Long term fuel trim issues

I have a 2008 Tacoma 4wd 6spd with 3in lift Bilstein and 265/70r17 duratracs. I noticed today on my UltraGauge that with my key on engine off the gauges says bank two long term fuel trim is at about 7% while bank 1 is 0 (what I would expect on both)

Iv been getting lower fuel mileage then I’d like. And actually seems like it’s worse on the highway. My ultra gauge says I average 15.2mpg general and it’s all calibrated and what not. However if I watch my short trip mpg I can get 18 on the back roads but average around 12-13 on the highway at 65 no matter what. Add a small trailer with one snowmobile (1000lbs) and I’m right down in the 8-10mpg range. Which I see people getting while towing full size campers. So Iv been searching to see if something is amiss and this certainly catches my attention.

Does anybody have any insight on what’s going on here. Why it would be at 7% like that. Can anyone confirm that something’s deff not right. Or give any steps I should take, things I should test etc.

 

I have nothing on the post but where did you get the wheel cover ?

 

google "long term fuel trims" and you will come up with a ton of info how to diagnose it. Since your issue is only on one side of the engine, that eliminates vacuum leak and MAF sensor since that would affect both banks. so that could leave you with O2 sensor, fuel delivery (not at the pump, but at the injector), or clogged cats. Try moving bank 1 O2 sensor to bank 2 and vise versa to see if the problem follows. Can try similar with injectors.

Edit, you'll want to watch the short term fuel trims after you do since the ECM wouldnt have had time to adjust LTFTs just yet

 

LTFT's change based on engine rpm and load. What are your LTFT's at say a crusing speed of 30 and 65 mph?

Get that info and we can go from there.

EDIT - 7%LTFT's are not bad. And bank seperations of LTFT's of that much are not unheard of, especially at lower loads where the differences in exhaust and how it mates up can create extra scavenging on one bank. FYI i have been tuning my MAF sensor tables in HPTuner's and before doing so I was constantly at 5-7% LTFT's on both banks above say 15% throttle. Below that bank differences started to show up where one bank would go say 3% negative and the other 5% positive.

 

I got it at just my local Walmart or auto parts store. I’m almost positive it was Walmart though. Cost like 5-8$ lol

 

We’ll see that’s where it gets intersting. I’m not worried about seeing 7%. That amount doesn’t concern me. What does concern me is it should be zero when the engine is not running shouldn’t it be? If you look you can see in above photo rpms are 0

so as for ltft I’m general on my truck something isn’t right. Iv been watching it for a little while now becasue once I installed my ultra gauge I was getting alarms for being over 10% on bank 2. So I upped it to 10.5% and then still was getting alarms. So I payed more attention and Iv seen bank two be as high as 13% while bank one is a normal 3-7%.

to answer your question about cruising ltft they are normal. Anytime my foot is on the gas pedal doesn’t matter if I’m barely touching it or on the floor pan. The numbers are pretty normal. As you can see in this photo

So if I’m on the throttle at all they are all good. When I always get the alarm is when I’m off the throttle. Wether it be idling coating or engine braking. That’s when bank 2 will go over 10% as you can see in this photo. Yes I know it’s only .16 over but it has been as high as 13% or more. I just didn’t get a pic of that. This is just to give an idea of what I’m dealing with.
So as you can see most of these things are adding up to something not being right it’s just about what it is that isn’t right. I think Im gunna start with the suggestion of swapping sensors to see if it moves with it. Maybe a bad sensor.

 

Generally speaking, anything within 10% is considered normal. Its not going to be zero all the time, what you're seeing is just the fuel system reacting to the calculated load and getting the engine what it needs.

If fuel mileage is the main concern i would look at mechanical stuff like tires (are they LT?) and driving habits

For comparison, ive got 275 LTs /4wd / 2-3 inch lift and i get around 16-18 no matter what i do. If I'm mobbing up the pass to the snow the mileage is even worse. With these trucks, if you're going over 60-65 on the highway forget about good gas mileage.

 

OP, I had the same thing with mine and is one of the reasons I decided to pull the injectors and send them out for specialty cleaning.

One of the things I kept running across researching the matter in the literature was that when someone was discussing the LTFT differences on a V-engine they seemed to frequently report that Bank 2 was higher. That was also the case with mine. I'm sort of kicking around the idea that this may occur due to a a very slight lag in timing chain travel/oil pressure VVT events that may occur between banks. So the idea being they are close but not exact. I have not been inside the engine so its a bit hard to do something other than just "think" about such matters.

I can tell you that once my injectors came back there was a noticeable drop in LTFT in general and between the banks but Bank 2 was still higher.

One of the things that you folks should know is that the ethanol added to fuel will drive the LTFTs high and is a known issue. If you like I will send you a special study detailing the results. But your LTFTs look very good IMHO and I would suggest that you do..............nothing.

 

These are pretty much the exact things that i see on my truck that i have logged over time. Bank 2 with 5 ish% greater LTFTs at low throttle openings then an evening out +-2% at crusing throttle and above. Just due to the design of the motor etc.

I wouldnt worry about LTFT's under 10% at crusing speed.... at low throttle openings like idle and just off idle LTFT's can be bigger simply due to how little fuel is flowing and any slight differences in fuel injectors are exaggerated.

 

Are you getting a code as well?
My ltft's are up to 15% and I'm presently running with a P0333 code. Knock sensor high input.

My throttle on the highway also feels flat. It doesn't want to move and will eventually downshift in response to giving it some gas. Around town, no problem.

It's not all the time though.

Some youtubing and a couple of the videos mentioned fuel pressure could be an issue. Both banks have high trims, but because I'm only throwing the bank 2 code

I'm beginning to think it's the fuel pump...

 

20-25% is the threshold to code

 

Thank you everybody for the replies. A lot of good information here. I’m still reading through it and thinking about all the variables but I will post back soon.

 

Fuel mileage is deff not my main concern. Obv I don’t want it to be ridiculous but it’s not a priority. Performance and power is more priority to me. So I wouldn’t say fuel mileage is my main concern. My main concern is making sure my truck is actually running correctly. If there is more power to have or more mileage to have because something is broken or not working correctly then I want that power and mileage back lmao.

Ever since I got my ultra gauge my driving habits have been super reserved. I would think if somebody drove like me in one of those trucks brand new they would prob get 20mpg. With that being said I am running lt265/70/r17 duratracs with about 3” of lift and 4wd and if your getting 16-18 on highway then you have bigger tires then me (assuming you have 17” wheels I’m not sure if 275 are bigger on 16s or not) and are getting 3-5mpg more then me. If your talking about backroad driving then that’s pretty on par with what I get. About 16-18 on back roads cruising 40 mph with little stopping.

 

So regardless of wether my percentages are within normal range or not. What’s up with the fuel trim not being zero with the engine off. I would think something has to be wrong there. Shouldn’t they both be zero since no fuel is being used so nothing to monitor and adjust let alone display the percentage its adjusting for. Has anybody else actually seen this condition with there truck?

 

Aren't LTFTs stored in the memory of the PCM? From what I know about fuel trims, the STFTs react practically immediately to the feedback from the "upstream" O2 sensor. (The downstream O2 sensor just monitors the condition of the cat.)

As you get "trends" in the STFT, such as the PCM having to constantly add (or subtract) fuel to obtain the optimal ignition, it adds (or subtracts) fuel to the LTFT, which results in lower STFTs.

The PCMs hold the LTFT amounts in memory for the next time you start your vehicle, so it has a "starting point" for when to add (or subtract) fuel. That's why newer vehicles seem to run so great for so long.

I think the only way to zero out your LTFTs is to disconnect the battery. Your truck might run a little rough until the PCM "relearns" how your engine runs, and makes "adjustments" to your injector pulse rate and duration (and spark rates & duration, etc.).

 

Like stated the truck stores LTFT's over restarts. even without it running it would show something as it will extrapolate up and down.

 

OP, you can trust your truck. If the fuel calculations get to an unsafe place (like 20-25%) it will code and turn on the check engine light. It knows what its doing.

 

Side note, I see your truck is a 6 speed. Is your highway mileage calculated pen and paper between fuel pumps or are you just going off what the Ultragauge shows? FWIW, my gas mileage drops on the highway similar to yours according to my Ultragauge. Goes from 17ish backroads to about 15ish highway. My truck is a v6 6 speed lifted on 285s. I think the gearing leaves a lot to be desired on these trucks.

Fill up at an exit, hope on the highway, go X amount of miles, and fill up again at another exit, calculate your Highway MPGs this way.

Anything over 55mph, the mileage seems to start to drop.

 

I think the light trips when the LTFT = +/-25%, so no need to worry about that yet...

 

Can anyone help me figuring out if this is a fuel related problem or do I just need to get the truck tuned. Engine has headers intake spacer and throttle body spacer and trd cold air intake. I keep getting a miss fire on cylinder 2 and 5 going down the high way the fast few months not sure where to start I think it could be fuel related because the truck sat for about 5 years and started it once in awhile but I have been driving it the past year and only threw check engine for missfire about 3 times so far.