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My BMW's E85 Phenomena

Ethanol & Flex Fuel Tuning

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Discussion and questions related to the course Ethanol & Flex Fuel Tuning

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Dear HPA Community, I have long been interested in using E85 as my primary fuel for my 1999 BMW 328iS. I tried it on a stock configuration and the car ran extremely strong until the Check Engine Light came on. The car seemed like it was drowning and my scanner said the car was running "Rich." I have no idea how this can make sense. I tried E85 again when using the next size up on injectors going from a stock of 21.5 pounds per hour to 24 pounds per hour. The car ran even better than before and the check engine has not come on in almost 2 years. I have not tuned the car or touched any fuel maps and it runs amazing.

My preconceived notions leading up to my questions:

1. E85 uses up to 15% or more fuel compared to gasoline.

2. I have to tune my car to tell it to use E85.

3. I have to tune the car to scale up the injectors when changing to a bigger size.

My questions are:

1. How on earth is it possible for the car to run Rich on smaller injectors and run normal on bigger injectors?

2. How does the car know what type of fuel it is to use without it being tuned?

3. Does the car even need a tune at this point either to tell it the injectors are larger or that it is using E85?

This situation has baffled me ever since. I do not know how it makes sense. Any input will be greatly appreciated. Thank you all so much.

That's an interesting situation you've got there. First of all you'll actually need around 35% more fuel by volume to run on E85 compared to pump gas so this is almost never going to work on a factory car unless it has flex fuel capability (which I doubt very much your '99 BMW has). The ECU can correct to a degree based on the narrow band O2 sensor readings and these will end up becoming long term trims that may function when the ECU is under WOT operation - That's my only plausible guess as to how the car is running. Certainly adding larger injectors will help but it's not an elegant or accurate way of making changes.

Ultimately I'd recommend getting a wideband onto the car and check the mixtures. I'd be incredibly surprised if they were optimal so a tune to suit would be very much recommended. Even if your fuelling is correct on E85, your timing almost certainly wont be.

Thank you so much for the reply Andre. The car runs so strong it is insane. I have Snap-On scanner for logging data as I do not have the privilege of owning a dyno at the moment. I have kept detailed logs and the fuel trims are close to zero during highway speeds. I do not thrash my car as it is my first and I want to take care of it but when I do give full throttle, it just flies. I have tired a wide band on it. It is the Innovate Motorsports LM-2 and values are close to 9.8 when selecting the E85 option. I am just lost for words but I am far from finished with my testing. Thank you once again for the input and I will keep that in mind going forward.

Hello everyone. I have a nice set of log files for your viewing pleasure. Brother Andre, here is what the Innovate Motorsports LM-2 shows. It is plugged into the exhaust manifold before the catalytic converter using their supplied bung. I will have more detailed logs coming soon as this one does not have the RPM but it can be somewhat easy to see where I accelerate and let off. The table shows the average and how it keeps hovering right around a lambda of 1. To avoid any confusion as well, the car is well modified but not to the extent where a serious tune is required, at least I think so. The first one I did is the M50 Intake Manifold swap and then Injectors which led to E85. After each mod I did, the car just ran well and there were no check engine lights or rough runs to mention. There is no tune on it right now either.

Short Ram Air Conical Intake.

24 lb./hr. Light Blue Top Hat Injectors.

M50 Manifold Swap.

ASC Delete.

ASC Delete Boot.

68mm Big Bore Throttle Body.


AFE Throttle Body Spacer.

Turner Motorsports Power Pulleys.

Mishimoto Electric Fan.

High Performance Ignition System.

The MAF is stock and the intake is before the MAF. The Throttle Body, ASC delete and the Boot are all after the MAF. If I am mistaken and these mods need a tune, does this still explain how the car runs so well on E85? Keep in mind the E85 one of the first mods. The throttle body and acs delete came after. Also, there is the stock Requested Lambda map for reference. Thank you for your time my friends. Let me know what you think.

Attached Files

My guess -- the fuel is not E85. Flex fuel vehicles will run with anything from E0 - E90, so other customers may not have noticed this. You need to use a fuel composition sensor to determine the ethanol content.

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