1997 yukon - bad gas mileage

[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