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Poor fuel economy

Fu Manchu

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Another thread on fuel economy. So my VZ Acclaim (2005) 185,000km is starting to use bit too much fuel, around 15-16L/100km on 98RON. Goes down a bit on the freeway. I've done a lot of work; changed fuel injectors, coils, spark plugs about 9 months ago. Last few months; fuel filter, cleaned out PCV lines, and PCV value was completely blocked after 15 years so i cleaned it, drilled extra hole in the PCV valve, cleaned MAF (it didn't look dirty), checked air filter, replaced shocks, struts, front springs. After i did the injectors/coils/plugs i got under 12L/100km for a while. I'm thinking maybe the Oxygen (O2) sensors. They are originals....others on here mentioned change after 100,000km. I put my OBD2 on today (no error codes come up), from cold drove about 15 minutes. Attached is the graph. Does it indicate any issue with the 2 sensors in this car? From cold, over 15 minutes, they go between 0 - 0.9v seems normal is it? Thanks!
Important to understand that if the readings are not ideal, it doesn't mean the problem is the O2 sensors. They may well be reading what they are designed to do and the problems can easily be elsewhere.
Like fault codes don't tell you something is broken. They tell you info that something is not getting ideal readings.
 

Subju

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Driving mathematically well makes a massive difference to how much petrol you use. Try not to use your brakes as much, look much further ahead than you normally do so you can predict traffic and skip gears if its a manual. Makes massive differences as well as using your engine to slow you down if you have a manual.
 

robgm

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Went on another 40km round trip mostly freeway 100km/h. Got 13.5l/100, so that’s much better.
 

vr304

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Would pay to replace your o2 sensors if they are old, they are a service item
 

robgm

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Yes i'm thinking to do this. Even though they appear working voltage range it doesn't mean they are giving correct signals. If people have done them after high Km's (180,000km) on this forum and had success with fuel economy then that's definitely a learning from others experience. I'll move over to the other O2 sensors thread on this.
 

mpower

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Yes i'm thinking to do this. Even though they appear working voltage range it doesn't mean they are giving correct signals. If people have done them after high Km's (180,000km) on this forum and had success with fuel economy then that's definitely a learning from others experience. I'll move over to the other O2 sensors thread on this.
my Monaro has similar k's, i swapped them out after one failed - 0 difference to fuel economy.
 

robgm

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Update 2 months later: After lockdown in Melbourne eased, we are doing higher KM per day - around 30km round trips. Now i'm getting, as of today; 12.0L/100km and on 91RON. Didn't change anything. O2 sensors on the OBD2 looked fine. So it looks like the short trips were the cause of higher fuel usage.
 

graham warburton

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Dumb questio. but in all the description, I did not see where you replaced the air filter
 

robgm

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Update again: The dashboard now says 11.9L/100km. 91 RON.
Air filter is fine. Almost 1 year ago i changed Fuel Injectors (one had failed, which caused a cylinder failure), coils (this also fixed misfire on idle with A/C on), and spark plugs. As well as doing PCV "valve" mod and cleaning PCV/manifold with carb cleaner. (First clean in 15 years).
All here (except PCV): YouTube Fuel Injectors Replacement

I installed all new shocks and springs the other month, handling is now tight and no more of the front hitting the road coming out of woolies.....video coming....

So i'm okay with the fuel economy now. Reason it was poor was due to Covid virus thing :-O
 
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robgm

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Stayed in the Gippsland area over the weekend (200km South East from Melbourne)...few hundred km drives...regularly doing 100km/h....got 11.0L/100km 91RON.
 
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