Bad gas mileage. Fix problem but still bad mileage.

Figure this one out.

Just bought the truck. '98 reg. cab 4x4 5 speed 124k.

Averaged 23 mpg first tank. Mix of highway, city, off road. Awesome!

Check engine light comes on. Temp sending unit. 12-14 mpg.

Changed part, light stays off, truck runs way smoother.

Now only getting 15 mpg.

Figured it ran rich for a while and screwed up the o2 sensor/cat.

Changed both of those parts.

Still bad mileage.

I know there are a ton of things I can do to correct and help mileage. Tire pressure, fuel filter, clean MAF. But those things aren't related to what actually happened. There is some major thing affecting mileage that needs to be addressed that probably screwed up while the truck was running poorly. I checked the spark plugs, they look great. Going to change them soon anyway just haven't gotten around to it yet.

Any thoughts?

Thank ya.



BTW I'm thinking maybe the duracrap temp sensor is not comparable to the way the oem sensor measures thing. Any body think this could be the problem? What brand should I use?

 

replace anything aftermarket with oem parts, nothing works right unless you use oem or oem brand parts on these trucks.

and sorry to say but your 23 mpg was a fluke because it wasn't running right.

4 cylinder will get average 18/20 and v6 averages 17/19

 

I get 20 in town with my 4 banger and 28 on the road. I'm at sea level and it's flat here in south georgia

 

With cruise control and on a very hot and long trip (250 miles/ 99°F+), I got 27.7mpg on my v6.

 

I live in FL, also at sea level and very flat. Either way I should be getting more than 15 mpg.

I've heard of how particular these trucks are about using the right parts and so on. Why so any more than any other vehicle?

btw I did use a Denso o2 sensor.

 

Funny it's like people with Tacos have already givin in to the bad gas mileage and accepted it.

I just want at least 20 mpg average without even trying.

Which is very realistic.

 

You have a 4cyl.. 20 is not even good for your truck.

 

I have a 4x4 V6 extra cab 5 speed with bigger tires, lift and armor.. I get 17 in town, 20 in the freeway unless I go faster than 65. then its like 17-18.

I had an 89 Toyota 5 speed 4x4 single cab with the 22re getting 22 on average.

You should be getting in the low to mid 20s with your truck 15-20 is terrible as you noted.

Start at the front with the fluids all the way back to the rear diff, greasing all things you can, oem dealer denso or ngk spark plugs, denso O2 sensors, proper oil weight, tire pressure, check throttle cable at the throttle body for adjustment needed, make it as tight as possible, Fuel filter if needed, air filter and mass air flow sensor, Throttle position sensor.

You bought a used truck there is a lot to replace due to old age.

 

Good input.

This truck gas been completely gone through by the previous owner. All kinds kinds of new parts. The point is though I was getting great mileage and then I didn't. I knew exactly what the problem was and fixed it. It ran badly before and then it didn't. I fixed the problem but my mileage didn't go back up as well. All within such a close period of time that none of the things mentioned can be the cause of such a dramatic drop. There are things I can do that will optimize my mpg but first I want to fixed the main thing whatever it is. Going to change the spark plugs though like I said even though they looked good. Going to also buy a new sensor from Toyota.

Usually when you have two problems at once they are interrelated.

 

This sounds very strange, I would very much like to see where it goes. My 4 cylinder sits at just under 20mpg with 33s a camper shell and no ODO conversion..

 

I never got better than 20-22 in my 04 4cyl 5speed 4x4. It had the factory 4.30s and normally had 265/75s on it. My 03 Dcab gets a pretty consistant 17-18 and I drive like a granny most of the time, and do fairly constant 60-65 on the way to work.

 

did you guys all miss the "regular cab, 5-speed" ?

23mpg is very attainable with the 2.7 and light weight of the truck. since it's a '98 he may also have the 15" wheels and smaller tires (225/75)?

another question is did you disconnect the battery and EFI fuse? may need reset after throwing the bad code, even if it's cleared.

MAF cleaning is a good idea (as mentioned previously)

you did not mention (or I missed it) but how did you track the mpg? from the time you got it or fresh tanks on both measure?

 

I have never been able to get better than 15/18 on my 98 4x4 2.7 5spd.

 

Must be your terrain and altitude, I get better than that with hills at sea level and a heavy foot.

 

Yeah, I just drove across country and even in Colorado and Utah I was getting 19mpg with a camper shell stock steelies and tires that weigh 53lbs each

 

IIRC, the 98 has the 2.4 in it, not our 2.7 second gen motor

I've gotten 22 and up per tank with my reg cab, 5 speed second gen 2.7s for over 125K miles. His might be a bit lower with the older motor but not THAT much lower

 

incorrect, the 2.4 was a base model engine only, all pre runner and 4x4 were a 2.7 4 cyl (3RZ) or the 3.4 V6 (5VZ) from 95.5-04 first gen.

 

And comparing the first gen to second gen is a different motor is almost every way.

 

Ah, good to know. I've only owned 2nd gens (06-08) which were all 2.7 as the base

I learn new shit all the time around here

 

I'm running the 31's that the previous owner put on. Bigger than stock, but again I was getting 23 mpg with that setup.

No I have not done that! This is the first I've heard of such a thing, I will definitely give it a try. Thank you!

I measured the correct way with fresh tanks. You know, filling it up first, then running it close to empty. Then using the miles divided by the gallons it takes to fill it up that second time.