Lightweight Flywheel Issues on Newer Honda K Series

Lightweight Flywheel Issues on Newer Honda K Series

Posted on By Matthew Dennehy

Newer Honda Models, Lightweight Flywheels & Limp Mode

Swapping stock flywheels for lightweight ones are becoming increasingly popular among automotive enthusiasts. The reasons are very clear too. A lightweight flywheel makes the car snappier and allows the engine to rev more freely. The lesser inertia in the flywheel makes your car respond to upshifting instantly, which is a great feature for road racing and driving in canyons. So, for certain applications, a lightweight flywheel is a great choice.

On the downside, the downshift is also instant for a  lightweight flywheel. This means RPM drops off really quick, which can be a bit of an inconvenience in street use. Also, a lightweight flywheel absorbs less vibration, meaning that the engine will be affected in the long term, even in normal street use.

Although lightweight flywheels have some downside, those were never dealbreakers for car enthusiasts. However, causing vehicles to frequently go into Limp Mode certainly is. And this is exactly what’s happening to many vehicle owners who installed lightweight flywheels in their 2012-2015 Honda Civic Si, 2009-2014 Acura TSX, and 2013-2017 Honda Accord vehicles factory equipped with the K series engine.


What’s Triggering Limp Mode?

It turns out these vehicles have a very sensitive crank position sensor. If you do not know already, the crank position sensor measures the angular velocity of the crankshaft. Then the ECU analyzes this data and detects any anomaly in crankshaft movement, which is then interpreted as specific issues.

Your stock flywheel has enough mass to dampen the crankshaft vibration and smooth things out. When you install a lightweight flywheel, it absorbs less vibration from the engine because of its reduced mass and inertia. As a result, the crankshaft vibrates more, which changes its angular velocity. On these specific platforms, crank position sensors are sensitive enough to pick up the difference, and the ECU mostly interprets it as misfiring in all four cylinders. So, your car goes limp whenever the engine vibration reaches a specific value. We have heard countless cases where vehicles being driven home right after getting a lightweight flywheel installed, went into limp mode. The vehicles that we know are affected by this issue are listed below:

  • 2009-2014 Acura TSX
  • 2013-2017 Honda Accord
  • 2012-2015 Honda Civic Si

So, is there any solution to this rather disheartening inconvenience? Yes, there is! If you have already installed a lightweight flywheel and facing this issue, all you need to do is re-flash the car using Hondata FlashPro (or another tuning solution) and disable the 'Misfire Detection' option. While turning it off is not an ideal solution, that’s all you have got.

In case you do not know, Hondata FalshPro modifies your standard Honda ECU and adds a lot of convenient options to it; turning off misfire detection is one of them. If you want to know how to do it, please watch this easy step-by-step tutorial here.

If you have been eyeing a lightweight flywheel but have not yet installed one, there is another option for you. The crank position sensor does not trigger misfire for just any weight difference. There are flywheels lighter than your stock one but have enough mass to avoid triggering misfire detection. With a bit of research in automotive forums, you may be able to find just the perfect flywheel, tried and tested by other car enthusiasts, that won't cause this issue. Typically, anything above 15lbs is fine by the sensor and won’t trigger misfire, but results may vary.


Failing Clutch Master Cylinders On 9th Gen Civic Si Due to Stiffer Diaphragm

We have seen frequent instances where installing aftermarket clutch kits with a stiffer diaphragm, lead to master and slave cylinders to fail in the 9th Gen Honda Civic Si. Naturally, any clutch kit with a diaphragm stiffer than the stock one will put more strain on the cylinders. In the case of the 9th Gen Honda Civic Si, the master cylinder is prone to failure when a stiffer diaphragm is used. Since you have already installed your expensive clutch kit, the best solution is just to upgrade the master cylinder. A good replacement option would be the 2001-2005 Civic master cylinder.


Passing Smog Test in the CARB States with a Reflash? Not Anymore!

Gone are the days when you could pass the smog test even with modified ECUs. It used to be that, as long as you pass the Smog Test, employees in those testing facilities won't care no matter how crazy your ECU looks. Well, those good old days are gone. Now, if you fail the OBD-II check, you will also fail the Smog Test altogether.

This is specifically bad news for owners of the vehicles listed earlier equipped with a lightweight flywheel. How so? Well, if you have installed a lightweight flywheel, then you have to use Hondata FlashPro to turn off the misfire detection. But doing that will modify your ECU, resulting in a fail on the OBD-II check. You can temporarily reflash your ECU using FlashPro before the Smog Test. But then misfire detection will be back on, causing your car to go in to limp mode. Unless it's a dedicated race car, the only option left for you is to replace the lightweight flywheel with the stock one.

If you plan to go lightweight for street use in a CARB State, you need to consider opting for a flywheel that weighs at least 15 lbs (please do your own research on what works successfully). Anything below 15 lbs will trigger misfire detection and subsequent Limp Mode.