1997 yukon - bad gas mileage

[westman995]

I have a 1997 yukon. 210k on the body, supposed 150k on motor, supposed rebuilt tranny.. Anyways, after owning this thing for like two years and having constant problems with it. I FINALLY have this thing running good and has the power i think it should..

Now, I feel as if the mileage is HORRIBLE, even for this truck, and i know these trucks dont get good mileage at all, obviously haha..

Right now i keep getting a p0141 code, stating bank 1 sensor 2 has a faulty heater circuit...

Now i have read on the obd2 codes site that it says "may notice poor fuel economy" I would like to know if that can be true? I always thought the two o2 sensors before the cats did all that stuff and the rear ones just "monitored" it kinda..

Im in the process of trying to get that sensor out so i can try another one, but its not in a good spot and its in there pretty good.Hope i dont have to remove the whole exhaust just to get it out.

Is there anything else i should look for?

I was getting a code before, i believe it was p0430 saying, i thought it was my exhaust leak but that leak was on the other bank, even tho after i fixed that leak that code has not came back, however the p0141 keeps coming back..

 

[KPOD]

Assuming your tranny full works, and has overdrive, how many MPG are you getting in the city and highway? Also, what are your RPMs when cruising at 70 on the highway?

 

[westman995]

I honestly have not taken this thing out on the highway since i got it running right.. After i put the fuel pump in i only checked it once and as far as i know, i got like 8-9mpg.. I know these trucks suck on gas, but it has to get a little better than that.

Hopefully that o2 sensor helps some, but im unsure if the rear o2 sensor does anything with mpg

 

[strad]

Rear o2 sensors are to monitor the performance of the cats. They have no other purpose. 11-12 city is what I see with my 99 4wd four door.

 

[westman995]

This is where i read that the mpg could be affected by that.

http://www.obd-codes.com/p0141

12 would be much better than 8, hopefully i can get that fixed.. Ill also try to check mpg again also to be sure.

 

[KPOD]

I just had my engine rebuilt, and with my trans not being able to stay in overdrive (at least I don't think it is, 2k RPMs at 70MPH on the highway) I got 12.5MPG with leaking gas lines and a real dirty CAI this last tank.

 

[_Dylan_]

2000rpm at 70mph would be correct with 3:73 gears.

I would change the sensor and runs a few tanks and see what happens.

 

[Gzes]

Ivwoukd do the fuel filter. Mine was getting like 6mpgs then when i put a new filter it jumped and i have the tbi which is worst at gas then your vortec

 

[SunlitComet]

Rear o2 sensors are to monitor the performance of the cats. They have no other purpose. 11-12 city is what I see with my 99 4wd four door.

they actually play a minor role in fuel trims for the good of the cats.

 

[kaoticlife]

2000rpm at 70mph would be correct with 3:73 gears.

I would change the sensor and runs a few tanks and see what happens.

I run 2100 to 2200 rpm at 80mph and I have 3:73 gears and 20" wheels with 275/55/r20 tires.

sent from tapatalk2 using rabbit ears and aluminum foil.

 

[19Yukon97]

I have a 97 4x4 2 door. the 3:73 gears. I get 19 on the highway and 14-16 in town.


Lots of things have been done to get that though.
Electric fans
k&n drop in air filter
longtube headers with a totally aftermarket exhaust. (3 inch piping to the muffler(50 series delta flow) with a 3.5 inch tailpipe after the muffler)
blackbear performance tune
the MPFI spider injection
new fuel filter
tires are inflated properly

 

[westman995]

I put a different sensor on it, the code hasnt came back, yet...

I thought it came back tongiht, but it was the p0430 code saying Catalyst System Efficiency Below Threshold (Bank 2)

I have seen this code on my truck before, but it doesnt always show up. Last time i seen it was before i replaced the fuel pump and at that time i had many problems with it. But now that most everything is working correctly, that code came back.

I am wondering if its still a sensor problem, or if the cat. converter is bad.

 

[_Dylan_]

usually means the converter is toast.

Buy some oxygen sensor spacers/isolators for the after cat sensors and gut the converter out.

 

[westman995]

usually means the converter is toast.

Buy some oxygen sensor spacers/isolators for the after cat sensors and gut the converter out.

What do those do?

I was thinking of removing them of possibly trying to gut them out. Maybe ill just gut them. How would i go about doing that anywas? Cut them open and weld back closed or...?

 

[_Dylan_]

Spaces the sensors out of the exhaust stream so the computer thinks everything is working fine. You can buy them on ebay.

I haven't done one on a tahoe, but on another car I removed the muffler and smashed it up with a pipe.

 

[westman995]

Spaces the sensors out of the exhaust stream so the computer thinks everything is working fine. You can buy them on ebay.

I haven't done one on a tahoe, but on another car I removed the muffler and smashed it up with a pipe.

I wonder if anyone has done them on these trucks, i looked them up n one place said they work for 90% of cars haha

 

[_Dylan_]

That's because almost every car uses the same standard thread size for the o2 sensor. It's not guaranteed to work, though I have read of some folks on gmt400.com that they have worked fine. I will be putting a pair on my truck next summer and I hope to gut the cats at the same time.

You can replace it if you don't want to trick the sensor. I don't know the exact price for a replacement but I'd guess around $300 minimum.
A clogged converter can cause mileage and power issues, I'd fix it soon.

 

[SunlitComet]

Replacement bolt on magnaflow cats assemblies for OBS 5.7l vortec are roughly $368 for 49 state grade. $638 for cali grade. Do the right thing and replace them if needed. It is is better for you, it is better for the suv, and it is better for the environment.

 

[Dhsjsndbbxjsne]

I run 2100 to 2200 rpm at 80mph and I have 3:73 gears and 20" wheels with 275/55/r20 tires.

sent from tapatalk2 using rabbit ears and aluminum foil.[/QUOTE
With my 97 GMC Yukon. I do 75mph it's at 1600rpm. And I get 21 miles to the gallon. The only thing I have done is amsoil xl

 

[Kelsda]

Oxygen sensors tell the computer what to mix in the fuel department wether lean or rich,false readings then can foul spark plugs could be the reason for poor gas mileage you could have a leak in the intake or exhaust manifolds. Oxygen sensors read gasses going into cat then out on other side constantly monitoring could be a burnt exhaust valve. What size tires are on that rig I have a throttle body injected 5.7 vortec with 265/75/18 tires on a two door getting 12-13 city and 15-16 hwy 3.73 gears. Run truck at night to normal operating temp then look under it at cat if clogged it will be glowing red you’ll know