1986 FJ73 Converted to HZJ73 Fuel Mileage (1 Viewer)

[davegonz]

I bought a 1986 FJ73 a couple of months back and have recorded an average fuel consumption of 14.037 mpg (5 fill ups). The speedo has been checked with GPS and is off by 3% or so. I'm just wondering why it is so low since the 73 is relatively light compared to my old HZJ80 (I averaged around 17mpg). Shouldn't it be closer to 20?

Checking the data plate on the firewall tells me that I should have 3.70 gears (K052). To confirm that this was the case, I jacked up both wheels in the back and counted pinion turns per wheel revolution. I counted 4 pinion turns per one wheel rotation. So, that means it's really a 4.10 gear set. I would think that 4.10 would be a good combo with my normally aspirated 1HZ and 33's.

The truck does have a tight factory soft top and AC (which is on most of the time here in Texas).

Any ideas other than slowing down (I usually do 65 max) or turning off the AC?

 

[Eurasiaoverland]

The 1HZ is not an efficient engine, but I agree that 14 mpg is pretty poor. Even if it were on 4.11s or 4.10s (a result of 4 seems a bit ambiguous and probably needs checking) I would guess it should be better.

So, from least to most severe:

Blocked air filter
Binding brakes
Dirty injectors
Injection pump poorly timed or tuned
Low cylinder compression in engine.

 

[davegonz]

Thanks. I'll work through the list and see what I find.

 

[Bblair]

Just for a reference my bone stock 93 HZJ73 averaged 19mpg on the 5 hour trip to Windrock for last years 70 series gathering.

 

[davegonz]

Thanks for another data point that proves something is up. Maybe...

 

[davegonz]

Just for a reference my bone stock 93 HZJ73 averaged 19mpg on the 5 hour trip to Windrock for last years 70 series gathering.

What gears are you running? 3.70 or 4.10?

 

[Bblair]

K082 axle 4.10 open, semi float

 

[JuanJ]

Hello,

Almost all 70 Series trucks have 4.11:1 gears.

Slowing down is an option. Remember, the 1HZ engine was not designed with American roads in mind. While it can hold 65, it becomes thirsty as it does it. Try keeping it at 55.

On the other hand, 70 Series aerodynamics improved over the 40 Series, but not at the level of a sedan, for instance. This is one reason why going over 55 is wasting fuel in my book.

To the list above I would add proper tire pressure. Check the recommended values for your tires.

Regarding the AC, if the amplifier is properly set up, its effect on fuel mileage is not that great. Regardless of the climate, AC is essential in my book. Otherwise, the ride becomes exhausting, and I am not talking about suspension or engine noise/rattle.






Juan

 

[davegonz]

Yep, AC is permanently on here in Texas.

 

[davegonz]

Since this is a converted diesel, any chance a clogged in tank sock filter affecting fuel mileage? Hell, do these 70 series even have them?

 

[Eurasiaoverland]

K082 axle 4.10 open, semi float

Just for the record, K082 is 37:9 (4.11). 4.10 (41:10) was only fitted to the 70 Series after 1999 I believe.

 

[Eurasiaoverland]

Since this is a converted diesel, any chance a clogged in tank sock filter affecting fuel mileage? Hell, do these 70 series even have them?

I doubt it, it will just restrict performance. After all, a blockage would cause less fuel to get to the engine. What gets there would be used as normal.

 

[Bblair]

Just for the record, K082 is 37:9 (4.11). 4.10 (41:10) was only fitted to the 70 Series after 1999 I believe.

 

[Combat Wombat]

Is this an original FJ73 with HZ setup bolted in? (There are two engine bay plates displayed in this thread and I cant quite tell which is which)
Just curious, as there may of been some sort of a difference between diesel and petrol diff ratios. (The auto A440f also had some sort of ratio difference between diesel and petrol)
I know that most non boosted 4x4 here in Aus will have a significant efficiency and cruising loss with 33" tyres.

 

[Bblair]

Is this an original FJ73 with HZ setup bolted in? (There are two engine bay plates displayed in this thread and I cant quite tell which is which)
Just curious, as there may of been some sort of a difference between diesel and petrol diff ratios. (The auto A440f also had some sort of ratio difference between diesel and petrol)
I know that most non boosted 4x4 here in Aus will have a significant efficiency and cruising loss with 33" tyres.

The second engine plate is mine, in response to @Eurasiaoverland saying he didn't believe the K082 axles were offered before 1999.
Apologize for the confusion and the thread hijack.

Regards,

Brian

 

[Eurasiaoverland]

The second engine plate is mine, in response to @Eurasiaoverland saying he didn't believe the K082 axles were offered before 1999.
Apologize for the confusion and the thread hijack.

Regards,

Brian

That is not what I was saying, but maybe I need to explain my post in more detail.

K082 is 37:9 (4.11). 4.10 (41:10) was only fitted to the 70 Series after 1999 I believe.

The final drive ratio is determined by dividing the number of teeth on the crown wheel by the number of teeth on the pinion.

K082 axles are 37:9, which means 37 teeth on the crown wheel and 9 on the pinion. This gives a ratio of 4.11

A ratio of 4.10, though near identical in practical terms, is a different axle, one with 41 teeth on the crown wheel and 10 on the pinion. These were fitted on the 70 Series from about 1999.

Pedantic I know, but people use this forum for reference information, hence my post.

Similarly, apologies for the thread hijack.

EO

 

[sodafeld1]

I average 23mpg in my 2h 1988 troopy. 2000-2100 rpm 90kmh on the freeway. Stop start traffic is not worth counting. At best 9l/100km.

As a reference to 2016 corolla 29 mpg start stop driving, petrol though.

My mate with a hz troopy does not get the same fuel economy as I, but goes faster up the hills and can pull more.

 

[FJBen]

Another worthless data point you didn’t ask for

My BJ74 13bt has averaged 20mpg mixed since I got her going in 2019 over 65,000kms.
That’s ok 33 and 34” mud tires at 5k elevation since 2020.

I’ve actually never run full highway tanks sadly. I also don’t run ac and for 1/2 the year I only have a safari style top on.


That said, I would expect the 1HZ to get 15-18 from all the data points I’ve heard. I don’t think you are far off. Maybe run a bottle or diesel hot shots extreme through it and see if that helps out any.

 

[davegonz]

I ran 2 bottles of LiquiMoly Diesel Purge over the weekend. Smoothed out the idle a little bit. Let's see how that might affect fuel mileage when I fill up again.

 

[FJBen]

I also would expect driving 55-60 to yield best results. I CAN drive 75 in mine but I feel like it’s just working it harder and I don’t.

It’s seems pretty happy at 62/64 with my 34” tires, but under 60 feels like it’s just easily plodding along without much effort.

It seems like driving 55 everywhere just p1sses people off. So you can always put your turn signal on and never turn it off and they will think you are a confused old man