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Fuel shutoff during deceleration?

3331 Views 3 Replies 3 Participants Last post by  dflach
I remember reading "somewhere" that the Insight shuts off the fuel supply to the engine during braking to further reduce fuel consumption/emissions and to help in slowing the car. Can anyone verify this? Also, I am wondering if fuel is also shut off during deceleration (before applying the brakes). If fuel is in deed shut off, at what point does this occur? - On a slightly different topic, does anyone know if the fuel injectors deliver fuel directly to the cylinders (inside of the combustion chamber), or is fuel injected into the intake manifold just prior to the intake valve (outside of the combustion chamber)? Some posters have mentioned a problem with their Insights not being able to "cruise" with light gas pedal pressure. Their Insights accelerate and decelerate fine, but they "jerk" with light pedal pressure. I suspect that the fuel injectors may be slightly dirty, but am only speculating.
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· Registered
281 Posts
While you may or may not be right about the dirty fuel injectors, there are several different things in the Insight that could cause a slight "jerk". The thing to keep in mind is that mechanical brakes cause the car to slow down in a very smooth progression of pressure from no braking to hard braking. Foot pressure becomes braking pressure.

When the ignition and fuel injection turn on and off, that's like throwing a switch. Whatever drag turning the engine off gives happens in one surge. There is no smooth transition. It's not a lot of drag, but what drag there is happens all at once.

There are several separate coils in the regenerative-braking-generator that are electronically engaged and disengaged. You can see this happen with the green "charge" lights on the dash. This is not a smooth transition, like brake pressure. These are I believe four separate stages that are switched in sequence. This gives you varying degrees of braking, but again, it is "digital", not "analog", and very low resolution at that. Each stage doesn't do a lot of braking, so the surges or jerks are subtle enough that most people don't notice them, but if you feel for them, you can definitely feel each one.

Then there's the anti-skid brakes. Slam on the brakes, or hit a patch of sand, gravel or ice and the brakes begin stuttering so that the wheels don't lock. It won't make you stop in shorter distance, but it will allow you to continue to steer while braking, whereas locked wheels will slide sideways as easily as forward. Anyway, this stuttering is also jerky.

Similarly, the increasing stages of boost (yellow bars on the dashboard) are also switched in, so there's a subtle jerk as each is engaged. It's a jerky car in this subtle kind of way. It would cost a lot more to give the electronics the same kind of smoothness that straight hydrolic brakes offers, and likely, there would be a loss of efficiency as well. True sine-wave inverters, for example, cost more and consume more power than modified (jerky) sine-wave inverters.

· Premium Member
766 Posts
I can verify that no fuel is delivered to the engine in fuel cutoff mode (foot off gas, car in gear, RPM above a certain amount) and in regen-braking mode (same as fuel cutoff plus foot on brake) from personal observation. Here's additional references:

Fuel cutoff mode: ... elcut.html

Regen braking mode: ... aking.html

You can see both on the instantaneous MPG display in L/100km mode -- your consumption will drop to 0 L/100km indicating that your car is not consuming any gasoline.

Don't have a reference but I'm certain that the fuel injectors are outside the cylinder. People with "hesitation" problems have reported on this forum that replacing the EGR valve fixed the problem.
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