2006 4.4 LR3 203,000 miles

Besides a desire for better economy, no issues or codes. But this weekend I put new ignition coils in, Delphi. Did those yesterday and was shocked by a nice boost in MPG which I did not expect. No codes after, no issues... Today, O2 sensors! The downstream have never been done at all so figured why no, got some Denso for cheap on closeout after all. One was a nightmare - different thread for that.... The upstream I had done before, so those went well. Did the driver one from above instead of removing front driveshaft. So all O2 sensors are new Denso now. Right off the bat I noticed if I tapped the go pedal, it would do that hesitate/cough thing and not instantly idle up like it did before. But it does idle smooth and when cruising along, power is there as well as the nice new boost in economy.

But... I am getting both banks too lean - make sense given the "cough" it was doing, that is a sure sign of lean from experience. But then for one bank I got too rich. Thoughts? I suspect the MAF. My only theory is the older MAF and older sensors were happy to sluggishly play together. New engine filter and cleaned the MAF a couple weeks ago. But now with O2 sensors responding fast maybe the aging MAF is showing to be the issue? So I think I will order one anyway, but I would love some input from the brain trust before I go on a parts tossing party and drain the bank account. Oh.. spark plugs are pretty new and good for 150-200k interval change - those fancy NKG rutheriaminimgoldexpensiium ones.

 

How about a smoke test for fun before the parts party?

 

Did you reset fuel adaptations with the new O2’s?

Seems odd to go from both banks lean to one bank rich. Wild O2 data from new bad O2’s, or old fuel adaptations trying to catch up to new O2’s? Just thinking out loud here.

Watching live fuel trim while driving around should be interesting.

 

Yeah, adaptations reset a couple times actually. After the coils and a couple times after the O2s to make sure they were reset. Will look at live data and see, but I am not super good at knowing what the live data represents.

 

I figured you would have already reset adaptations, but you never know. I forget the basics all the time.

I know you know all this, but...

Live Fuel Trims: Spikes high or low, in the rough range of +20% (lean) or -20% (rich) at idle, under load, etc. can give you an idea of what running or driving conditions are causing the lean or rich codes. Are you still fighting lean both banks AND rich on one bank? Watching live FT at idle while poking, prodding, tweaking the intake ducting can help you find an air leak causing a lean code. Monitoring FT's before and after any work is a good way to see if you're actually helping or hurting.
Live MAF data: I can't figure out what is good, bad, or normal here. According to the book below, a bad MAF can cause both lean or rich, so maybe you're on the right track to an easy fix with where you're headed already. Either way, looking at the live data before and after is solid confirmation.

Here's the punch list from the book:

Good luck!

 

Thanks, that helps. Today no lean codes, just rich on bank 2. I am going to drive it a ew days and see what comes up. I did pull up live data briefly and long term trims were -8/-10 or so. Short trim -1/-4 or so... I need to sit down and do a proper set of readings. I will also re-clean throttle body and re-clean the MAF.

 

I was getting the same rich/lean codes on my LR3. I replaced the old MAF with a new unit. I haven't had problems since then 🤞

 

I imagine you're on this already Dakota, but have you cleaned or checked your throttle body? I've experienced off idle hesitation with a dirty throttle body before.
Those fuel trims aren't *too* bad imho - have things settled down more now?

 

It was just cleaned a month or so ago. Well I am not ignoring this thread, just not a ton of free time during the week. So I only watch things on the way to and from work. Seems things have cleared up on their own for reasons I am not sure about. The lean codes seems to come up after adaptations were reset. Then as things adapted, it went rich. Rinse/repeat until I was only getting rich codes. And now I am getting none at all. I will continue to watch things and try the live data again under controlled conditions. But it is like the O2 sensors needed a "burn-in", which is of course not a thing with them. So at this point, a little oddity is all I can consider it. Hell, it could have been a fuel issue for all I know. Just timed right with all the work I did.

 

Ugh.... spoke to soon. So after nearly 3 days with no CE light, it came up. On the way home from work, no codes, no CE. Took the dog for a run and the CE came on. Both banks lean. I have not reset adaptations for days now, so that is not it. Guess I will clean things and order a new MAF to run it out. Will also grab some live data over the weekend.