Using too much fuel??

[TRD_ZERO]

Just wanting to know what i can check or replace or watnot.
My ae101 fxgt seems to use a fair bit of fuel. I checked the codes and at first the knock sensor came up. So i thought it was using alot of fuel because it was in limp mode. Not the case now as ecu was reset and there are no more codes so its not running in limp mode and running rich. Why else would it be using so much fuel? Ill get more exact kms per liter a little later.
For the meantime id like to know what i could check?

[Akane]

errrm, O2 sensor?

[sergei]

What is your engine temperature like?
Are you good with digital multimeter (ie know how to select voltage range and read it)?
So here is what to check:
While the car is warmed up and idling, plug in the multimeter in 20V range into E1 (negative probe) and VF (positive probe) in the diagnostic connector, give it a little bit throttle so it idles ~2000rpm, check what it reads?

If it reads 0V, recheck connection and reread the result.
If it still reads 0V, set multimeter in 2V range, and plug the positive probe into OX terminal. If that reads constant voltage below 0.5V then your Oxygen sensor is clogged/dead. If it fluctuates but does not go above 0.5V your Oxygen is on almost dead. If it is above 0.5V, somewhere between 0.85 and 1.25 range and voltage is steady, then something entirely else at fault (water temperature sensor, stuck open thermostat, AFM etc).
If it is fluctuating, and if it is fluctuating about 8 times per 10 seconds (from ~0V to 0.85V or above), then Oxygen sensor is OK, the ECU is in closed loop, and in this condition VF should be ~2.5V in this case (if it is 1.25V (or even 0) then it is compensating what it seems lean condition, if it is 3.25 or even 5V it is compensating rich condition).

You might need to check ignition timing, the knock error might have been detected due too much base advance and/or shit fuel.
If you use 91, and drive moderately the fuel economy will be a lot worse than with 95/98 (91 will end up more expensive).

[Bling]

Wow some good advice there ^^ Will give that a try to check my o2 sensor is all good.

[TRD_ZERO]

Yeah thats the sort of answer and step by step info im after, great stuff.
Ill be trying the above in a minute or two. I did a search and had one guy commenting that with his o2 sensor unplugged it doesnt really make that much difference he said he was actually getting better fuel economy.

[TRD_ZERO]

OK so i gave it a go and my readings hung around 1.2.. and when i touch the throttle it dropped to .9.. The way i read your instructions it seems my oxy sensor is fine. Correct me if im wrong.

So what else could it be? Im thinking it isnt the thermostat because it warms up normally and my last car didnt have a thermostat so i know what its like not having one/jammed open.

AFM? Does it maybe need a clean or just replace it entirely?

I must say when the car is cold when first started up it idles terribly like 800rpm and is rather hesitant when driving. But when its warm it perfectly fine except runs rich. Any ideas

[MAGN1T]

When the car is idling and warmed up the sensor voltage should cycle up and down slowly as mentioned but the highest readings shouldn't be any higher than .9V and the lowest readings should be maybe .2 or .3 volt.
Otherwise the sensor is faulty.

Steve

[sergei]

if it is constantly at 1.2V (and VF is 0V) it means that ECU is dumping fuel and/or ignoring Oxygen sensor. If Oxygen sensor would be stuck @ 1.2V somehow ECU would try to compensate and you would be running somewhat lean (VF would be 3.75V or 5V as ECU registers rich condition).

You will need to check for:
TPS
WTS
AFM
Timing
and leaky injectors.

[Stott69]

how bad is the idle? Check the vacum lines too, may have a split in the one to the vac sensor

[sergei]

how bad is the idle? Check the vacum lines too, may have a split in the one to the vac sensor

There is no vacuum sensor, but split AFM pipe would cause bad idle, or any other air leak.

[TRD_ZERO]

OK here is exact readings:
When pluged into e1 and vf1 i get a reading of 2.25v
When plugged into e1 and ox i get 1.001 when giving a little rev it goes down to .99.. then back up to 1.001.

Idle is only bad when cold sits around 900 and goes up and down +- 100 until warm then its fine and isnt so erattic

Injectors wont be at fault cause ive put my old blacktop ones in. Ill be doing a long trip on saturday ill fill it up and see how many kms i get to a tank.

[sergei]

If vf is 2.25V it means the Oxygen sensor is functioning properly.
The reason why you see 1.0V constant is probably your multimeter is not fast enough/filtering it.

[MAGN1T]

If your car is using too much fuel then it's probably running too rich. Having a look at the plugs would be a good first step as that would confirm it if they're black.
You don't even know that, you've just dived straight into the electronics.
Afterall insufficient timing would also cause bad economy but it would also run a bit hotter.

Steve

[TRD_ZERO]

I Changed the plugs two days ago and the plugs i pulled out were completly black with tiny white tips. Since changing it i feel the car drives better. Ill be able to test the fuel economy properly tomorrow on my long trip but looks like things could have changed since ive done all those small things.

[MAGN1T]

If it was mine I'd be pulling the plugs back out for another look. Several times too. If they're still black then the easiest thing to do is to fit a new oxy sensor.They have limided life.

Steve

[Crucible]

blocked air filter?
Fuel pressure?
Base timing?

the plugs are definatly a good starting point to see whats what.

[Crampy]

You can borrow my AFM or ECU from my Silvertop if you need to fault find any more. I'm out Hobsonville way.

Also, if the O2 sensor is poked, you can pull them out and heat them up witha butane tourch and that can bring them back to life (sometimes).

[TRD_ZERO]

You can borrow my AFM or ECU from my Silvertop if you need to fault find any more. I'm out Hobsonville way.

Thanks man i might just take you up on that after i replace a couple other things.

So i filled it up and have been doing abit of open road driving in this great weather. Ive noticed the car runns rather cold on the open road. The temp is about quarter when cruising at 100 and when i get into towns temp goes up to just under half like it should, shouldnt it be just under half? So id say maybe a faulty thermostat?

Also ill give a better description of that crappy idle only when cold. When car is started when cold it idles at 1100 and reves 100 each way you can feel the car vibrating because of this like its spluttering.
Ive checked and also dont think its any hoses cause this is only happening when cold and if it was a vaccume line it would do it no matter cold or warm. Could it have something to do withthe cold start and cause it runns cold it runns rich? Im just guessing here.

[sergei]

If temp goes down on highway your thermostat is poked.

As for spluttering on cold, how old are your plugs?
Could also be that your distributor cap is on the way out.

From what I gather, it is unlikely your oxygen sensor is pocked (otherwise you would not get 2.25V @ VF pin).

[TRD_ZERO]

Plugs arnt exactly new but they are a big difference with wat i changed them from but that didnt seem to make much difference with the crappy idle when cold.
Will be changing thermostat asap.
Why has no one suggested the ISCV? Could that not be affecting it?

Ill change the dizzy cap and see what changes.