AFR lean on hot idle

[kc427]

I logged by Evoscan long time ago, the FuelTrim_InUse is at max, 4.6875.

Just started engine from hot, and then moved the car
Just_Hot_Start_Engine_and_Move.jpg


After few minutes driving, then I pulled over and stopped the car.
After_short_cruise_and_pull_over.jpg

As you can see, both "FuelTrim_Low" and "FuelTrim_InUse" were at max, but when just hot started the engine, the O2Sensor could keep about 0.5-0.6v, for about 30 second. After I drove the car and cruised around, and then pulled over and stopped the car, the O2Sensor was close to 0v, but the "FuelTrim_Low" and "FuelTrim_InUse" were still at max.


Yes, at the end, if cannot find the root cause, possible, I will flash the ECU with smaller the Injector Size, hopefully, it can work to keep idle 14.7 all the time.

[lateshow]

Changing your latencies around 14V deals with this problem....

[kc427]

Injector_Latency_Voltage.jpg

This latency voltage table? But what value to change?

[crazydriver81]

The question is - what causes/can cause this leaning out? Chnaging ECU values to adopt to it could not be right.

I had the Chance yesterday to check a friends VR-4 (PFL Manual, PLX wideband, Walbro 255lph, stock ECU). Both driven same roads and Speed.
His car was idling perfectly at 14.7 - mine leaned out to 16ish and you could hear the difference if listening to exhaust.

[crazydriver81]

I took a bit care to see when this leaning out happens at my car. Maybe this will give some more insight for you ECU Gurus out there.

1. engine warm - if I start the engine and let it Idle it'll start at 14.7 but soon drop to 15.8-16.0, eventually, when really hot, even to 16.4ish AFR's
2. engine cold - no weird behavior until warmed up. It tries to keep 14.7ish
3. engine warm - when driving all is fine. As soon as I am coming to standstill following behavior: no gear, just rolling towards e.g. traffic lights engine idle with AFR 14.7-15.0. When standstill, engine will idle still at 14.7-15.0 for 10-15 secs and then you can feel engine idle speed dropping and AFR's going to 16ish.

I further realised, that my idle speed seems a bit high but idle speed screw is already all the way in (new screw and seal already). ISC is cleaned out and supposed to work (you can here it click and it shows steps on MUT. IPS and TPS are setup correctly. For a manual car on idle, is the rpm needle supposed to sit at the respective marking or above? I know from AT cars when in D and you are on the brake, that the rpm needle is exactly on the marking. But with a manual car....

[swinks]

Stefan, idle by-pass screw shouldn't be screwed all way down as you said. Usually it's 1 to 1.5 turn from fullu closed position. Once screw is setup, then ISCV (stepper motor) should be setup in desired base position using a MUT or Evoscan, as this may change depends on idle screw.
For manual car, you best stationary idle should be somewhere 800 to 900 rpm, with custom camshafts it would be much lower, i.e. 700 - 800 rpm.
As for afr reading... Well I had twice similar issues:
1. with my Galant VR4 turned out that I had problems with fuel pump and fpr
2. with Evo I had messed up throttle body settings, so I had to setup from scratch all (tps, ISCV, idle screw) using Evoscan. "Parking" ISCV was the most challenging one because Evo has additional SAS system.
3. After some consideration, I would suggest also possible leak in exhaust system, somewhere upfront o2 sensor, leaking gasket is enough to make such mess.

Option 3 is most likely IMO.

[kc427]

Stefan, idle by-pass screw shouldn't be screwed all way down as you said. Usually it's 1 to 1.5 turn from fullu closed position. Once screw is setup, then ISCV (stepper motor) should be setup in desired base position using a MUT or Evoscan, as this may change depends on idle screw.
For manual car, you best stationary idle should be somewhere 800 to 900 rpm, with custom camshafts it would be much lower, i.e. 700 - 800 rpm.
As for afr reading... Well I had twice similar issues:
1. with my Galant VR4 turned out that I had problems with fuel pump and fpr
2. with Evo I had messed up throttle body settings, so I had to setup from scratch all (tps, ISCV, idle screw) using Evoscan. "Parking" ISCV was the most challenging one because Evo has additional SAS system.
3. After some consideration, I would suggest also possible leak in exhaust system, somewhere upfront o2 sensor, leaking gasket is enough to make such mess.

Option 3 is most likely IMO.

Isn't that the statinary idle should be 650rpm±50? That's from the workshop manual.

[kc427]

I took a bit care to see when this leaning out happens at my car. Maybe this will give some more insight for you ECU Gurus out there.

1. engine warm - if I start the engine and let it Idle it'll start at 14.7 but soon drop to 15.8-16.0, eventually, when really hot, even to 16.4ish AFR's
2. engine cold - no weird behavior until warmed up. It tries to keep 14.7ish
3. engine warm - when driving all is fine. As soon as I am coming to standstill following behavior: no gear, just rolling towards e.g. traffic lights engine idle with AFR 14.7-15.0. When standstill, engine will idle still at 14.7-15.0 for 10-15 secs and then you can feel engine idle speed dropping and AFR's going to 16ish.

I further realised, that my idle speed seems a bit high but idle speed screw is already all the way in (new screw and seal already). ISC is cleaned out and supposed to work (you can here it click and it shows steps on MUT. IPS and TPS are setup correctly. For a manual car on idle, is the rpm needle supposed to sit at the respective marking or above? I know from AT cars when in D and you are on the brake, that the rpm needle is exactly on the marking. But with a manual car....

my car is exactly same situation as yours, so I am not alone

[swinks]

Isn't that the statinary idle should be 650rpm±50? That's from the workshop manual.

That is correct for a/t. With manual transmission I had set up base idle the same like Evo: 800 rpm ish... Worked perfect for me.

[kc427]

OK Guys, seems something was FIXED on last weekend, and now, when engine is warm, so I start the engine and let it idle and the AFR won't drop to 16.0!!! well, it will drop to around 15.x or almost 16, but then it will back to around 14.7 at around 5 seconds!!!

OK, let me share what were done during last weekend:

- Changed another used AFM(originally, 1st AFM has lean idle issue, then change to 2nd AFM, same lean idle issue, now, last weekend change to the 3rd AFM)
- Changed from Ultra Silicone Spark Plug Wire 7mm(was bought brand new from Japan) to brand new NGK Power Cable
- Changed new spark plug NGK BKR7EIX-P
- Changed new oil catch tank, and also connected back to intake hose, so in "closed loop". Becasue the old oil catch tank was vent to atmosphere, and the intake hose side was plugged so no vacuum leak
- Ultrasonic cleaned all injectors. Note, before and after clean, flow rate is almost the same, no big difference, so maybe not dirty? Or maybe due to only using Shell V-Power in 10 yrs? Also, the injectors are around 200cc/min, it seems wired so I put this question in another thread(https://www.clubvr4.com/forum/showth...flow-rate-size)

Sorry that I changed all these together and didn't know which was the root cause.

Anyway, I will keep watching the result in these few weeks, and update you guys.

[kc427]

I took a bit care to see when this leaning out happens at my car. Maybe this will give some more insight for you ECU Gurus out there.

1. engine warm - if I start the engine and let it Idle it'll start at 14.7 but soon drop to 15.8-16.0, eventually, when really hot, even to 16.4ish AFR's
2. engine cold - no weird behavior until warmed up. It tries to keep 14.7ish
3. engine warm - when driving all is fine. As soon as I am coming to standstill following behavior: no gear, just rolling towards e.g. traffic lights engine idle with AFR 14.7-15.0. When standstill, engine will idle still at 14.7-15.0 for 10-15 secs and then you can feel engine idle speed dropping and AFR's going to 16ish.

I further realised, that my idle speed seems a bit high but idle speed screw is already all the way in (new screw and seal already). ISC is cleaned out and supposed to work (you can here it click and it shows steps on MUT. IPS and TPS are setup correctly. For a manual car on idle, is the rpm needle supposed to sit at the respective marking or above? I know from AT cars when in D and you are on the brake, that the rpm needle is exactly on the marking. But with a manual car....

Stefan, my car has the same problem as yours, so you can see my previous post and see which is capable to be done on your car, hope you can fix that too

[crazydriver81]

OK Guys, seems something was FIXED on last weekend, and now, when engine is warm, so I start the engine and let it idle and the AFR won't drop to 16.0!!! well, it will drop to around 15.x or almost 16, but then it will back to around 14.7 at around 5 seconds!!!

OK, let me share what were done during last weekend:

- Changed another used AFM(originally, 1st AFM has lean idle issue, then change to 2nd AFM, same lean idle issue, now, last weekend change to the 3rd AFM)
- Changed from Ultra Silicone Spark Plug Wire 7mm(was bought brand new from Japan) to brand new NGK Power Cable
- Changed new spark plug NGK BKR7EIX-P
- Changed new oil catch tank, and also connected back to intake hose, so in "closed loop". Becasue the old oil catch tank was vent to atmosphere, and the intake hose side was plugged so no vacuum leak
- Ultrasonic cleaned all injectors. Note, before and after clean, flow rate is almost the same, no big difference, so maybe not dirty? Or maybe due to only using Shell V-Power in 10 yrs? Also, the injectors are around 200cc/min, it seems wired so I put this question in another thread(https://www.clubvr4.com/forum/showth...flow-rate-size)

Sorry that I changed all these together and didn't know which was the root cause.

Anyway, I will keep watching the result in these few weeks, and update you guys.

Thanks for sharing that Kenneth.

I can rule out for my side:
- spark plug leads
- spark plugs
- injectors
- fuel pump (as I had same issue before with the TRE pump as I have it now with the genuine Walbro unit)

What I know is, since I have no oil catch tank, that the hose between both rocker covers has split at one position. Need to check that but don't think that this will be the root cause.

After going through the Jap workshop manual, I will check FPR solenoid and resistor pack. If this is within spec, I can borrow an AFM to double check from a friends car, which is running perfectly as it should (same fuel pump, same wideband gauge). Last but not least I will swap the stock FPR for a higher rated unit from a V6 N/A. I suspect the FPR to be failing on my car as idle got actually worse when disconnected the vacuum line on idle (normally this should raise the fuel pressure and not cause leaning out even more). Keep you updated..

[kc427]

Thanks for sharing that Kenneth.

I can rule out for my side:
- spark plug leads
- spark plugs
- injectors
- fuel pump (as I had same issue before with the TRE pump as I have it now with the genuine Walbro unit)

What I know is, since I have no oil catch tank, that the hose between both rocker covers has split at one position. Need to check that but don't think that this will be the root cause.

After going through the Jap workshop manual, I will check FPR solenoid and resistor pack. If this is within spec, I can borrow an AFM to double check from a friends car, which is running perfectly as it should (same fuel pump, same wideband gauge). Last but not least I will swap the stock FPR for a higher rated unit from a V6 N/A. I suspect the FPR to be failing on my car as idle got actually worse when disconnected the vacuum line on idle (normally this should raise the fuel pressure and not cause leaning out even more). Keep you updated..

I think it is worth to try the AFM to double check and to eliminate that first because that AFM confirmed good to use.

BTW, I just recall one more symptom, and I am not sure you have the same or not. For example, I start the car from cold at home, then drive normally for more than 15 minutes, maybe 30min, eg to shopping center, then the car is hot enough, and at that moment when idle, everything is fine, can get 14.7. Now, shutdown the car, wait for about 1 minute or 2, then start the engine again, and the first 20-30 second, it's 14.7, but after 30 second, it begins to drop to as low as around 16. Now, the point is, before I shut down the engine, it's 14.7, but after shut it down and restart the engine, it can as lean as 16. That's why I guess it is related to the electrical issue. Anyway, I will also keep checking my car and see the problem is really solved or not.

[kc427]

UPDATE:

I have changed back the AFM to previous one and using for few days, and drove about 3 times now, and there is still NO ISSUE happened. The AFR is still around 14.7 when at hot idle. Back to my change list I wrote, most likely the root cause may be the injector!!! Let me drive the car for 1-2 weeks, and if there is no more problem, we may conclude that the injectors cause this lean on hot idle problem. Will keep you guys updated later.

[crazydriver81]

As for me, I think I've found a correlation for leaning out and ambient temperatures.

What I observed one morning when it was around 14°C outside and humid - no unusual leaning out. When I drove back the exact same route in the later afternoon with 25°C and sun outside it started to lean out. Also, when coming from a motorway trip, the car leans out when idling. So it narrows, tht it might be AFM, who is the culprit

However, while fiddling around with a MUT-3 tester in the workshop, my ECU did not seem to get the IPS signal. Had not enough time that day so I need to investigate further.

But yeah, what I am asking myself is - how should people without wideband lambda realize this leaning out is happening?

[ersanalamin]

As for me, I think I've found a correlation for leaning out and ambient temperatures.

What I observed one morning when it was around 14°C outside and humid - no unusual leaning out. When I drove back the exact same route in the later afternoon with 25°C and sun outside it started to lean out. Also, when coming from a motorway trip, the car leans out when idling. So it narrows, tht it might be AFM, who is the culprit

However, while fiddling around with a MUT-3 tester in the workshop, my ECU did not seem to get the IPS signal. Had not enough time that day so I need to investigate further.

But yeah, what I am asking myself is - how should people without wideband lambda realize this leaning out is happening?

You know something when I tried adams 264 regrind cam without shim the lc2 gauge read engine running very lean on idle about 18-19, idle was rough. when the shim put under hla, idle is normal and afr gauge stay around 14,7. any conclusiion on this? bad HLA (unstable/thin air stream density on valve opening and closing) caused engine running lean?

[kc427]

As for me, I think I've found a correlation for leaning out and ambient temperatures.

What I observed one morning when it was around 14°C outside and humid - no unusual leaning out. When I drove back the exact same route in the later afternoon with 25°C and sun outside it started to lean out. Also, when coming from a motorway trip, the car leans out when idling. So it narrows, tht it might be AFM, who is the culprit

However, while fiddling around with a MUT-3 tester in the workshop, my ECU did not seem to get the IPS signal. Had not enough time that day so I need to investigate further.

But yeah, what I am asking myself is - how should people without wideband lambda realize this leaning out is happening?

For my car, every morning when start driving, there was no leaning out. But, once I stopped the engine, eg, 10 minutes, then started driving again, it was lean. It likes when start engine from cold, there is no leaning out; however when start the engine from hot or warm, there is leaning out. This symptom has happened for years on my car until I changed AFM, cleaning the injector, etc (post #30), and now no more leaning out even start the engine from hot or warm, and even though I swapped back to use the old AFM that I suspected it has problem. Anyway, hope you can solve this leaning out problem by changing the AFM, and no more problem. But for my car, cleaning the injector is the root cause.

[crazydriver81]

Further progrees in investigating this issue with leaning out as my symptoms got worse over past days (car would even lean out while constant cruising occassionally and idle when hot was at 18-20ish AFR's)

- IPS and TPS setup has been checked and was correct
- replaced the breather hose between valve covers and to the intake side with new, strengthened silicone ones

Started to investigate 02 sensor as I suspected this to be the cause. Because car would idle fine when warm afetr driving (e.g. when stopping at traffic lights) until after a few (maybe 10-20) seconds something changed and AFR's as well as RPM's drop (not much but noticeable). I found that the narrow band emulation obviously plays up with voltages. It gives some weird voltages when on idle (e.g. it displays 16.ish AFR's but still sends 0.5V to ECU). Additionally I think the signal from the PLX wideband is a smoothed out signal, while narrowband sensors give a rectangular signal. Maybe this confuses the ECU? Even pulling the plug so that the ECU does not get any O2 sensor signal did not sseem to confuse the ECU so I'd say the ECU does ignore the o2 sensor and is running in open loop all the time (maybe it detecs that voltages do not fit actual load or whatsoever and goes into open loop mode)

Changed over the AFM by a known working one. Improved the situation so far, as that while driving the car behaves normal again (swinging around 14.7ish AFR). But car still leans out when hot idling - but not as worse as it has been before.

I ordered in a new stock O2 sensor from BluePrint - suprinsingly only 50 EUR new and comes with factory plug. The wideband kit will serve only to monitor all the stuff from now o. I really hope that this will finally eliminate this issue. Fingers crossed.

[kc427]

Your PLX looks weird when simulating the narrowband signal to the ECU. I remembered when I installed my PLX, I also installed the capacitors came with the package. The manual says the capacitors are used to filter out those electrical noise. In addition, I used shielded cable to connect from the PLX to the ECU. Since the voltage is so low, and little interference can affect the voltage on the wire, all O2 sensor cable are shielded by ground.

[Nick Mann]

I run a PLX with narrowband emulation and don't have a problem. I'm not saying your PLX is good, just that it is not a normal issue if it is the PLX.