The fuel pump is always on. Trust me. I have a surge tank with a fuel pump powered off a relay triggered by the voltage signal to the oem in tank fuel pump. As my pump sits in my trunk with no back seats to really block the noise, I can hear it whine away. Here's a pic:


"fuel cut" refers to no longer injecting any gasoline in the engine. Just because there is fuel pressure does not mean that the injectors are cycling. You can have fuel cut without stopping the fuel pump.

 

You are my new favorite person.

 

Radium...so sexy.

 

wait... what!!!!!!

 

That's it i wonder if i yell at it telling it what i'm doing it will listen? lol

 

Then the Evo is the exception to the rule.

And no, its not based loosely on facts..lol

What I said is 100% accurate, what is happening is the fuel is being cut off to the Cylinders thus causing no combustion, when the engine is require to do work, its turned back on..this is what is causing the jerking(Because this is oscillation of sorts is happening many times very quickly). This happens in most manual cars.(I apologize that it isn't cut off at the pump, but it IS in fact cut off)

 

For those keeping score at home, so far we have had fuel-cut via the fuel pump, ignition-cut while fuel is still flowing, and coasting fuel- and/or ignition-cut when the car is going under 5 mph. And even if it turns out that one or more of these ideas doesn't apply to Evos, it's because the Evo is the exception to the rule.

 

Its not fuel cut. You experience the same thing in a car with a carburetor and a mechanical fuel pump. My mustang use to do this same thing under certain circumstances. The fuel system needs to stay pressurized with our style of fuel system. Injector duty cycle drops to 0 under in gear coast conditions. The fuel pump however stays on. I dont know about X's but 8/9's would lower the voltage to the pump at low loads, but never cut power completely. Even fuel cut is done at the injectors.

 

Sounds more like driver error combined with stock/worn engine mounts to me.

 

I know what you're explaining. I don't know what causes it, but it's normal and you're not giving it enough throttle.

 

I'm trying to explain it in laymen terms as to what is occurring.

I'm not sure how much I can clear it up any more than i already have tried to.

I will try once more.

First, let me try to explain in a general sense what happens when you have a car in gear, and you are using its momentum to carry the car. (this normally occurs when going down a hill)
There is no fuel being sent to the cylinders at this point as the ECU is able to detect that work is being done by the wheels onto the crank.(I hope you all can understand this concept)
This happens in any gear, so long as the potential energy of the car is being transferred as it moves.(An example of this is when you clutch drop a car to start it[aka pushing the car and letting the clutch out in gear in order to spin the crank shaft of the motor])

Anyway.


What is happening in this instance, is that when you are a low speed in a low gear, and your car is moving under its own momentum, the fuel to the cylinders is shut down. The engine is NOT producing power. Due to the slow speed at which you are traveling, the compression of the air in the cylinders is harder to overcome. Since there is no combustion going on in the other cylinders to help with the motion the car begins to slow, at a point the ECU realizes(As someone stated earlier) that it requires a combustion to keep the engine spinning.

At this point, there is an oscillation occurring.
What I mean by this, is you are slowing down, your potential energy is turning the crank though the wheels on the road, at some point, the potential energy being transferred is not enough to keep the engine spinning. The ECU kicks in and fires off a few strokes..then it shuts down the flow again. This happens many times a second and this is why you are jerking.

As I stated earlier, you can all test this in your car, and see when the fuel is no longer flowing to the cylinders, and when you press on the gas you can almost sense when the fuel kicks back in.

I wrote this in a hurry, and will try to fix some of the terminology later.
I hope that you can understand what is going on here.

 

O.M.G. (and I'm atheist)

 

I sure hope you get it now... Geez

 

Hope you get it now :-p

 

What he said. Try and give it constant low throttle or if your are gonna be off the gas for a while try leaving it in 2nd gear. Should limit the amount of jerk but not completely get rid of it at slower speeds. Or you can just keep the working the clutch and get that left leg calf muscle on beast mode!!! If its not already...