Hi all,

Relatively new to the forum but has been super helpful so far. I've got an '07 LR3 with ~146k on it. Overall, fantastic vehicle, but currently trying to tackle two problems that may or may not be related. Within the past few months, fuel economy has dwindled down to ~13 mpg avg (historically 17+). Oil change every 5k (Mobil1 5w30 HM), recently replaced air filter, and cleaned MAF sensor, and I haven't seen any improvement.

Then last week, check engine light came on. P0420 (cat system efficiency below threshold - bank 1) and P2097 (post cat fuel trim, bank 1 - too rich). P0240 has been a common one for years. Same cat was replaced back in Feb '18 (120k service), so I find it hard to believe it burned up in only 25k. I'm leaning towards O2 sensors, but I suspected I would be getting other codes as well.

Before I jump to exhaust/O2, I was planning on doing the following just b/c they're easy:

1. Clean throttle body
2. Check intake for leaks
3. Replace PCV valve
4. Run BG 44k in fuel tank

Haven't noticed any major idle issues: temporary shake at start up as idle drops, and mild (if any) vibration once warm. Slight ticking noise on cold starts, but quiets down after engine warm. Spark plugs were also changed 25k ago. Next step would be proper induction/injection cleaning at my local indie shop, but I understand that would likely require new plugs and yet another oil change.

Looking for any advice or feedback on how I should try to tackle this. Anything I should prioritize first? Other things I may be neglecting or should ignore? Thanks in advance!

Last thought: could a bad front diff cause enough friction to impact fuel economy? This is diff #2 for me with ~65k on it. Started noticing the whine again a few months ago. Changed fluid, which unfortunately had water intrusion (was under tremendous pressure, filler plug shot out once unthreaded and fluid spewed out of fill hole). Brown sludge. No bueno. Since replaced fluids and put new breather vent on, but seals are shot. To be addressed ASAP. Rear diff and transfer case were clean, no issues.

Cheers!

 

Do you only drive short journeys as this is a killer for cats. Seems that you may have gone through deep water or the breather on front diff is not connected properly. If seals are gone then you would see oil on the drive shaft so check that the boots have not got holes in them.

 

Thanks! Yeah, my daily commute for past two years is pretty short (~2 miles each way) during the week, so that would make sense. But most of the miles logged are still highway. And even with short commutes, one would hope a $1,000 cat would last more than 25k / 2 years. And on the fuel economy decrease, that's only occurred within the past 3 months.

I'll try to tackle the upstream items to see if that helps. Otherwise, sounds like another cat (or maybe just O2 sensors).

And for the diff, the damage was already done before I swapped over to the updated breather and changed fluids last week. Found a significant amount of fluid on skid plate and some accumulation at the front drive shafts. Must have happened between oil changes. Vehicle has been in the family since new, so no water crossings to my knowledge. Not sure how I managed to get that much water intrusion. I plan to get under the vehicle this weekend and will inspect the breather tube and connector at the diff. I'll try to post some photos on the leaks.

 

Fluids on the skid plate possibly indicate a pinion seal leaking which can be changed in place.

 

I have the same codes.
Here is what was found on mine
Valve covers are leaking (this could cause excess air into the system)
Plugs need to be done


I was not interested in buying 2K in cats so I am going aftermarket and doing it myself. Lets see how it goes.
I will replace the plugs, O2 sensors and the Valve cover seals as well.

 

Didn't notice anything out of the ordinary with the valve covers, but will look into it more. Cleaned MAF sensor and throttle body and replaced PCV valve. Wasn't expecting any material improvement here, but easy maintenance nonetheless. Will be addressing O2/cat in the next week or two.

 

IT is what the mechanic found on mine when he looked at the issue on a lean code. My drivers cat is shot. I just order my set and they are sitting at home now so I will do the covers this weekend and the plugs and then the cats next weekend (it is my daily driver after all.

It was more of a thought after the mechanice suggested it could be the cause of the lean issue with air being sucked into the engine. I also read that somewhere else (maybe the UK forum)

 

Remember the P0420 is about the efficiency of the cat. If you run gas with a lot of ethanol it burns clean enough that it will trigger this code as there is not much difference between the up stream and down stream O2 sensors. If you make short trips in stop and go traffic with it idling a lot, it may never heat up enough to work properly. As for 2097 code, it may be rich, or it may not be, so look at the long term and short term fuel trim values. Make sure it fits in the rule of 10's. Long term plus or minus the short term should be less than 10% and as close to zero as possible. Also they should not be more than 10% apart. That should help guide you more than just the codes. If they are not, there are numerous places to learn about fuel trends and possible problems. this is not a Land Rover specific issue. But I do agree we tend to have a lot of issues with these beasts.

With the 2097 it does not think it has too much air. and is adding fuel to make up for it. If long term is rich, look at bad spray pattern from injectors or bad down stream O2 sensor.

My first step would be to clear the codes, reset the adaptive learning and put fuel with the lowest amount of ethanol in it to see how it reacts before I buy a single part.
The first thing I would purchase is a can of Mr. Gasket Cat cleaner, follow the directions above and see what codes you get. After that you may be more inclined to replace down stream O2 sensor or as recommended by some for each side, replace them as a pair.

Hope this helps.

Jeff
Standard Disclaimer: I could be wrong.

 

As they say "Houston we have a problem" did you find the oil leaks that showed up on the skid plates

 

Rufflyer, great info here. My only hangup is finally getting around to buying a Gap tool. I've been stubborn trying to find used, but hopefully this will help sort out the root cause of the problem before jumping to the conclusion of a bad cat.