1hdt fuel mileage (1 Viewer)

[Lumpskie]

@HillCountryTX

Like @IanB said, aerodynamics really come into play at 70mph and over. That being said, my 80 gets 18-19 mph driving 75-80 mpg as my daily driver. If your fuel system components are working properly, and your AFRs are correct (meaning that you're not blowing black smoke and EGTs are good), I would just jump to 35" tires and call it a day. My rig drives better on the 35s than it did stock and it helps my fuel economy a bunch. At 3000 rpm, there's just no way that you'll get decent mileage out of these things.

 

[HillCountryTX]

@Lumpskie and @IanB ...thanks y'all!

I'm just not sure my fuel system components are working properly. How would I verify? In other words, what should I be looking for? My HDJ81 doesn't blow black smoke (just a puff on startup, which sounds like that's standard) at all, I change the motor oil every 5,000 kms (Shell Rotella T 15w40), and everything else 'seems' ok (no hesitation, no odd idling, idle rpms are around 700 rpms, etc.). However, I do not have an EGT probe (pyrometer) installed, so I'm assuming everything is ok on that front. The only part that concerns me is that the previous owner *might* have had the fuel adjusted or messed with something else. I only say this because there is a "Celcat" (Cerium Oxide) installed which supposedly helps increase fuel mileage and reduce emissions (probably magic fairy dust), which I plan on removing!! When I looked at the fuel screw it appears like it hasn't been touched (yellow paint on the threaded part and locking nut)...but who knows!?!? I just feel that I should at least be getting 18-20 mpg (US Gallons) like what @Lumpskie is getting as the daily driver.

Bigger tires make sense at highway speeds as it keeps the rpms down lower...but wouldn't the added rotational weight affect your mileage in stop n' go traffic? I'd love to justify going to bigger tires for sure but our current 31x10.5r15 tires still have plenty of life in them...

 

[IanB]

The torque of the diesel seems to deal with the weight and gearing changes of bigger tires well, as long as you're not in a hurry as it doesn't help acceleration. I'm averaging about 17.5mpg mixed use, and my best tank was 20.8mpg achieved doing about 90 in some hilly stuff, it goes down from there as speed increases I've found.

 

[carbon60]

I've had my 1994 HDJ81 since last June.

The best I ever saw was flat highway, almost completely empty, stock, 33s: 10.5 l/100km. Then I turned her into a pig, adding bumper, winch, RTT, storage, hundreds of pounds of humans and their gear…

This weekend, combined average of 16l/100km, 500 km of dirt/300 km of secondary tarmac, meaning 30-90 kph.

 

[HillCountryTX]

Thanks @IanB and @carbon60 ...it helps to hear real world numbers with our vehicles (Carbon60...I'm guessing you have an automatic like IanB?). It also gives me reason to continue to look into improving the fuel mileage, as the only deviations from stock on our truck are the ARB front winch bumper (no winch), roof rack, and a low-profile sleeping setup in the very back. Even with only one person driving and almost no gear, stock tires, stock wheels, and brand new Denso injectors, we're still getting, at best, about 16.7 mpg (US Gallons), or 14L/100km, in city/highway driving and being light on the pedal.

 

[carbon60]

Thanks @IanB and @carbon60 ...it helps to hear real world numbers with our vehicles (Carbon60...I'm guessing you have an automatic like IanB?). It also gives me reason to continue to look into improving the fuel mileage, as the only deviations from stock on our truck are the ARB front winch bumper (no winch), roof rack, and a low-profile sleeping setup in the very back. Even with only one person driving and almost no gear, stock tires, stock wheels, and brand new Denso injectors, we're still getting, at best, about 16.7 mpg (US Gallons), or 14L/100km, in city/highway driving and being light on the pedal.

I do have the auto.

I think 14l/100km combined city/highway is pretty good. To get better than that, you probably need extended periods at 90 kph.

 

[Lumpskie]

Where do you guys have your aneroid rod turned on your boost compensators? I have mine on the least aggressive side right now. Maybe that combined with my 35s help fuel economy. But, the worst economy I've had, once tuned, was 17 mpg (corrected). This is with my commuting at 75-80 mph. My rig has a rebuilt pump and injectors. Maybe that's helping my fuel economy as well.

 

[carbon60]

Where do you guys have your aneroid rod turned on your boost compensators? I have mine on the least aggressive side right now. Maybe that combined with my 35s help fuel economy. But, the worst economy I've had, once tuned, was 17 mpg (corrected). This is with my commuting at 75-80 mph. My rig has a rebuilt pump and injectors. Maybe that's helping my fuel economy as well.

Mine is, in theory, stock.

17 mpg "worst case" is impressive, for sure.

How much does the rig weigh?

A.

 

[Lumpskie]

Mine is, in theory, stock.

17 mpg "worst case" is impressive, for sure.

How much does the rig weigh?

A.

Thanks. I don't know how much mine weighs. It's stock except for my rear ARB, which doesn't have any swingouts. I will say that, before my boost compensator was properly tuned, I did get a 15mpg tank. (It might be worth your time to double check where the orientation of your aneroid rod) But I've never had anything that bad since. Do you have a pyrometer/EGT gauge? Here's a pic for reference:

 

[Mighty690]

I've only filled up once on my new HDJ-81, which is stock down to the OEM tires size, but I got a well-measured 21mpg. On my 80s I've found 65 mph (true) gives me good mileage. 70mph and north... things not so rosy.

 

[HillCountryTX]

This is great y'all, thanks! @Lumpskie, I have not checked the boost compensator/aneroid rod at all. I will have to go research this on the forum and see if it is an easy/hard thing to do. Hopefully it's somewhat straightforward. Like I mentioned before, I have no idea if the previous Japanese owner messed with this sort of thing...yikes.

I realize each rig is different, but seeing these other real-world mileages makes me think I'm definitely on the poorer fuel mileage side of things, unfortunately. I'd be happy to get 18-20 mpg (US Gallons), as I know most folks would...it seems like it's possible and I may be one or two settings away from getting this. However, I will not be spending $$$ to gain 1 mpg

 

[carbon60]

I don't know how much mine weighs. It's stock except for my rear ARB, which doesn't have any swingouts. I will say that, before my boost compensator was properly tuned, I did get a 15mpg tank. (It might be worth your time to double check where the orientation of your aneroid rod) But I've never had anything that bad since. Do you have a pyrometer/EGT gauge?

I really do need to check the boost compensator. I do not have gauges, yet.

 

[IanB]

Wow, what have you got in that thing to drive the weight up? I pulled mine onto the scales on Friday and got 1430kg front axle, 1230kg rear axle, for a total of 2660kg (5864lbs), full tank of fuel, full interior, sliders and rear bumper, etc.

Our front axle weights are nearly the same, but you've got a LOT of junk in the trunk it would appear! My front bumper is aluminum and weighs like 60lbs, if you've got a steel front bumper that could explain the front axle difference.

 

[carbon60]

Wow, what have you got in that thing to drive the weight up? I pulled mine onto the scales on Friday and got 1430kg front axle, 1230kg rear axle, for a total of 2660kg (5864lbs), full tank of fuel, full interior, sliders and rear bumper, etc.

Our front axle weights are nearly the same, but you've got a LOT of junk in the trunk it would appear! My front bumper is aluminum and weighs like 60lbs, if you've got a steel front bumper that could explain the front axle difference.

Yeah, steel ARB bumper, winch, bush style sliders/steps/bars, 220 lb RTT, storage system, fridge, food, water, extra 40l of diesel, tools, myself, etc, etc, etc: basically full load out for a camping trip of indefinite duration.

A.

 

[Sarmajor]

My truck gets about 550 - 600 km from a full tank.
But I have a JDM hdj81 with a 73 litre tank that I can squeeze 75 litres into sometimes.

 

[carbon60]

My truck gets about 550 - 600 km from a full tank.
But I have a JDM hdj81 with a 73 litre tank that I can squeeze 75 litres into sometimes.

Huh? My JDM 1994 HDJ81 has the same tank as the gasser: 95l. There was a model with a smaller tank?

 

[IanB]

Huh? My JDM 1994 HDJ81 has the same tank as the gasser: 95l. There was a model with a smaller tank?

Looking back, I've put a bit over 80L into mine on a few occasions, so I'm going to say I've got a 95L tank as well in my JDM HDJ81 as I don't run it right dry. I've never heard of a smaller tank that this, just aux tanks to add capacity, FWIW.

 

[MonsterCruiser]

Looking back, I've put a bit over 80L into mine on a few occasions, so I'm going to say I've got a 95L tank as well in my JDM HDJ81 as I don't run it right dry. I've never heard of a smaller tank that this, just aux tanks to add capacity, FWIW.

Yup, me too. I've put 83l in at one time before. I haven't verified the capacity, but if my low fuel light comes on I'm adding about 75l at that level. Not to say that the fuel level sender couldn't be off.

 

[HillCountryTX]

Does anyone have any additional suggestions for things to check to improve my fuel mileage? I'm currently at 145,000 kms right now on my HDJ81 5-speed. We can't break the 15-16 MPG (US Gallons) barrier, no matter how light our foot is.

Here's what I've done so far:
1) Replaced the original injectors at 144,000 kms with brand new Denso injectors...no significant gain in fuel mileage was noticed after several tanks of diesel We use Diesel Kleen as a fuel additive since we purchased it back in November of 2016.
2) Checked air filter...it's clean and free of oil/dirt, and was replaced at 132,000 kms.
3) All fluids and the fuel filter were changed at 132,xxx kms by the super-helpful folks at LandCruisersDirect, where I bought my HDJ81 from.

Upgrades over stock: ARB front winch bumper (no winch), roof rack (Thule square bars with bike holders/canoe holders), and sleeping platform.

Here's what I've gathered from some previous suggestions in this thread:
1) Speed/accessories/weight kills your mileage...although there are many posts in which folks have a decent amount of 'upgrades', travel at reasonable highway speeds (65 - 75mph) and they are still getting 18 - 20 mpg (US Gallons).
2) Get bigger tires (we have the stock 31x10.5r15 tires and stock wheels as well)...since larger diameter tires will enable the relatively high-revving 5 speed engine to keep lower RPMs at highway speeds, thus reducing fuel usage.
3) Check your injection pump timing/aneroid rod setting/off-boost compensator - anyone have something specific here? I don't have a pyrometer/way to measure EGTs and this is where my knowledge drops off quickly...

Thoughts?

 

[IanB]

@HillCountryTX Your tires are making the engine rev very high to maintain highway speed, I think going to 33's would make a big difference there. They call it "rubber overdrive".

Add a boost gauge and EGT gauge, and then using a manual boost controller you can raise the boost from 10psi to 15psi, without adding any additional fuel this serves to lower EGT's, and makes it much easier to drive without really flogging the engine. On my HDJ81 (auto), I find that I'm pushing 10psi at 100km/h (60mph), any faster means more fuel is required, as there's no more air available at the stock setting. The best way to describe it is it extends the powerband of the engine by about 500rpm, which is a lot on these low revving motors, and allows you to drive the truck easier and still achieve the same acceleration, better fuel economy should follow.

If you're still hungry for more, check out the official fuel pump tuning thread for all the info you can digest on the topic of tuning your injection pump.