Bank 2 long term fuel trim increases from approx 3.8 to 7.2 after idling for 10 minutes

[Tummler]

Bank 1 LTFT increases during the same period but the increase is much less (.5 or less). I also note that the LTFT for bank 2 is consistently 2 to 4 higher than bank 1.

The reason for my inquiry extends beyond mere curiosity. The right catalytic converter has been throwing a code for quite a while now, and I am proceedind under the assumption that whatever is causing the elevated LTFT for bank 2 likely contributed significantly to the premature death of my catalytic converter, so I would prefer to resolve this issue before replacing the old catalytic converter.

One last observation: cooler ambient temperature seems to lower the LTFT for both banks by approximately 2.

EDIT: It's entirely possible I am simply observing normal, to be expected operating parameters since this is the first time I have tracked LTFT with this level of specificity.

 

[2001LC]

Year?

I'll very often see variation in FT, from BK1 to BK2 of ~2%.

I find monitoring fuel trims, more relevant. When on HWY (not ascending or descending) cruising at ~65 MPH, holding gas pedal & RPMs steady (no change whatsoever). I look for LTFT of: 0 to 5 % which is considered normal range. ~2%, is ideal for my altitude in the mile high city.

LTFT, is what ECM is adjusting fuel injector, by increase or decrease its pulse duration. To get a baseline STFT near 0%. A positive LTFT, is how much ECM is increasing fuel. Which is to say: correcting for a lean engine running condition.

STFT is what o2 is currently detecting fuel mixture is. A negative STFT, is a lean running engine. (lean on fuel in mix)

lean engine running condition. Either, fuel starvation (weak fuel pressure/flow) or vacuum leak. The system is set, so that prolonged over 20%, set off a DTC.

ECM is gathering info from MAF, ECT (engine coolant temp) and o2, to control fuel injectors.


It's smart of you, to look for cause, before replacing a CAT.

I've found the number 1 cause of CAT failure, other than prolonged idling, which fouls them.

1. Bad MAF sensor, resulting in excessive rich fuel condition dumping raw fuel in CATs. Burns them up.
2. Vacuum leaks. Most vacuum leaks affect both bks equally. Exceptions: Intake manifold gasket leak one BK or loose spark plug (walking out).
3. Bad o2. Which we get a DTC (code) for, if dead. Can also be gunk on prob of o2 or mud/gunk clogging air sample intake of o2 (where wires enter).
4. Low uneven compression coupled with prolonged idling and or frequent short drives without getting on HWY now and then to cook-off CAT & o2..
5. The FSM notes exhaust leak. I've yet to see exhaust leak, take out a CAT.

FWIW:
I've two different OBD devices, that I use with iphone.
One; is Bluedriver, I like best for fuel trims. But it is limited on what data points and how many can be monitored effectively at same time. But it's readout of engine data, seems spot on and real time.
The other; is OBDII, which is open software, gives many data point including AT fluid temp and AHC pressures. But FT data, seems delayed and skipping real time point to point data..

 

[Tummler]

@2001LC My LC is a 2006.

What effect, if any, would a clogged catalytic converter have on fuel trims? It’s entirely possible my catalytic converter was fouled during a couple impromptu meetings that took place in my LC at site inspections where the only thing the parties could agree on that it was too damn hot to stand outside and argue with each other.

Thinking (I’m sure poorly) from first principles, I wound assume an exhaust restriction would cause a negative fuel trims because the back pressure prevents oxygen from entering the cylinder durikng the intake stroke. On the other hand, I wouldn’t be surprised if increased back pressure has ther effects that more than offsets the decrease in oxygen.

 

[2001LC]

@2001LC My LC is a 2006.

What effect, if any, would a clogged catalytic converter have on fuel trims? It’s entirely possible my catalytic converter was fouled during a couple impromptu meetings that took place in my LC at site inspections where the only thing the parties could agree on that it was too damn hot to stand outside and argue with each other.

Thinking (I’m sure poorly) from first principles, I wound assume an exhaust restriction would cause a negative fuel trims because the back pressure prevents oxygen from entering the cylinder durikng the intake stroke. On the other hand, I wouldn’t be surprised if increased back pressure has ther effects that more than offsets the decrease in oxygen.

Is "couple impromptu meetings that took place in my LC" your way of saying; Prolonged idling? How long and often do you idle?

If a CAT clogged, it would create excessive back pressure. Really IDK! But I think: You'd likely see LTFT negative and STFT would be positive and likely high %. Since fuel injector would continue spraying fuel, but air intake would be restricted due to back pressure. More fuel than air in mix ratio, is a rich condition. BTW: We measure for clogged exhaust/CAT, with a .5 to 5 PSI pressure gauge, connected at A/F sensor.

It be very helpful to know not only year. But mileage, a bit about service history of engine and any engine mods. Also all DTC (codes) you've seen over past few years Going back before P0430, even to mile 1?

Here's what I'd do:
First I'd inspect the S.A.I. filter. While doing so I'd look for vacuum leaks. If for any reason intake manifold ever removed. ie S.A.I., water bypass joint, knock sensors, rodent wire damage or stater service. I'd be looking very close at intake gaskets for vacuum leaks.
Also look for exhaust leaks at head/exhaust manifold, A/F and O2.
I'll not be surprised; if your S.A.I. filter missing.

S.A.I. Filter Modification, in VVT engines. To prevent its failure! Alert Alert!

We've a $2.00 part in the S.A.I. (secondary air injection) system of the VVT engine, that is taking-out ~$7,000.00 $15,000 $25,000 (inflation) in parts. WOW! I've a very easy and cheap WORK AROUND. You are going to love this ;) This thread is dedicated to the 4.7L 2UZ-fe VVT engine, in the...

forum.ih8mud.com

Second, I'd do a compression test. I'd not be surprised if compression on the low side, even below spec, more so on BK2. At same time inspect/replace spark plugs, coil boots and or coils if I've reason to. I'd also be looking very closely at MAF sensor and air filter.

You can also try this:
I run 44K (2 cans to full tank) and or Chevron Techron (separate tanks of gas), something like Cataclean or sledge hammer. You'll find youtubes of some using paint thinner.

I'd also run engine at 4,500 RPM for ~12 minutes on a drive. Warning, make sure engine oil and coolant all good first.
First run at high RPM for ~3 minutes, the ~6 mins, 9 mins working up to 12 mins. This heats CATs, A/F and o2 cooking off carbon. It's like turn your oven on self clean mode, cooking. We start out run, for only a few minutes at first, for two reasons. First, to monitor engine, on how it handles running at high RPM. Second, to work to burn-off any wet carbons (raw fuel on oil), reducing chance of igniting within CAT and burning them up.

You may find, after tuning engine and running fuel and CAT cleaners and high RPM cook-off and you stop idling more than ~2 minutes. P0430 takes longer to come back. But it likely will come back.

 

[Tummler]

@2001LC Quick response to the easy questions as I sit in a corner at a party being anti-social. I'll follow up with more information later.

My Land Cruiser is a 2006 with 175,000 miles. The only other codes were the 4 codes that I have seen several people claim are associated with problems with the charcoal canister. This was accompanied with the infamous intermittent gasoline smell. I recently replaced the charcoal canister, which appears to have addressed the codes and smell. I unfortunately do not have the 4 codes handy as I did not write them down, nor can I find the posts discussing them.

Completely stock engine. I am the second owner since approximately 100,000 miles. All service work prior to me performed at the dealership. Since then, I have handled maintenance and done everything by the book.

A "couple impromptu meetings that took place in my LC" was precisely my way of saying prolonged idling. I can think of 4 or 5 such sessions, but I honestly have no idea how long. It wasn't multiple hours, but was definitely more than a couple minutes. I am certain they didn't go on for too terribly long because of the AC quickly falling behind while sitting stationary. I always kept my eye on the temp gauge looking for overheating. This was before I learned that relying on the temp gauge in these vehicles is asking for trouble.

I will check out the items you mentioned and follow up.

 

[2001LC]

Post up the LTFT & STFT while driving at steady RPM & speed on flat HWY.

 

[cwmoser]

I obcessed over LTFT's and STFT's for some time.
I use Torque Pro App on my Android phone.
On my 2002 LX it has been perplexing ever since I purchased this truck - when it had 24K miles to now at 73K miles.
I've tried 3 different MAF sensors and they return differing results.
Just recently I reinstalled my original MAF after I cleaned it with some MAF Spray Cleaner.
At idle I do get near zero numbers but most all other driving it varies sometimes as high as 10.
I asked a Tech at a well known Toyota/Lexus Indy shop about this and he stated that LTFT and STFT numbers
"are all over the place".

At idle, these but all over the place driving:

 

[jerryb]

commanded afr and output afr. That's all that needs to be looked at. Voltage, AFR or lambda, Whatever you want to go by.
You're real world driving, graphing the data at real driving scenarios. I use voltage, highest and lowest vacuum.

There is no rich or lean until you're outside of the injector and ECU adjusting controls. That's when the CEL comes on. That's when people should worry.
Lots of toyota MAFS work just fine.

 

[2001LC]

ECM (PCM) takes over fuel trim control, once engine at operating temp.

Always keep in mind. LTFT is what ECM, is doing to correct STFT to get baseline near 0%. STFT is actual, fuel mixture at the moment.

I'm mostly interested in reads, while steady cruising on HWY, as stated above. It's where fuel and air mix & flows, O2 sensors (A/F in VVT), CATs are at optimal. I find this gives best indication of engine performance.

I've two different bluetooth OBD devices. Bluedriver & OBDmxII for iphone:

Bluedrive is closed architecture software, OBDmxII is open. The Bluedrive gives a real-time moment to moment read out of FT. Whereas the OBDmxII software I downloaded and use, seem delay and not as precise readings of FT. The OBDmxII however, gives more data points (PID) to choose from. I can see AT fluid temp (very useful), CAT, & AHC Mpa.

When watching FT, while driving. It becomes very apparent that any throttle movement, rapidly changes FT. As well as load (ascending or descending a hill) on drivetrain.

With either OBD device. I log the info for entire time it's connected. I can then go back and study the logs. To know, if I'm on flat ground and holding throttle steady when reviewing logs. By also log of RPM & MPH. I also like to see ECT & IAT and note OAT and weather conditions.

I focus in on HWY speeds ~65MPH -+10MPH. I need to see the MPH steady at say 65MPH and RPM steady at ~2,200 RPM (tire size and transmission dependent).

In the mile high city we have a lower air density, so less air (oxygen) in cu. ft. of air. When we ascend the Rocky MTN, climbing to 2 miles ASL (above sea level). The air becomes even thinner (less dense). This is where fuel delivery system shinns, reduce fuel to compensate for less oxygen. We get better MPG, but loose some HP. A dirty air filter will restrict air flow, so we'll see better MPG also. But I do not recommend dirty air filters. Engine does not run at optimal performance and we're sucking in dust damaging engine.

LTFT, is computer (ECM/PCM) adjustment to fuel amount to a bank of cylinders, via control of fuel injector pulse. To get STFT as near a baseline of "0%" ( perfect combustion point (stoichiometric air/fuel mixture (14.7 parts of air to 1 part of fuel). A moving target, PCM works to hit (baseline).

Lean (too little fuel in the mix) one bank only:

Lean one bank, LTFT of a bank, is over+5%, is where we become concerned. Which indicates a STFT of less than -5% (lean), being corrected.

Number one issue, I've seen. Is fuel injector need cleaning, cleaning & rebuilding or replacing. I see this more in low mileage. Why? They tended to sit without being started, for long periods. Fuel get old, results in some gunk clogging injector screen. 44k, Chevron Techron, Seafoam, Cataclean, etc. fuel tank additives work well if a clogged. I ran all of above and Seafoam fogger trying to clear a CATs. Pulled intake manifold and found the intake ports super clean. I suspect Cataclean, did the most to cleaning these head intake ports, which I used it last. Interesting all 8 of the fuel injector, tested prefect (flow and pattern), pre cleaning and rebuilding by Chuck at FIS. In fact, he call and ask what did I do. He not seen this before, with 15 year old a 160K miles engine.

Sitting long periods. Fuel leaks out fuel rails & injectors. Then oxygen and moisture may rust needles of injectors and fuel pressure regulator. These fuel injectors & FPR need replacing.

Injector to IM seals leaks. Not common if never disturbed. But with age, the rubber seals are drying and shrinking. So we'll likely see more of these seals just fail, with time.

Vacuum leak at intake manifold (IM) to head gasket. Which I've never seen, with factory install IM. But have, when intake manifold R&R service work done improperly. Like when starter, knock sensor, S.A.I., water bypass joint service work done.. Service history helps give clues here.

Warped IM. Which I've never seen on a 100 series. Neither in the aluminum or plastic IM of the VVT engine. But I have read about some, claiming to have happened in non 100 series 4.7L.

We've other possible causes of lean condition in just one bank. They're downstream of IM. Like valves, compression, spark plugs, COP, even exhaust leak pre or at o2 or A/F sensor, even a weak o2 (not enough yet, to kick-off DTC resulting in a CEL) or weak signal to ECM form o2 (high resistance in wires).

Lean both banks:

When we see both BK1 & BK2 very lean (to much air). This indicates a vacuum leak 80% of the time. 98% these vacuum leaks, are before intake manifold. Either a vacuum hose, air tube or throttle body (gasket, most times) is most common. As they affect both bank equally as they increase air to in intake manifold, which feeds air to both banks equally. The LTFT will be a high positive number. As PCM works to increase fuel to compensate for the the extra air from vacuum leak. STFT will be seen more in the negative.

I have seen both intake manifold gasket leak. Someone forgot to torque down the intake manifold. OUCH! I found this about 100K miles after service, best we could tell based on service history. Engine suck a lot of dusty. Killed compression, valve guides and CATs.

Restricted fuel flow issues, result in lean condition also. We may have proper air flow. But fuel is being restriction to both banks. This is almost always a weak fuel pump, bad fuel pressure regulator, clogged fuel pick up soak screen and or clogged fuel filter.

Here's one that both BKs lean, but interestly: BK2 ran leaner.

What was interesting was BK2 tended to run leaner than BK1. It was bad (rust), clogging pick up screen, weakening fuel pump and clogging fuel filter. After replacing fuel pump and fuel filter (engine bay). Both BKs FT came in line. With LTFT under 3% and STFT hovering around 0%

Remaining hard rust deposits, from old rust gas station storage tanks.

Magnet used to pick up iron (rust).

Very nasty fuel filler.

Bottom line. Don't be to concerned. If BK to BK FT varies from each other a bit. Provided under 5% -+. Check while engine at operating temp. Both idling and cruising on HWY.

 

[Queglay]

Just commenting here because of my observations recently where people see bank 2 leaner than bank 1 and for my own current scenario. I think if fuel pressure is low then bank 1 being closer to the fuel source gets to satisfy its injectors first. bank 2 gets the scraps (even lower pressure) as its further along the rail. so if fuel pressure is inadequate but still enough to avoid total failure, then bank 2 will be leaner and have higher FT's so the injector pulse is compensating for poor fuel delivery more because its the last stop in the chain that gets satisfied.