Fuel Consumption on Idle and on key starts

[bughaw787]

Does anyone know how to compute fuel consumption when the engine is on idle given the Engine displacement and RPM.

Tried searching the net and the most i can get is:
Typical Engine Idle Fuel Consumption:

500-700RPM >>>> Half a Gallon/Hour (1.8918 liters/Hour)
900-1200RPM >>>> 0.75 GPH (2.8377 LPH)

----------------------------------

FC on a 2-second keystart is about 0.0024/Gallon (0.0091/liter)

[niky]

You'll need an O2 sensor to back-calculate... some cars run slightly rich or slightly lean at idle... so you can't always tell from displacement and rpms.

The only really accurate way is to actually test it with a flow-meter attached to your fuel line.

[feeter]

Just want to share this...
Our Starex idled last night, with aircon for at least 5 hours. The fuel marker before is just slightly lower than the halfway marking, then when I checked after the 5-hour idling, the marker drops to near the baseline. Horrible isn't it? But when I drove it again, the marker rises up again to one- fourth marker and the expected FC for the entire trip was achieved accordingly.

[v6dreamer]

Just want to share this...
Our Starex idled last night, with aircon for at least 5 hours. The fuel marker before is just slightly lower than the halfway marking, then when I checked after the 5-hour idling, the marker drops to near the baseline. Horrible isn't it? But when I drove it again, the marker rises up again to one- fourth marker and the expected FC for the entire trip was achieved accordingly.

Why would you do that? 5 hours of idling w/ a/c on! Of course its horrible not to mention how many liter of gas you've burn for nothing, I understand if this is a long driving, but sitting that car idling for so many hours... I dont get it.

[bughaw787]

You'll need an O2 sensor to back-calculate... some cars run slightly rich or slightly lean at idle... so you can't always tell from displacement and rpms.

The only really accurate way is to actually test it with a flow-meter attached to your fuel line.

*niky

Was just thinking (especially if you have a new ride), the car would basically be running on a standard mix on idle. Doesnt have to be exact - an estimate would be fine so that we can have a general idea on FC.

[mazingerZ]

Why would you do that? 5 hours of idling w/ a/c on! Of course its horrible not to mention how many liter of gas you've burn for nothing, I understand if this is a long driving, but sitting that car idling for so many hours... I dont get it.

Baka brownout at nanood na lang sila ng DVD sa starex sir v6.

[v6dreamer]

Baka brownout at nanood na lang sila ng DVD sa starex sir v6.

Oo nga noh! Bakit hindi ko pala naisip yon.

[aga_cruz]

mga peeps saken mga 2 hours lang naka idle yung mb100 ko bakit kaya bumaba din ang fuel gauge???

pero nung itinakbo ko tumaas naman kahit papaano?

[coiter]

actually naiisip ko rin yan (FC on idle) just to guage kung gaano kalaki effect ng pagaantay sa sasakyan or kung trapik.

i guess the only way is the usual way kung saan magpa full tank ka, idle ka for kahit mga 1 hour (para medyo considerable ang bawas), then pa full tank uli. kung ano nadagdag sa 2nd full tank, yun ang liters/hour mo. divide mo by 60 para maging per minute para mas accurate.

pag alam mo na yan, most likely di ka na uli tatambay sa sasakyan mong naka on or lalo kang magngingitngit sa traffic kasi bilang na ang gas mo kada minutong di ka gumagalaw! hehehe

[bughaw787]

actually naiisip ko rin yan (FC on idle) just to guage kung gaano kalaki effect ng pagaantay sa sasakyan or kung trapik.

i guess the only way is the usual way kung saan magpa full tank ka, idle ka for kahit mga 1 hour (para medyo considerable ang bawas), then pa full tank uli. kung ano nadagdag sa 2nd full tank, yun ang liters/hour mo. divide mo by 60 para maging per minute para mas accurate.

pag alam mo na yan, most likely di ka na uli tatambay sa sasakyan mong naka on or lalo kang magngingitngit sa traffic kasi bilang na ang gas mo kada minutong di ka gumagalaw! hehehe

kaya lng sayang sa gas - tambay ka pa sa gasolinahan - holdap/carnap naman katapat natin dyan.

[rion]

Just want to share this...
Our Starex idled last night, with aircon for at least 5 hours. The fuel marker before is just slightly lower than the halfway marking, then when I checked after the 5-hour idling, the marker drops to near the baseline. Horrible isn't it? But when I drove it again, the marker rises up again to one- fourth marker and the expected FC for the entire trip was achieved accordingly.

Fuel marks are like that, when you turn off your engine. and turn on again, the pointer will point differently.

even flow meters cannot really make accurate readings. based from myth busters. may airflow na halo kasi eh. (saving fuel myths episode) (aircon vs no aircon with open windows) their best result was really running both vehicles in a race track on full tank and when will it starve.

imo, if you want accurate result, route your fuel outside like to a coke or something. hehe...

btw, I recall in discovery channel about a huge army tank that consumes a galon just to start it up.

[bughaw787]

mga peeps saken mga 2 hours lang naka idle yung mb100 ko bakit kaya bumaba din ang fuel gauge???

pero nung itinakbo ko tumaas naman kahit papaano?

If the numbers are right (first post) - you at least consumed something like 3.8 liters of gas (at current prices - around P190) just for idling for two with no mileage to show for it.

As for the gauge moving somewhat back up, car movement usually do that.

The numbers given were based on north american conditions and did not state whether if conditions are cold or warm, with or without AC or heater.

[kinyo]

Some new cars have digital display of fuel consumption, in km/li, which can be used to determine consumption at idle, in conjunction with the speedometer.

[mackkcam]

huhuh ang mahal na nag gas, ang 500 ko dating 10.++ liters, ngaun 9.++ liters na lng!!! waaaaaaahh that is good for 3-4 days na sana, mukhang 3 days na lng!!

[niky]

The digital readouts are not accurate... they're very general only.

The coke bottle idea is actually the most accurate. Tuason Racing created a rig like this to show off the economy of the Focus TDCi versus a gasoline 2-liter H****. You attach a bottle to the hood of the car and attach the fuel hose to that bottle. At low rpms, you're not going to need more fuel than gravity can feed to the engine (in case your fuel pump is in-tank)... so it'll work.

[bughaw787]

*niky

you know how to do this? safely?

[niky]

Not personally, but I've seen it done, and it's simple. You just need the proper fitting for the bottle you'll use for the fuel, and o-rings to secure the hose. The biggest problem is the fitting to hold the fuel bottle... TRS molded a fiberglass holster to the hood to hold it in place safely. That will cost money to make. But if you're only doing this for the sake of finding out idling consumption, then it should be safe to do with a holster clamped to a platform beside the car.

I'd suggest a start-up test and a warm idle test... but you'll have to clamp the return hose to another container to make sure fuel returned to the tank doesn't go uncounted. My car drinks an enormous amount of gas on cold startups as the fuel pump primes the fuel rail, but that fuel isn't actually used, and is returned slowly to the tank through the return line. So it seems like a liter or two, when it probably isn't that much, at all.

The test is not difficult to do, just time consuming to design and set up.

[janmike]

i have an old carburetor type car and recently it started to consume gas really fast and it's just on idling speed! so i tried setting up a bypass in between the fuel line and the gas filter into a liter of soda bottle just to give me an idea how much the engine is eating up gas. take note that i tested this with a dry carb fuel bowl down to the gas filter. so i cranked the engine a few times and the fuel pump started to sip fuel on my 1 liter gas. and when it started a third of the gas was already pumped out of my 1 liter..and so i waited. in a minute or two it started to pump again a third of the fuel and the next two minutes it was completely gone! and another two minutes the engine stalled and puffff the fuel line was dry!! 1 liter in just about 6 mins!!! i saw some leaks on the carb but not enough to spill a considerable amount of gas. obviously something is wrong along the line and definitely the carb is faulty. but where in the carb? and could there be any other part that is causing this?

[niky]

Sounds like your idle jet is leaking something fierce... either that, or your choke is stuck open. Can't tell unless we see it firsthand.

Either way, it's a fair bet it's time for a carb overhaul.

[janmike]

Sounds like your idle jet is leaking something fierce... either that, or your choke is stuck open. Can't tell unless we see it firsthand.

Either way, it's a fair bet it's time for a carb overhaul.

yep must be the idle jet (and secondary jets maybe?? or float bowl not closing??)..the choke butterfly on the other hand is fixed wide open (one click start hot or cold engine, no problem at all!?). to my understanding you needed this partially closed on cold start-ups and fully open in normal operation tama ba?? or is this the culprit?