NewB

[DaNav]

Hi all,

We've recently purchased a manual 2017 STX Navara (70000 kms) which we were really happy with until we drove it from Perth to Exmouth and returned fuel consumption of around 11 to 11.5 litres/100 km, mostly cruising along at 105 kmh with the occasional passing of the odd road train. 2 ppl on board, not much gear as we're in accommodation, clear skies, no headwinds, not towing. I know manufacturers, ummmmm, maybe stretch the truth a little with fuel consumption, but this seems beyond stretched and more like a problem.

While searching the forum I read @amber.2's fuel consumption issue which seemed to have started after removing a shunt to the negative side of the starting battery.
There's a few mods to the Nav we bought, including a dual battery installed under the tub, via a RedArc SB12 solenoid, and I'm thinking maybe this shunt has been removed when the dual battery was installed.

Can anyone please provide some detail about this shunt - if possible a photo would be awesome so I know where to look - or if anyone has had similar experience and has thoughts to throw my way that'd be appreciated also.

Thanks in advance

Dave

 

[SJM683]

Does it have standard size road tyres like factory?
Steel bar work, canopy, etc will all have an effect too.

Dirty air flow meter, leaking fuel rail pressure relief valve, bad earths under the bonnet (often paint under the factory points), and many other things can start affecting consumption.

Some models did indeed have smart charge which requires the sensor near the battery negative terminal.
You should expect to see 10L/100kms or less, I used to get 8L/100km average in our 2008 ST-X with alloy bull bar.

 

[DaNav]

Does it have standard size road tyres like factory?
Steel bar work, canopy, etc will all have an effect too.

Dirty air flow meter, leaking fuel rail pressure relief valve, bad earths under the bonnet (often paint under the factory points), and many other things can start affecting consumption.

Some models did indeed have smart charge which requires the sensor near the battery negative terminal.
You should expect to see 10L/100kms or less, I used to get 8L/100km average in our 2008 ST-X with alloy bull bar.

Thanks for the reply.
Tyres & wheels aren't factory but similar (slightly bigger) diameter & circumference to within 1%
Yes, there's an alloy bull bar and an OCAM rear bar, canopy, 270 awning which is sizeable and will add wind resistance, so I expected to be slightly higher than the figures quoted by Nissan but wasn't expecting 11 to 11.5 kms/100.
I've got a dirty MAF sensor on the list to check when we get it home and will also run a few of the CEM products through a few tanks to see if that helps - they made noticeable improvements to the old GU TD42.
Leaking fuel rail pressure relief valve and earths weren't on my list to check so will add those and see what we find.
Thanks again for the reply.

 

[Rhino1174]

Hi well I think your a lucky man I got a 2010 auto st and it has a canopy and 2”lift standard tyres and can’t get it to run under 14l/100km since replacing engine old engine 8 to 10s this engine 14 and have no idea why we have chased it for 6mths and can’t figure out why?? so good luck with it

 

[Chapster]

Hey Rhino did the new engine include injectors or did they come over from your old engine?

I'm in a similar boat. The best by <200k YD25 has ever got is 11L/100km on a long trip but around town its 13+.

Bloke next to me at the tip last Thursday bought his 2006 D40 for $5k with an engine with over 300k clicks. Blowing black smoke which he fixed with a $200 intercooler hose. Since fixed reckons he gets 8-9 L/100km around town and 9-10 towing his trailer. No wonder he reckons its the best purchase he's made. Lovely bloke too so good luck to him.

Fuel economy seems a damn lottery so I will watch this thread with interest. I've been on a similar 12 month plus quest to improve mine. Best of luck Dave.

 

[Rhino1174]

Hey Rhino did the new engine include injectors or did they come over from your old engine?

I'm in a similar boat. The best by <200k YD25 has ever got is 11L/100km on a long trip but around town its 13+.

Bloke next to me at the tip last Thursday bought his 2006 D40 for $5k with an engine with over 300k clicks. Blowing black smoke which he fixed with a $200 intercooler hose. Since fixed reckons he gets 8-9 L/100km around town and 9-10 towing his trailer. No wonder he reckons its the best purchase he's made. Lovely bloke too so good luck to him.

Fuel economy seems a damn lottery so I will watch this thread with interest. I've been on a similar 12 month plus quest to improve mine. Best of luck Dave.

New engine was complete only thing swapped from old was the alternator engine came out of a 2012 model with 80,000k on it egr is blocked off so was old one it’s just a real head scratcher the turbo is working fine have cleaned intercooler and triple checked all hoses for anything and nothing seems to make a darn difference to it we even tried a tilix setup bypass the ecu for boost and still 14l/100 on open road around town hits 20 to 25/100 literally 200km out of a tank at best yet it’s not pumping excess fuel out back brakes aren’t dragging just do t add up

 

[DaNav]

I've had similar problems on 2 different cars over the years.

1st time was a 1998 Terrano II which developed a significant lack of power and fuel economy dropped away. That turned out to be a failed air flow meter. It had only done a tad over 30000 kms and was just out of NCW but Nissan wouldn't have any part in warranty claim. It turned out to be quite a common problem with that model. Cost $1400 for a new one.

Next time was a 2008 Prado, which started lacking power and fuel economy went to 14 to 15l / 100kms and check engine light on. Codes pointed to EGR problem so we had the EGR valve replaced and cleaned out manifold without luck. Turned out to be a damaged vacuum hose and cracked MAP sensor filter - about $80 worth of parts.

Obviously neither were Navs, but will be checking similar items on the Nav to those mentioned above.

 

[Erick]

The difference between going 95-100km/h to doing 100-105km/h is noticeable in my 2005 navara. Nearly 2l/100 km. 10.5 down to 8.5/9.

 

[DaNav]

The difference between going 95-100km/h to doing 100-105km/h is noticeable in my 2005 navara. Nearly 2l/100 km. 10.5 down to 8.5/9.

Yeah, that's a good point Erick. A mechanic told me many years ago that a car uses 25% more fuel at 110 km/h compared to 90 km/h. I've found it noticeable how much more fuel a 4 cyl turbo diesel uses at 110 and 2500 rpm compared to my Clubby which rolls along gently at about 1700 rpm.

 

[Scuba Steve]

Mine does the same, most vehicles do the same thing.

 

[Rhino1174]

The difference between going 95-100km/h to doing 100-105km/h is noticeable in my 2005 navara. Nearly 2l/100 km. 10.5 down to 8.5/9.

I only dream of getting close to 10/100 I already drive like a grandpa try keep below 100km on highway don’t make any difference if I do 80 or 110kmh it still way over 14l/100 at best the bit I can’t work out is how can two engines be so different or what have I missed that’s causing the excessive fuel consumption

 

[Erick]

That sort of overfuelling will shorten engine life, mainly thru polluting the oil but also just general wear and tear thru soot. How does ur exhaust pipe look? It should just turn ur finger black but have no actual soot. I have heard MAF sensor units can go south and cause overfueling at anything above idle. Computer won’t pick that up so no fault appears.

 

[Rhino1174]

That sort of overfuelling will shorten engine life, mainly thru polluting the oil but also just general wear and tear thru soot. How does ur exhaust pipe look? It should just turn ur finger black but have no actual soot. I have heard MAF sensor units can go south and cause overfueling at anything above idle. Computer won’t pick that up so no fault appears.

Well I have given the maf sensor a clean and the map sensor also while I was at it replaced all vacuum lines so will cross fingers I will order new sensors if that don’t work as they are not expensive and worth a try the exhaust is black but not excessively built up

 

[Colonel]

After deleting the egr, replacing all vacuum lines, replacing scv, fitting catch can, cleaning intercooler, fitting new timing chains, cleaning maf sensor, and trying to drive conservatively, I still average 12.3 l/100km unladen on the freeway.
Yd25 is just a thirsty little engine I think.

 

[Rhino1174]

After deleting the egr, replacing all vacuum lines, replacing scv, fitting catch can, cleaning intercooler, fitting new timing chains, cleaning maf sensor, and trying to drive conservatively, I still average 12.3 l/100km unladen on the freeway.
Yd25 is just a thirsty little engine I think.

It is a weird beast as I said identical engine in mine was 8l/100km then it done head and literally destroyed itself so had new one put in now it’s shocking on fuel just don’t add up how can 2 engines be so different on fuel economy in same vehicle with all same running gear nothing different?

 

[Chapster]

@Rhino1174 , @DaNav , @Colonel Any of you having any luck getting to the bottom of your fuel economy problems?

 

[Rhino1174]

hi unfortunately no joy still can’t figure it out just been thru entire vehicle done all earths even added couple extra from battery to body and engine just in case I haven’t given up yet there has to be a reasonable explanation

 

[Damian m]

Hey guys,
In my experience the biggest factor I found in mine was the tyres. I've always run at's but brand wise they offer vastly different economy, up to 200ks per tank running along the same roads. At the moment I'm getting 700ks before I fuel up. Avg 65 litres per fill. Running Toyo tires at the moment too.
I thing I do also notice is the quality of the fuel makes a big difference too.

 

[dennisjh69]

@Rhino1174 , @DaNav , @Colonel Any of you having any luck getting to the bottom of your fuel economy problems?

Seems to be that the manuals get better fuel economy. I get 9lit/100k most of the time. D40 2.5 litre. Not that you would sell an auto I guess. I am old school and been driving manual since I got my licence 60 years ago.

 

[Old.Tony]

Seems to be that the manuals get better fuel economy. I get 9lit/100k most of the time. D40 2.5 litre. Not that you would sell an auto I guess. I am old school and been driving manual since I got my licence 60 years ago.

So you're driving with a Gen-Z anti-theft device (also known as a "clutch" ) ? Great stuff!

Actually there's a lot to be said for the newer autos, which lock the TC in more than just top gear, but part of the auto's poorer economy comes from the high stall speed of the torque converter. Nissan supplied a TC with a stall speed of around 2700rpm, and Wholesale Automatics (Victoria, Australia) were selling one with a 2400rpm stall speed. Still in the peak torque band (which is 1800rpm+ ) but not revving as hard with the consequential reduction in fuel consumed.

What a lot of newer readers may not know is that the torque converter - apart from providing a smooth transition in the drive train between gears - is a fluid drive, it's not a direct meshing of gears. Each turn of the engine does NOT translate into a complete turn of the gearbox input shaft so some RPM is wasted. There's a torque converter clutch (TCC) which engages in the higher gears (in my model, that's only in overdrive, but later models can lock in lower gears) removing this "waste" - but manuals simply don't have this problem.

And many Gen-Z's who haven't learned how to drive a manual simply can't. Oh there's plenty of proof.