The longer I drove....the leaner it got!

[55Belair]

I've just gotten through tuning the VE, the car was still in SD OL and I still had the WB hooked up. Without my laptop with me, I took the car for a leisurely drive and noted that the wideband kept showing the AFR going leaner and leaner until eventually it maxed out. It started at right around 14.7 and slowly climbed. The car ran well and didn't seem to run worse as it got leaner.

I stopped at a friend's house for 20 minutes and when I left, it was normal again when I left his house and the same thing happened. The car runs well. I would post my tune but someone changed the site gui and I see no place to do that.

Anyone have any ideas what would cause this?

[kingtal0n]

off handed guess: the IAT is heat soaking

There is no way to adjust IAT compensation for normal driving. Only IAT for PE mode.

That means we have no control over the lean/rich stepping caused by IAT which is reading falsely high

The fix is either to relocate the IAT to a better place,
Reconfigure the IAT to be less sensitive (bad idea I think)
Or install a variable resistor (0-2000ohms~) to manually dial the IAT back down when it heat soaks

Other possible causes for leaning out behavior:
1. voltage drop (increase injector "lag" delay resulting in shorter pulses) combined with poor injector delay map
2. heating of injector coils/circuits (heat causes resistance which reduces current) same as voltage drop I guess
3. could be wideband reading incorrectly (exhaust leaks, air leaks, old sensors, etc...)
4. Im sure there is more (I've had lists like this before and there is more possibilities) but thats all I got atm

[5FDP]

My only thoughts are that the sensor is slowly wigging out with heat and going wonky or that over time your fuel pressure is slowly dropping as you drive.

[anniversaryss]

This is common in speed density open loop. The IAT gets heat soaked and the pcm adjusts.

You can try two things under airflow > cylinder charge you could disable it or put 1 across the whole bias table.


Now this isnt the right way but you can try this as a test

What happens is any number below 1 is more biased to changing AFR based on IAT temps, anything above 1 is more biased toward ECT.

Not saying this is 100% your isse but its a good place to test being common in speed density open loop.

[55Belair]

This all makes sense, thanks for replying. This is a bit of a bummer as I just finished reconfiguring the intake due to excessively high IAT. I have the 5 pin MAF so the IAT is located in the MAF, relocating the IAT is not as simple as if it were a separate unit.

There is no exhaust leak and the fuel pressure is good, the WB is only 3 weeks old and has not been continually installed. I'll go for another drive today with the laptop installed so I can log the IAT along the way. I'll try biasing the table to the ECT to see if anything changes.

Couple of questions, could this be the IAT sensor slowly packing it in? When the IAT fails, how do they usually do so?
Since I will be running this car in CL with the MAF, is this a big deal when I get back to running it normally, or does it absolutely need to be addressed?

[kingtal0n]

you can relocate the IAT. Simply purchase a 2-wire GM IAT (I got mine from diy auto tune)
Then unplug those 2 wires from the maf's iat, and use them in your new iat sensor.

I Put mine in the intake pipe before the mintake manifold, however it still heat soaks from 110->145*F~ (35*F too hot sometimes)
So I plan to move it down closer to the intercooler outlet.

I would not recommend using a MAF sensor if you are turbo or plan to turbo.
Honestly most of the time the maf is more trouble than its worth. They are... finicky. I do love them, I have loads of experience with them, and that is why I am letting you know right up front that even though they make tuning 'easier', there are so many down sides to using a maf in a performance application, its almost not worth it.

Okay next. The coolant bias trick. Yeah I remember that... tried it... hated it. What happens is now the coolant temp has more control over A/F ratio, and it does the same thing the IAT did except only when the coolant gets hot instead. It just turned out to be even more inconvenient for me, and requires a bunch of extra VE tuning everytime you change that bias to make it 'better'
I Just disabled it after a couple weeks of messing with it. Two sensors throwing around the A/F ratio is too much. One is already annoying enough. imo

IAT failure... is rare. You have to abuse it somehow or get it very old I would guess. I wouldn't worry about that too much? If you get a new one.


And last - Yes closed loop O2 compensation will 'fix' the leaning IAT obviously as it corrects a/f back to 14.7:1 . I'm sure of that even though I never used closed loop a single day in my life in an V8 application for myself. The thing is it might show a wide range of stored values (LTFT) over time, since at first, it will be compensating a very little (small LTFT, cool IAT) and as you noted, the IAT gets hot and everything wanders, the LTFT would grow, I Would think, as this happens. Which means everytime you shut down it will remember the "hot" LTFT (very lean) and when restarted it will be too rich now, until the fuel trims catch back up... or the IAT re-heat soaks.

This just my best guess though.

[89 Caprice 6.0L]

Happen to have a AEM 30-4110 gauge? Mine did the same thing other day too,pegged the gauge out at over 18,but it was running fine.Had the scanner on at the time with short and long term trims on. When the gauge maxed out,the scanner was showing that the long term trims were 0 and the short term trims were running -2,car was running fine.Same as you,let it set for a while and it reads like it should.Has been working fine since.

[Russ K]

If the car was actually going so lean that the wide band maxed out, the car would be hesitating/bucking badly. Log the front O2 MV, if it drops below ~ 200 MV, then you are truly lean. But I think your wide band is the issue.

Russ Kemp

[55Belair]

Oddly enough, my WB is the AEM 30-4110 , interesting!

Took the car out for a spin today while plugged into the scanner. I did note the IAT creeping up slightly but didn't seem to move up as fast as the WB was moving towards lean. The O2 voltage never went below 800 mv. The WB never did max out today but did run north of 17 for awhile. The car still runs well and comes on like a bear when I got into it a bit. I tend to agree that if it were going full lean, it would have a huge change in behavior, it doesn't change at all.

kingtal0n: Thanks for the detailed reply. This is not really a "performance" application - more of a cruiser with a bit of a sleeper aspect to it so for my purposes I'm thinking the extra driveability that the closed loop O2 compensation brings will be better suited to the car's intended use.

At this point, I think I'll try putting the car back in closed loop O2 compensation and keep an eye on the fuel trims and O2 voltages. Thanks for all the replies, I learned a lot from this.

[anniversaryss]

Oddly enough, my WB is the AEM 30-4110 , interesting!

Took the car out for a spin today while plugged into the scanner. I did note the IAT creeping up slightly but didn't seem to move up as fast as the WB was moving towards lean. The O2 voltage never went below 800 mv. The WB never did max out today but did run north of 17 for awhile. The car still runs well and comes on like a bear when I got into it a bit. I tend to agree that if it were going full lean, it would have a huge change in behavior, it doesn't change at all.

kingtal0n: Thanks for the detailed reply. This is not really a "performance" application - more of a cruiser with a bit of a sleeper aspect to it so for my purposes I'm thinking the extra driveability that the closed loop O2 compensation brings will be better suited to the car's intended use.

At this point, I think I'll try putting the car back in closed loop O2 compensation and keep an eye on the fuel trims and O2 voltages. Thanks for all the replies, I learned a lot from this.

Yes run closed looop it sounds like your wideband is on thre fritz.
Funny thinking about it. I have a friend same wideband. Does somthing similar

[55Belair]

OK, so now we have at least 3 of these AEM 30-4110 WB's doing the same thing. I'm thinking that a call to their customer service is in order, mine is less than a month old.

[kingtal0n]

OK, so now we have at least 3 of these AEM 30-4110 WB's doing the same thing. I'm thinking that a call to their customer service is in order, mine is less than a month old.

wow bad batch. Unlucky strike.

not working as intended, I really hope it is your guys' controllers because,

The LS engine so far for me has run reasonably well into the 16.4's~ I bet I could get 16.7ish and still have it fairly cruise smooth.
Now that we are talking about it might as well point out that this is how one achieves maximum fuel mileage, that is, using open loop to direct a/f ratios conducive to saving fuel (gasoline 14.8+). It seems that stoichiometry is not actually ideal for economy, it just placates emissions, perhaps something to do with this:
Effect-of-air-fuel-ratio-on-gasoline-vehicle-emissions.png

Anyways heres another one I found in a quick search also:
Effects-of-air-fuel-ratio-variation-on-the-fuel-economy-and-power-generation-of-a.png

And sort of ensures smooth operation and a reasonable carbon coating, there are small but notable changes as one cycles through airfuel ratios on gasoline at various temperatures because it is quite complex compared to other fuels and can create hard carbon conglomerates if mis-treated. As enthusiasts its up to us to decide how much lope we want in our cams, how much tenuously experimentally decided the cruise should be. Do you care if the vehicles in question(s) achieve their maximum efficiency/mileage? If so, then data log incremental MPH (60 through 80mph usually) and divide miles/gallon out for each situation with maximum timing and leanest air fuel ratios, minimize weight and generate the data you can compare and see, "okay between this and this is ideal" and be done with it forever. Or change something, tire compound/size, or a driveshaft or bearing and do it again. It CAN be done. It doesn't have to be done and probably wont take you from 20 to 25 or 25 to 30 over time, nevertheless there is a couple percentage waiting at the right MPH A/F timing vacuum dutycycle.

bonus rounds
personally I keep it between 14.9 and 15.2 most of the time for cruise. Anything before about 50kpa, I gradually lean it out for fuel savings. Right around 50KPA I turn to 14.7. For me thats like a safety spot, stoich at 50-55. Its a mini power enrichment spot for me in areas I would see in logs that transition frequently (fast rate of change of TPS) using filters in the scanner if I needed to.

I don't believe in tuning the VE map flat to 14.7 and using only a PE or BE, that is ridiculous. The VE map is literally the most important and highly regarded map in the entire ECU and should be thoroughly used to every advantage when you are sitting right there with access. There are so many computers I would do work to get access to the internal VE maps somehow. Anyways just think of an interpolation of these values to make it simple:
13's at 0 to 10-15KPA for high vacuum stability of operation and cooling at high engine RPM with low throttle position and high manifold vacuum when the engine is hot from being just run through the gears and the user is not letting fully off the accelerator pedal
15.2 to 15.5 from 20 KPA
to 14.7 by 50KPA
14.0 to 13.8 for 60-65KPA
70KPA if you don't care about fuel economy, start with the 12.8's. Just give it the gas if you got the cash. Otherwise 13.2 to 13.8's work within 1-3% as well.
by 85-90KPA you should really be dedicated to WOT and not trying to save fuel, use roughly 12.5's usually for ideal torque with the LS platform. This is where I let PE start "working" to immediately drop the A/F. If you are trying to save gas you can still use 12.8-13.2 but it will likely be down on torque a bit.
The engine would likely run well at 85KPA and 14.0:1 most truck applications with the LS style V8 is highly tolerant of poor conditions and poor fuels thanks to good engineering. But the most torque will be made with significantly richer air fuel ratios because it puts more available fuel molecules in positions favorable to combustion reaction chemistry in time ranges where the piston is also in favorable positions for high pressure to apply appropriate forces to the crankshaft (not too early, not too late). I hope that wasn't too much.
For example if you put exactly 14.7:1 it should be perfect. But actually that is only if we consider the reaction in 1 single frame as happening all at once. In reality the combustion reaction occurs over a significant portion of time 'frames' from the perspective of the engine's piston and crankshaft, which can be evaluated individually (there are infinite slices of rotational angle so there are infinite situations that could be looked at) or as an integral function where we combine all the area under the curve of the the forces applied to the crankshaft as the piston is forced down by the evolving combustion reaction and the crankshaft is still turning which changes the rod/crank angles which is significant part of calculation. As the angles change between rod and crankshaft, the same force on the piston does more or less useful energy transfer, so there is indeed an optimal rod angle where we would prefer the highest cylinder pressure, and accompanying range near there where its still very good and the reaction is still going, and this is what is 'timed' for generally. Yet timing alone cannot control combustion reaction rate since temperature also plays a fundamental role... it is why timing is so hard to dictate without knowing exactly what engine, what fuel, what temperature, etc... it is a very personal number and changes also as engines and coatings can change inside the pathways of an engine.
So anyways if we tried to evaluate one of those frames individually, it should be obvious that you couldn't expect every single fuel molecule to be "getting used up" or that they are all being "used up" in that one frame (put into proper position at that instant), since we know from inspection that the reaction seems to continue over a small time frame like in milliseconds or microseconds(?), and we are only looking at one small piece or slice of time. So the question is, how many fuel molecules are available for reaction? The richer A/F ratio will put more fuel molecules into position such that combustion concludes faster and reaction actually speeds up apparently. Combustion reactions take place when the velocity of molecules and collision together result in a reaction. They have to both line up correctly (can be easy or difficult depends on shape) and collide with enough energy. there is no enzyme here, it is a very sort of violent connection that takes place suddenly and the energy is released instantly, dangerously. Putting more fuel molecules into favorable positions means more energy will be released more suddenly, and if the piston is in the right spot with the right angle crank/rod there will be more torque from inspection again. At least this is what how I believe it works. I know we are taught that richer a/f ratio cool things down and I think that is because of the fate of the extra fuel molecules, they have no oxygen to combine(no heat was evolved due to their presence) yet that still had to evaporate from liquid to gas state, which as we know soaks up heat energy quickly with most molecules (phase change to gas). Maybe that is what we are seeing as "cooling". Because once it is in a gas state, all it can do is move through the exhaust and leave the tailpipe. If the exhaust is hot enough it may combine with oxygen that got into the exhaust somehow and explode.

[Ben C]

Way to derail thread with shit. Start another and ramble away there.

[89 Caprice 6.0L]

When my gauge was new,the first ride around the block,it just pegged out straight lean.Driving it some more,it would read like it should,then it would go straight lean. I called and sent it back to have it repaired. They repaired the "heater driver circuit,replaced diode"and it has been working good since,except that one time.Just to keep an eye on how it's running, I always run with the scanner on it, just to keep an eye on whats going on.I trust the scanner more than the gauge. If it does it again,12 month warranty,it will go back and get fixed again.

[55Belair]

When I first installed mine, it pegged to full lean also - I thought the engine was actually that lean. It started giving me useable numbers after I added 10% more fuel and seemed to work fine after that. Do you know if this "heater driver circuit" was in the sensor or in the actual gauge?

I've sent an email to AEM customer service (they were closed), I'll post how this turns out.

[kingtal0n]

Way to derail thread with shit. Start another and ramble away there.

Its not a de-rail and it isn't a ramble of any kind.

That was a one-off description/discussion of air fuel ratio full of valuable information that would normally need to be scrapped together

If you find any passage in the above off-topic in any way, shape or form, well I will gladly remove it, thanks

[89 Caprice 6.0L]

I sent the gauge back,that is where the problem was.Will be watching on what they tell you. I bought mine 3-3-2019,sent in to repair 4-3-2019, what was mentioned before,a BAD batch?

[55Belair]

Just heard back from them - that was quick!

The tech asked about how I had it powered and grounded and how far downstream I had the sensor installed. He suggested I remove the sensor and do the brake cleaner test which he sent me a link to:

https://www.youtube.com/watch?v=rmnxKLjM25g

The sensor failed, it will go full lean in open air but will not go full rich when wrapped in a rag soaked in brake cleaner, it would only read 14.5 in the rag and then stuck there even when the rag was removed. I'm guessing the sensor is pooched but will wait until I hear back from him.

Stay tuned. (No pun intended)

[3strokeEngine]

Its not a de-rail and it isn't a ramble of any kind.

That was a one-off description/discussion of air fuel ratio full of valuable information that would normally need to be scrapped together

If you find any passage in the above off-topic in any way, shape or form, well I will gladly remove it, thanks

Some people just feel the need to be mad at something man lol, if you dont like what someone has to say.... then dont read it

Anyways back on point, im tuning a 97 silverado with a 98 blackbox swapped and the tables are very limited. Theres no IAT bias table available to prevent sensor heat soak so i had to run the IAT to a 10k ohm rheostat so i dont have fueling going all over the place in open loop speed density.

For example on a 80 degree night my AFR would be spot on, but if i sat in traffic for 30 mins my afr would swing more than half an AFR lean. With no tables to adjust this in OLSD i was stuck using the rheostat.

The other nice thing about doing that with the IAT is you can adjust the mixture while you drive for maximum performance (rich of peak) or cruising down the highway (lean of peak). This old 350 iron headed vortec runs 16:1 AFR at 70 mph unloaded. But if i want to tow 8000 pounds i can adjust the IAT fuel trim to slightly rich of peak for safety.
Its the best of both worlds! Of course you need a wideband in the car permanently installed or atleast EGT to do this with out "shooting in the dark"

[kingtal0n]

Some people just feel the need to be mad at something man lol, if you dont like what someone has to say.... then dont read it

Anyways back on point, im tuning a 97 silverado with a 98 blackbox swapped and the tables are very limited. Theres no IAT bias table available to prevent sensor heat soak so i had to run the IAT to a 10k ohm rheostat so i dont have fueling going all over the place in open loop speed density.

For example on a 80 degree night my AFR would be spot on, but if i sat in traffic for 30 mins my afr would swing more than half an AFR lean. With no tables to adjust this in OLSD i was stuck using the rheostat.

The other nice thing about doing that with the IAT is you can adjust the mixture while you drive for maximum performance (rich of peak) or cruising down the highway (lean of peak). This old 350 iron headed vortec runs 16:1 AFR at 70 mph unloaded. But if i want to tow 8000 pounds i can adjust the IAT fuel trim to slightly rich of peak for safety.
Its the best of both worlds! Of course you need a wideband in the car permanently installed or atleast EGT to do this with out "shooting in the dark"

In post #2 I suggested the same thing
https://forum.hptuners.com/showthrea...l=1#post580038

I used it alot at first. But then after a couple times of forgetting I had it turned one way or the other, it was messing with my cold starts.
So I just paid more attention to the VE map, made it a bit richer for idle in traffic areas. So when it first starts (I don't use cold enrichment much) it will sit 14.4's which annoys me until the IAT warms up about 15*F~ which brings it to around 14.7's.
Then finally it heat soaks into the 15's which is fine. I can live with that.
Still, going to relocate the sensor.
Having another adjustable dial in my car where I already have other switches and dials... I mean. Its fun but unnecessary just for something like a heat soak problem (IMO).
I will keep it though because it can also be used it to add timing/remove timing on demand. Since IAT has a table for vs timing behaviors... that seems to be far more useful of a feature for this dial.