I am the wrong guy to give MPG tips. Mine is currently getting 9mpg and that’s with non ethanol gas. About the same as before the new cats. I think I remember hearing a rattle and that was the reason I had them swapped out. Now I have to add that I’ve got 33”s, 3” lift, ARB front, AB rear and a SD rack. I only put 2500 miles or so on it a year so I haven’t spent much time trying to improve it. I’ve thought about installing new injectors but the truck is so damn tall it won’t fit in my garage and I prefer to do that kind of stuff out of sight of neighbors. I did the coil packs in the driveway and pulled the intake and should have done the injectors then but I wasn’t thinking about it. Chasing higher mpg in these things in general is often fruitless. It might improve when fixing mechanical issues, I dunno.

I did the rear resonator delete before I did the cats and Magnaflow, it gave my truck a bit of a rumble. After the cats and Magnaflow I was glad I had already done it. There wasn’t much difference from the stock exhaust after the resonator delete and the new cats and Magnaflow but it was enough to know I’d done something. Kind of wish I had gone with the next size down Magnaflow but and I might still do it. The truck is 20 years old now is think it would be cool for to be able to actually hear it coming but I may be a little old for that myself.

 

@Frank4 good input on the magnaflow stuff. Thanks!

I've purchased new Magnaflow Cats and should have them installed this week.

I completely understand the realities of an old pushrod V8 powering a heavy truck with a driveline that takes a lot of effort to get moving. Don't misread my MPG question as a complaint, it's just trying to diagnose a possible issue. 11mpg on a stock truck, on the highway, is a sign of an issue since that is well under the original EPA tested fuel mileage rating. The EPA rating in my experience, is usually conservative.

All of that said, I have not done all highway miles for most of a fuel tank since putting in new injectors and fixing vacuum leaks. My commute is 5 minutes and the truck barely gets up to temp, so it's probably sucking fuel do cold running anyway. My cats are ticking as well. I'm hopeful that there will be some marginal drivability improvement with new cats, but not getting my hopes up!

 

I hear you on your MPG’s. 11 mpg is pretty dang good in my book, I’d be thrilled. Maybe it’s just me but I wouldn’t expect the MPG rating from 20 years ago to be accurate on at 20 year old motor. And really if more people accurately calculated their MPG I’d be willing to bet the numbers would be closer to yours than the window sticker. I’ve seen claims on this forum as high as 16 to the low 20’s MPG and I find it hilarious.

If you are getting 225 miles to a tank BEFORE the gas light comes on your are doing well in my book, little under 11.5 mpg.

 

@Frank4 that seems to be the consensus of my mechanic as well. I can do about 205 miles before the fuel light, but again, all start and stop in town driving. A lot of it while the motor is between 130-170 degrees since I do a lot of short trips.

I was driving home last night, at about 55mph on the highway the truck felt like it bogged down. The exhaust note changed, and then it puffed out some smoke and some sort of debris.

Now the exhaust note is different than before, much louder, but it runs the same.

New cars can’t get here soon enough. I think I fried those things running the truck super rich when that fuel injector failed...

 

I Think these numbers are accurate:
-24.6 gallon fuel tank
-gas light comes on when you have 3.75 left in the tank.


So your 205 miles out of 20.8 gallons (9.85MPG) makes me feel much better about my 9MPG out of the same volume of fuel at sub 200 operating temps, stop and go.

And yes I’d be looking to get those cats on ASAP.

 

Magnaflow 94105’s are here. I’ll get them installed when we get back in town from a family trip on Monday.

It’s amazing how obviously worse the performance is with clogged cats. I think they were due for a change when I got the truck, but after 3,000 miles of lean codes and then a failed fuel injector they are clogged up.

Truck runs really well, I’m super excited to see how it runs with new cats!

 

Got my cats replaced and now both of my upstream O2's are new as well.

Wow, different truck. It feels like it has 100hp more. Way more responsive.

 

You have experienced something few LandRover owners have, actual seat of the pants improvement when hitting the throttle.

Congrats

 

Replacing plugged Cats will make a big difference in power, but I don't think you'll notice much MPG difference. I deleted the plugged Cats on a Dakota I used to have, giving me a lot more power, but I didn't notice a fuel economy change.

 

@Harvlr that seems to be the case. Immediately noticed a throttle response improvement. Exhaust note sounds better as well, much healthier. Idle is a little better.

i think MPG’s are marginally better. It’s hard to tell because my fuel gauge only goes up to the 3/4 mark, and I think the fuel light comes on 30-40 miles earlier than it should.

Last time I filled up my fuel light had just come on, and I was only about to put just over 16 gallons in. Interesting.