rb25: Fuel Map and ECU Mysteries

[totoro001]

Alright, I really just want to make sure I'm not losing my mind. I've got an AFC NEO on my rb25 s1 with an untuned ECU. I've worked at getting a decent non-dyno tune with my wideband and I think I've got it setup fairly well, but once the car warms up and has been running for a while, my fuel map goes all nuts and it seems to be almost unchangable. Now I recall reading somewhere that when the car warms up to it's normal operating temperature, it advances the timing a bit and changes the fuel mix. Am I mistaken in this? And does anyone know any craft way around this issue? If I retune when it's warmed up, then it ends up running super rich when it's cold. If I tune when it's cold, it'll run super lean when it's warm.

Another little issue I'm seeing is that if I leave the car in gear, but let off the gas (for instance while driving and going down a hill), the fuel mixture leans way out. Just wanted to verify if that's normal or maybe there's a sensor somewhere that's not working/plugged in.

I've lost all faith in the previous owners of this car so it wouldn't surprise me if there were other sensors that weren't plugged in or functioning since I've already found a couple.

[Darius]

Everything you described is correct and normal. GOOD JOB!

Seriously though, until the engine is up to operating temp, the idle will be richer and the timing more retarded (~5*). Therefore, you should be tuning at operating temp and nothing else. You don't race your car out of the driveway immediately after a cold start do you?

The engine goes very lean when you take your foot off the gas and leave the car in gear since it is effectively using air to slow the car and you aren't adding gas. Mine usually runs up to 22:1 or off the scale lean when off-throttle. If I put it into neutral, the engine drops to idle at 14.7-15:1.

If the engine is running that rich when it is cold, you should be able to trim the fuel at idle enough when it is warm to lessen the richness upon cold start. Monkey around with it a little.

As far as the fuel map changing the fuel mix, yes the fuel mix is changing to be richer as the rpm and load increase. You don't run it at 14.7 all the way to redline or you'll have broken metal parts flying everywhere.

What can you change with the AFC NEO? Can you simply modify the fueling for a given rpm? It isn't able to calculate load is it?

[WhatsADSM]

Alright, I really just want to make sure I'm not losing my mind. I've got an AFC NEO on my rb25 s1 with an untuned ECU. I've worked at getting a decent non-dyno tune with my wideband and I think I've got it setup fairly well, but once the car warms up and has been running for a while, my fuel map goes all nuts and it seems to be almost unchangable. Now I recall reading somewhere that when the car warms up to it's normal operating temperature, it advances the timing a bit and changes the fuel mix. Am I mistaken in this? And does anyone know any craft way around this issue? If I retune when it's warmed up, then it ends up running super rich when it's cold. If I tune when it's cold, it'll run super lean when it's warm.

Another little issue I'm seeing is that if I leave the car in gear, but let off the gas (for instance while driving and going down a hill), the fuel mixture leans way out. Just wanted to verify if that's normal or maybe there's a sensor somewhere that's not working/plugged in.

I've lost all faith in the previous owners of this car so it wouldn't surprise me if there were other sensors that weren't plugged in or functioning since I've already found a couple.

Yea most of what you described is normal.

First off realize that when you are cruising around and the car is up to temperature it is in "closed loop". Which means the computer is looking at the oxygen sensor and attempting to keep the AFR at ~14.7:1. So even if you go on your SAFC and say add 10% in the "lo" map the ECU will see the car running rich and pull 10% right back out.... hence the map will look "unchangeable" as you described it.

Quick note about the full lean while off throttle. That is totally normal the ECU is shutting off the injectors when you are coasting and above a specific RPM. This is primarily for fuel consumption/emissions. Totally normal, totally safe.

Now that I have described the basics of the crusing (i.e. closed-loop maps) lets talk about the WOT maps. When you go WOT your car goes into open-loop mode which means that it no longer looking at the oxygen sensor and trying to keep the AFR at 14:7 (which a standard narrow-band is tuned for). Instead the computer simply looks at its internal maps and delivers that much fuel. So in this case, say you add 10% on the SAFC "hi" map (which is what you should be tuning your WOT map with), the computer will not be looking for that increase in fuel and thus you will get the extra fuel you tuned for.

In conclusion:

- My suggestion is unless you have changed the fuel system a lot and there is something wrong with the crusing maps just leave them alone in the SAFC. You are more likely going to confuse the fuel trimming in the ECU and do more bad than good.- Tune the SAFC hi throttle map for a safe tune at WOT.- Don't bother tuning it when it is not warmed up. Under cruising it should be running a little richer, which is normal. Under WOT is the same and honestly you shouldn't be WOT unless the car is warmed up anyways.- And finally because I wouldn't sleep well at night without telling you this SAFCs are okay for minor tweeks but if you are making large changes you should be looking at something like a ROM tune because with the SAFC you are not only changing your fueling but also your timing.

[totoro001]

Seriously though, until the engine is up to operating temp, the idle will be richer and the timing more retarded (~5*). Therefore, you should be tuning at operating temp and nothing else. You don't race your car out of the driveway immediately after a cold start do you?

See, you'd think that I'd think of that, but right now, my brain is powered by magic and unicorn tears, so I didn't think that far ahead.

Quote »The engine goes very lean when you take your foot off the gas and leave the car in gear since it is effectively using air to slow the car and you aren't adding gas. Mine usually runs up to 22:1 or off the scale lean when off-throttle. If I put it into neutral, the engine drops to idle at 14.7-15:1.[/quote]Ohkay good, this was freaking me out. At idle it would sit at right around 15 and I thought I was losing my mind.

Quote »If the engine is running that rich when it is cold, you should be able to trim the fuel at idle enough when it is warm to lessen the richness upon cold start. Monkey around with it a little. [/quote]I'll give this a try, might be tricky but I'll definately fiddle with it.

Quote »As far as the fuel map changing the fuel mix, yes the fuel mix is changing to be richer as the rpm and load increase. You don't run it at 14.7 all the way to redline or you'll have broken metal parts flying everywhere.

What can you change with the AFC NEO? Can you simply modify the fueling for a given rpm? It isn't able to calculate load is it?[/quote]Unfortunately the AFC Neo isn't smart enough to sense load, though it might not need to. What it primarly does, is it either strengthens or weakens the signal that it gets from the intake to fool the car's ECU. So the ECU is still handeling the load. I think if I fire it up, let the car warm up, then tune it once it's all good and warm, it might be ok. I'll give that a try and try and tweak it a bit so it's not angry at idle. I fear I might just end up scrapping the whole AFC idea and tossing in an AEM ECU if this doesn't work.

Thanks for at least helping me figure out I'm not insane.

[totoro001]

Yea most of what you described is normal.

First off realize that when you are cruising around and the car is up to temperature it is in "closed loop". Which means the computer is looking at the oxygen sensor and attempting to keep the AFR at ~14.7:1. So even if you go on your SAFC and say add 10% in the "lo" map the ECU will see the car running rich and pull 10% right back out.... hence the map will look "unchangeable" as you described it.

Quick note about the full lean while off throttle. That is totally normal the ECU is shutting off the injectors when you are coasting and above a specific RPM. This is primarily for fuel consumption/emissions. Totally normal, totally safe.

Now that I have described the basics of the crusing (i.e. closed-loop maps) lets talk about the WOT maps. When you go WOT your car goes into open-loop mode which means that it no longer looking at the oxygen sensor and trying to keep the AFR at 14:7 (which a standard narrow-band is tuned for). Instead the computer simply looks at its internal maps and delivers that much fuel. So in this case, say you add 10% on the SAFC "hi" map (which is what you should be tuning your WOT map with), the computer will not be looking for that increase in fuel and thus you will get the extra fuel you tuned for.

In conclusion:

- My suggestion is unless you have changed the fuel system a lot and there is something wrong with the crusing maps just leave them alone in the SAFC. You are more likely going to confuse the fuel trimming in the ECU and do more bad than good.- Tune the SAFC hi throttle map for a safe tune at WOT.- Don't bother tuning it when it is not warmed up. Under cruising it should be running a little richer, which is normal. Under WOT is the same and honestly you shouldn't be WOT unless the car is warmed up anyways.- And finally because I wouldn't sleep well at night without telling you this SAFCs are okay for minor tweeks but if you are making large changes you should be looking at something like a ROM tune because with the SAFC you are not only changing your fueling but also your timing.

Wonderful, I'm just happy that I'm not insane and stuff isn't totally jacked up. Do you happen to know at what point (50% throttle, 70% throttle, etc) that the ECU goes into "open loop" mode, or is it only WOT? That would definately explain why it sits at around ~15 AFR while it's just cruising no matter what I do, so that sounds good and I'm just glad i'm not destroying the motor. I'll just create a "hi" throttle map and go from there. Thank you for your help

[WhatsADSM]

Unfortunately the AFC Neo isn't smart enough to sense load, though it might not need to. What it primarly does, is it either strengthens or weakens the signal that it gets from the intake to fool the car's ECU. So the ECU is still handeling the load. I think if I fire it up, let the car warm up, then tune it once it's all good and warm, it might be ok. I'll give that a try and try and tweak it a bit so it's not angry at idle. I fear I might just end up scrapping the whole AFC idea and tossing in an AEM ECU if this doesn't work.

Thanks for at least helping me figure out I'm not insane.

The SAFC sure does sense load. If you wired it up normally it is doing so through the TPS.

This is why you have a lo/hi map in the SAFC. lo is the low load, hi is the high load (read WOT).

[WhatsADSM]

Wonderful, I'm just happy that I'm not insane and stuff isn't totally jacked up. Do you happen to know at what point (50% throttle, 70% throttle, etc) that the ECU goes into "open loop" mode, or is it only WOT? That would definately explain why it sits at around ~15 AFR while it's just cruising no matter what I do, so that sounds good and I'm just glad i'm not destroying the motor. I'll just create a "hi" throttle map and go from there. Thank you for your help

Each manufacturer tunes them a little differently. Sometimes it is specifically a TPS load point (~80% is common). I've also heard of some manufacturers that have air flow based switch overs as well (such as when the MAP/MAF readings get above a certain point then go to open-loop mode and run rich). To be honest I am not exactly sure how the rb25 code specifically does it.

My suggestion is to:1) Make sure the TPS is reading correctly on the SAFC. Very easy to do, just sit in the car with the engine off but the key in the "ON" position and monitor the TPS value on the SAFC. It should go from 0-100% accordingly when you push the gas petal through the range. 2)Set your th-points in the SAFC (which is the points where the safc switches from its lo/hi maps) to lo 40% and hi 80%. That means below 40% (while crusing it will use the lo map), above 80% it will use the hi map, in between those values it will blend the lo/hi map accordingly.3) Start using your hi map to tune the car under WOT.

[totoro001]

Each manufacturer tunes them a little differently. Sometimes it is specifically a TPS load point (~80% is common). I've also heard of some manufacturers that have air flow based switch overs as well (such as when the MAP/MAF readings get above a certain point then go to open-loop mode and run rich). To be honest I am not exactly sure how the rb25 code specifically does it.

My suggestion is to:1) Make sure the TPS is reading correctly on the SAFC. Very easy to do, just sit in the car with the engine off but the key in the "ON" position and monitor the TPS value on the SAFC. It should go from 0-100% accordingly when you push the gas petal through the range. 2)Set your th-points in the SAFC (which is the points where the safc switches from its lo/hi maps) to lo 40% and hi 80%. That means below 40% (while crusing it will use the lo map), above 80% it will use the hi map, in between those values it will blend the lo/hi map accordingly.3) Start using your hi map to tune the car under WOT.

Ooh well cool beans on the load sensing. And yes I know my TPS is working because I had a mighty battle with that thing when I originally installed the AFC. I'll tweak my throttle points to 40 and 80, and tune starting at the 80 and go from there. Thanks again!