do here? Well there are three ways to prevent this, and as usual knowledge and understanding what you're dealing with is always the first place to start.
05:56 The best solution is a proper flex fuel system, which can adjust your tune automatically as the ethanol percentage changes as we've earlier discussed.
06:06 This is how OE manufacturers deal with it, and from a car owner's perspective, it's simple as we don't need to do anything.
06:14 If you don't want to go for a full flex fuel system, then you still have some options.
06:20 At a minimum I'd recommend fitting a wide band air fuel ratio gauge somewhere you can easily see it while driving.
06:27 This will let you monitor the air fuel ratio, and you'll be able to see if it drifts rich or lean after filling up with a fresh tank of ethanol.
06:36 A better solution would be to add both a wide band gauge, and an ethanol content gauge, so you can monitor both parameters.