Guys, I was just again put in front of the fact that my Disco really is only getting 9-10 m.p.g.

I've red, and participated in different conversation on the mather, and even if I tell myself that it's winter up here in Canada, the gas is winter gas , and the incredible cold we've been getting makes it worst due to the thickness of the oils and stuff, this kind of mileage is absolutely unacceptable unless your driving a huge lifted Hummer. I've got friends with H2 and huge Armadas that get better milleage than me. And I'm a very easy andpacific driver.

But I was thinking about it all. I changed my after cat O2 sensors about a month ago, and it's been this hard on gas since then. How could this be explained???? Would it mean that the before the cats ones have to be changed also???

The codes from the ones that went bad were erased when I changed them.

 

You are not giving us anything to work with, Year, model , miles and tune up history?
How much of your driving is city how much on the road?
Mike

 

Sorry, You're absolutely right. 2000 D2, 52000 miles, plugs were changed 2 weeks ago to try and solve this problem, wich didn't work. I had a K&N air filter that I removed yesterday, to reinstall my stock new one( thanks to you).I've got the ACE system which is an additional pulley to turn.

The only thing I can think of, is those 2 O2 sensors that I changed with LR OEM ones. It's been exactly since then that I've been getting such bad milleage. My question is why ???

 

So....Can new O2 sensors cause this ???

 

It shouldn't cause bad mileage. You may want to have some read the numbers off the O2's to mke sure they are not causing this problem.
At your mileage, your plug wires are not the best, might want to consider putting in a st of 8mm Magnacor wires, this will help a little.
Are you running high octane gas?
Mike

 

High ocatne gas all the time, I asked my dealer to put the Disco on the computer to verify if there were differences of reading between the front and rear O2 sensors. The service manager said that it was pointless because of the fact that if there was a difference in flow, the check engine light would come on due to a code.

During the same week-end that I changed the O2 sensors, I had a very bad exhaust leak at the Y pipe fixed, due to bad gasket on both sides. And that's when it all started. Before the fix, I was getting approx. 14 m.p.g and now, 9-10 m.p.g ?????

 

Darover, did you do the exhaust gasket replacement yourself?

I'm assuming you're talking about the gaskets between the manifold and y-pipe. If you are, and you didn't do this yourself, you may want to check with whoever did it to make sure there wasn't more to it than just the gaskets. Those y-pipes have a tendency to crack at the upperflange weld. When trying to detect the location of a leak, it'll often feel like the exhaust gas is coming out of the gasket between the flanges when it's actually coming from just below that point.....at the underside weld. If, by chance, this was the issue with your exhaust, the dealer (whoever did the repair) may have thrown a spot-weld on it. The main reason Iraise this question is because 1) a severepre-cat leak can contribute to cat andO2 failure and 2)where the cats are part of the y-pipe unit, a failure (crack) anywhere within that unit may give you a case for manufacturer replacement. I believe that US law requires manufacturers to replace failed cats up to 100,000 miles.

The y-pipe on my '00 cracked on both sides and I recently replaced it with a direct-fit aftermarket unit that I gotfrom a localforeign parts store fora little under $400 (it was actually made in Canada). It was perfect fit and I'm guessingthe catsflow a bit better than the OEM.

In any event,just because you're not getting codes doesn't mean that the O2's and catsare functioning optimally. O2's are one of those things that.....if one fails, the rest probably aren't far behind. I'm guessing that you replaced the one sensor because it failed. That said, you may want to do the other three and see if that helps.

 

Actually, I did the 2 aft. cats sensors, and was considering changing the 2 pre cats ones. A muffler shop did the job, but the truck does sound as if there isa leak when cold. Although it really clearly was the gaskets that failed. Something else could have come up with the exhaust. I'll check it out.

 

Oh yeah, I just re-read and saw that you did both aft-sensors. I'd definitely replace the pre-cats. To my knowledge, they have more impact on the fuel mixture than the aft's......which have more to do with monitoring the functionality of the cats.

Regarding the exhaust leak, next time you do a cold-start, open the hood, reach down and feel around the flange area (the area where you just had the gaskets replaced). If you still have a leak or crack in that area, you'll feel it hitting your hand.

 

Will do. First time I actuallywish to have a problemEspecially if fixing it means better m.p.g. I'll definitely change those pre-cats O2 sensors sooner or later.

Sooner if the engineer to which I brought my SLS pump to, can fix it. Later if he can't and I have to either do a factorycoil spring conversion, an Old Man Emu suspension, or buy a new pump. Still debating this one.