Stock ECUs cuts spark/fuel when coasting in gear?
 

Hi everybody,

a buddy of mine who reprograms ECU for performance/fuel savings told me that on his 1995 Mirage that the car cuts fuel and spark if the car is in gear, above 1500RPMs and decelerating. He said he believes that many other 4 cylinder imports also did this, but I'm curious if anybody else has heard of this before? I emailed him back to ask how he verified this, but I thought it was pretty cool.

sandalscout

Yeah, it's fairly common. Sometimes the ECU will have dump a little bit of gas into the engine during an in gear coast if the cat cools off enough.

The only vehicle I can say for 100% is on my 89 Honda
Civic Wagon.

On it I monitor the O2 sensor readings and the fuel is clearly cut off when the gas pedal is released, the car is coasting, in gear and the engine rpm is above about 1200.

Dude, this is SO COOL. Is this possible in ANY car? Is this just a programming thing that can be done without any physical mods. PLEASE let us know.

Another ip question is can this be done for a car that is slowing down regardless of gearing. I wold prefer to be able to coast in neutral so I dont have mechanical drag from all the other car parts that are forced to be in motion when the car is in gear. That combo (of neutral coast with feul/spark OFF) would be best for FE.

The only problem with having the engine cut fuel and spark when in neutral is the engine will stop spinning completely. This means you'll have to physically restart the engine. They cut fuel and spark when coasting in gear because this keeps the accessories running, and allows them to just reinitialize spark and fuel to get the engine to start running smoothly again, so the operation is seamless.

What you are proposing would be possible, but it would take a whole lot of work, including having the car recognise when the car went back into gear, to allow it to spin the engine back up and then restart in a smooth manner, which is going to be very difficult. Not to mention power steering, AC, water pump and alternator will also stop spinning.

It's probably pertinent to mention that the reason they can cut fuel/spark while in gear is due to available momentum to keep the engine spinning :thumbup:

Ya, you only get the fuel cut in gear.

when honda started putting the cvcc engine in the civic, I think it was 1975 or so, they had a sensor on the tac, and a switch on the intake manifold, and another on the clutch, so if the clutch was released, the engine speed was above 1,200rpm or 1,500rpm on some modles, and the intake manifold vaccum was high, it would swtich three solinoid valves on the carburator, compleatly cutting fuel to the engine, as soon as you touch the clutch, the engine speed drops to far, or the manifold vaccum is to low (accelerator pressed) the gas comes back on, and this was 30 years ago with a carburator, it just makes sense to do.

sorry if this was unclear, but this was on a stock ECU, he makes fuel changes for turboing, etc.

Thanks for the clarification, it's a neat idea!