O2 sensors and MPG

[xr7cat]

OK I have a 97 SHO with about 138K. Car runs good, I've had the car since March. I've noticed the gas milage to be about 20 - 21 mpg. When I first had the car I was seeing 22-23. Most of my driving is highway speed being in Texas.

Only things I see that changed to affect the mileage is a hot summer with the a/c running a lot. I was also running premium when I first got the car, then switched to regular as it runs fine on it.

I am just wondering if replacing hte O2 sensors will help the MPG. From what information I have it does not look like they have ever been changed.

I'm also wondering if changing the coil packs would be worth anything mileage wise. Car has no codes and runs good. The coil packs are original ford types. I do have a set of new coils on the shelf.

Any thoughts?

 

[gmorrell]

If the O2 sensors are original at 138K, the car should be on its third set of sensors by now. 60K miles is considered a good life for a narrow band O2.

As O2 sensors age, they get slow to switch, and they shift lean, so they keep telling the PCM "I'm lean...", the long term fuel trims keep getting richer and richer, and fuel economy goes down.

If the upstream O2's really are original, replace them, reset the PCM and see what happens.

If there aren't any ignition problems or mis-fire codes, replacing the coils will probably do nothing but waste your time.

The EPA makes the states fiddle with the gasoline seasonal oxygenate concentration (ethanol). Usually the ethanol concentration goes up in winter and down in summer. Ethanol has fewer BTU's per pound than gasoline, so it has a direct effect on gasoline energy content. The more ethanol they blend in, the lower your MPG goes. I don't know what they do in Texas, but here in Colorado, my fuel economy changes by near 20% as the ethanol content changes seasonally.

 

[gsilva]

I think my 02's are original at 183k. I guess I need to change them. I have gotten as much 28 mph on the highway and the car runs great.

 

[tardboy21]

a. unless you have owned the car your whole life, they are probably not original
b. 28mpg out of a V6 SHO is normal, almost impossible for the V8 unless its mostly downhill.

With regards tot he OP,
I would try changing gas back to premium for a tank or two and see what happens. But premium isn't that much more than regular here anyways.

If the drop was more drastic I would definitely suggest 02's. If you have the spare cash, it wouldn't hurt to put some new 02's on though.

 

[stephen newberg]

I think my 02's are original at 183k. I guess I need to change them. I have gotten as much 28 mph on the highway and the car runs great.

a. unless you have owned the car your whole life, they are probably not original
b. 28mpg out of a V6 SHO is normal, almost impossible for the V8 unless its mostly downhill.

Over 186k on mine and still on originals. On long pure highway trips I get 28-30mpg in the prairies, but not in the Rockies. And all the downhills are in the Rockies.

pax, smn

PS: and yes, I have owned it since it was 6 months used and the O2s really are the originals.

 

[tardboy21]

:snap:

 

[gsilva]

Which is faster V6 or V8?

 

[stephen newberg]

I think it is commonly acknowledged that the Gen I is the quickest (well, prior to the new Gen IV, which wins that one hands down) with the best quarter mile times. The fastest is likely the Gen III as it has the highest top speed, but again, the Gen IV may take over there. I have not heard what its top speed is. So, quickest was Gen I, fastest was Gen III. But now the new 2010 Gen IV may take both categories.

pax, smn

PS: I am assuming you are talking from the factory, here, and already know that the Gen I & II are V6 powered while the Gen III is V8 powered. The Gen IV is back to V6, but is no longer naturally aspirated, as it runs twin turbochargers.

 

[SuperHO]

i'd say switch back to premium...it's $3 more a tank, and in my 98, well worth it. also, the AC could account for that kind of loss as well.

 

[gsilva]

I just wanted to gloat. It's faster and gets better gas mileage also.

 

[tardboy21]

but they don't have as nice a back seat as the Gen3/4.

http://www.funnyordie.com/videos/b70226fc1f/what-happened-in-albuquerque-from-the-goods

 

[gsilva]

The best back seat I ever had was in a 59 Chrysler.

 

[1madSHO]

1993 accord... but I geuss thats because of events that occured on it.

 

[stephen newberg]

I just wanted to gloat. It's faster and gets better gas mileage also.

Quicker maybe, but not faster. And the gas mileage is not a clear win either, as it depends hugely on driving style.

What speed do the Gen I/IIs top out at, actually? Now that I think about it, I do not remember. Less than 144mph, though, I suspect...

pax, smn

 

[Funmart6]

My my.... what a strange turn this post has taken.

I have gotten 28 highway mpg at 70-75 mph. As far as "best seats", 1981 Eldorado front passenger seat, lays almost flat..... ah the memories.

 

[gsilva]

I've heard as high as 143 for a top end for the V6 but I'm sure that is for a new car. I don't think mine is going to get close to that unless I start doing some updates. I've been in the 140 (Don't tell the CHP) neighborhood but that was with cars with more hp. How fast is the GenIII?