Downhill : neutral or coast in gear

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Originally Posted by CRXer

the man asked a simple tech question & wanted to know an answer & he gets the "but what about the children" brigade tellin him the finer aspects of wrappin yourself in cotton wool by always being in gear & the full fuel savings report...........

seriously..if u got nothing to contribute........dont make it obvious u got nothing

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BAM!!!! :thumbsup:

just one more thing - from memory - cruising between 90-110km/h in 5th is the most efficient speed apparently... on 5spd 1.6-2L cars

ive also been wondering about this ..

was told , injectors shut off , when coasting , and throttle is closed... so using 0 fuel ..
hope this is true . :)

i used to roll in N alll the time .. haha

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Originally Posted by preludacris

ive also been wondering about this ..

was told , injectors shut off , when coasting , and throttle is closed... so using 0 fuel ..
hope this is true . :)

i used to roll in N alll the time .. haha

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yes - "at speed" if u coast in gear , the injectors are off and the engine is run by momentum. I cannot say exactly at what load they go on and off - but the reason why you get more k's per tank on highway driving is that there is longer instances of "coasting" etc.

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Dont roll in N guys ~ its used for the transistion bewteen gears NOT a "gear".

Thanks to all those with positive and informative replies. I'm just trying learn how engines work. Maybe I should have used the wording "less fuel injected" rather than "save fuel" to prevent people telling me to go catch a bus. Safety comes first so I'll continue to do what I've always done, which is coast in gear, regardless of how much fuel is actually used or not.

I asked the same question to a fellow engineer who knows more about cars than I do and he did tried to do some research for me. He reversed engineered some of the EFI system on a R31 Skyline RB30 engine.

He said that on this ECU when your foot is not on the accelerator the Throttle Position Sensor detects your foot is off and then uses Fuel Cut / Fuel Recover tables to determine what revs to stop injecting (to prevent exhaust backfire) and then when to continue injecting again.

For this ECU there are two sets of tables for neutral and non-neutral injection when TPS is closed (accelerator off). I think from memory the non-neutral may have slightly richer injector settings (especially for autos where load is put on the engine from the torque converter)

He sent me the graphed results for fuel cut and fuel recover. The results are rpm vs against temperature. They show non 0 values, but since he didn't pull the injection amount from the ECU to display it i can't be sure that is the case. From my workplace photobucket and webstorage is blocked so I can't put up his graphs just yet.

After a big more digging I've found out from a mechanic who works for Team Dynamik that some engine management systems do cut fuel completely by means of no injector pulses, where as others tend to pulse the injectors at a low duty cycle. But in EFI cars, all cars have a fuel pump which always runs, a fuel rail, pressure regulator and return line to tank. Fuel is always doing a full loop. The regulator maintains roughly 3 bar on the rail and this is where the injectors get their pressurised fuel from for injection.

Good stuff, i always wanted to know about this.

i honestly didnt know it was mroe dangerous, looks like i learnt something from the noob forum..

first piece of information i have learnt from ozhonda in about a year ?

dont they teach u dis shiet when ure on your Ls driving around in ure manual cars..
should get a driving instructor or sumfing
dey would teach you the right way to do it

sure but u dont get the finer details about how the engine works etc
i always wondered if fuel was injected when coasting :thumbsup:

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Originally Posted by kraiye

sure but u dont get the finer details about how the engine works etc
i always wondered if fuel was injected when coasting :thumbsup:

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exactly, also, some ppl like ME, never went ot manual lessons. learnt at home BY MY SELF and have all my family laugh at me stall. :thumbsup: took me a few hours to get used to..

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Originally Posted by CRXer

Ok..let me have another go at this......

i was told a while ago,by string i think,to open up a .bin editor & see that the fuel values for coasting are not zero.....

well,i went one step further & datalogged a coasting event & what do i find...........

coasting= injector opening of 0ms,duty of 0%

this is in keepin with what honda says that they shut off the injectors when rpm over about 1000rpm & closed throttle.

I was told by a few of strings lap dogs (i apologise if it wasnt u,& whoever it was was still tryin to be civil except for his parasites)that i didnt know wtf i was talking about.

Anyway heres a shot of the log showin at the cursor(black dotted line) duty =0,inj = 0

Anyone want to comment?

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Did you do my hill experiment? A video of the test (with sound) would be superb. I tend not to believe what your computer is telling you (and then me). I'd rather you do the hill test and hear your fuel being combusted instead.

in gear ftw!

Wouldn't you be able to tell with an AF gauge?? Even a narrow band one??

Cause as soon as you step off the throttle the guage should read fully lean because theres no fuel being injected, therefore no fuel in the mixture passing the O2 sensor. yeah??