HHO Technical Checklist

Last Updated: Jun. 07, 2014


HHO will improve combustion efficiency. This is a scientific fact. When introduced into the engine along with the petroleum based fuel, it causes the flame speed to increase. This allows more of the petrol to burn during the power stroke. This will just happen. And it will be a dramatic increase over the combustion without the HHO. After the combustion efficiency is improved, the ECU is often fooled by the reduced quantity of unburned hydrocarbons and increased oxygen content, and often will add fuel to compensate. This can ruin your mileage gains.

The simplicity of what we have to do to have a successful HHO installation is: a) get some HHO into the engine, and b) adjust the sensor inputs as necessary so the ECU is not blocking the gains. That's all. If we can do those 2 things, we will always get vastly improved fuel economy and vastly improved (decreased) emissions. While this checklist was written with HHO users in mind, it will work for any other technology that improves combustion efficiency. You will find that you can adapt many of these steps to apply to whatever technology you are using to debug your project. Other combustion technologies include (but are not limited to): water vapor injection, fuel preheating, fuel vaporizers/atomizers, fuel cracking technologies (using additives to break down the fuel), etc.

You should check out these items working from the top down. They have been ordered this way on purpose so that the most likely problems are higher on the list. Also, the problems that are the easiest to test appear higher on the list than those that are difficult and/or expensive to test for.

The thing you have to realize is that the technology works. And because it does, all vehicles can be solved. If you are having a hard time getting the results you should, you just need to go through these items and find the reasons your gains are being blocked. If you keep at it, you will locate the problem and you will achieve the gains you are seeking.

1. Is your fuel saving device making HHO?

The most common bug we encounter trying to debug systems is that HHO is not being produced, or is not getting into the engine for some reason. Check your system. Measure the output of your HHO cell by doing a water displacement test. Bob Boyce recently said that a system should provide 1/4 - 1/2 liter/min of HHO per liter of engine displacement. We have since found that this amount may be too much, but it can serve as a guide to get you in the ballpark. Another thing that should be checked here is whether your unit is making HHO and/or steam. Some of the early cell developers would run their units with too much amperage and the unit would produce more steam than anything else. If your unit runs too hot to touch, you have a steamer, not an HHO cell.

1a. Are you unable to get your cell to produce the amount of amps you need?

There are 2 main reasons that a cell won't pull the expected number of amps it was designed for. The most obvious reason is that there isn't enough electrolyte – potassium hydroxide (KOH) or sodium hydroxide (NaOH). But probably you've already tried to add more electrolyte to solve this problem before turning to this debug checklist. But another problem can cause this situation: Too much foam being produced inside the cell. This is a less obvious reason, but can cause a complete failure of an HHO system. What happens is that even if no foam shows in the reservoir, there is foam inside the cell. The cell will then stop the convection of the liquid and block any new electrolyte from getting into the cell. The level of electrolyte in your reservoir will actually rise after starting up the system; and it may even overflow into your dryer, bubbler or even into your engine. This indicates foam inside your cell, and it's handled by adding a pool/spa defoamer.

1b. Is your device making too much HHO?

At present, it is a little known fact that you can make too much HHO. Let’s be a little clearer. We are doing supplemental hydrogen systems. There are systems that are designed to run on hydrogen exclusively, and we are not talking about these. We are talking about a system that runs on another fuel (gas, diesel, propane, LNG, alcohol, etc.) to which we are adding hydrogen to improve the combustion. In these systems, the correct amount of hydrogen will give the best gas mileage. Adding more hydrogen will actually reduce gains. Add too much hydrogen and your mileage will actually lose all of your gains. We've seen this many times, and it's more frequent as suppliers build bigger and more efficient systems. This subject is discussed more fully in this article: How Much HHO. But to give you a hint, we use 25 amps on our large truck cells for 15 liter semi-trucks. We find that more amperage (and more HHO) actually reduces the gains, and that at 25 amps the best mileage is achieved. Well, we've seen people use 25 amps on a 1200cc engine... and wonder why they didn't get any gains. When they reduced their amperage to 6 amps, they got great gains.

2. Is the HHO getting into the engine?

We have seen cases where a leak in the system was keeping the hydrogen from getting into the engine. A split hose can cause this, or one that is not attached at all. A check valve oriented in the wrong direction can block the HHO from getting to the engine. One time we found that the lid to a dry cell's reservoir had a leak and when this was fixed the situation resolved completely. Spray your hoses and connections with soapy water to expose any leaks in your system. Fix any that you find.


Whenever you are checking for leaks DO NOT CHECK WITH ANY OPEN FLAME NEARBY! That includes smoking near the system. This goes for any part of the installation process, as well. Even if you are checking to see if HHO is flowing through the tubes. Keep in mind that Hydrogen is an extremely flammable gas. Treat the situation much as you would if you were filling your car up with fuel at the station. KempCo Industries will not be held liable for System damage, or even personal injury, in cases such as this. But, please don't be discouraged into thinking that HHO technology is dangerous. As long as HHO is handled properly and safely, everything will work out just fine.

3. Do you have an EFIE installed?

Vehicles with carburetors and/or diesel engines do not require an EFIE. But all other fuel injected engines will need to have its electronics handled to get the gains of an HHO system installation. Usually the only sensors that require handling are the oxygen sensors that are upstream of the catalytic converter. Most 6 and 8 cylinder engines have two of these, and most 4 cylinder engines have one.

4. Do you have the right type of EFIE?

Most Japanese and German cars/trucks from about 2000 forward use wide band oxygen sensors. This is a new type of sensor that will not work with EFIEs made for narrow band vehicles. If you have a doubt about which type you need, please feel free to use our System Recommendation Form, and we'll help you determine which EFIE is right for your vehicle. You do not have to be a customer of ours to benefit from this free service. If you have Wideband sensors, you will need to get the appropriate Wideband EFIE from our online store.

5. Is your EFIE installed correctly and on the correct wire?

Refer back to the instructions for the type of EFIE you installed. If you are using a product from another company, you can still refer to our installation instructions which usually are a little more complete. The section for finding your signal wire is pretty extensive and includes a video1 of what your signal wire should look like when measured on a volt meter. If you have the correct phenomena for your signal wire, make sure you have the upstream sensor, and not the downstream sensor. Installing the EFIE on the wrong wire is one of the most common mistakes that come up on our support lines.

5a. Are the screw terminals on the EFIE's terminal block screwed down tightly?

You will need a small flat head screwdriver for the terminal block screws. Many people use a jeweler’s screwdriver to tighten the terminal onto the wires going into the EFIE's terminal block. However, you can't really get the terminal tight enough with a screwdriver that has only a 1/8" diameter handle. These terminals need to be tightened down snugly, or they may not make a secure connection. Use a larger handled screwdriver with a head that is still small enough to fit the terminal block's set-screw.

6. Reset your vehicle's onboard computer

Some computers are able to "learn" and adapt to the new conditions that exist in your engine. Since you have made a major change by adding an HHO system and EFIEs, you may need to reset the computer to erase what it learned about the system when it was inefficient, and start over again with the new improvements installed. You can reset your computer by disconnecting your battery ground wire from the car, and leaving it off for 15 to 20 minutes. Then reconnect it again. You shouldn’t need to do this every time you make a change to the EFIE's setting. But it’s a good idea to do it once you have installed your new system and are adjusting it for gains.

7. Is your EFIE functioning correctly?

This is rather easily tested. For the analog (downstream connections) on the Narrowband EFIE, measure the voltage between the connection ports of the sensor wire and the ECU wire (from the input to the output of the EFIE) for the oxygen sensor/s in question. You should see the voltage that the EFIE is adding to the sensor signal. It should read for instance “.25 volts”, if that's what you set it for.

For the (upstream connections) on the Narrowband EFIE, this digital signal will be different than the analog signal of the downstream EFIE. At the corresponding ports, you can read the EFIE's output versus ground. You should see it changing between .2 and .8 volts rather rapidly. Although, depending on your meter, it may not show the actual voltage; but instead it will round them out. Also, the green lights should be blinking. If you don't see this, you are most likely on the wrong wire, or (although rare), the EFIE may be malfunctioning.

For the upstream connections on the Wideband EFIE, you must disconnect a lead and measure the current from the output of the EFIE to ground. Your meter must be sensitive enough to measure the expected output which is from 0 - 1.5 milliamps.

Before proceeding to the following steps: Please be definite that all of the above steps are correct. The following are less likely to be the source of the problem, and require some additional expense. So if you are planning to do expensive handling, you’ll want to make sure that the simple items above are taken care of. Further, if the checklist steps above are out of spec., the following steps, even though expensive, will not resolve the situation.

8. Is your air cleaner dirty?

A dirty air cleaner can ruin gas mileage. It causes a richer mixture by restricting air flow to the engine. You can often just blow off the air cleaner with compressed air, but severe cases require replacement. Factually, you really can't go wrong with replacement because you will certainly recoup the cost in gas mileage improvement. We recommend Baldwin air cleaners.

9. Do your oxygen sensors need to be replaced?

Oxygen sensors wear out. I have seen estimates that say you should replace them after 40,000 miles. In my experience they can get many more miles than this, but if you have 100,000 miles or more on your oxygen sensors you must replace them. Note, use of leaded gas at any time can cause the early demise of an oxygen sensor, so keep this in mind. If you are experiencing engine stalls or fast idle, this can be a symptom of bad oxygen sensors. If they are old, it is likely that replacing them will give you a good increase in mileage all by itself. We have seen a number of HHO projects completely debug by doing this step.

10. Is there something else mechanically wrong with your engine?

If your engine is not working properly, adding an HHO system will not correct that. You will often find that if your engine is not working properly, just fixing it can give you a dramatic increase in mileage, all by itself. If you had any kind of check engine light before starting the project, you should get this fault explored and handled. If you're not sure, reset your computer, turn off all of your HHO, EFIE, and any other added modifications, and see if you still get a fault code. If so, get it fixed first, before adding your modifications. Sometimes fault codes don't show up as a check engine light, but can still be read by a standard reader. If you have a vehicle that was manufactured in the US after 1995, it will have an OBD testing port and you can take your car to a parts house, and they will often read your codes for free (in some places this is not allowed anymore), and help you get them handled.

11. Do you need to treat your downstream sensors?

In the past for most cases, the downstream sensors were not used in air/fuel ratio calculations. Therefore they did not need to be treated. But we are finding quite a few cases where that's not true anymore. Dodge/Chrysler and Honda from about 2002 forward have documented that they are using the rear sensors as part of their air/fuel ratio calculations. Jeeps are also doing this. We have also debugged projects by treating downstream sensors on Ford F-150s and Mercedes, even though there is no documentation that the downstream sensors are used in air/fuel ratio calculation. It is now a primary suspect when fuel mileage is not being achieved when the steps above are all found to be in. We've never seen wideband sensors used downstream from the catalytic converter, so narrow band EFIEs are needed. A further note is that you should not use Digital Narrow Band EFIEs on the downstream sensors. These were designed to work with the phenomena that we expect from the upstream sensor activity. You can use any analog narrow band EFIE to treat these sensors.

12. Do other sensors need adjustment?

After treating the oxygen sensors, the most likely sensor still needed to be treated is the MAF (Mass Air Flow) sensor or the MAP (Manifold Absolute Pressure) sensor. In most vehicles you have one or the other, but not both. In some vehicles you’ll have both, and when you do, you want to treat the MAF. After treating the MAF or MAP, the other sensors that can be tuned with profit are the IAT (Intake Air Temperature) and CTS (Coolant Temperature Sensor). Many cars only need to treat the upstream oxygen sensor(s). When this fails, we have found that most of the remaining projects will debug completely by treating the downstream oxygen sensor(s). An appropriate EFIE device (like the ones we carry) will take care of both the upstream and downstream sensor(s). In the rare cases where more tuning is needed then the MAF (or MAP if there is no MAF) has solved the case. We almost never need to treat the IAT sensor or the CTS. So treat the sensors in that order.

13. What did we miss in the steps above?

All vehicles can be solved. Some of them are a little tougher than others due to the way the ECU was programmed. But they can all be solved. The technology works. If you have gotten to this point and your vehicle is still not been solved, one of the above steps is still out. You need to find it and get it corrected. And then your results will shine through.