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Poor fuel economy

robgm

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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!
 

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mpower

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how are the cats? blocked cats also don't help. is the power down as well?
 

robgm

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Power seems fine. How do i check the cats?
 

mpower

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Power seems fine. How do i check the cats?
they can really only be checked off the car as far as I know but they can become blocked when the material breaks up - your car has a few k's so was a thought.
 

robgm

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I checked for air leaks around the manifold/plenum. There's a couple of hoses i can hear air... what are these i can't find them in the Haynes manual?
Also, i pulled out the PCV valve several months ago to clean and drill bigger holes, and i put back in, but i only had some blue threadlock from my RC car. It feels a bit loose, so i'll pull out and get some red threadlock to use on it.
 

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Fu Manchu

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The one you have there is the HVAC Vacuum line.
Block that off and see if the car runs better.
The PCV hoses are common to leak. You can still buy them.
There can also be leaks from the barbs they connect to on the intake plenum.
Some are blessed with pressed in brass barbs. Only the hose can leak.

Then there are some that are plastic and screw in. They can be replaced with brass barbs. There’s a thread on it. Search and you’ll find it.
I did one in 2019 in my VE Calais thread.

Then, then there are the plastic ones pressed in with an o-ring seal. Of course these bugger up spectacularly.

Which do you have? Try twisting the plastic ones out to see if it’s threaded.

You can reinstall threaded brass barbs outlined in the thread. There is a YouTube video on it too.

Some replace the rubber ends with regular vacuum tube by cutting off the flogged put rubber and pushing the plastic pipe into it.

Oh and there’s plenty of slack in the booster hose on the plenum end. Snip of 10-15mm and push on again. You’ll get a good seal.
 

robgm

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Is the HVAC vacuum line the thin tube with the white thing attached to it? I can hear air escaping where it attaches to plenum. What's the larger hose in the photo because that also has air escaping - it's a bit loose on the plenum even it has those metal clips - i tried vaseline to seal it but i think that's not working?
I don't think my PCV hose is leaking. Its more likely the PCV valve where it attaches to the manifold....as i said, i used weak threadlock on it and i think its come loose....i'll pull it out and put red threadlock on this weekend. I remember its really loose if you just push back in without thrreadlock.
 

Whiteshark68

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The one thing you do not say is what is your average speed is to get that fuel usage or what sort of trips you are doing
 

robgm

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i think that small white thing is in the line to the power brake booster. Vacuum off the plenum.
Trips have been short (under 5km) due to lockdown. But recently done some 20km and freeway to see if any different. Yes it improves but not as much as few months ago. I'm thinking the PCV valve is loose i'll redo it today.
 

Fu Manchu

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The small white thing is the vacuum line for the HVAC. The thin tube is the HVAC tube. The white thing is a one way check valve.

The booster has a bigger diameter hose and is as I described. It's check valve is on the brake booster where it goes in.

The PCV system is not just the valve. It includes the two hoses from each side of the intake plenum, and the throttle body. Also to the intake pipe before the throttle body. These will harden and not seal so well.
 
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