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Old 11-03-2019, 08:25 PM #16
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I doubt the engine would even run at 7.2 AFR
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Old 11-03-2019, 09:38 PM #17
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See people keep telling me the front 02 in the early years isnt the A/F sensor but yet it is. Granted I get that it reads voltages and calculates the A/F. However, if they goto crap your milage does as well. So basically are acting as A/F sensors just not wide band.

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Old 11-04-2019, 12:02 AM #18
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I doubt the engine would even run at 7.2 AFR


When itís 37 degrees it does. Itís in enrichment mode.

Try starting a vehicle with a carburetor without setting the choke and pumping the gas pedal once or twice and see how well it starts and stays running.


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Old 11-04-2019, 12:19 AM #19
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See people keep telling me the front 02 in the early years isnt the A/F sensor but yet it is. Granted I get that it reads voltages and calculates the A/F. However, if they goto crap your milage does as well. So basically are acting as A/F sensors just not wide band.

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You are absolutely correct. It uses the front narrow band sensor to determine the actual AF ratio and then tweaks the long and short fuel trims to get to whatever it is shooting for. As soon as you see closed loop for the fuel system itís using it.

When the sensor fails it reverts to open loop and runs on fixed parameters to determine injector pulse width based on TPS, MAF, RPM, ECT, IAT. It tryís to run around 12:1 AFR to prevent a lean condition and be drivable.

On a carbrated vehicle or motorcycle the O2 doesnít swing rich and lean so itís much easier to use. (Just not as accurate) go wide open throttle and watch your front sensor voltage. It will instantly stop swinging high low and settle in between .88v and .95v because it goes open loop. If your engine and fuel system is ok anyway. It shoots for 12:1 at WOT in open loop but know way to know if it made it. I will watch my LTFT to make sure itís near 0 and Iíll also do a WOT acceleration watching the voltage of the front sensor to make sure my pump and filter are flowing properly.

Fuel injection swings rich and lean on purpose. One of them is to provide oxygen to the catalyst in the converter to burn the unburned hydrocarbons. The catalyst absorbs it and then gives it off. With out it you would need air injection at all times like the old days when engines had belt driven ďsmogĒ pumps pumping air into the exhaust manifold and into the CAT around halfway back the honeycomb.


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Old 11-04-2019, 09:23 AM #20
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You are absolutely correct. It uses the front narrow band sensor to determine the actual AF ratio and then tweaks the long and short fuel trims to get to whatever it is shooting for. As soon as you see closed loop for the fuel system itís using it.

When the sensor fails it reverts to open loop and runs on fixed parameters to determine injector pulse width based on TPS, MAF, RPM, ECT, IAT. It tryís to run around 12:1 AFR to prevent a lean condition and be drivable.

On a carbrated vehicle or motorcycle the O2 doesnít swing rich and lean so itís much easier to use. (Just not as accurate) go wide open throttle and watch your front sensor voltage. It will instantly stop swinging high low and settle in between .88v and .95v because it goes open loop. If your engine and fuel system is ok anyway. It shoots for 12:1 at WOT in open loop but know way to know if it made it. I will watch my LTFT to make sure itís near 0 and Iíll also do a WOT acceleration watching the voltage of the front sensor to make sure my pump and filter are flowing properly.

Fuel injection swings rich and lean on purpose. One of them is to provide oxygen to the catalyst in the converter to burn the unburned hydrocarbons. The catalyst absorbs it and then gives it off. With out it you would need air injection at all times like the old days when engines had belt driven ďsmogĒ pumps pumping air into the exhaust manifold and into the CAT around halfway back the honeycomb.


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Thanks for sharing. Makes complete sense. As the electrical system sensors are used to monitor all the systems. We would be able to determine proper function of the fuel system. Dirty air filter, provided the electrical sensors are functioning properly. However, the scan tools will show us bad sensors by the error codes.

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Old 11-04-2019, 12:39 PM #21
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Yes, it is not ever to be used as an actual sensor. I was just curious if the parameter was available like on my Saturn, And if it behaved like it. That’s why I kept calling it target.


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Fair enough, but claiming that you cant reach stoich unless you are at 191 degrees and tell everyone that's the case isnt a "target" number. To me it seems to you are taking your data from the scangauge and implying that it's very accurate. Maybe I'm just missing something big here as you sound very knowledgeable about the subject and I know that my knowledge of the situation is very little.
Lol I'm more confessed then when we started this conversation. I'm going to plug in the codes into my scangague and see what mine says. Is there anything I need to do besides enter the codes in?

Edit: wait a minute I think it finally clicked. Correct me if I'm wrong, so basically you are saying that the numbers are just a target that the ECU or whatever is trying to achieve? It has nothing to do with your actual afr readings? If that's the case then I cant see why that would be useful in any way since your afr readings are going to be different. If the target is saying 14.7:1 at 191 engine temp, we dont know where your afr is at, they already could be at 14.7. I mean if we knew for sure that the afr was very close to the target at set temperature, but judging from my actual afr readings, they are at 14.7 well below this temp that so that means that these "target" numbers have no relevance to any useful information since they dont correlate to your actual afr readings. This is why I dont think trying to raise your engine temps would guarantee to raise your afr since you dont even know what the afr are at the current state and if they need to be adjusted. If there was hard evidence that the target numbers work directly with the afr then that would make sense. But my afr readings haven't shown this from what I can remember.

I'll enter the codes and see if going through the different engine temperature I see any correlation between the target numbers and the actual afr readings. Sorry I'm a little slow with understanding these things, comes from the lack of experience in this.
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Old 11-04-2019, 12:58 PM #22
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I appreciate the explanation. As per my afr gauge, mine also runs rich at first, but bounces around 14.7 fairly quick which is normal. I dont think you are getting an accurate reading with the scan gauge. Mine is also a 97. To make the engine run hotter so that you can achieve stoich seems a little extreme in this case. I dont believe you are getting an accurate reading. Even my afr bounces around quite a bit at idle/cruising within a seconds time it can change 2 or 3 times from 14.5 to 14.9 range with some 14.7, 14.8 in the mix. I have my doubts that what you are seeing is really 14.0 on the scan gauge at 181 degrees.

I think it's a bit of a stretch to say that you cant achieve stoich unless your temps are over 191. I mean no disrespect, imo I just think you are making assumptions on data that isnt true. I mean it wouldnt be hard for the ECU to regulate the afr for a 10 degree variance in engine temp. It does it at quite a bit lower temperatures just fine based off my wideband O2 sensor that I installed.
This right here is the true story. Bouncing between slightly rich and slightly lean is the correct way for an engine to operate when in closed loop (which the 5VZ is under most conditions). Because the early ECUs cannot keep the engine exactly at stoichiometric, they oscillate between slightly rich and slightly lean to average out to stoichiometric.

I bet that 'target AFR' number that the OP is reading isn't quite what he thinks it is... It very well could be a multiplier for something that is based on coolant temp, etc.

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Old 11-04-2019, 01:21 PM #23
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This right here is the true story. Bouncing between slightly rich and slightly lean is the correct way for an engine to operate when in closed loop (which the 5VZ is under most conditions). Because the early ECUs cannot keep the engine exactly at stoichiometric, they oscillate between slightly rich and slightly lean to average out to stoichiometric.

I bet that 'target AFR' number that the OP is reading isn't quite what he thinks it is... It very well could be a multiplier for something that is based on coolant temp, etc.

-Charlie
I think you are right. My afr numbers dont match up to the posted target numbers, not even close, but I want to do some testing myself. I think this is why no one uses the scangauge codes for the afr numbers. It's hasn't been useful to judge anything.
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Old 11-04-2019, 02:59 PM #24
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I think you are right. My afr numbers dont match up to the posted target numbers, not even close, but I want to do some testing myself. I think this is why no one uses the scangauge codes for the afr numbers. It's hasn't been useful to judge anything.
It does work on the '99+ trucks (a different code, I think)... but it just isn't very useful. It does sit near 14.7 almost all the time and does drop to around 13 when floored. It is just too slow to be useful for tuning, and otherwise doesn't really tell you the health of your engine.

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Old 11-04-2019, 03:12 PM #25
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It does work on the '99+ trucks (a different code, I think)... but it just isn't very useful. It does sit near 14.7 almost all the time and does drop to around 13 when floored. It is just too slow to be useful for tuning, and otherwise doesn't really tell you the health of your engine.

-Charlie
Yeah that's pretty much what I read. If you are wanting to know afr for most cases, it was recommended to install an aftermarket wideband kit.
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Old 11-04-2019, 03:52 PM #26
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Yeah that's pretty much what I read. If you are wanting to know afr for most cases, it was recommended to install an aftermarket wideband kit.


This is why I called it Target and not Actual. This Thread was never intended to to state that I found a PID for the ScanGauge that would eliminate the need for a real AF monitor for Performance Tuning.

What is your LTFT itís an important parameter and tells you how close your fueling is to the factory non blown fuel map.


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Old 11-04-2019, 06:24 PM #27
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This is why I called it Target and not Actual. This Thread was never intended to to state that I found a PID for the ScanGauge that would eliminate the need for a real AF monitor for Performance Tuning.

What is your LTFT itís an important parameter and tells you how close your fueling is to the factory non blown fuel map.


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Yeah it's starting to make more sense now. Im still questioning whether any data from the code you posted will have any credible information pertaining to afr. I'm trying to have a better understanding of my STFT AND LTFT, and to be honest I'm still really confused about it. I can monitor them through the scan gauge, but I've been trying to figure out my fuel map for the 7th injector based off my afr. Since this is all new to me, it's been a lot of trial and error. From what I remember, you want the value to be closest to 0 right? When it's in the negative, that means the computer is pulling fuel, right? Positive means it's adding fuel? What does the actual number mean on the scangauge is it a percentage or does it have a different value? Like what would signify that its adding 100% or whatever max is? There doesn't seem to be any consistency with my current map. I need to spend more time logging it. It's not my primary vehicle so it gets thrown on the back burner when I get to busy with work.
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Old 11-06-2019, 02:37 PM #28
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Well Iíve gotten to prove one way or the other if the above parameter was the target AF and sadly itís not.

I had to block off more than 50% of my rad to get my temps above 191. Sadly at 193 degrees in stop and go traffic the PID was showing 14.8.

So I will continue walking through the memory locations and see if anything shows up that looks like AF ratio or even actual AF ratio

There are many memory locations to look at from 00 to FF.

Every time the STFT maxes out at either 30 or -30 it adds a 1 or subtracts a 1 to the LTFT and zeros itself. Look at it as the LTFT is the whole number and the STFT is the right of the decimal point. (LTFT.STFT)

To me the LTFT is something to watch. Because once you know the normal reading and you all of a sudden see it at say 10 or -10 itís time to start looking and whatís causing the ECU to start adding or pulling fuel.


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Old 11-06-2019, 04:18 PM #29
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This is how much I had to block to get my engine above 191. In stop and go city driving I hit 193. Open road was 190-191. And some here have a problem getting theirs down to the upper 190ís.


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Old 11-06-2019, 04:27 PM #30
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Just so people can follow I figure I would add this. :-)

What are fuel trims?

Some may have noticed the fuel trim PIDS (parameter I.D.'s) on their scan tool datastream and wonder what they're for. So, what are fuel trims and what do they do? Hopefully we can clear up any confusion. A proper understanding of fuel trims can result in a quicker diagnosis and alert you to future problems with your vehicle. Basically, fuel trims are the percentage of change in fuel over time. For the engine to operate properly, the air:fuel ratio needs to stay within a small window of 14.7:1. It has to remain in this zone under all the various conditions an engine encounters every day: cold start-up, idling in heavy traffic, cruising down the highway, etc. So, the engine computer is trying to maintain this proper air:fuel ratio by fine-tuning the amount of fuel going into the engine. As it adds or takes away fuel, the oxygen sensors monitor how much oxygen is in the exhaust and respond by telling the computer. The oxygen sensors could be likened to the computer's "eyes" that watch the mixture of oxygen in the exhaust. The computer monitors this input from the heated oxygen sensor(s) continuously when in closed-loop. If the o2 sensors inform the engine computer that the exhaust mixture is lean, the computer adds fuel by lengthening injector pulse, or "on-time", to compensate. Conversely, if the o2 sensors inform the computer that the exhaust is rich, the computer shortens injector pulse, adding less fuel to compensate in order to bring the rich condition down. This change in fuel being added or taken away is called Fuel Trim. Really, the oxygen sensors are what drive the fuel trim readings. Changes in o2 sensor voltages cause a direct change in fuel. The short term fuel trim (STFT) refers to immediate changes in fuel occurring several times per second. The long term fuel trims (LTFT) are driven by the short term fuel trims. LTFT refers to changes in STFT but averaged over a longer period of time. A negative fuel trim percentage indicates a taking away of fuel while a positive percentage indicates an adding of fuel. Think of it like this: You're driving from the beach at sea level into the mountains. On a short-term basis, you may go up and down several hundred feet at a time as you ascend the mountainous terrain. But, over the long-term, you are actually ascending from low to high altitude several thousand feet, gradually. It's similar with short and long-term fuel trims. STFT are immediate ups and downs in fuel, while LTFT are what is occurring over a longer period. A normal STFT reading will generally fluctuate between negative and positive single digits 2-3 times per second. Usually they'll stay around positive or negative 5%, but they may occasionally go up towards 8 or 9% depending on the efficiency of the engine, age of the components, and other factors. A normal long term fuel trim reading will appear to stay the same, giving a long term average of fuel added. It, too, should be close to zero, positive or negative single digits under normal circumstances. It will fluctuate much slower, possibly appearing static. Normal STFT Reading Fuel Trim - Normal Condition If you experience ST or LT fuel trims that are in the double digits positive or negative this would indicate a abnormal adding or lessening of fuel. This could be due to leaking fuel injectors, an unmetered air leak or something similar. For example, if the o2 sensors are reading lean due to, say, a vacuum leak, the engine computer will compensate by adding fuel. Lean STFT Reading Fuel Trims - Lean Condition The STFT will start to climb immediately to reflect the computer adding fuel. While the computer is adding fuel it still watches the o2 sensors until the o2 sensors are indicating that the lean condition no longer exists and proper air:fuel ratio is met. The computer will maintain this heightened addition of fuel until the leak is corrected. The scan tool will show STFT readings that are in the positive double digits, indicating that the computer has been adding too much fuel for normal operation. After a while the LTFT will also reflect this relative addition in fuel. Now if the vacuum leak is bad enough, the computer will not be capable of adding enough fuel to achieve proper air:fuel ratio. It will add fuel until the STFT reaches it's max calibration, usually 25%. Then a code is set in the computer indicating that the engine is running lean (P0171 or P0174) and the STFTs have maxed out. The opposite would be true if an engine was running rich due to a fuel leak (P0172, P0175). Rich STFT Reading Fuel Trim - Rich Condition Keep in mind that the computer has no idea if the o2 sensor is reading properly in some cases. For example if an o2 sensor was sticking rich, the computer would assume it was reading correctly and begin taking away fuel to compensate. This is referred to as a "false rich" condition. The computer would be leaning the engine and setting a possible P0172, P0175. The codes would indicate the engine was running rich but it ACTUALLY is running lean. If you use only the false rich codes to diagnose and don't observe all the fuel trim and o2 sensor data, you may make a false diagnosis. Also, each bank has it's own fuel trim reading. If your engine is a 4 cylinder, then it has only one bank, Bank 1. On a V-style engine you can isolate which bank is running rich or lean by watching that bank's fuel trims. If one bank is running properly, and another isn't you can narrow down a developing problem to one side of the engine or the other. Using your new knowledge of fuel trims, you can take the guesswork out of interpreting your fuel system's condition and possibly save some hard-earned money.
__________________
1997 4X4 V6 5 Speed Sr5 4 Runner (97 5 speed )
1997 4X4 V6 Red limited 4 Runner (97 Limited)
1998 4X4 V6 Sr5 Red 4 Runner (98 Tetanus1 )
1998 4X4 V6 Sr5 Silver 4 Runner (98 Tetanus2)
2001 4X4 V6 Sport Green 4 Runner (01 Green Sport)
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