Q: Misfire and engine reduce power

asked by on October 25, 2016

So my car has been misfiring cylinder 2-3 I just changed the spark plugs and ignition coils still having the same issue and there's no power going to the car everytime I floor it the check engine light keeps coming on! I will have to turn the car off and turn it back on so the light can go off but if I floor it again the same issue happens !

Mods on the car : Ultimate racing intake Vrsf chargepipe/TIAL flange BoV Remus quad exhaust Vrsf intercooler 5in Jb4 tune

My car has 72100 miles.
My car has an automatic transmission.

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When there are misfires under full throttle and there are performance modifications involved, the first potential issue to look at is a lack of fuel. You also state there is "no power going to the car when flooring it". I’m going to assume the motor is lacking power as opposed to the car losing electrical power. Making the distinction between electrical power and horsepower is important because they are two different symptoms. This is followed by the check engine light, which is to be expected when a car has such problems. Knowing what code or codes are set is the first step to diagnosing your issue. Lacking that, I will explain some possible reasons a lack of fuel is resulting in misfires in only two cylinders.

Fuel supply is dependent on pressure and volume. These two properties of fluid flow are very often misunderstood. There can be good pressure, but a stock pump may not be able supply enough volume to maintain the pressure when you floor the pedal. During a full throttle condition, fuel pressure must be maintained to properly atomize before it enters the cylinder and there must be enough fuel to supply all six cylinders with enough. Why only two cylinders are affected is a factor of how the fuel rails and fuel supply lines are organized on the intake. The injectors closest or farthest from where the supply line is connected to the fuel rail will get fuel first. At least this is one scenario that can play out in regards to fuel supply issues such as this.

What you want to take away from this is the need of a motor to be supplied with enough fuel under full throttle conditions. I would use a camping propane bottle with a valve and hose. I connect the hose to the intake manifold, open the propane valve and give it full throttle. This supplies the motor with more burnable fuel. If the problem goes away, you have confirmed the need for a fuel pump with more volume, or, the injectors may not be large enough. Testing this is done by full throttling it with a fuel pressure gauge connected to a long hose. I duct tape the gauge to the windshield. If the pressure drops significantly during full throttle operation, you need a fuel pump with greater volume. Keep in mind, pressure is dependent on volume, but volume is not dependent on pressure. If the fuel pressure does not drop, you may need larger capacity fuel injectors.

If you are losing electrical power under full throttle, you can throw all that out the window. A few things happen under acceleration. G forces push all parts of the car to the rear of the car. If there are any wires or components that are moving at this time, they could be creating a bad connection under acceleration. It’s important to note, whenever we modify our cars, we have effectively become an engineer. Your car is no longer stock and I can’t speak to anything that has been done that I cannot see. If you have done something that increases the output of the coils, they could be over taxing the coil drivers. If this is the case, everything done to attempt to add more fuel will not make any difference. You will now need to upgrade the module that drives the coils and most likely need upgraded coils. Without knowing exactly how your modifications have been carried out, it is difficult to know how they are affecting the motor as a whole. Testing coil and driver output takes some expensive equipment and extensive training with direct testing and time.

Some other things to inspect are the condition of the spark plugs. Are they black, brown or white? Are they wet, caked with carbon or completely clean? These kinds of details are valuable in figuring out what is going one. The main thing to understand is you have modified your car and that takes it out of the pattern failures we see from most owners who only commute.

If you need assistance on this issue, a certified YourMechanic technician can be dispatched to your location to inspect your engine misfires and suggest any necessary service or repair.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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