Crappy economy

[Sphinx]

Wonder if anyone can help with a fault diagnosis. 5 litre VS that's experiencing fuel ecomony of around 17 Lt/100 and has a roughish idle when stationary. It's a 95 Stato and there's no warnings displayed on the dash.
Possibly dirty injectors? oxygen sensor faulty? Some other reason why it would run rich?

I've got a COME chip/cam package, yella heads and it used to average about 13.5 ltrs/100 but over the last two weeks it's up around 17 and it does the same run nearly every day of the week. If not injectors, then what else could it be?

 

[Joes_meat]

I'd pull out the O2 sensors first, see if they're coated in carbon. If they are you *can* clean them to an extent with carby cleaner and see if that has any improvement. Or (it works on falcons, don't know about commodores) unplug the O2 sensors and drive the car. If it drives the same they're buggered.

Could also be throttle position sensor. I've no idea where it is on the 8 but it would have to be around the throttle body. You test it with a multimeter. I'm not sure what the figures should be for your car though.

You could also check the ICS (Idle control solenoid) to see if it's full of junk. If it is, give it a good clean out. Even if it doesn't solve your economy problems, it's still a good idea.

That's all the "free" maintenence I can think of off the top of my head. You can take your injectors to get ultrasonically cleaned but that'll cost a bit.

How rough is your idle? Are all the cylinders firing?

 

[bns-sticky]

Do what I do, goto Holden get them to plug the little computer into your car and check all the sensors that way. They use a little computer and if they are half decent they wont charge you for it. It only takes about 5 min if that.

 

[Sphinx]

All 8 are firing nicely and the idle isn't too rough. got her booked into holden so they can plug in the tech1 and check her out.

 

[kopper69]

Check for fault codes. This might bring up something with the oxy sensors, in which case I would be replacing them. If not i would investigate further before i spent the $. Things like making sure the spark plug leads are tight. If you have a multimeter you can measure the resistance of the leads to determine whether they are in need of replacement. Spark plugs are a cheap fix too. Might be worth replacing them if they havent been done for a while. Check air filter is clean, blow with compressed air if possible. Clean throttle body is another cheap economy fix.

 

[burnz]

check map sensor on firewall (vacumm hose)

 

[Torquen]

would a build up of carbon make your economy ****??
cause myns running a bit on the expensive side atm. what does it cost to get a caron clean out allso?
cheers jesse.

 

[stncld]

dont know about this one, but in my old beast, it was filthy injectors (thanks, woolworths feul), and dodgy O2 and coolant temp sensors. Also check if the exhaust is choked up (prob. in the Cat). That can assist in thirstyness!

After replacing all the sensors on the car, and doing numerous other mods, she was running around 6.5L/100Km. Would be good bar ULP was 1.30/L at the time here in Rockhampton. (might add here she was a 3.9L NA V6 with dyno proven 470RWHP. Panels were a bit rough though!)