I've now had the truck serviced at ATEB ($3000+). Injectors were done, pump checked, synthetic throughout the entire driveline, synthetic oil, and using Stanadyne performance plus on each tank. The fuel system was also cleaned out. ATEB tells me the truck is in perfect shape, compression is good, and there are no problems with the turbo. I am getting 12.8 litres per 100 km of mixed driving. I'm starting to wonder if this is a normal variance among these trucks. I have a friend running almost the exact same tire size, driving the same way, who is getting more than 22% better economy. The truck is not burning oil or smoking much. I DO NOT drive the truck hard, and am told the rear end is a stock ratio. I'm at a loss to explain this discrepancy. Anyone have any useful suggestions? Please keep in mind this truck has been thoroughly gone over by a shop specializing in this vehicle, they have set it up for maximum fuel economy, and they are telling me there is nothing wrong with it.
1HD-T fuel economy woes
- Thread starter Martin White
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
That is a bit lower than I would expect. It is 22 mile per gallon IMP. 18.5 us MPG
You could also see if you can adjust your fuel delivery a bit lower. I somehow doubt the place you took it too did this.
What is ATEB? and why was your bill soo darn high? You could almost rebuilt the engine for 3k.
You could also see if you can adjust your fuel delivery a bit lower. I somehow doubt the place you took it too did this.
What is ATEB? and why was your bill soo darn high? You could almost rebuilt the engine for 3k.
Last time I checked mine I was around 12.25 Liters per 100 Km's on the highway at about 105 KPH. (I run full synth everywhere too)
Tires, weight, air pressure, speed, etc... all with make a differemce.
Your 12.8 is not that bad. Also, what size tires are you running? If they are not stock, you will have to work out your odometer difference. It will no longer be accurate. Mine with 285/75/16 is now 9% out.
If your friend is getting 22% percent better, I think he is calculating his wrong ot he must be stock.. I image you would get your best economy between 1800-2000rpm in a 1HDT. On the highway I run around 2200-2250rpm.
Hope this helps,
Nick
BTW: I too always run fuel condidtioner with every tank.
Tires, weight, air pressure, speed, etc... all with make a differemce.
Your 12.8 is not that bad. Also, what size tires are you running? If they are not stock, you will have to work out your odometer difference. It will no longer be accurate. Mine with 285/75/16 is now 9% out.
If your friend is getting 22% percent better, I think he is calculating his wrong ot he must be stock.. I image you would get your best economy between 1800-2000rpm in a 1HDT. On the highway I run around 2200-2250rpm.
Hope this helps,
Nick
BTW: I too always run fuel condidtioner with every tank.
Last edited:
Here is Wayne's test run with a HDJ81:
https://forum.ih8mud.com/showthread.php?t=51487
He is getting better economy then both of us.
But he was also stock.
We both have lift's accessories and larger tires.
BTW: When I measured my economy it was not on flat ground. There is no flat ground where I am.
I am always going up or down over something.
Cheers,
Nick
https://forum.ih8mud.com/showthread.php?t=51487
He is getting better economy then both of us.
But he was also stock.
We both have lift's accessories and larger tires.
BTW: When I measured my economy it was not on flat ground. There is no flat ground where I am.
I am always going up or down over something.
Cheers,
Nick
Last edited:
Fuel Economy
Hi Martin,
I'm driving an 1HZ and I find a HUGE difference between highway and "city" driving so the "mix" of your "mixed" driving may be significant.
On straight highway driving I've gotten as good as 10.5 l/100. On almost straight city driving I've gotten over 15 . . .
I was wondering why the big difference but, with the auto, I'm running mostly around 12-1700 rpm's in town doing 40 - 50 km/hr while on the highway I'm doing 2000 rpm's at 100 km/hr.
Michael
Hi Martin,
I'm driving an 1HZ and I find a HUGE difference between highway and "city" driving so the "mix" of your "mixed" driving may be significant.
On straight highway driving I've gotten as good as 10.5 l/100. On almost straight city driving I've gotten over 15 . . .
I was wondering why the big difference but, with the auto, I'm running mostly around 12-1700 rpm's in town doing 40 - 50 km/hr while on the highway I'm doing 2000 rpm's at 100 km/hr.
Michael
- Thread starter
- #7
Further details
ATEB is a very well respected local (lower mainland, B.C. Canada) shop specializing in JDM vehicles. The money I spent was not only on what I mentioned; I restricted what I mentioned to that relevant to the fuel economy issue. They also checked out my brakes, turbo and did a few other things.
With respect to my tires, they are BFG MT's in 255-85-16 which I run at 45 psi for road use. I have calculated all my fuel consumption using GPS so I know it's accurate. My correction factor is 9.21% so I have taken that into account.
As for my buddy, he also uses GPS and is as number careful as myself, so if he says he's getting 26.5 miles per imperial gallon you can count on that number being accurate. He is running Bridgestone Revo's in 285-75-16 so his tire is also not stock.
We are both thinking that it is possible that the gear ratio on my rear end may indeed have been changed in spite of the fact that it appears not to have been. Some research has been done suggesting these engines are very sensitive to highway RPM and I seem to be running at higher RPM than he is at the same speed.
I do have a very heavy tube bumper on the front of the vehicle but other than that and the tires, I still don't see these changes accounting for a 22% difference.
ATEB is a very well respected local (lower mainland, B.C. Canada) shop specializing in JDM vehicles. The money I spent was not only on what I mentioned; I restricted what I mentioned to that relevant to the fuel economy issue. They also checked out my brakes, turbo and did a few other things.
With respect to my tires, they are BFG MT's in 255-85-16 which I run at 45 psi for road use. I have calculated all my fuel consumption using GPS so I know it's accurate. My correction factor is 9.21% so I have taken that into account.
As for my buddy, he also uses GPS and is as number careful as myself, so if he says he's getting 26.5 miles per imperial gallon you can count on that number being accurate. He is running Bridgestone Revo's in 285-75-16 so his tire is also not stock.
We are both thinking that it is possible that the gear ratio on my rear end may indeed have been changed in spite of the fact that it appears not to have been. Some research has been done suggesting these engines are very sensitive to highway RPM and I seem to be running at higher RPM than he is at the same speed.
I do have a very heavy tube bumper on the front of the vehicle but other than that and the tires, I still don't see these changes accounting for a 22% difference.
What is your RPM on the highway at 100kph? And what is your buddy's?
Do you both have an Auto? If so is it the same auto?
Correcy me if I am wrong, but I am pretty sure a 285/75 and a 255/85 are almost the same size. So if the RPM is way out, that will tell you if the rear end if different. If your RPM's are about the same, then the difference is in the engine tuning.
Other than that, he migt be running a leaner fuel mixture, or the timing of your engines could be different. Does your fiend have an intercooler?
Also the rolling resistance on a mud terrain is WAY worse than the Revo. That will acount for some difference as well.
Cheers,
Nick
Do you both have an Auto? If so is it the same auto?
Correcy me if I am wrong, but I am pretty sure a 285/75 and a 255/85 are almost the same size. So if the RPM is way out, that will tell you if the rear end if different. If your RPM's are about the same, then the difference is in the engine tuning.
Other than that, he migt be running a leaner fuel mixture, or the timing of your engines could be different. Does your fiend have an intercooler?
Also the rolling resistance on a mud terrain is WAY worse than the Revo. That will acount for some difference as well.
Cheers,
Nick
i have seen some fantastic fuel returns and i have seen some poor ones. maybe this will make you feel a bit better.. the average fuel milage return on the 2LTE is 24 IMP mpg. 22 is still a good return when moving a 6000# vehicle down the road.
what RPM are you turning?
might be a dumb suggestion but what air filter are you running and the last time changed out?
get the truck onto a lift and rotate the rear tires one complete turn and cout the # of times the driveshaft rotates and this should give you a close gear count...
cheers
what RPM are you turning?
might be a dumb suggestion but what air filter are you running and the last time changed out?
get the truck onto a lift and rotate the rear tires one complete turn and cout the # of times the driveshaft rotates and this should give you a close gear count...
cheers
Martin White said:
I've gotten as much as 11.5 litres per 100km before and usually can get 12.5 litres/100km if careful, all in city driving (shifting really early and controlling the urge to race is difficult at times)
Hope you find the culprit.
Mot
- Thread starter
- #12
Further info
My friends truck and mine both have the A442 tranny (same year, 1990) with the auto transmission. The lockup occurs at about the same speed. His truck is not intercooled. We met up today and my RPM is about 5-6% higher at the same speed than his truck, BUT he's running 285-75-16's (32.8" diameter) and I'm running the 255-85-16's (33.3" diameter). Taking that into account, my RPM's seem to be about 10% higher than his at the same speed, which suggests to me that the rear end in my truck has been swapped to 4.56's.
Did they put any of these in stock trucks in Japan? Was this a factory option? Maybe that's what threw off ATEB because they said it didn't look like it had been changed. I don't think they pulled it apart to check and I don't think they did the shaft turning to check either. IF the rear end is really a 4.56 any idea what kind of difference going back to 4.11 is going to make? I'm going to go to a more "fuel efficient" tire as well that is better suited to my conditions of driving. Thanks for all the useful suggestions. I'm feeling a little better.
I put almost 200 km on the truck today, all highway, and I noticed that the fuel consumption on long highway drives seems to be quite a bit better than strictly short trips. I don't have 100% accurate numbers because I have yet to do a strictly highway trip but it looks like close to 10%.
My friends truck and mine both have the A442 tranny (same year, 1990) with the auto transmission. The lockup occurs at about the same speed. His truck is not intercooled. We met up today and my RPM is about 5-6% higher at the same speed than his truck, BUT he's running 285-75-16's (32.8" diameter) and I'm running the 255-85-16's (33.3" diameter). Taking that into account, my RPM's seem to be about 10% higher than his at the same speed, which suggests to me that the rear end in my truck has been swapped to 4.56's.
Did they put any of these in stock trucks in Japan? Was this a factory option? Maybe that's what threw off ATEB because they said it didn't look like it had been changed. I don't think they pulled it apart to check and I don't think they did the shaft turning to check either. IF the rear end is really a 4.56 any idea what kind of difference going back to 4.11 is going to make? I'm going to go to a more "fuel efficient" tire as well that is better suited to my conditions of driving. Thanks for all the useful suggestions. I'm feeling a little better.
I put almost 200 km on the truck today, all highway, and I noticed that the fuel consumption on long highway drives seems to be quite a bit better than strictly short trips. I don't have 100% accurate numbers because I have yet to do a strictly highway trip but it looks like close to 10%.
maybe my math is wrong but how did half an inch of diameter (1.5% speed adjustment) difference in the tires yield a 4% increase in the difference between relative revs?
Coming back to the original 5-6% difference in RPM, that is what, about 100 RPM at highway speed? Were the vehicles running side by side when the RPM was compared or were these consecutive runs? If not side by side are you sure he doesn't have the speedo correction gear installed for 33" tires? Even a speedo calibration difference might account for that difference so eliminate the speedo by running side by side.
if it turns out you do have 4.56 gears you will have them front and rear. if you advertise here you may find someone willing to swap them out for their own 4.11 stock gears for you for no charge. baxter650 or yellowchaos locally might think about it.
Coming back to the original 5-6% difference in RPM, that is what, about 100 RPM at highway speed? Were the vehicles running side by side when the RPM was compared or were these consecutive runs? If not side by side are you sure he doesn't have the speedo correction gear installed for 33" tires? Even a speedo calibration difference might account for that difference so eliminate the speedo by running side by side.
if it turns out you do have 4.56 gears you will have them front and rear. if you advertise here you may find someone willing to swap them out for their own 4.11 stock gears for you for no charge. baxter650 or yellowchaos locally might think about it.
Martin White said:
I would be hesitant to think the stock rpm gauge is deadly accurate. It could also be out.
If you are in the neighbourhood for tires keep them skinny and load rated E nice and tough.
Your 255/85 is a good tire size. Its only 10.5 inches or so wide and as you say about 33 inches. Toyo M55 comes in that size. A good tough tire.
If you really want to get a better overdrive out of tires install some 36 inch michelins.
- Thread starter
- #15
When we did the comparison we were running side by side at exactly the same speed, on a highway, comparing via cell on a lightly driven road. So I don't know what else to think. You're right about the circumference difference. I was thinking of our ODO corrections - his is about 6.0 % and mine is 9.21% - a difference of about 3%, but my logic was flawed as 7/9 would say. I'm going to get this looked at soon. Thanks for all the helpful responses.
I guess first thing to look at will be your gears. Lets hope they are wrong, then you can do the swap and be all happy with it. I'm sure someone would trade you for them. even.
Isn't there a differential/axle code on the firewall spec. plate?
- Thread starter
- #18
Spec plate
Yes, it's there. I'm not sure how to read it but I'll do a search and see what it's telling me. As far as I know though, all the stock trucks came with 4.11's.
Yes, it's there. I'm not sure how to read it but I'll do a search and see what it's telling me. As far as I know though, all the stock trucks came with 4.11's.
I am still thinking your friends fuel is turned down.
Your truck and mine do about the same millage and both run good.
His has probably been modified somehow.
How does his truck feel for power?
Same, better, worse?
In a hill with both of you on the throttle, does one pull ahead?
Cheers.
Nick
Your truck and mine do about the same millage and both run good.
His has probably been modified somehow.
How does his truck feel for power?
Same, better, worse?
In a hill with both of you on the throttle, does one pull ahead?
Cheers.
Nick