Diagnosing Poor Fuel Economy

[Cheap6]

It's not the pcv that causes the carbon build up in the intake but it is good to know it is functioning correctly. The carbon build up is from the EGR.

Actually that's a good thought. A blocked or restricted EGR port or valve will hurt fuel consumption. Worth a look.

 

[SavVYute]

Would a blocked port affect the fuel consumption?
If the valve was stuck open it would. And that would have thrown a code if it was.

 

[Cheap6]

Yep - lower EGR flow = lower inlet manifold pressure = increased pumping loss. Also an increased tendency to knock = retarded ignition timing.

The valve position is measured and if it sticks it will set a code but not necessarily if the port is blocked and the valve still moves.

 

[voney]

Just checked the PCV Valve as per SavVYute's instructions. Seems to be fine.

As far as the EGR is concerned, do I just pull it off and give it a clean with carny cleaner? Or is there some test I should do to it?

 

[zersys]

I wouldn't go Bosch for the o2 sensors. I bought them thinking it was OEM because there's a few Bosch parts in commodores, turns out it wasn't, and about four months later it threw a code at me. Many people experience the same result.

Unfortunately I couldn't find the OEM Delco sensors anywhere so I had to bite the bullet and get some from Holden. Cost me $130 .

They actually say NGK Japan on them, but they look exactly like the Delco one on my other bank. Not sure what's going on there...

 

[voney]

So, I've now got a code 23 (Intake Air Temp Sensor Voltage High) and the fuel usage is really high. I think it's my fault though because I "cleaned" the sensor with contact cleaner when I was doing the MAF the other day so that could be it.

So that's another $40 i have to spend.

 

[Cheap6]

As far as the EGR is concerned, do I just pull it off and give it a clean with carny cleaner? Or is there some test I should do to it?

Carb cleaner will work but don't let it run back into the electrical part if you can avoid it. You might need a new gasket too. The pipes can be poked through, carefully, with a length of Copper wire, with the end looped over on itself, to scrape the Carbon build up off. I suppose it's obvious, but you should avoid pushing the residue into the inlet or exhaust manifolds.

The inlet temp. sensor (the one in the air box) is pretty robust. Are you sure that it's damaged and not just unplugged or the connectors in the harness haven't pulled out or similar?

 

[theghostoftime1978]

my vt has been sitting around 14/l but its not stock, has chip, plenum and manifold spacers, pod and good bosch motorsport leads and platium plugs...its alright for a car thats nearlying 250,000km...anyway the other day i had to change a idler pulley while i was at it, i notice i had a vacuum leak behind right side rocker cover. plugged that up and now car is back to its awesome 11L/100. and i dont drive like miss daisy.

 

[SavVYute]

The air temperature sensor would have chilled when you hit it with the carb cleaner.
Colder it gets the higher the voltage output.

Maybe clear your codes and rescan it . It may have rectified itself.