Fuel Consumption on Idle and on key starts

**rion** · May 15th, 2008 11:45 AM

Originally Posted by 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.

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** · May 15th, 2008 11:50 AM

Originally Posted by 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?

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** · May 15th, 2008 11:57 AM

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** · May 16th, 2008 09:49 AM

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** · May 16th, 2008 07:44 PM

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** · May 17th, 2008 03:07 PM

*niky

you know how to do this? safely?

**niky** · May 19th, 2008 11:42 AM

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** · August 4th, 2008 03:50 PM

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** · August 5th, 2008 11:31 AM

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** · August 5th, 2008 02:44 PM

Originally Posted by 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.

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?