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VS commodore poor fuel economy

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I’ve had my auto 1996 vs spac commodore for a little over a year and while it’s been very reliable it’s had terrible fuel economy. When I first got it I used to get about 400kms to a tank just driving around (not city driving but not highway) but in recent months I’ve been struggling to get 300kms to a tank. In the little over a year I have done a lot of work I’ve serviced/replaced spark plugs, fuel filter, spark plug leads, cleaned throttle body, cleaned MAF sensor, new idle air control valve, The whole cooling system, oil pressure switch, transmission service with filter, valley gaskets manifold and plenum gaskets, cleaned the whole plenum, both temperature sensors, brand new Bosch oxygen sensors, 6x brand new injectors from sprints, brand new alternator. I have also done about 4-5 oil changes with filters. There’s also a couple other things I’ve done/changed but can’t remember right now. Any ideas on what else to look for? Thanks.
 

gtrboyy

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Start with basics...like fault code check & common faults for that model.

Should find all that info with forum search...you'll need to learn all that stuff if you're one fixing it anyway.

Some issues can also be caused by dud parts even if brand new...lot of crap brands out there people buy cheapest they can find & part doesn't work is getting common as can't really get genuine anymore.
 
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Start with basics...like fault code check & common faults for that model.

Should find all that info with forum search...you'll need to learn all that stuff if you're one fixing it anyway.

Some issues can also be caused by dud parts even if brand new...lot of crap brands out there people buy cheapest they can find & part doesn't work is getting common as can't really get genuine anymore.
They weird thing is the fuel economy didn’t get bad once I changed a part it just slowly got worse and worse for a couple weeks and now struggles to get 300kms it’s like something on the car just kept getting worse and I’m not sure what needs replacing at this point. It has no fault codes and runs perfect only issue is sometimes when sitting in traffic I get a very strong fuel smell which can be so strong it starts to make everyone in the car a little nauseous but I can’t find a leak anywhere. Only thing I haven’t really looked at is the fuel regulator and apparently there’s a return hose in the fuel tank which may have failed?
 

losh1971

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It's likely the FPR, when they fail they get smelly. It's fairly common issue with VS V6..
 

losh1971

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The problem you will have is you're going to need change the FPR set up because there are no factory FPRs anywhere and likely never will be.
 
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The problem you will have is you're going to need change the FPR set up because there are no factory FPRs anywhere and likely never will be.
Do you mean the fuel pressure regulator? I have pulled the vacuum off the regulator and it doesn’t smell like petrol at all. I have looked around quite a lot and cannot find a brand new one so I do have an aftermarket oasis fuel regulator to fit but just haven’t had time yet.
 

losh1971

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I can't confirm but your symptoms are suggesting FPR yes.
 

gtrboyy

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Something is on it's way out that hasn't yet failed that is making it run rich...could be anything from earth to 02 sensor,coolant temp sensor,vacuum leak who knows.

Could even be one of the replacement parts is a dud.
 

VSLesFez

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I also had the same bad fuel smell for a long time,the fuel tank cap seal wears out,it does not seal properly..The other guys are correct to .My fuel return line small diameter pipe was brocken. I replaced mine recently..I had to lower the fuel tank drivers side to get to the tank return metal pipe on the tank.It wasnt too hard.. No more strong bad smells,but my petrol cap leaks still,There is a host of reasons why our cars use too much fuel..Im struggling with my headaches.\ and ideas.I changed just about everything there is with mainly new parts..
One area we dont look at or consideder is the ECU.Im struggling with memory loss in my ECU..I beleive our ECUS must be removed and sent to a reputable ECU reconditioner and reflashed all the parameters and memory components.I also have to find a good or excellent reconditioner place.Regards LES
 

losh1971

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The PCM on a VS usually works or it doesn't. The tune is on the chip and doesn't change and VS technology only allows limited adjustments for the PCM to make while driving.
VS PCMs are not a common failure point. However, as mentioned above CTS is.
 
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