Fuel trims

[2001LC]

Looking at fuel trims, what do they tell use?

I happen to be monitoring fuel trim on a hot spring day with OAT of about 85 F. I was running AC on full cold so sound of fan drowned out most others. I'd been driving ~15 minutes on city streets. While at a red light I felt a bump than another bump. First thought was AC compressor cycling, but very hard (not good). So I shut off AC. Drove a bit further and park for 10 minutes as I went in a store. Then got in and drove home. On the way home it happened again at a red light, but AC off this time. Now I'm thinking could this be transmission issue, as I'd not yet set level with a true temp reading of ATF.

Here's what fuel trims looked like:

So i got out my mini VCI cable and hooked up to the tech stream. As I worked to get transmission fluid up to 115F by putting in gear (R,D,4,3,2,1) and loaded by raising RPM (putting engine under a load), I saw a misfire on cylinder one. This only happened while under a load.

So I swapped coil #1 with that of #3 and misfire moved to #3. So even though no CEL or nor was coil dead, it was dying (going bad)

Here's fuel trims after coil replaced and monitoring trims on ~15 minute city drive at OAT of ~85 F.

What do you think:
Good?
OR
Could I use some further improvement, possible a full set of OEM coils?

 

[Spike555]

I fall into the mindset of let sleeping dogs lie. Don't go chasing water falls or rainbows, let them come to you.
Fuel trim's mean nothing to me because I do not know how to read them or what they mean.

If it were me, I'd wait until there was a CEL, and then fix whatever it was.
I feel hiccups at hot idle in everything I drive, every single work van ever, every single car I've owned. I can say the only place I've never felt one was with a diesel. Never chased it. Never had a problem.

I am curious as to how far you chase this and what you come up with.

 

[jerryb]

my long terms are close to zero always. Short usually slightly negative. I can't remember what the book says.
maybe long terms in the 3.5 range is normal. I wouldn't worry.
I'd think more injectors and vac leak + MAF before a coil without a CEL. But it's a c omplete system.
cats and actual air fuel ratio, AFR.

I don't know if Nippon denso make a fuel injection manual, as in a while book just dedicated to ND modern injection. You seem like the type that would enjoy reading something like that.

If ND doesn't have a publicly available book, BOSCH does and for the most part it's all the same.
To me I find all that stuff very interesting to read. Search around for the best rated modern fuel injection books. There's stuff online about fuel trims. All that can get very lengthy.

this was my go to book and gives a very good basic understanding from the beginning of constant injection systems and onto air flow meters and then mass air flow .

I have not found a little more up to date book that expands on this one. Ive been out of the game for a while.
This book is very worth the little bit of money. You'll understand fuel delivery better than most anyone.
https://www.amazon.com/Bosch-Fuel-Injection-Engine-Management/dp/0837603005

 

[white_lx]

When an engine runs it measures the amount of air from the air flow sensor. The amount of fuel injected is known, because the properties of the injectors are know. So, in theory the fuel trim should be zero for for stoichiometric combustion conditions (just enough fuel for the amount of air).

However, because there could be vacuum leaks, injector fowling or fuel pressure issues, additional or reduced injector opening time may be required to delivered to right amount of fuel at that moment based on the O2 sensors. That percentage is the fuel trim.

Here is a really good description of fuel trim. As per the video, LTFT and STFT combined for each bank should be less than 10%.



Here is an interesting fact. Gasoline with ethanol has a lower caloric value then pure gasoline (because ethanol is already partially oxidized). As a result fuel trims will vary depending on the percentage of ethanol in the fuel. Below is an example of pure gasoline (E0) v.s. gasoline with 20% ethanol (E20).

 

[2001LC]

Thanks for the video @white_lx The "LTFT and STFT combined for each bank should be less than 10%" in his video, is of current his reading at idle. Which even my current reads both before and after coil #1 replaced are within this 10% combine average he speaks of. Notice also, my reading are during drive with AC cycling in stop and go traffic.

I found this article helpful in understand fuel trims. Fuel Trim?

In the 1st picture of OP, it's apparent STFT bank 1 (left side of engine) high to low of -100 to 65% is much wider than bank 2's reading of -14.1 to 14.1. The wide swing from RICH to LEAN in this case, was indicating an intermittent issue.

It very apparent in second picture with STFT bank 1 readouts of -11.7 - 10.2% trim's, that replacing the #1 coil stabilized bank 1 correcting this condition.

But notice in second picture bank 2 STFT -14.8 - 20.3% is wider spread than bank 1 STFT -11.7-10.2%. This difference is certainly not much, but could there be room for improvement?

This may indicate variance in coil outputs. I suppose the only way to know without equipment to test balance of each coil, is replace all coils with new OEM Denso's. If replacements make a difference (improvement) in balance, this should also improve MPG.

I saw ~14.5 MPG at ~68 MPH averages, with AC on COLD with a OAT of ~95 F. That is certainly not a bad MPG at all. But what is .75 or even 1.5 MPH average (5 to 10%) increase worth over the next 100K miles.

Here's a readout of techstream after #1 coil replaced. This was in shop just idling with no drive time.

Notice Catalyst Temp B2S1 is 556.9 which is .2 F less than bank 1 A/F (B1S1) 0f 557.1. Now this is a very small difference, but indicates at that moment bank 2 is a little RICHer (cooler).

 

[white_lx]

In the 1st picture of OP, it's apparent STFT bank 1 (left side of engine) high to low of -100 to 65% is much wider than bank 2's reading of -14.1 to 14.1.

I missed the ranges that were shown in the screenshots and focused on the current trim values (larger font).

(Looking back now, I just realized that your app lists "-100% - 65%" which means -100 to +65% because the second '-' is a dash and not a minus. This in contrast to the '-100% - -65%", which would have indicated -100% to -65%. A better separator would have been the word 'to'.)

This may indicate variance in coil outputs. I suppose the only way to know without equipment to test balance of each coil, is replace all coils with new OEM Denso's. If replacements make a difference (improvement) in balance, this should also improve MPG.

Yes this makes sense. If this was a leak or fuel delivery issue, the STFT would go to zero, but since it is varying so much it must be some randomness. Not sure if STFT would be able to pick up the individual coils and would be chasing each cylinder firing.

How do these numbers compare to other vehicles that you have worked on ?

[edit: I quickly ran out and checked my vehicle. STFT was pretty stable and around 0%, but maybe Techstream is not fast enough to see quick variations as in individual cylinder issues? I did however notice that both LTFT were -8%. Maybe time to clean the MAF? Or could be the high octane ethanol-free fuel. Edit of the edit: although the MAF looked clean, I cleaned it and LTFT dropped to -4%. I'm going to leave it at that.]

Notice Catalyst Temp B2S1 is 556.9 which is .2 F less than bank 1 A/F (B1S1) 0f 557.1. Now this is a very small difference, but indicates at that moment bank 2 is a little RICHer (cooler).

I believe the temperature is measured indirectly from the resistance of the O2 sensor heating element. So, I'm not sure that these are significant differences (larger than the measurement error).

 

[2001LC]

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How do these numbers compare to other vehicles that you have worked on ?

***


I believe the temperature is measured indirectly from the resistance of the O2 sensor heating element. So, I'm not sure that these are significant differences (larger than the measurement error).

Unfortunately I don't have simular driving fuel trim data from other 100 series.

 

[white_lx]

Unfortunately I don't have simular driving fuel trim data from other 100 series.

I think this is one of those things I'm going to start recording for overall health indication of a vehicle. Might be very useful. Not sure if the next seller is going to allow me to check fuel trims before I make an offer on a vehicle .

Regarding the coil and coil health. I learned something new yesterday: Denso has a feedback signal on the coils. This is the reason for the 4th wire on the coils (power, ground, fire signal and feedback signal). The feedback signal is used to verify that a spark occurred.

I'm not sure if this signal is the only one used to determine missfires or if there are other signals that could result in a missfire condition as well. If a missfire is detected the particular injector for that cylinder is disabled to prevent catalytic converter damage. A lot of interesting information here: http://technician.academy/toyota-coil-on-plug-diagnosis-matthew-shanahan/

The feedback signal can probably not be used to determine coil health as it is probably just a 'yes/no spark occured' signal. However, by checking the current through the ground of all coilpacks on a scope, one would get a direct measurement of the health of all coils in a single measurement without removing the coils. Here is an example of such measurement (for coil health one would look at the actual peak values of each coil, not just presence of a firing signal):



I'm not sure if the LX/LC has an easily accessible ground wire for all coil packs to verify the current. Even a simple loop around this wire to the scope should be sufficient for relative measurements. Also interesting to note that all coil feedback signals are connected together, so by looking at the one signal, you see all feedback signals on a single channel.

 

[abuck99]

If this thread becomes the landing spot for others to post techstream trim results- it would provide a good resource for comparing various years & mileage 100’s

 

[white_lx]

If this thread becomes the landing spot for others to post techstream trim results- it would provide a good resource for comparing various years & mileage 100’s

2000 LX470, 82.5k miles, LTFT1/2 = -4% (E0 fuel, just cleaned MAF).

 

[2001LC]

I think this is one of those things I'm going to start recording for overall health indication of a vehicle. Might be very useful. Not sure if the next seller is going to allow me to check fuel trims before I make an offer on a vehicle .

Regarding the coil and coil health. I learned something new yesterday: Denso has a feedback signal on the coils. This is the reason for the 4th wire on the coils (power, ground, fire signal and feedback signal). The feedback signal is used to verify that a spark occurred.

I'm not sure if this signal is the only one used to determine missfires or if there are other signals that could result in a missfire condition as well. If a missfire is detected the particular injector for that cylinder is disabled to prevent catalytic converter damage. A lot of interesting information here: http://technician.academy/toyota-coil-on-plug-diagnosis-matthew-shanahan/

The feedback signal can probably not be used to determine coil health as it is probably just a 'yes/no spark occured' signal. However, by checking the current through the ground of all coilpacks on a scope, one would get a direct measurement of the health of all coils in a single measurement without removing the coils. Here is an example of such measurement (for coil health one would look at the actual peak values of each coil, not just presence of a firing signal):



I'm not sure if the LX/LC has an easily accessible ground wire for all coil packs to verify the current. Even a simple loop around this wire to the scope should be sufficient for relative measurements. Also interesting to note that all coil feedback signals are connected together, so by looking at the one signal, you see all feedback signals on a single channel.

Interesting video! I notice he made point on only "a "coil being replaced, that perhaps all should have been. It's not that they're bad or failing. But variation in firing due form age. IMHO, these variation have small ripple effects in balance of engine performance.

My fuel trims may be about as good as one can get, IDK. I've not experiment with this before, so don't have data to make the call. But the articles I've read indicate I'm well within range on fuel trims. I just found it interesting how they indicted which bank a coil was failing in. That variation between banks could give clues to balance between banks.

I've very high level of confidence in air/fuel after all the work done on The Unicorn (2007 LC). Coils and A/F & O2's sensors are about only stuff I've not addressed. But in most engine the coils and sensors would not be only parts to consider.

What we're really talking about is fine tuning. Tuning to get maximum performance out of a pure stock setup engine.

I'm going to stick my head in the shop at Dealer, and ask if anyone has scope to read health of coils.