Under 8 MPG (2 Viewers)

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Squeegee said:
They didn’t design the turbo to run on a factory obdII vehicle. It’s just a giant turbo that spools slow so the stock ecu can keep up, which is a terrible way to turbo a vehicle.
Click to expand...
It’s not a giant turbo it’s a 62mm turbo, you really can’t go too much smaller, I run a 58mm with a stand-alone and it’s maxed out on shaft speed at max RPMs. If you go too much smaller you’ll have the boost drop off at high rpm’s and you’ll be making a lot more heat.

And hopefully you know that Haltech is not plug and play for USDM auto 80 series…. Only Australian ECU, manual trucks.
 
Lots of questions.
What size tires?
What axle gears are you running?
What transfer case gears are you running?
What is your tire pressure?
What brand of O2 sensors?
When did the poor fuel economy start?
How often does the speedo go out?

I just got back from a trip to the mountains. I logged about 250miles corrected to a tank. The light didn't come on but it was close. Specs in my signature.

1700248646762.png
 
lumbee1 said:
Lots of questions.
What size tires?
What axle gears are you running?
What transfer case gears are you running?
What is your tire pressure?
What brand of O2 sensors?
When did the poor fuel economy start?
How often does the speedo go out?

I just got back from a trip to the mountains. I logged about 250miles corrected to a tank. The light didn't come on but it was close. Specs in my signature.

View attachment 3484218
Click to expand...
Tires (already mentioned) 35x11.5r17. Actual diameter is 34.5.

Stock gears

Stock t-case.

Tire pressure is set to factory, aired at Costco with their air mixture.

O2 sensors (already mentioned) were replaced about 2 months ago. One OEM, 1 Denso. One is NLA from Toyota.

Can’t really say for sure on when it started. This is my 2nd vehicle. Only been driving it daily for the past 4 months while my STI engine is being rebuilt (currently at tuner & dyno). Also already mentioned.

Speedo is very intermittent. Maybe once a month, for several moments to a minute, at a time.
 
scottryana said:
It’s not a giant turbo it’s a 62mm turbo, you really can’t go too much smaller, I run a 58mm with a stand-alone and it’s maxed out on shaft speed at max RPMs. If you go too much smaller you’ll have the boost drop off at high rpm’s and you’ll be making a lot more heat.

And hopefully you know that Haltech is not plug and play for USDM auto 80 series…. Only Australian ECU, manual trucks.
Click to expand...
Whoops I thought it was bigger than that! Regardless, if you’re running a stand alone, then why are
scottryana said:
It’s not a giant turbo it’s a 62mm turbo, you really can’t go too much smaller, I run a 58mm with a stand-alone and it’s maxed out on shaft speed at max RPMs. If you go too much smaller you’ll have the boost drop off at high rpm’s and you’ll be making a lot more heat.

And hopefully you know that Haltech is not plug and play for USDM auto 80 series…. Only Australian ECU, manual trucks.
Click to expand...
Whoopsy! I thought it was way bigger! And yes I know it’s not a plug and play. But it’s the closest thing we got. I have friend running a haltec on his turbo’d 4runner and uses the stock ecu to run the trans. I’m assuming that’s the path you chose as well.
 
Since you have a afr gauge that helps a lot with diagnosis. Your fuel is being burnt properly. That leaves the following: timing is too retarded for some reason, or there is excessive resistance happening in power delivery either in the exhaust is restricted or brakes dragging or transmission issue like the torque converter. You have 250k miles and on original cats? Wow that's crazy. Cats don't last forever. I would pull the cats and install a test pipe. Also your torque converter clutch may have a issue and not locking up properly. If it's the original torque converter, that's a lot of miles on a torque converter clutch.
 
I really hope it’s not the cats, or the torque converter either, for that matter. Both sound costly.

A test pipe would be a quick & cheap temp option. To test that diagnosis.

Maybe in about a week, hopefully, I get my STI back from the tuner. Then I can start looking into the cruiser since it won’t be my daily driver at that point.
 
Fueled up today.

Full tank run which had about 1 hour of consistent freeways on it. Driving between LA/OC counties here in CA. Totally flat driving.

Odometer was at 169.7 miles & filled 20.47 gallons, which came in at about 8.290 MPG.

IMG_4567.jpeg


IMG_4568.jpeg


IMG_4569.png
 
I usually don’t use Google maps. I used my map app via IOS, but it should be the same.

For example, my trip to Irvine from Long Beach was 30 miles, each way, so 60 freeway miles on the last tank.
 
I recently discovered that the 'stock' tire pressure was incorrect for the upsized tires that I have on my 97. I'm running LT285/75R16 which are about 33". I've been averaging around 12 in mixed driving, have been getting about 13 on the freeway.

After researching tire inflation tables, I determined the tire pressure should be 38 PSI. After inflating up to the proper pressure I managed 15.7 on a road trip on 'easy', flat desert roads at 65 mph. This was adjusted for the 5% larger circumference of the larger tires. I would normally have gotten about 13.5 on the same conditions with the lower pressure. City mileage seems to be up about 1mpg as well.

I don't think that stock pressure would be appropriate for the 35" tires you are running. I also don't think it will drop you to 8 MPG to have it lower than required, but it could be a contributing factor. I don't see the specific tire size you are running in the inflation table I'm using otherwise I'd tell you what that table recommends for it.
 
Well, I’m definitely going to take this rig back to the shop soon.

Yesterday, cold start. At idle, rpm’s flutter up & down, then stalled. Cranked it again & started fine. Normal driving after.

Another cold start leaving work. Rpm’s flutter. I was quick enough to pop in neutral & increase throttle. It didn’t stall that time but registered 2 codes. PO130 & PO133.

Those are both related to O2 sensors. Which were replaced about 2 months ago.
One was OEM, one was Denso because it’s NLA from Toyota.

I’ll update the post when I know more.
 
I have that RPM issue from time to time. You might try this. Unplug the O2 sensors and repeat the drive. See if the MPG's change. Also, do you have an OBDII scanner? You can get them on Amazon and use an app like Torque on your phone to read the O2 values realtime. It can be indispensable in situations like this. If you are interested, read the link below to understand how the engine handles fuel mixture. In short, if your base injection duration as calculated by sensor readings is off enough, the O2 sensors cannot compensate for it and the vehicle can choke itself or starve itself of fuel at idle. If the engine is running so poorly the O2 sensors cannot maintain adequate temps, they look like bad O2 sensors to the ECU even though they are actually Ok.

I have 280k on my stock cats and they are fine. I had a shop do a back pressure test on them and they are perfect so I wouldn't go replacing just because of mileage. If they aren't warming up north of 360 degC with the engine revving (indicating they aren't catalyzing) then have an exhaust shop back pressure test them and clean them if necessary. The metals in a cat are what they are and if you don't ever over heat to the point it melts or clog it with soot to the point it can't be blown out, it will never wear out.

Vf1 voltage

Vf voltage information about Oxygen Sensor
alflash.com.ua

Anyway, with the O2 sensors unplugged the engine will default to STP (Standard Temp and Pressure which is what we have in SoCal). If it improves it means you have sensor or collection of sensors that might even be within range but are biased such that they are altering the base injection duration too much for the ECU to handle. If it makes no difference, then unless you have something like say a leaky injector (would show up in the offending cylinder's spark plug so maybe pull those and post pics), you might just have a torque converter that simply never locks up due to the overgearing condition. That with some carbon buildup and you are using fuel to make transmission fluid hot vs. move the truck while bogging the engine causing spark knock / timing retardation which will increase fuel consumption.

You should really regear though either way. I am at 4.88's and 35's. While it revs on the highway I can get north of 13MPG and it's peppy off the line... for a Land Cruiser of this vintage. If you never intend to go to 37's and do a lot of highway you might 4.56. I don't mind the higher revving as the truck is great off road and when towing my offroad trailer with the 4.88's and 35's.

There are still a lot of other things that could be going on. Data from an OBD scanner might be the ticket but I'd say start with a drive with the O2's unplugged and let's see what we learn.


Frank
 
If it's totally flat and you drive it easy 37s can be like a over drive ;)

Maybe she does 😂
 
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