In Front of the Flywheel - September - 2017

How Much Alcohol Is Too Much?

Many technicians today still don’t have to deal with ethanol. Others do, but they aren’t usually the ones who get caught with their pants down when it comes to these problems.

Some basic knowledge and testing procedures will greatly save diagnostic time when that one-in-a-thousand ethanol issue rolls in your door and sends you spiraling down the rabbit hole.

One thing you can be sure of: Every technician will have to deal with E85 at some point, even if gas stations in the area don’t offer it. One example is the customer who goes on vacation in a non-flex-fuel vehicle and accidentally fills the tank with ethanol at an unfamiliar station. This is an easy mistake to make, especially on a road trip, because of how common ethanol is along major highways.

E85 has to be available along the interstates for many reasons, one of which is fleet vehicles. Here’s a perfect example: When I was working with the Illinois EPA emissions testing program, a colleague picked me up in a state vehicle to drive five hours to a seminar. We needed to fill up before we left and he asked, “Where do we get E85 around here?”

I knew of one station in town, but what’s wrong with gasoline? Apparently, Illinois state rules required flex-fuel-compatible, state-owned vehicles be filled with E85. As a result, our round trip included multiple stops at stations offering E85.

What kind of problems can ethanol cause? The most common ethanol issue is too high an ethanol content in a non-flex-fuel vehicle. Because this is such a common issue, we’ll start here. This situation can cause lean diagnostic trouble codes, positive fuel trim corrections, low power, and poor fuel economy. So where do you start your diagnosis?

All of the complaints could be caused by a variety of problems: failing fuel pumps, bad mass airflow sensors, restricted catalytic converters, and cracked air inlet tubes, just to name a few. I’ve often been called to shops for such complaints, only to be greeted with, “We already replaced those things… what did we miss?”

The key to finding the root cause of the complaint, in this case ethanol, is to follow a structured and logical approach. Much like most of our usual driveability diagnostics, this logical approach needs to include fuel trim correction analysis. The procedure isn’t really any different than the way you probably already approach diagnostics; but ethanol requires learning a new signature.

For example, a failing fuel pump or a bad mass airflow sensor usually yield slightly positive fuel trim correction at idle and total fuel trim corrections increase with engine RPM. Vacuum leaks, on the other hand, behave the exact opposite: high positive fuel trim correction at idle that decreases when engine RPM increases. These fuel trim behaviors are the different signatures of each individual condition. Basically, the vehicle’s fault dictates how the fuel trim behaves when we change engine-operating conditions.

Just as these faults have their own fuel trim signatures, so does high ethanol content. When a vehicle designed to operate on conventional gasoline — with an air/fuel ratio of about 14.7 to 1 — has E85 in the fuel tank — with an air/fuel ratio of about 10 to 1 — the correction is the same, regardless of driving conditions. That’s because the engine is running lean by the same percentage under every driving condition.

The result is positive trim corrections that are relatively the same across the board. The scan data capture (figure 1) is from a vehicle with too much ethanol in the tank. The data on the left has a total fuel trim correction of +25% at idle while the data on the right is +24% to +25% at 2500 RPM.

When the same vehicle is driven under varying conditions, the total fuel trim corrections never stray far from the 25% mark. Although these fuel trim numbers are bad, the fact that they stay within a relatively small window is a strong indicator of ethanol in the tank: ethanol’s fuel trim signature.

There are always exceptions to this rule. The wrong set of fuel injectors could cause the same fuel trim behavior, due to a different injector flow rate. This possible-but unlikely fault usually occurs right after a repair, such as an engine replacement with a salvage yard unit, or even a set of nonflex- fuel injectors installed on a flex-fuel application.


If your fuel trim analysis points toward a potential ethanol problem, your next step is to prove it. An ethanol test is really easy to perform. There are a few variations, but one of the simplest requires a fuel sample, a graduated cylinder, water, and food coloring.

The test relies on the fact that oil and water don’t mix; ethanol and water do.

You should be able to find a 100-milliliter graduated cylinder for around ten bucks.

  • Fill the graduated cylinder half way, or 50 milliliters, with water, and the rest of the way, 50 more milliliters, with the fuel sample.
  • You can add food coloring to make the test results more obvious (optional).
  • Gently shake the sample and allow it to settle for a few minutes.

Gasoline will float on top of the water while the ethanol mixes with the water. So the dividing line of the two liquids will rise as the water and ethanol combine.

Once the liquids have separated, count the increase in water over the original separation of 50 milliliters, and then multiply the difference by two to estimate the ethanol content.

For example, the graduated cylinder on the left has a clear division at the 53-milliliter mark (figure 3). That’s an increase of three milliliters. When we multiply 3 times 2 we get 6, or 6% ethanol. This is a very reasonable result for oxygenated gas that often has labels on the pumps that say: “May have up to 10% ethanol added.” In most cases, around 4% to 8% is normal.

The graduated cylinder on the right has an increase of 16 milliliters, or 32% ethanol. This sample came from the fuel tank of a vehicle that had low power and lean diagnostic trouble codes. Just what you’d expect if the owner filled the tank with E85 instead of regular gas.

If you don’t want to spend any money or wait for a cylinder to arrive in the mail, use a plastic bottle. The results won’t be as accurate, but you should still be able to detect ethanol.

  • Take an empty bottle and pour a cup of water into it. Use a permanent marker to mark the level.
  • Add a second cup of water and mark new level. Now the bottle is divided into two equal quantities.
  • Dump out the water.
  • Add water to the first line and fuel to the second.
  • Cap and shake the sample and wait.

Notice the difference between the marks and the fuel sample using the plastic bottle method (figure 4). The dividing line between the two liquids is still obvious, even without adding food coloring. You may not be able to determine the exact ethanol percentage, but the substantial increase is obviously too much for a non-flex fuel application.

High concentrations of ethanol can cause issues when used in nonflex- fuel vehicles. Finding and testing for excessive ethanol is simple:

First, observe the fuel trim numbers under different operating conditions. If the fuel trims are high but relatively flat, suspect ethanol.

Second, take a fuel sample and test it to prove your theory.

Rich, lean, and performance issues can all be caused by many different faults, including fuel pressure and volume, but don’t forget to check the fuel itself.

Engine or electrical diagnostic issues you’d like to see addressed? Let Scott know. Send him an email at and you just may have your question covered in GEARS Magazine.