Causes of Bad Fuel Economy.

[big_zop]

Yes I am really getting about that much.

Last Monday I refilled with $50, giving me about 40L. This bumped the fuel meter to 1/2 way. I travelled about 80km from then until Thursday and the fuel meter was at 1/4 way, so i had lost about 20 Liters. If I were to travel say 100km not 80 That would have probably been 25L. That is how I got that figure.

Again, you are making the assumption that the sensor is correct. Just because it says its empty and you put in 40L to get it to 1/2 and now its at 1/4, doesnt actually mean that the figures you indicate are correct.

The only way to get a better indication is to fill it up completely, reset the trip meter and fill it to the brim again. Its quite possible to have a decent amount of fuel left in the tank when it indicates empty, my car has roughly 10L which is enough to throw your figure way out.

[thechuckster]

a borked O2 sensor will only affect cruise and warm idle and only with a limited range (the ECU would fall back to the fixed map rather than apply minor O2-sensor-driven correction to fueling).

Also have a look at the CAT - it might be blocked/melted/borked.

The auto might also be an issue if it's slipping a lot and the convertor not locking up when engine/box is warm and cruising.

You can test the ECU coolant sensor by connecting it to a multimeter and dunking it in hot water - resistance should drop as it heats up.

You can test the ir temp sensor in the AFM in similar fashion but use your breath as a heat source (duh) as the AFM wont take kindly to a hot, watery soak.

The clean plugs and lack of sooty exhaust suggest the engine is running fine and there's something else afoot (e.g. box, driving style?, leaks, etc.).

Lastly, dont forget that most toyota fuel guages are non-linear in bahaviour (and the variation across models is also non-linear). Fuel level sensors seem to be the one thing that toyota never gets right.

[LeeRoy]

Yes I am really getting about that much.

Last Monday I refilled with $50, giving me about 40L. This bumped the fuel meter to 1/2 way. I travelled about 80km from then until Thursday and the fuel meter was at 1/4 way, so i had lost about 20 Liters. If I were to travel say 100km not 80 That would have probably been 25L. That is how I got that figure.

I will try turn the fuel pump on and have a look around for leaks from the fuel tank to the engine, other than that any other suggestions would be good. Ussually I would be getting 12/100 which is what I got on my previous car which was the same model.

Thanks.

Again, you are making the assumption that the sensor is correct. Just because it says its empty and you put in 40L to get it to 1/2 and now its at 1/4, doesnt actually mean that the figures you indicate are correct.

The only way to get a better indication is to fill it up completely, reset the trip meter and fill it to the brim again. Its quite possible to have a decent amount of fuel left in the tank when it indicates empty, my car has roughly 10L which is enough to throw your figure way out.

Besides this he is also assuming that as the fuel decreases that the gauge will move in a linear fashion. However, fuel tanks are not a perfect shape, they are thinner or thicker in places - so the top 1/2 on your fuel gauge may hold 25% of the tanks volume, and the bottom half may hold 75%.

Ever notice how the gauge 'hovers' at some points but rapidly declines at others?

Maybe get some definitive results - ie from dead full to dead empty/the car wont even idle, and then report.

[Big rob]

DO NOT take the tsrm as gospel when diagnosing a 1GGTE. I was of the opinion that many of the debugging was exactly the same as the 7MGE but there are slightly differnt acceptable values.

I found in Japanses a 1GGTE engine manual and a 1GGE/1GE engine manual in english on this forum. Search for it and it will be here.

BTW I thought my 1GGTE economy was bad at 13/14L/100km. It used to be 10L/100km, so as a percentage it is rather high however yours is ridiculus.

On another note, most if not all the instrumentation relies on differnt sensors than the ECU. So if your temp sensor is reading fine on the gauge, this doesnt mean the ECU one is ok.

[Z2TT]

When on empty, so absolutely no strokes showing, it's on 5 Liters, at that point the car will begin to hesitate when going on different surfaces like up a hill.

As for getting definitive results, I'm nearly on an empty tank, car is beggining to turn off. 170km reading on the Trip Computer, from 40 Liters of Fuel.
Would the type of fuel I use be a factor in fuel consumption? I use 95 RON.

[Big rob]

No there should be little difference to the type of fuel.

Have you found the 1ggte manual yet?

http://www.toymods.net/forums/showpo...2&postcount=14

I'd first check the O2 sensor, the cold start switch, the water temp switch. I've also been informed that the cold start injectors like to leak over time, it shouldnt be really neseccary in Aus so just plug it up at the fuel rail. Make sure its plugged off there and not just remove the power to it cause its still gonna leak if its leaking.

After that maybe clean the injectors and play with the AFM. Try someone elses ECU and AFM if you've got one handy.

[Z2TT]

I think there is only one cold start injector, It's located on the underside of the inlet manifold, I could take that out and see if it leaks.

The links on the post you showed me don't work.

[thechuckster]

also go borrow someone's wideband O2 sensor - will help with diagnosis (e.g. when I unplug X, the AFR's are no longer under 10:1).

[ra28_miles]

sticking brakes? that set of disk you gave me looked like a brake shoe was binding.
if its an auto the 1 way clutch in the torque converter could be stuffed/slipping. You won't see any real power loss thou only the revs won't drop as much in stall.
Could be a cold start issue not getting to the ecm, ecm thinks the engine is still cold
May be an injector but over fueling tends to equal melted pistons/black bumper- O2 sensor should see this
Could be a dirty MAP sensor- equals dirty bumper

[Z2TT]

You mean the drum section for the handbrake? Yeah that was off the old soarer, which resulted from the previous owner doing lots of handbrake drifts.

How would I go about finding out if the one way clutch is sticking, any tests?

As for cold start issue, don't think so as when starting up I can smell the rich mixture, however when warm cant smell it.

My car doesn't have a map sensor, but an AFM.

[ra28_miles]

do a stall test. With the brakes on, drop the car into drive and see how low the revs drop. Compare to manufactures specs.

the revs should drop as the car warms up aswell.

being a diesel mechanic not so about map and afm sensor but they do have boost sensors

[Z2TT]

Isn't a stall test the one where you hold the brakes on drive and rev it and see what it revs too?
As for seeing what RPM it idles at with the brakes on in drive, when warm - 500 rpm

[ra28_miles]

stall test is defeintly in drve at idle with brakes applied. don't do this for too long as the torque converter will get hot.

[Vios-GT_07]

Isn't a stall test the one where you hold the brakes on drive and rev it and see what it revs too?

that's the test to see what rpm your torque converter locks up to.. e.g. a 3500 rpm hi-stall converter will be able to rev up to this rpm with your test..

[Z2TT]

Does anybody know what the stall speed should be for a stock converter on a 1g-gte.