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-1 to +1 is ideal, -5 to +5 is acceptable under certain conditions, beyond that something is up (for all cars). It does not depend on mileage.
There are 3 LTFT bands: idle, low load and high load (something like that), so the value may change depending on what you're doing, but ideally it stays around 0. What values is it fluctuating between?
My ltft at idle is between 1 and 3.5 usually.( I've seen it at 5.5 before) That's with a fresh rebuild with 500km on it roughly, gutted cat, BHR coils and wire kit and ms cai.
LTFT will vary depending upon a wide range of variables.
Just a few include:
-Ambient air temp
-Altitude
-Engine temp
-Catalyst calculated temp
-Air flow obstructions
-Engine compression/age
-Vacuum leaks or damaged seals/gaskets
It is normal to see 0-10% from STFT+LTFT, larger learned values may indicate a concern (aging oxygen or air flow sensors, aging fuel injectors, etc), however some cars as they age or depending upon their environment can see larger values, especially if the environment is dynamic, such as desert climates where you will go from very hot air temp to very cold between day and night drive cycles. If you are seeing 10% or more on just LTFT, there may be a concern worth investigating, however the system is designed to compensate for quite a lot, so you may not experience drivability, performance issues, or even a CEL despite the large adjustments being made.
What do you mean by fluctuating LTFT? Are you experiencing any drivability concerns or issues with fuel economy and startup? What are your local conditions like for climate and do they change greatly between drive cycles? How healthy is your car (compression, wiring and vacuum line condition, maintenance, etc)?
Also, remember that LTFT shouldn't fluctuate a ton EXCEPT...
The ECU maintains 3 different LTFT values and it switches between them based on MAF rate.
The MAF rates, IIRC, are
Idle 0-8 g/s
mid 8-20 g/s
high 20+ g/s
Keep that in mind. If you see the LTFT suddenly jump from +2% to +15%, make sure you didn't cross one of those boundaries at that jump.
In fact, if you want to really analyze LTFT, log all the data you want in addition to LTFT and MAF rate. Then group the data broken down by MAF rate because comparing LTFT from idle vs cruising at 15 g/s isn't useful.
Also, remember that LTFT shouldn't fluctuate a ton EXCEPT...
The ECU maintains 3 different LTFT values and it switches between them based on MAF rate.
The MAF rates, IIRC, are
Idle 0-8 g/s
mid 8-20 g/s
high 20+ g/s
Keep that in mind. If you see the LTFT suddenly jump from +2% to +15%, make sure you didn't cross one of those boundaries at that jump.
In fact, if you want to really analyze LTFT, log all the data you want in addition to LTFT and MAF rate. Then group the data broken down by MAF rate because comparing LTFT from idle vs cruising at 15 g/s isn't useful.
Long story short, a year ago it was fluctuating between 5 and 25% ltft. After replacing aftermarket intake back to stock, new cat, o2 sensor(included with cat??) and maf, the ltft seem to fluctuate between 4% and 15%. The dealer is unable to find any vacuum leak. Just some days ago i got a problem with the cat - P0420 -powertrain catalyst system efficiency below threshold(bank1).
The cat is confirmed defective but under warranty. The dealer is unsure how to proceed after replacing it. This will just keep happening. According to Mazda, 0-10% ltft is normal. There is no other cel for missfire or anything like that. Could it be down to compression?
Bad coils kill cats. How old are your coils? The dealer should be very aware of thise already.
Can you see what the MAF airflow in g/sec is on a warm idle with the car parked? It sjould be 5+. If its lower and LTFT is high, you have a vac leak. Just need to find it.
They should also be anle to trst compression. LTFT is not a good indicator of that.
Coils just replaced three months ago, mazda c ignition coils(N3H1-18-100C from Mazmart). As far as i know Mazmart is a reputable webshop? They dealer did say one of them was bad. Could the coils go bad because of the fluctuating LTFT, i.e. wrong mixture?
Will check maf. I think it was between 4,9 and 5,3 g/s. Does the oem cat include O2 sensor? Maybe thats the thing we forgot to change last time.
Just though I'd mention that ltft usually drops to 0 and -3% with moderate to hard acceleration.
Coils go bad on their own, what happens inside the engine doesn't affect them.
The cat does not include the sensor, but the post cat O2 has little to no effect on fuel trims. The front O2 does that.
Fuel trim is the end result of a number of sensor inputs and its there to ensure the right mixture (rather than a sign of bad mixture). So if say you have a vacuum leak and ingest extra air, the computer learns to trim in +X% more fuel to compensate. As long as its not topping out fuel trim at +25% its technically OK in that the computer is adapting to whatever is happening. +15% is on the high side, but you could keep driving and it'll continue to deal with it. Its just unusual.
Can you desrcibe a bit more how it fluctuates? When is it high, when is it low, etc.
Like I said, a rapidly fluctuating LTFT is usually just the ECU switching between the three different trims. Unless you're seeing the LTFT fluctuate rapidly and to a large degree at idle, it's probably nothing to worry about.
LTFT is a symptom. It's an indicator of how the engine is running relative to how the ECU thinks it should be running. Think of it as a derivative of the function of commanded AFR v.s. actual AFR.
LTFT is NEVER a cause of something. It's always a result of something (too much air getting in without being measured by the MAF or not as much fuel is being injected as the ECU thinks is being injected).
If your LTFT is high at idle (low MAF rate) but low at higher MAF rates then that could mean that you have a mild vacuum leak. A mild vacuum leak would be most noticeable at idle because the throttle plate is closed and intake pressure is low (greater pressure differential means larger airflow through the same size hole). Once you open the throttle up, intake pressure increases closer to atmospheric which means less air is sucked through the vacuum leak. Also, it's a relative percentage. If you're pulling 5g/s at idle, then a 1g/s leak is 20%. However, if you're flowing 20g/s then a 1g/s leak is only 5%.
Coils go bad on their own, what happens inside the engine doesn't affect them.
The cat does not include the sensor, but the post cat O2 has little to no effect on fuel trims. The front O2 does that.
Fuel trim is the end result of a number of sensor inputs and its there to ensure the right mixture (rather than a sign of bad mixture). So if say you have a vacuum leak and ingest extra air, the computer learns to trim in +X% more fuel to compensate. As long as its not topping out fuel trim at +25% its technically OK in that the computer is adapting to whatever is happening. +15% is on the high side, but you could keep driving and it'll continue to deal with it. Its just unusual.
Can you desrcibe a bit more how it fluctuates? When is it high, when is it low, etc.
As far as i remember, the front O2 sensor has never been replaced. I was thinking to suggest replacement of cat(warranty) + coil(warranty) + o2 front sensor, then check the new readings? It could have been the 02 sensor all this time. The dealer said they have used multiple tools to check for leaks even with a special spray ++. Atleast 3 mechanics have inspected the car. Thanks everyone, and also great explanation NotAPreppie . I will post back with video from 0DB2.
Don't change the feont O2 if you have no codes for it. The ECU has a number of built in diagnostics it regularly performs on O2 sensors and if they don't behave as expected, it throws the corresponding code. Also that O2 sensor is not cheap.
Also your symptoms don't fit a bad O2 sensor. Have you considered just clearing the trims (disconnect the battery) and seeing if it learns the same trims again?
Loki, IIRC, the 20-brake-stomp (NVRAM reset) doesn't clear fuel trims on an S1. It just clears the ESS profile. To clear the trims, you have to leave the battery disconnected for up to 30 minutes.
Also, changing the front O2 is a pain in the *** and will make you hate yourself, your car, and the laws of physics with the fire of a thousand suns.
Kanie12, what actual symptoms are you experiencing right now? Any driveability problems?
Loki, IIRC, the 20-brake-stomp (NVRAM reset) doesn't clear fuel trims on an S1. It just clears the ESS profile. To clear the trims, you have to leave the battery disconnected for up to 30 minutes.
Also, changing the front O2 is a pain in the *** and will make you hate yourself, your car, and the laws of physics with the fire of a thousand suns.
Kanie12, what actual symptoms are you experiencing right now? Any driveability problems?
Ok. So right now the car is at the dealer and we haven't come to any agreement. They blame my 3rd party coils(N3H1-18-100C from Mazmart) for the death of the cat, go figures! So far i understand the problem, since there is a vacuumleak, the engine is compensating by adding more fuel causing it too actually run rich. This is confirmed by AFR above 15. Some of the excess fuel might end up burning up in the catalytic converter, which in the end will kill that cat, right? Would't there be some kind of missfire cel if one of the coils were bad?
I found this:
• Oxygen Sensor – An oxygen sensor collects and sends information to the Electronic Control Unit. This is used to control the fuel/air mix. If the oxygen sensor is faulty, or it has been contaminated with silicone from anti-freeze or sealant, the fuel/air mixture will not be corrected and excess fuel will enter the catalytic converter, causing it to overheat.
The cat has been glowing for a year, even the previous cat had same issues and ended up sealed. According to Mazda a glowing cat is normal.
The dealer cannot void the warranty on claim of 3rd party components, as the coils are factory Mazda parts. Get MNAO involved and see if you can get them to correct course.
What prompted you to take your car to the dealership? What driveability problems are you having?
Yes, a bad O2 sensor can cause a problem but it usually results in severe driveability issues. Bad ignition components are a far more likely culprit.
Basicly it was just small loss of power, which I thought was connected to the vacuum leak, which the dealer hasn't been able to solve in a year. There was also a metallic intermittent noise on acceleration, like something was loose. I did ask the dealer to check it, but they said it was due to rusty heatshield. I did record the(attached)noise. I suspect the noise was coming from inside the failing cat. A month later I got the CEL which I mentioned earlier, "cat performance under threshold, bank 1".
I have also contacted mazmart and they wrote that failure on three month old coils was extremely unusual and indicative of other problems.
If I were you, I'd get my car back and pull the UIM. Test each of the solenoids on the back by attaching a MityVac hand pump to the vacuum side (the port opposite the wire harness connector). Pump it to 10 psi and see if it holds that level of vacuum for a minute or two.
The thing about a vacuum leak there is that it won't show up in the usual tests. Spraying carb cleaner is tough because it's wedged between the UIM and firewall. Pumping smoke into the intake won't show it because there's a one-way check valve that won't let the smoke propagate through to the solenoids.
The cat could have started failing prior to replacing the coils and it just took time before it was bad enough to start showing symptoms.
Ok. So right now the car is at the dealer and we haven't come to any agreement. They blame my 3rd party coils(N3H1-18-100C from Mazmart) for the death of the cat, go figures! So far i understand the problem, since there is a vacuumleak, the engine is compensating by adding more fuel causing it too actually run rich. This is confirmed by AFR above 15. Some of the excess fuel might end up burning up in the catalytic converter, which in the end will kill that cat, right? Would't there be some kind of missfire cel if one of the coils were bad?
I found this:
• Oxygen Sensor – An oxygen sensor collects and sends information to the Electronic Control Unit. This is used to control the fuel/air mix. If the oxygen sensor is faulty, or it has been contaminated with silicone from anti-freeze or sealant, the fuel/air mixture will not be corrected and excess fuel will enter the catalytic converter, causing it to overheat.
The cat has been glowing for a year, even the previous cat had same issues and ended up sealed. According to Mazda a glowing cat is normal.
Your dealer has no idea what he is doing. Get your car out of there.
A glowing cat is definitely not normal anywhere in this universe.
They can't randomly blame anything without supporting evidence (this is an actual law in the US).
That they have been aware of glowing cat for a year and didn't recommend a repair sounds borderline suable incompetence. It will kill your engine if allowed to continue.
What is the actual AFR? Above 15 is not incorrect. Your understanding is slightly wrong in that trims don cause the car to run rich. They prevent it from running lean and get it back to the required AFR. The extra air thats getting in through the leak would make it run lean.
Your dealer has no idea what he is doing. Get your car out of there.
A glowing cat is definitely not normal anywhere in this universe.
They can't randomly blame anything without supporting evidence (this is an actual law in the US).
That they have been aware of glowing cat for a year and didn't recommend a repair sounds borderline suable incompetence. It will kill your engine if allowed to continue.
What is the actual AFR? Above 15 is not incorrect. Your understanding is slightly wrong in that trims don cause the car to run rich. They prevent it from running lean and get it back to the required AFR. The extra air thats getting in through the leak would make it run lean.
The dealer has offered to cover the cat free of charge. I will pay for the coil myself since it was not purchased from them. I went ahead and asked them to replace the front 02 sensor with a new Denso sensor. Will post back with readings when i get the car back on thursday. Thanks!
So i got the car back from the dealer, i attached the readings at idle and acceleration. I dont see glowing cat now, but i didnt drive it past 120km/h yet. I see that the maf is abit low, but its rpm dependent right`? At 840 rpm its around 5.0.
Good news on non glowing cat. How was it inside?
So in the Idle picture your MAF is at 4.3 (shoild be 5) and fuel trim is +18 (should be 0). You clearly have a vacuum leak. If they can't find it, they should at least acknowledge that this data proves there is one.
Good news on non glowing cat. How was it inside?
So in the Idle picture your MAF is at 4.3 (shoild be 5) and fuel trim is +18 (should be 0). You clearly have a vacuum leak. If they can't find it, they should at least acknowledge that this data proves there is one.
07-22-2019, 09:24 AM
. I will post back with video from 0DB2.
