gas-saving tips

[Davinci_360]

I have an '89 Lemans 1.6 L w/ Throttle Body Injection and I know for a fact that the fuel injector cuts out when engine braking.

I discovered this while using a test light to diagnose some some fuel control issues. Had a wire probe that connected to the fuel injector circuit, and had that connected to a LED w/ some resistors on it. Basically it would light up (flicker actually) when the engine computer sent pulses to the fuel injector. When decelerating, it would be completely dark.

As a result, I've always used engine braking while driving.

1 question though ...

I've heard that when you use engine braking you can cause undue wear and tear on your engine and tranny - is there any truth to this???

[KING_3]

I've heard that when you use engine braking you can cause undue wear and tear on your engine and tranny - is there any truth to this???

somehow yes. because when you think of it, when you have 2cars travelling the same distance, one engine brakes and the other does not, the engine would have more revs on the car that does engine brake than that which does not. but on the odometer you won't see that difference

[KING_3]

any more proof of fuel-injectors being cut-off during engine braking.

Should we now use engine braking instead of putting it into neutral while decelerating?
Got to know the correct driving style to save gas

[benzino]

engine braking doesnt use any fuel.
when the engine is in neutral, it idles. Idling requires fuel.

By engine braking you save petrol and brake pads.

The only way you could damage transmission components is if you shifted down going too fast cause it would smoke your clutch..

[buddha102]

i dont think we care about fuel anymore nor ever cause we got woo's that go to 30+MPG

[wolfsreign]

hmmm... so thats very good reading. ive ALWAYS gone down hills in N. no matter what. or when i start going down the street.. i go to about 30-40mph, then netural it until the stop sign, then put it in drive... so basically im using more gas... @.@
who knew.?

now on.. i shall stay in drive and go down the hill at 4,000rpm.. xD
~wolf

[Big Jeff]

hmmm... so thats very good reading. ive ALWAYS gone down hills in N. no matter what. or when i start going down the street.. i go to about 30-40mph, then netural it until the stop sign, then put it in drive... so basically im using more gas... @.@
who knew.?

now on.. i shall stay in drive and go down the hill at 4,000rpm.. xD
~wolf

i put my car in 3rd or 4th gear and take my foot of the gas pedel

[KING_3]

engine braking doesnt use any fuel.
when the engine is in neutral, it idles. Idling requires fuel.

By engine braking you save petrol and brake pads.

The only way you could damage transmission components is if you shifted down going too fast cause it would smoke your clutch..

have someone already actually proven that it works this way for all cars with ECU's, or more specifically daewoo's

hope we can find some reference experiment/testing that proves this

I've read somewhere that even when you are engine-braking the injectors still feed some amount of fuel to the engine to keep it alive. Also i've read that rather it is only the car's momentum that keeps the engine alive. (that's why i am still confused )


Just another thought, let's say you are engine-braking and your foot is off the gas pedal. The throttle would then be closed but there is still the by-pass hole (from where the air is taken during idle) where little air is coming in. Given this, the ECU would think it is idle, and also feed little fuel to compensate for the little air.

Appreciate more enlightenment. Thanks guys

[wolfsreign]

would appreciate moreeee facts.

but yes, down the hill with the foot off the gas. i dont like lower gears as they make the rpm's higher.. and it just feels wrongs. like if i drop into 3rd (A/T) it feels like the tranny will fly apart. idk my feelings.

but king, my suggestion would be the vacuum like other people are/were using.. that way you could actually tell with YOUR car, the idle, the accelerating, and the engine braking.

but also with logic.. (common sense) (not being mean) if the car is using momentum.. the ecu would turn off the injectors.. and close the bypass, thus nothing would be fireing.. or "compressing" so wouldn't this then lead to the crank and rods like not spin correctly?

but then thinking, it is connected to the tranny.. which rotates the crank, which rotates the cams and water pump..
so then.. technically.. the ecu could turn off the injectors and just compress the bypass air..? thus saving fuel even more...

then comes the question of what if you need to accelerate in a split second.. everything would have to turn back on...

just some ideas.
~wolf

[Big Jeff]

i have a vacuum guage on my car and when it is in 3rd gear going down hill it reads 25" vacuum

it pritty much reads that once the engine is warm, and i have taken my foot off the gas

[wolfsreign]

whats idle vac?
whats accelerating vac? (say 2k rpm)
whats D4 engine braking vac?

just want some comparisons please. to see if it does cut fuel or not.

and is this Only for daewoos?
~wolf

[daewoomofo]

common sense says that if the ecu cut fuel the engine would die. the engine still has to maintain a propper air/fuel mixture to keep it running correctly. there is no way that it could cut the fuel off (imo).

[Davinci_360]

I think part of the confusion here comes from the difference between automatic and manual transmissions.

I can certainly vouch for a manual transmission - engine braking does stop the fuel injectors, and ignition system. You're essentially allowing the resistance of the compressed air in the cylinders to slow down your vehicle. The factory service manual calls this "decelleration mode". The inertia of the car, transferred from the wheels through the transmission, keeps the engine turning. Similiarly, when the car is stopped and you take your foot off the clutch, without giving it any throttle, the engine stalls. The momentum (or lack there of) will slow (and eventually stop) the engine turning over.

On an automatic transmission, however, I believe the engine is always turning the torque converter, so you don't see the same effect on your fuel economy. I think that's why automatics always have lower MPG ratings than manual transmissions.

I hope that makes sense.

[daewoomofo]

if the engine cut fuel and spark then it would stop running. have you actally seen the injectors stop spraying and the spark plugs stop sparking?

[Big Jeff]

if the engine cut fuel and spark then it would stop running. have you actally seen the injectors stop spraying and the spark plugs stop sparking?

the inject are always running as are the sperk plugs, when you are engine braking your thorlle body is in ilde posittion so it is only adding fuel it need for idle, so are you are actually caring the car oon the wrong mixture, but the ECU won't adjust it coz the TPS is saying it closed