LTFT high except at idle and WOT ???

[tlib99]

Ok I have a 4Runner with the 2.7 5sp 4x4. I got a scan tool for Christmas and have been studying fuel trims and how to use these readings for diagnosis. So what I've noticed on the scan gauge is my LTFT at idle is a solid 3.9. But as soon as I push on the accelerator they jump up to 14% while the STFT is right around 0 going between + and - 1-2%. I let off the accelerator and the long term drops right back to 3.9. And while on the highway I'd floor it and the LTFT would correct back to the 3.9%. Very weird I believe. So my research tells me that is a fuel delivery issue instead of a vacuum leak. Not sure how to check the fuel pressure cause there is no test port for my fuel pressure gauge. Also, no CEL and no codes stored. I've cleaned the MAF, and the o2 is fairly new as is the catalytic converter. Any guesses as to why that's new? Haha, jerk cat thieves. So, any help in the direction I should go would be great. Thanks.
Oh yea, I did a smoke test to just rule out the vacuum leak and noticed smoke from the egr vacuum modulator, not the egr valve but the green modulator above it. Kinda suspicious of that, could that be the problem? Or is that normal? The smoke was coming out around the chrome ring that goes around the modulator. I pulled it off and blew and sucked on the bottom port to check the diaprahm, and it seemed to hold in both directions, meaning it had resistance. So any ideas or if anyone has a scan tool maybe we can compare readings. Thanks ya'll

 

[JayRolla]

Ok I have a 4Runner with the 2.7 5sp 4x4. I got a scan tool for Christmas and have been studying fuel trims and how to use these readings for diagnosis. So what I've noticed on the scan gauge is my LTFT at idle is a solid 3.9. But as soon as I push on the accelerator they jump up to 14% while the STFT is right around 0 going between + and - 1-2%. I let off the accelerator and the long term drops right back to 3.9. And while on the highway I'd floor it and the LTFT would correct back to the 3.9%. Very weird I believe. So my research tells me that is a fuel delivery issue instead of a vacuum leak. Not sure how to check the fuel pressure cause there is no test port for my fuel pressure gauge. Also, no CEL and no codes stored. I've cleaned the MAF, and the o2 is fairly new as is the catalytic converter. Any guesses as to why that's new? Haha, jerk cat thieves. So, any help in the direction I should go would be great. Thanks.
Oh yea, I did a smoke test to just rule out the vacuum leak and noticed smoke from the egr vacuum modulator, not the egr valve but the green modulator above it. Kinda suspicious of that, could that be the problem? Or is that normal? The smoke was coming out around the chrome ring that goes around the modulator. I pulled it off and blew and sucked on the bottom port to check the diaprahm, and it seemed to hold in both directions, meaning it had resistance. So any ideas or if anyone has a scan tool maybe we can compare readings. Thanks ya'll

Im not sure how our ecu but the Low term fuel trim is not affected at WOT. So dont worry about that, once you hit above a certain % throttle position, rpm and load the ecu switches to open loop fuel map which the fuel trims are not used anymore.

Fuel trims are for adjusting the fuel map on the go according to air pressure, density all that fun stuff. Some ecu's have 0-20% correction up and down. So when tuning a cars say larger injectors you want them around 0%. So idle within 5% is perfect. Once you hit the gas they will fluctuate but you want them within the 20% to make sure the ecu can full adjust. If they are pegged all the time its dangerous because the ecu cant adjust anymore. This is usually only caused by bad tuning of more fuel delivery.

So when checking the fuel trims you want to make sure you driving a very stready rpm, gas pedal the same and watch the trims, they should level out. I think you are fine.

Guess bigger question is what is running bad? Are you having issues?

 

[tlib99]

Thanks JayRolla. I've just started educating myself on ltft's because of an issue I am having on my 99 silverado. I totally forgot about it going back to open loop at WOT. But all my research says try to maintain that O% +/-. So when I see mine at highway speeds, steady speed, it's running 14+. And runs in the "normal" range at idle. The research has been on 4cyl, 6cyl, and 8cyls. All reporting the same LTFT's when running at top efficiency. Close to 0% (+/-5) The reason I started checking it on the 4R is because of what I feel is poor fuel mileage. I completely understand all the factors that affect fuel mileage, and I'm sure that topic alone gets beat into the ground on these forums. But it's my understanding that Fuel Trims are the first place to look when diagnosing vehicle efficiency. So when my city mileage is better than my highway mileage, that to me is cause for some investigating. That's just my opinion, and my opinion has been wrong before. HA,HA. So I thought I'd throw this question out there and see if somebody maybe had a scan tool and see how their fuel trims run. If the majority of reports comeback to be similar to mine then I'll feel comfortable with what mine is doing.

 

[JayRolla]

Thanks JayRolla. I've just started educating myself on ltft's because of an issue I am having on my 99 silverado. I totally forgot about it going back to open loop at WOT. But all my research says try to maintain that O% +/-. So when I see mine at highway speeds, steady speed, it's running 14+. And runs in the "normal" range at idle. The research has been on 4cyl, 6cyl, and 8cyls. All reporting the same LTFT's when running at top efficiency. Close to 0% (+/-5) The reason I started checking it on the 4R is because of what I feel is poor fuel mileage. I completely understand all the factors that affect fuel mileage, and I'm sure that topic alone gets beat into the ground on these forums. But it's my understanding that Fuel Trims are the first place to look when diagnosing vehicle efficiency. So when my city mileage is better than my highway mileage, that to me is cause for some investigating. That's just my opinion, and my opinion has been wrong before. HA,HA. So I thought I'd throw this question out there and see if somebody maybe had a scan tool and see how their fuel trims run. If the majority of reports comeback to be similar to mine then I'll feel comfortable with what mine is doing.

Have you researched to see what the max adjustment % is. In the cars I tuned it was about 16%. So yes on the highway you might be pegged and not getting full adjustment. Your right though, it should settle its way back too 0%.

 

[tlib99]

In my research I've not come across what the max is for toyota, as far as when it will throw a CEL that is. Its seems to be pretty common to throw a code at 20-24% from what I've noticed across all brand of vehicles.

See my silverado has the opposite problem. It has high LTFT at idle and then comes down at driving speeds, rather highway or in town driving. Which is usually a vacuum leak. Which I finally found and it is an intake casket leak. But even at highway speeds is was 7-9% which makes me think the leak is bad enuff that it won't correct back to near 0. So hopefully gonna get that fixed this weekend and rescan and see if my LTFT corrects. And if they do, I'll bet my mpg will go back to 17 mixed driving compared to the 12-14 I've been getting. And that will make me plum tickled.

I'd like to check my fuel pressure but not sure how without the test port. And the 2.7 fuel filter is in a not so nice location. So any secrets on that procedure would be very welcomed.

All the other readings on my scan tool are good, like the o2, MAF, IAT, ECT are I guess the main ones.

 

[JayRolla]

In my research I've not come across what the max is for toyota, as far as when it will throw a CEL that is. Its seems to be pretty common to throw a code at 20-24% from what I've noticed across all brand of vehicles.

See my silverado has the opposite problem. It has high LTFT at idle and then comes down at driving speeds, rather highway or in town driving. Which is usually a vacuum leak. Which I finally found and it is an intake casket leak. But even at highway speeds is was 7-9% which makes me think the leak is bad enuff that it won't correct back to near 0. So hopefully gonna get that fixed this weekend and rescan and see if my LTFT corrects. And if they do, I'll bet my mpg will go back to 17 mixed driving compared to the 12-14 I've been getting. And that will make me plum tickled.

I'd like to check my fuel pressure but not sure how without the test port. And the 2.7 fuel filter is in a not so nice location. So any secrets on that procedure would be very welcomed.

All the other readings on my scan tool are good, like the o2, MAF, IAT, ECT are I guess the main ones.

Yea that sounds about right. Mitsubishi ecus max around 19% and older ecus never had a cel. Since your fuel trim is not maxed, you really are not losing gas mileage from it. I have tuned out fuel trims with full engine management systems and its such a small tweak to fuel its not even funny. There is no way that 14% adjustment is causing bad fuel economy. If anything your ecu is doing its job. A lot of times adjustments to the maf sensor would tune it out and not touching the fuel compensation at all.

In past I have installed little underhood gauges on the fuel filter for fuel pressure readings but like you said not a good location. But usually had a after market FPR with a gauge.

Realistically I have never tried to fix fuel trims on a stock vehicle. I was always after installing a different maf, fuel pump, fuel pressure change, and or larger injectors. And most tuners as long as fuel trims are within the adjustment range they are happy. Some just leave them maxed since it can be such a PITA to figure out. I was always happy with 10-15% on my cars because 0% seemed impossible in CO with the changing weather and changes in gas/e85 mixes.

 

[tlib99]

Hey thanks JayRolla for all the input. I'm still real curious if some one else chimes in with their scan tool readings on stock especially. Cuz for sure exhaust, CAI, different MAFs, will play a part in how the ECM is reading things. But it's my understanding that the o2's are what sends the signal to the ECM. So if the O2 is reading a lean condition, say because of a vacuum leak or poor fuel delivery, then it will tell the ECM to send more fuel. And the way I understand it 14% is about how much more fuel, in my case I'm burning. I know 2-3 mpg doesn't sound like much but tank after tank it adds up. IMO. Again I really believe this thing should get better than 18.2 all highway mpg.
Please anyone following this, let's hear some scan tool data. Please and thank you, lol.

 

[iowajosh]

I don't think it quite works that way. It takes +14% to make the 02 sensor happy. You aren't burning 14% more. I think it means you are getting slightly less fuel from the injectors than the ecu anticipates or you are getting more air than expected.

You should start a 3rz thread. I've played with mine some trying to get it to run nice and it has been frustrating.

 

[tlib99]

Hey iowajosh, yea I'm sure it doesn't work that way, but like my silverado, the LTFT is at 24% at idle then in all driving ranges it's around 7-9%. My mileage went from 16.8-17.2 mpg to 13-14 mpg. So when I take 13 x 24% it equals 3.12, so add that to 13 and its 16. Same results on the 4R. I'm to confused that it happen to work that way but that was my fuel mileage before the fuel trims started to rise. I have an app that I log every fuel fill up, so I have almost 2years of data. On the silverado that is. The problem with the 4R in fairly new.

 

[gamefreakgc]

Running rich/lean is rarely ever a fuel delivery issue, unless you know you have dirty fuel and/or a clogged fuel filter.

More likely is that you are need of some maintenance done on your vehicle. How many miles do you have on the front (assuming you have two) O2 sensor? Toyota recommends them replaced every ~90k miles to ensure accuracy. Are you up to date on spark plugs and spark plug wires? Have you ever cleaned your MAF sensor? All of these will help get your MPG's back to where they should be.

Lastly, are you sure you are not looking at Bank 1 and Bank 2 fuel trims? Long-term fuel trims don't bounce around. But Bank 2 fuel trims would since that's the reading from your rear O2 sensor (again, assuming you have two).

And smoke from your EGR is a bad sign. You've got a vacuum leak. Could be the cause of your reduced MPG's since unburnt oxygen is entering your engine and down to your O2 sensor, causing it to increase fuel (thinking that the motor is running too lean).

I'd worry less about your Scan Gauge readings and more on the issues at hand.

 

[JayRolla]

Yea it does not work that way. 14% fuel trim adjustment is not 14% less fuel economy. Just a 1% change in ecu injector compensation can change that entire number drastically. So in no way are you losing 14% fuel economy due to that number. Again to me the 14% reading you are getting just means you ecu is doing its job. In my life of tuning many cars I have never seen a car that all three trims are within the 0-5%.

You also relize just a change in air temp, moisture, elevation will affect these numbers. Not to mention the 10% ethanol mix in the gas is not consistent which also changes afr and fuel trims. You ecu is just working to keep the motor happy.

 

[tlib99]

Running rich/lean is rarely ever a fuel delivery issue, unless you know you have dirty fuel and/or a clogged fuel filter.

More likely is that you are need of some maintenance done on your vehicle. How many miles do you have on the front (assuming you have two) O2 sensor? Toyota recommends them replaced every ~90k miles to ensure accuracy. Are you up to date on spark plugs and spark plug wires? Have you ever cleaned your MAF sensor? All of these will help get your MPG's back to where they should be.

Lastly, are you sure you are not looking at Bank 1 and Bank 2 fuel trims? Long-term fuel trims don't bounce around. But Bank 2 fuel trims would since that's the reading from your rear O2 sensor (again, assuming you have two).

And smoke from your EGR is a bad sign. You've got a vacuum leak. Could be the cause of your reduced MPG's since unburnt oxygen is entering your engine and down to your O2 sensor, causing it to increase fuel (thinking that the motor is running too lean).

I'd worry less about your Scan Gauge readings and more on the issues at hand.

HMMM, well, if you read my original post you would see I stated I have cleaned the MAF, and my O2 sensors are both new due to the fact the catalytic converter got stolen.

And I'm pretty sure running rich or lean can very much be caused from a fuel delivery issue. Understanding LTFT is one of the first things to read with an OBD2 scan tool with live data readings.

I have a 4cyl, so I only have 1 bank. On a scan tool the o2 readings are o2s1 and o2s2, which o2s1 is the sensor in front of the cat and o2s2 is post cat.
I'm confused why you would suggest to worry less about my OBD2 scan tool readings? Pretty sure that is the best place to start when looking for an issue with running condition of a vehicle.

And the 4R is very well maintained, new plugs and wires less than 6months ago because of a head gasket leak. Also mentioned in a previous response I mentioned I wanted to check the fuel pressure but was looking for some advice on how others have done it since the 2.7 doesn't have fuel pressure test port.

 

[JayRolla]

HMMM, well, if you read my original post you would see I stated I have cleaned the MAF, and my O2 sensors are both new due to the fact the catalytic converter got stolen.

And I'm pretty sure running rich or lean can very much be caused from a fuel delivery issue. Understanding LTFT is one of the first things to read with an OBD2 scan tool with live data readings.

I have a 4cyl, so I only have 1 bank. On a scan tool the o2 readings are o2s1 and o2s2, which o2s1 is the sensor in front of the cat and o2s2 is post cat.
I'm confused why you would suggest to worry less about my OBD2 scan tool readings? Pretty sure that is the best place to start when looking for an issue with running condition of a vehicle.

And the 4R is very well maintained, new plugs and wires less than 6months ago because of a head gasket leak. Also mentioned in a previous response I mentioned I wanted to check the fuel pressure but was looking for some advice on how others have done it since the 2.7 doesn't have fuel pressure test port.

Install a fuel pressure gauge. Cheap on ebay.

Go into a shop and ask how many times they look at Fuel trims to help diagnose a car. They will say pretty much never. Go into a dyno shop and they will say everyday. Its not normal to use the fuel trims as the best place to start. Also if your FPR was bad you would know, your truck will run very rough from lean, blow smoke from rich, not start and or have gas under vehicle. Ive tuned with FP before and you would now if yours was off. Im sure thats not the reason your trim is with reasonable levels.

 

[tlib99]

Ok, I'll look into installing a fuel pressure guage.

Just a couple videos I found very intersting and enlightning on auto diagnostics.
1: ScannerDanner, an autotech teacher
2: Schrodingers Box, he's an engineer of some kind

I've been educating myself from these videos, and in no way feel I know it all now about
diagnosing auto issues. So when I found out this info I was assuming it was common knowledge in the auto mechanic world, and I was just getting up to speed. So I guess I'll continue to research and apply what I learn and see how it turns out.

Thanks to everyone who has responded. I'll report any changes.

 

[JayRolla]

Ok, I'll look into installing a fuel pressure guage.

Just a couple videos I found very intersting and enlightning on auto diagnostics.
1: ScannerDanner, an autotech teacher
2: Schrodingers Box, he's an engineer of some kind

I've been educating myself from these videos, and in no way feel I know it all now about
diagnosing auto issues. So when I found out this info I was assuming it was common knowledge in the auto mechanic world, and I was just getting up to speed. So I guess I'll continue to research and apply what I learn and see how it turns out.

Thanks to everyone who has responded. I'll report any changes.

No you are right, it is common knowledge for good shops. LOL. Im just saying you can diagnose and fix issues other ways. I always do the easy stuff first and then fall back to diagnosing with ways like you say. But if im fixing a vacuum leak im going under the hood, maybe running some propane around the vacuum lines and listening for an idle up on motor to find the leak. Im not going to go to my data logging tool.

 

[gamefreakgc]

HMMM, well, if you read my original post you would see I stated I have cleaned the MAF, and my O2 sensors are both new due to the fact the catalytic converter got stolen.

And I'm pretty sure running rich or lean can very much be caused from a fuel delivery issue. Understanding LTFT is one of the first things to read with an OBD2 scan tool with live data readings.

I have a 4cyl, so I only have 1 bank. On a scan tool the o2 readings are o2s1 and o2s2, which o2s1 is the sensor in front of the cat and o2s2 is post cat.
I'm confused why you would suggest to worry less about my OBD2 scan tool readings? Pretty sure that is the best place to start when looking for an issue with running condition of a vehicle.

And the 4R is very well maintained, new plugs and wires less than 6months ago because of a head gasket leak. Also mentioned in a previous response I mentioned I wanted to check the fuel pressure but was looking for some advice on how others have done it since the 2.7 doesn't have fuel pressure test port.

Was just suggesting the most common maintenance items, and you didn't mention you replaced both O2 sensors. You did use DENSO sensors, right? Also, Magnaflow and other high-flow cats are known to cause O2 sensor issues and poor MPG's due to not fully converting the exhaust gases.

Bank 1 and Bank 2 fuel trims do not refer to the engine, but the O2 sensors. Both the 4-cylinder and V6 have those readings. Some scan gauges/diagnostic tools label them differently or won't pick them up, depends on quality.

On my gauge, anything between +/- 17.9% means it's in normal operation (looking at the Bank readings). Anything more will eventually trigger a CEL. This is the only reading worth using for me, since it just tells me if I've got a vacuum leak somewhere or not and if my cat is functioning properly.

Also, if you've reset the trims recently (disconnected battery, removed EFI fuse), it can take upwards of 100+ miles to develop a true LTFT.

 

[JayRolla]

Was just suggesting the most common maintenance items, and you didn't mention you replaced both O2 sensors. You did use DENSO sensors, right? Also, Magnaflow and other high-flow cats are known to cause O2 sensor issues and poor MPG's due to not fully converting the exhaust gases.

Bank 1 and Bank 2 fuel trims do not refer to the engine, but the O2 sensors. Both the 4-cylinder and V6 have those readings. Some scan gauges/diagnostic tools label them differently or won't pick them up, depends on quality.

On my gauge, anything between +/- 17.9% means it's in normal operation (looking at the Bank readings). Anything more will eventually trigger a CEL. This is the only reading worth using for me, since it just tells me if I've got a vacuum leak somewhere or not and if my cat is functioning properly.

Also, if you've reset the trims recently (disconnected battery, removed EFI fuse), it can take upwards of 100+ miles to develop a true LTFT.

How is that true when the actual o2 that does anything reads the mixture before the cat and or muffler?

 

[gamefreakgc]

How is that true when the actual o2 that does anything reads the mixture before the cat and or muffler?

Ah, maybe that wasn't too clear in my last post. Works like this:

Bank 1 (pre-cat) can be used to determine rich/lean conditions due to vacuum leak, open injector, etc. since it's before the catalytic converter does it's business. The sensor is trying for that stoic 14.7 air/fuel ratio when it closed loop. In open loop, the front O2 readings are ignored (I think you already know this since that's where the tuning component comes in). This is also why short-term fuel trims don't matter a whole lot, since what does matter is the actual air/fuel ratio being read by the front O2 sensor. As long as it can compensate both ways without maxing out and triggering a CEL it's operating as usual. I believe it takes a reading roughly 8-9 times every ten seconds, it explains the function in the FSM.

Bank 2 is the exhaust leaving your converter. This is sort of the "smog pass" sensor that will detect high HC or O2 readings in your gas. If it reads high HC (fuel) for example, it will decrease the fuel at the injector to compensate. Or the opposite if it reads high O2. This is why I brought up the Bank vs. LTFT readings since the two are similar. Those of us with OBD-I vehicles can sometimes get blindsided with repairs for not passing smog, since we do not have a O2 sensor after the cat. Those with OBD-II vehicles normally do not have this issue, due to the second O2 sensor always monitoring the exhaust gases. Basically though, you can't get good readings off the rear one other than to determine if your cat is failing or not.

 

[tlib99]

Oh I agree, if you have years of experience under the hood! You can most likely be affective doing it that way. But for the one who hasn't and the ones who don't want to through parts at it till you finally get it right, I believe understanding the OBD2 system is very affective.

For example, my silverado, it runs out great, would never guess anything was wrong with it until you noticed your fuel mileage taking a hit. So then you plug your scan tool in and start seeing what's going on. And as I stated, the fuel trim levels is the first place to look. So on my truck I had high LTFT's on both banks at idle only. So I research that and fine that high LTFT's at idle both banks is most generally a vacuum leak. Now of course one would clean the MAF and do a visual, listen, and then as I did start spraying starter fluid on vacuum lines and around the intake. When I got nothing there then I smoke tested it and found my intake was indeed leaking. That's all! Lol!

So now here I am with y'all trying to figure out the opposite condition with the 4RUNNER. Which, after watching the videos I mentioned earlier, they suggest this condition is a fuel delivery issue. That could be a bad fuel pressure or bad injector spray patterns and such. So that's why I mentioned how y'all are checking your fuel pressure. Now I would say my idle is a slight unstable but not obvious, and it does feel rather doggy on the highway. And I say that knowing it is only a 4cyl but still my old 97 RAV4 with the 2.0 I think was peppier. And that thing wasn't gna win any races.

So, I apoligize for my determination that my LTFT's are telling me something, thus my request that there might be another scan tool "nerd" with the same motor could share with me their scan tool readings, so I can move on. Haha

Maybe I should start another thread called. What are your LTFT (long term fuel trim) readings!

 

[tlib99]

Ah, maybe that wasn't too clear in my last post. Works like this:

Bank 1 (pre-cat) can be used to determine rich/lean conditions due to vacuum leak, open injector, etc. since it's before the catalytic converter does it's business. The sensor is trying for that stoic 14.7 air/fuel ratio when it closed loop. In open loop, the front O2 readings are ignored (I think you already know this since that's where the tuning component comes in). This is also why short-term fuel trims don't matter a whole lot, since what does matter is the actual air/fuel ratio being read by the front O2 sensor. As long as it can compensate both ways without maxing out and triggering a CEL it's operating as usual. I believe it takes a reading roughly 8-9 times every ten seconds, it explains the function in the FSM.

Bank 2 is the exhaust leaving your converter. This is sort of the "smog pass" sensor that will detect high HC or O2 readings in your gas. If it reads high HC (fuel) for example, it will decrease the fuel at the injector to compensate. Or the opposite if it reads high O2. This is why I brought up the Bank vs. LTFT readings since the two are similar. Those of us with OBD-I vehicles can sometimes get blindsided with repairs for not passing smog, since we do not have a O2 sensor after the cat. Those with OBD-II vehicles normally do not have this issue, due to the second O2 sensor always monitoring the exhaust gases. Basically though, you can't get good readings off the rear one other than to determine if your cat is failing or not.

I'm pretty sure bank 1 and bank 2 relates directly to the motor. Bank 1 being the side that has the number 1 firing cylinder and then of course bank two is the side that has the 2nd. And you can have a normal LTFT reading on one bank and a lean or rich reading on bank 2. This then tells you your situation is on that side of the motor.