Huge mileage increase after replacing cats and sensors! (1 Viewer)

[Formulaonehd]

So my rig has always got between 10-11 mpg as long as I've owned it- pretty much regardless of how it's driven. Towing, wheeling, whatever, I always figure on getting 10 mpg and that is usually pretty close.

Recently I spent a big chunk of change on the truck and replaced the Y-pipe, both cats, both sensors, the front calipers, rotors, and pads. I rebuilt the front end about a year ago and there was no change in mpg at that time, but after all this last work my mpg has increased dramatically.

From the usual 10-11 mpg, my last 350 miles came in at an average of 15.1 mpg! Holy st!

I went back and checked each fill-up to make sure I didn't miss one and the mpg was similar in every interval; from a low of 13.8 to a high of 15.6. This is crazy!

I got a P0171 code one time right after I ran-in the new cats so I figured it was just a fluke, and since resetting the code it has not returned. I got a little worried today that I might actually be running too lean due to all the changes, so I unhooked the battery for an hour to reset the ECU and will continue checking the mpg for a while to see if anything changes. But right now I feel like this truck is a real fuel sipper!

Thats great mate. Did you take any photos of the Y pipe? I want to compare what you have to my aftermarket extractors (PO did this) my mileage is quite impressive aswell , well at least compared to the general likes of 80s owners. Converted from L/KM to miles i get a similar usage to yours

 

[artech]

Thats great mate. Did you take any photos of the Y pipe?

The old one or the new one?

 

[Formulaonehd]

The old one or the new one?

The new one, did you have the whole manifold outlet upgraded ?

 

[Berzerker76]

I'd be more inclined to think your brakes had more to do with your MPG than any of the exhaust components and sensors. Could be your old calipers were sticking and causing your brake pads to drag excessively, increasing your rolling resistance and killing your mileage. With new components everything is rolling freely as it should.

 

[1973Guppie]

I'd be more inclined to think your brakes had more to do with your MPG than any of the exhaust components and sensors. Could be your old calipers were sticking and causing your brake pads to drag excessively, increasing your rolling resistance and killing your mileage. With new components everything is rolling freely as it should.

If your brakes are dragging that badly you will (or should notice) some major heat and smoking.

Clogged cats from my experience will make a truck run like crap. No experience with a mpg gain but it makes sense with the engine running better because it can breath you could see a mpg gain.

 

[fuzzywuzzy]

Been failing smog and slowly getting to the point where next step will be cat replacement, fingers crossed I see even a similar MPG increase. Good on ya'!

 

[elripster]

My old 60 (3FE) had one cat clog and the other wasn't far behind (you could see a little light through one and none through the other) and it made for very poor performance and MPG's. The engine is basically working to push exhaust with energy that could have gone into moving the truck.

In my case O2 sensors were what caused the clog so fixing both really improved the truck.

Frank

 

[RiverCityDave]

I

My 80 gets MPG's in the 14's on the highway with the AC off at 70ish MPH with 4.88's and roughly 34" tires.

Your truck per your sig is stock so what you report makes sense. I got over 16 MPG highway out of mine before lift/tires/gears.

If one replaces something like an O2 sensor and sees no difference it probably means the original sensor was good and (for example) the poor MPG is due to something else. But, since you changed the cats too it is also possible the engine is enjoying a reduction in back pressure so benefits could be due to one or both changes.

Either way good MPG! It helps give us a benchmark for how our trucks can run.

Frank

I thik this is likely the case. I have had a cat start to kick the bucket in the last couple of months, and my mileage has suffered accordingly. I expect to get back to the upper 14's once I replace it.

 

[artech]

Well, I've been wheeling the heck out of my rig so many fill up intervals have had hours of low range crawling on them, but leaving those intervals out of the accounting my gas mileage over the last thousand miles (of paved roads) has risen to an average of 14.7 mpg with no real highway cruising miles. Most of this is on surface streets and local roads, no on-ramp type highway driving at all.

That's almost a 34% increase in gas mileage from the 11 or so I was getting previously. Wonder how bad my head gasket is now from all that exhaust backpressure over all those years? No wonder the exhaust gaskets kept wanting to leak!

There's the catalog pic of the Walker y-pipe for the fellow who asked, mine is covered with mud right now!

 

[shocktower]

It's how my business was built.

The "CATS" meow

 

[stock]

Clogged cats from my experience will make a truck run like crap. No experience with a mpg gain but it makes sense with the engine running better because it can breath you could see a mpg gain.

How do you check for clear cats?

 

[1973Guppie]

How do you check for clear cats?

in my case my trusted exhaust guy pointed it out after 180k miles, parts of the mesh were breaking apart and rattling inside the cats.....

 

[artech]

No idea really, I changed mine due to corrosion and had no expectation of any performance increase. My flanges on the cats and sensor bungs on the pipes were rusted to the point where they just wouldn't seal any longer, so I had to replace them to pass annual inspection. I replaced the sensors because I read you were supposed to with new cats, even though they were only a couple of years old. Then the nice bonus of better mileage happened, so now I need to figure out how long the cost/savings payoff is before I'm actually ahead for spending that money.

 

[studawg]

Im guessing you've been running the same gas all the while? You didnt switch from E10 to pure gas did you? That alone would raise your MPG.

 

[artech]

Im guessing you've been running the same gas all the while? You didnt switch from E10 to pure gas did you? That alone would raise your MPG.

Nope, whatever is cheapest at the pump. Up here it's mostly all E10 and E15 right now. Once I get the average nailed down I'd like to run a few tanks of premium through and see if there's enough difference in mileage to offset the higher cost.

 

[studawg]

Going from E15 to E10 would give you a slight increase in mileage. There is nothing to suggest that "regular" vs "premium" is going to make any difference in MPG. However, if your choices are 3 grades of gasoline, all of them cut with some percentage of ethanol, the "premium" is probably going to have the highest percentage of ethanol, which would cut the energy content in it, thus lowering MPG. Ethanol raises the octane of the gas, but lowers the energy content, thus lowering the MPG. All things to consider when trying to gauge gas mileage. The problem with all this is that they do not closely monitor how much ethanol is actually going into the gasoline. It may be 5%, 10%, 15%. You can test it, Ive heard some tests coming back with up to 30% ethanol.

 

[artech]

I'm just happy to not get gas with a ton of water in it, that seems to be more prevalent since they started the ethanol blends. I have taken the long way home for several days at a time just to burn up the occaisional tank of crap gas so I could get some good clean stuff in there.

They also make a 'winter blend' gasoline for the northeast, I know it changes the numbers somewhat but not sure what changes or by how much. I know most folks that monitor their mileage closely can spot the difference in blends almost immediately. It hasn't made that much difference in my rig previously, but now it might.

 

[fz1boxer]

i need to eek out 1 more year before i can go cat free,mine is showing symptoms of clogged cats,down on power and mileage is sucking.
i guess getting the walker setup and then replace the cat with a straight through would work.
does anyone make headers for the 4.5?

 

[Formulaonehd]

If you have 6 independent measurements both before and after, it may be highly statistically significant. You can enter the 12 values on several on line calculators of Student's t test and see what the CI and significance is.

Sceptic much haha

 

[REKCUT]

How do you check for clear cats?

The shop i delt with drilled a small hole in exhaust ahead of cats and checked for back pressure. Don't remember how much was limit but it seems like it was a low number. 4 pounds or something. again not sure on number