Click for Coverage
Due to the EU’s Global Data Protection Regulation, our website is currently unavailable to visitors from most European countries. We apologize for this inconvenience and encourage you to visit for the latest on new cars, car reviews and news, concept cars and auto show coverage, awards and much more.MOTORTREND.COM
  • JP Magazine
  • Dirt Sports + Off-Road
  • 4-Wheel & Off-Road
  • Four Wheeler

AEM 50-State Legal Water-Injection Kit

Posted in How To on October 1, 2012
Share this

It was only a matter of time before someone spent enough time and money working with the California Air Resource Board (CARB) to get executive-order exemption numbers for water-injection kits on diesel engines. As long as it is correctly controlled and proportioned, injecting water into a diesel engine can not only lower exhaust gas temperatures (EGTs) and the amount of heat energy absorbed into the cylinder walls, it can also improve emissions by helping inhibit NOx formation. If anything, the CARB should be promoting water-injection kits!

But regardless of how good something works, it still needs to be tested using the proper channels and then certified before any automotive enthusiasts can legally use it on a pollution-controlled vehicle. AEM Electronics was the one to finally do the footwork and prove to the government that water injection is safe and beneficial, making AEM’s water-injection kit (currently) the only 50-state legal kit sold today.

Now, before you ask: No, this EO (executive-order) exemption number does not cover AEM’s water/methanol kits. It’s only for AEM’s water-injection kits. The company’s next step will be to get a CARB EO number for its water/meth kits.

But a straight water-injection system (no alcohol) gives most of the benefits of water/methanol injection. The only big difference is that there is no fuel (the alcohol) injected. With a 50-state-legal water-injection kit, a diesel owner should still see a slight improvement in fuel economy, lower EGTs, and slightly more power due to cooler intake temperatures. For about $500 and totally legal for use anywhere in the USA, we’re guessing ours is just the first of many diesel trucks we’ll see with a CARB-certified water-injection kit.

50-State Legal Applications

2001 to 2010 Duramax
1994 to 2003 7.3L Power Stroke
2003 to 2007 6.0L Power Stroke
2008 to 2010 6.4L Power Stroke
2003 to 2007 5.9L Cummins
2008 to 2010 6.7L Cummins

PhotosView Slideshow
03. The boost-referenced progressive controller gradually adds more water (injected into the air intake) as the boost pressure increases. The kit starts injecting water at a working pressure of 15 psi and keeps injecting more until it maxes out at 25-psi (still injecting, but does not increase amount of injection). Since the kit is CARB legal, the controller is a fixed unit that has no adjustability.

04. If you don’t have a good EGT gauge and boost gauge in your truck, AEM has those options for you, too. We actually did have both gauges, but both were broken so AEM supplied two new gauges that will allow us to monitor the difference when the system is armed.

The red and yellow wires comes out of the instrument cluster will be hooked to an “on/off” switch so we can manually switch it with the truck running. When switched on after already driving, the system will not arm until boost pressure has gone down to zero. The little green LED light left of the EGT gauge indicates when the system is working, armed, and injecting water.

PhotosView Slideshow
08. As difficult as it is to get 50-state legality on an aftermarket product, AEM has done it for the new water-injection kit.

09. There is a definite difference when towing with the water-injection kit armed. Most noticeable were the exhaust gas temperatures that dropped a couple hundred degrees when under load. You can actually feel the kit kick in at 15 psi, even though there is no added fuel being injected. The cooling effect of the water is enough to feel a little extra bump in power--about as much as an aftermarket air intake would add.

AEM recommends that the kit will use about a tank of distilled water per every full tank of diesel when towing loads. We’ve kept the kit on just driving around (unloaded) and found that the water will last through a few tanks (of diesel) before it goes dry. Since the boost pressures are higher when towing, we use more water when yanking a big trailer behind us.


AEM Performance Electronics
Hawthorne, CA 90250
Tire Pros

Connect With Us

Newsletter Sign Up

Subscribe to the Magazine

Browse Articles By Vehicle

See Results