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Old 11-10-2009, 02:27 AM   #77 (permalink)
EcoModding Lurker
Join Date: Dec 2008
Location: lone star state
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the fuel cut. (car controls tech) Don't need to be hard. no fuses, gee.

all cars are different (and for sure the ignition can be quite different. old to new DIS.
up to 4 coils on new cars. (4 cyl)

Best way to cut fuel is just drop the gas pedal. (let it flop back)
in gear. ( as other trained ppl here have said) Yes, car will slow on not too steep a hill. but does work well.

the IDLE switch closes and the ECU detects VSS high, vacuum high ( low load) and Low RPM.
RPM comes from cam , crank or both sensors.
Some cars have virtual Idle switch , just uses the low voltage on TPS pot. (like my suzuki 1.8L sport). works that same , less parts.

Features common to EFI:
secondly the ECU will cut fuel anytime the spark read back fails.
most cars with EFI have a spark read back wire that tells ecu that spark is really happening, if this signal is to stop then all fuel injections are cut , immediatly.
89-98 Suzuki's have this wire and is on the schematic and does kill fuel if wire is cut. It uses the Back EMF from the coil primary as the trigger.

,just putting a simple switch SPST (normal closed) will work for the CMP sensors (located in the Distributor or the Cam.) You dont need a schematic for 2 wires.
but you do need the cars ecu schmatic, all public Libraries have them (at e-soruces online)

But watch out some cars with crank and cam (cmp) sensors can run with one dead.
The crank sensor is use to deskew the timing from a sloopy tim-ng belt or chain. Cam sender tells which cyl. is firing.

My 96 suzuki sidekick can run sans, crank (CKP) sensor.

The is not a green endevor because you are lettting the CATconv. cool off and that makes nasty startups.
Cold cat = smog.

so , just coast down the hill normal. Not in neutral. Just about all neutral coasting is over speed, so why overspeed.
Real coasting is illegal in most states.
when you dump the clutch on rain soak roads this can be dangerous. (ask any motorcyclist about that trick)

idling uses some gas.
fuel cut uses none to nill.

that my take.

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