K20iVTEC

Just went out to get a quick datalog and I'm not even close to maxing out the injectors. Hit 68% duty cycle at 7500 rpm when i shut it down because a/f was getting into the upper 14's. So I sent an email to my tuner...

davidc1

I'm no engine tuner, but how about it being slightly lean just because everything is hotter than hell right after the run and just burns the fuel a little more completely by the time the exhaust gets to the 02 sensor?

After all, the 02 sensor isn't displaying what you are putting into the engine ti's what's coming out. Think about it this also...if you shut your engine down after idling, the 02 gauge will gradually go leaner and leaner as any remaining fuel in the exhaust fumes by the 02 sensor start to evaporate...So, if the cylinders and exhaust manifold are hotter than hell, the amount of fuel left in the fumes of the exhaust will be a little less, and then as those components cool a little, it comes back up. Sort to the opposite of what happens when shutting the engine off after idling.

s2000Junky

no

davidc1

Can you educate me?

s2000Junky

Can you educate me?
[/quote]

If we assume for a moment that there is no 02 sensor feedback controlling a target afr to hold the ratio on point, then what happens when an engine is running hot vs normal operating temp, is there is less oxygen parts per fuel parts present and being combusted, so you will see a richer afr picked up from the wideband typically, not a leaner one. But based on the OP circumstance, I see this as not a factor influencing his problem, but rather a fuel tuning issue as mentioned, likely from fuel table corrections out of calibration based on a higher temp threshold that wasn't seen at the tuner/dyno from either a higher coolant temp or AIT. Remember on this car especially, when its hot, it effects the air temp coming into the engine, either hot right from the air source under the hood, and or being heated as it travels up through the intake and manifold and then finally as it again gets heated at the head/valves before its cumbusted. What the AIT sensor is seeing is usually quite a bit off from whats actually being cumbusted, and so its important to have the 02 sensor calibration in closed loop and WOT target feedback properly compensating for a range of intake and coolant temps. Some will go a step further and have EGT sensors as part of the control loop, but thats more in turbo applications where the EGT is much higher then NA or supercharged. So fuel tuning/calibration based on all the fuel correction tables at play is the first thing I would check, so until that is ruled out, its just going to be a wild goose chase.

Your reasoning has some logic behind it, but the problem is the circumstance in which that would happen isn't a likely scenario in this application, and if it were, it wouldn't have the drastic effect the OP is seeing on his afr at idle and WOT anyway.

davidc1

Can you educate me?
[/quote]

If we assume for a moment that there is no 02 sensor feedback controlling a target afr to hold the ratio on point, then what happens when an engine is running hot vs normal operating temp, is there is less oxygen parts per fuel parts present and being combusted, so you will see a richer afr picked up from the wideband typically, not a leaner one. But based on the OP circumstance, I see this as not a factor influencing his problem, but rather a fuel tuning issue as mentioned, likely from fuel table corrections out of calibration based on a higher temp threshold that wasn't seen at the tuner/dyno from either a higher coolant temp or AIT. Remember on this car especially, when its hot, it effects the air temp coming into the engine, either hot right from the air source under the hood, and or being heated as it travels up through the intake and manifold and then finally as it again gets heated at the head/valves before its cumbusted. What the AIT sensor is seeing is usually quite a bit off from whats actually being cumbusted, and so its important to have the 02 sensor calibration in closed loop and WOT target feedback properly compensating for a range of intake and coolant temps. Some will go a step further and have EGT sensors as part of the control loop, but thats more in turbo applications where the EGT is much higher then NA or supercharged. So fuel tuning/calibration based on all the fuel correction tables at play is the first thing I would check, so until that is ruled out, its just going to be a wild goose chase.

Your reasoning has some logic behind it, but the problem is the circumstance in which that would happen isn't a likely scenario in this application, and if it were, it wouldn't have the drastic effect the OP is seeing on his afr at idle and WOT anyway.
[/quote]

Cool! Thanks for the well written explanation.

Is my assumption about how the AFR gradually gets leaner and leaner as the engine is turned off correct? Meaning, any unburnt fuel in the exhaust system at the point of the 02 sensor just gradually evaporates and AFR just goes up and up.?

s2000Junky

Can you educate me?
[/quote]

If we assume for a moment that there is no 02 sensor feedback controlling a target afr to hold the ratio on point, then what happens when an engine is running hot vs normal operating temp, is there is less oxygen parts per fuel parts present and being combusted, so you will see a richer afr picked up from the wideband typically, not a leaner one. But based on the OP circumstance, I see this as not a factor influencing his problem, but rather a fuel tuning issue as mentioned, likely from fuel table corrections out of calibration based on a higher temp threshold that wasn't seen at the tuner/dyno from either a higher coolant temp or AIT. Remember on this car especially, when its hot, it effects the air temp coming into the engine, either hot right from the air source under the hood, and or being heated as it travels up through the intake and manifold and then finally as it again gets heated at the head/valves before its cumbusted. What the AIT sensor is seeing is usually quite a bit off from whats actually being cumbusted, and so its important to have the 02 sensor calibration in closed loop and WOT target feedback properly compensating for a range of intake and coolant temps. Some will go a step further and have EGT sensors as part of the control loop, but thats more in turbo applications where the EGT is much higher then NA or supercharged. So fuel tuning/calibration based on all the fuel correction tables at play is the first thing I would check, so until that is ruled out, its just going to be a wild goose chase.

Your reasoning has some logic behind it, but the problem is the circumstance in which that would happen isn't a likely scenario in this application, and if it were, it wouldn't have the drastic effect the OP is seeing on his afr at idle and WOT anyway.
[/quote]

Cool! Thanks for the well written explanation.

Is my assumption about how the AFR gradually gets leaner and leaner as the engine is turned off correct? Meaning, any unburnt fuel in the exhaust system at the point of the 02 sensor just gradually evaporates and AFR just goes up and up.?
[/quote]
No problem.

Yes, I can verify that this does happen. You can even pull the sensor out of the exhaust and wrap it in a gas soaked rag and see the afr go rich and then lean as the rag is removed.

K20iVTEC

update... so i got a couple data logs one when it was 85 degrees outside and the other when it was 50 degrees outside. Even though there was a 35 degree difference the iat's were only about 10 degrees apart. Also during my data logs the a/f values never went as lean as they did before. In the colder data log the a/f tends to go a little lean (14.2:1) in the midrange around 6k rpm and then go back to 13 towards redline. On the warmer day the a/f never gets above 13.8. I sent these logs to my tuner and he sees no problem when comparing both data logs. He isn't seeing a significant difference in injector ms to account for a lean condition. My wideband isn't wired into the k-pro ecu so he isn't seeing the a/f numbers. So unless i wire it in so i can record the a/f there isn't much he can do for me. I don't understand why only for like a week or 2 it was running very lean at wot. Could it have been bad gas? Maybe fuel pump starting to shit out or maybe the aem wideband? Don't know what i should do.... guess ill look up instructions on how to wire and calibrate the wideband so i can log my a/f.... should i be concerned with this? i can assume the tune is good because i know Jeff Evans knows what he is doing so i am leaning towards a problem with my fuel system

flanders

What kpro version do you got?
The newer one has an option to run closed loop from an aftermarket wideband which I would highly recommend.

K20iVTEC

Yea I have kpro4...