Poor fuel economy D40 SE auto

[SED40]

2015 D40 Silverline SE diesel auto that constantly achieves 450km per tank no matter how it’s driven or loaded. I am wondering if anybody has been in my shoes and has found a fix? I love my NAV it drives great, it’s so handy and capable but am at my wits end and seriously considering selling.

I have had Nissan reset the fuel computers twice and it didn’t seem to help. I am considering a diesel tune but am unsure.

I have owned it since new and the fuel usage has always been poor. 80000km on the clock now. bullbar, 2 inch lift, 32 inch all terrains and roof racks. I see people on this forum with tanks getting them 600+ so there has to be something wrong here.

 

[Tappet]

Welcome to the forum. That does seem quite high fuel consumption. I think the SE was was a Thai built truck and some reason the Auto Thai versions do have the highest fuel consumption of all the variants. I would steer away from remapping of the ECU. I would do the simple and less expensive tricks first. Clean the MAF sensor. Make sure that air cleaner filter is new. ERG block is a worthwhile and quite inexpensive mod. There is heaps of info on this forum about it. It raises combustion temperature and in most cases increases efficiency. Muffler delete has been well reported to give .5 of a liter per 100K less fuel consumption. Adding a tillix valve can help to. It bleeds of a tiny amount of boost prior to the boost sensor This fools the ECU so the engine is receiving more boost than the ECU believes (for want of a better way to put it.) Which in turn gives a leaner Air Fuel Ratio. However you do need a separate boost gage to see where your at with them. There is is a bloke on here called Old Tony he knows a fair bit about them.

Try the search on here there is stacks of info but I must admit it can be tricky to use

Always do one thing at a time and that way you'll know what fixes it.

 

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check for fault codes, (i dont think this is relevant but i had diesel leaking into sump, could tell when checking oil level when cold, the diesel floats on top of oil leaving clear wet area on dip stick ) my old qd32 (3.2 ltr)motor uses that amount of fuel

 

[Old.Tony]

^ Thanks for your kind words, Tappet

Yes, the Tilix valve is good but if it's not set to provide near-full boost you'll actually lose power and have slightly worse economy.

Apart from that, it's an auto, and the torque converter (which is not a direct drive and thus loses engine revolutions) has a stall speed around 2400 to 2700 rpm - which means that it's at its most efficient around in that area, so if you keep the revs steady in this TC stall window as you're accelerating you will keep the drive train at its most efficient too, and use less fuel (I've tested this and it works).

The other important thing about the auto is the torque converter lockup (engagement of the torque converter clutch, or TCC). This locks the torque converter so that no revolutions are lost (increasing efficiency) but requires certain conditions to be met. It needs a certain speed, a specific gear, a certain engine load and everything running "within normal range" (temp of engine coolant, gearbox, that sort of thing). You'll notice the TCC engaging around 70km/h in top gear under light load - the engine RPM will drop without changing gear and the car will maintain speed. It will continue this way until certain conditions are broken - vehicle speed drops below 70km/h, engine load increases over 75%, gear is manually changed (this is how it works in mine, others might vary a little in numbers but should be close).

As for fuel consumption, are you filling the tank completely, and how much fuel are you putting in after driving 450km? If the full 80 litres (dangerous, because it lets the pump run dry) then your economy is 17.8 litres per hundred km.

I would suggest a couple of things, after filling the tank completely:

* Adjust your driving style for one tank, to accelerate within the TC stall window only
* Encourage the gearbox to engage the TCC by relaxing the throttle a little as the car passes through 70-75km/h (you'll spot your exact speed after a while)
* Try not to use full throttle at all

It would also be an advantage to grab an ELM327-compliant OBD2 bluetooth adapter and use an app like Ian Hawkin's Torque (Android) to monitor things like boost pressure (important). If you're not getting around 20psi boost during normal acceleration there might be something not quite right with turbocharger control (my own BCS has failed a couple of times, so I replaced it with the Tilix valve).

 

[SED40]

Thanks Tony, Izzi and Tappet for the replies.

I usually put between 65-70L back into it. My fuel gauge doesn’t seem the ost accurate (needle doesn’t move at all the first 150km and drops like a brick after 250) and Im never brave enough to push things further.

I have noticed the TCC doing it’s thing before but wasnt ever sure exactly what was going on there. I’ll make a conscious effort to engage it and drive between the revs you mentioned tony.

After seeings how that goes I will check the MAFS and looking the ERG BLOCK mentioned by Tappet.

 

[SED40]

Taken great care to drive over the last few weeks within 2400-2700rpm when accelerating and back off once I reach my speed to encourage the TCC to engage. My latest tank fillup had me driving for 442km and putting 64.3L back in giving me 14.56L/100. So an improvement there.

My OBD2 bluetooth adapter arrived in the mail and I just took it the car for a 20 minute drive. Screenshot of the data attached. The app recorded in bar instead of PSI so you have to convert it. I hit around 20 psi a couple of times during the drive but was really having to put my foot down to do so. Most of the drive under normal acceration had me 0.3-.05 bar which is half of what I expected to see.

Does the data seem normal? I have a EGR blank plate ready to install also but wanting to try things one at a time at this stage. Thanks fellas!

 

[SED40]

I may have mucked up. In the post above, the is sensor called calculated boost. Just found another in the app called intake manifold absolute pressure. Looks more like what I should be looking for under normal acceleration. The app is called car scanner on iphone for the record.

 

[Old.Tony]

If the second chart is in PSI as the title suggests, you're getting an extraordinarry amount of boost on occasion - the peak shortly before 10:21 shows 35 psi? That's rather high, and might result in the ECU triggering a limp mode. The average boost seems a fraction low for even level-road driving. If I had to guess, it looks like the turbo is producing lower boost than normal and peaking way too high, so my first suspect would be the boost control (and on older cars like mine, the vac hoses). There was an issue with some of the newer cars that had electronic turbocharger actuator controls that Nissan recalled these over. There's also the possibility of a boost leak, look over the air path for black oily emissions.

I guess the next step for you is to determine what kind of actuator control you have. If it's electronic, has it been back to Nissan to have the thing replaced?

If it's vacuum controlled (a black hose will run from the top of the actuator forward to a device attached to the intercooler intake) then what condition are those hoses in? Is there any hardening of the rubber, or cracking, that might be allowing vacuum (thus pull on the actuator, thus reducing the amount of boost) to escape? Auto shops (like Supercheap Auto in Australia) sell this 3mm inside diameter hose for around $5/metre (and you need about 3m).

Some more precise boost information would also assist. The graphs provided show a period of several minutes of operation, but boost varies numerous times during a few seconds. It would be interesting to get a boost graph that showed a modest-powered takeoff from 0km/h to 30km/h with about 3-4 seconds of holding at 30km/h (this should allow you to perform the exercise inside any shopping mall like the Blues Brothers did, but please find a less populated place). Also on that graph would be good to see what the throttle input and engine RPM figures are.

 

[SED40]

Thanks for your help and advice.

Those spikes in the Intake Manifold absolute Pressure graph were at times were I was driving from a stop to about 80km/h. Revs were about 3500 so driving quite hard. Will follow up with some more precise graphs as suggested in the next couple of days.

I just checked and I do have the same vacuum control as you from the sounds of it (see photo). I checked the hoses running out from it to the device attached to the intercooler intake and while they seem hard the didn’t seem to be brittle or have any cracks (was hard to tell, there’s like a outer sheath to sections of the hose). no oily residue on the hoses either. While I was there I pulled out the MAF sensor (clean as a whistle) and checked the air filter and box.

For the record the car has been back to Nissan for the fuel consumption Issue. Was told it is within acceptable levels and when I said not good enough they reset the ECU for me but said further investigations would require them to have the car for a week to run a full tank of fuel.

 

[Old.Tony]

Yours is definitely vacuum-controlled. The outer sheath is supposed to protect the hoses from heat, but they usually fail on the connection point, and will either turn easily (hardened and shiny inside, not a good seal) or will have cracked and simply fall off when pulled. I've replaced mine 3 times now.

The next test will be whether the BCS (the device on the intercooler's input pipe just near the alternator) is functioning correctly. The finer detail graphs should give us some idea of that.

 

[Luke b]

Hi all
I have the same year / transmission D40 and was getting the same fuel consumption. I have a bull bar / winch / KO2’s as well. I installed a throttle controller (hike it) and found after many tanks of testing that the setting CO3 on the controller enable me to get at least 520km and on a recent trip to Hat Head got over 620km on a tank ( it was all highway) I think they are a bit thirsty , a mate gets 700km in his Colorado. I have resigned myself to now getting a gravity extender fuel tank to have peace of mind on long trips , still would like to investigate any ideas to improve economy

 

[SED40]

Hi Luke, I have a mate who bought the same model as mine at the same time who also had the same economy as us 450-500 a tank. There must be a reason why, would be great if we can figure it out for ourselves and others. Is yours also a Thai model? I drive a 79 series landcruiser for work with all the extras and its getting the same fuel economy! I will look into the throttle controller though thanks. I’ll take any extra km I can get.

So I just did the new graphs. Can only display 2 items per page. Looks like I am definitely under boosting for some reason?

 

[landmannnn]

. View attachment 34793

That must be cleanest engine bay I have ever seen, especially for a 10+ year old vehicle.

 

[SED40]

That must be cleanest engine bay I have ever seen, especially for a 10+ year old vehicle.

Cheers. It’s actually a 2015 model so not too bad. I gave the whole car a good clean up late last year when I was considering selling.

 

[Old.Tony]

If the graphs are accurate, the turbocharger is definitely underboosting. You should expect something in the order of 18-20psi at moderate throttle levels and engine RPM around 2500 (full boost is available at around 1800rpm). The question is now, is it because of the BCS not responding enough, a loss of vacuum in the system, a failing actuator on the turbocharger or a failing turbocharger?

So the next thing(s) to check: usually the BCS just ups and dies, it doesn't "get slow", so if it's providing boost control to some extent then let's assume for the moment that it's okay (because the only way to check it properly is to throw it on an oscilloscope or to replace it with a known working one). Assuming you've checked the vac hoses, the next thing is to check the actuator. A new piece of 3mm internal diameter hose long enough to reach from your mouth to the top of the turbocharger is all that's required. Connect this to the actuator and suck on the other end as you watch the shaft underneath. It should move considerably, and you should not "lose suction". If it's not moving (and moving easily), something may be wrong with the vanes in the turbocharger (sooty deposits, perhaps?) or just the actuator, which is what you'd expect: a rubber diaphragm closing the chamber where the vac hose connects, pulling up on the arm beneath. If the diaphragm is damaged, you'll lose vacuum and effectiveness (and thus turbo boost pressure). The actuator is replaceable and could come from a turbo that has had a failed shaft (although, of course, new is always better).

Finally, the expensive one: how's the shaft on the turbocharger? Does it turn smoothly with no discernible wobble (side-to-side movement of the shaft indicates worn bearings and will limit the turbocharger's rotation). Are there any signs of metallic powder (glitter) in the intercooler hose? There should be some oil smear in there, pull some out with a clean finger and examine your finger under a bright light. Metallic flakes indicate turbocharger wear and are a sign that the turbo doesn't have a lot of life left in it.

 

[Luke b]

Hi Sed40,
I have a Thai D40 (failed to mention earlier I also have a 2” lift as well) , I think what old tony and yourself are doing is great and I will follow old Tony’s words of wisdom and conduct the same test with my obd when I get a chance. I will post results for a direct comparison to yours , it will be interesting to see the results , cheers

 

[Pedro55]

Cheers. It’s actually a 2015 model so not too bad. I gave the whole car a good clean up late last year when I was considering selling.

Hi Everyone
I'm have almost the same as Luke, I have the same year, transmission, bull bar, KO2’s with Nissan roof rack Thai built D40 getting the same fuel consumption since new only 43000ks on it as I don't get away much. When towing is much worse have told dealer many times when servicing and same reply, reset ECU and no faults found so will be watching your replies for any help to improve. Thank all

 

[GunMentalGrey]

My 07 STX was up on consumption for a little while, due to lack of boost. Also plenty of black smoke and down on lower due to the lower boost. Replacing the perished vacuum hoses fixed it.