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The problem - cruising at 80+ MPH for a few minutes, the AFR readings on the O2 conditioner display (a AFR500 from Ballenger Motorsports) show 14.0, but the datalog will show the AFR ramping down to low 12's (occasionally bouncing up to the low 13's) until sustained cruising stops. At which time AFR readings seem "normal".
The car - 99 NB1, 1.8L, 2871 clone Chinacharger, Kraken manifold, 2.5" exhaust, Bosch 4.9 LSU WBO2 sensor, Ballenger Morotsports AFR500 O2 signal conditioner. MSPNP2 running 3.4.2 code. Otherwise unremarkable. I don't know if this is commonplace with either the WBO2 sensor, or the AFR500 - but this seems new to me.
PS - I did a sensor calibration back in March if that means anything.
Just looking at your timing table, it finally gets out of idle four rows out of the 12 you have and skips from 3600 to 5000 at one point, it looks extremely course resolution in the areas where you drive in
Just looking at your timing table, it finally gets out of idle four rows out of the 12 you have and skips from 3600 to 5000 at one point, it looks extremely course resolution in the areas where you drive in
Yeah, it is coarse there. I was doing some fine tuning just out of idle a while ago and never re-adjusted it. But my timing is mega-conservative so I'd be surprised if that was causing problems. But I'm open to comments.
The fact that the injector pulsewidth doesn't appear to be changing while it goes richer, map, rpm, spark are all stable, and this is done at cruise which is typically lean (and hot) - how far from the turbo exit is the o2 sensor placed? I'm thinking it's a heat issue.
The fact that the injector pulsewidth doesn't appear to be changing while it goes richer, map, rpm, spark are all stable, and this is done at cruise which is typically lean (and hot) - how far from the turbo exit is the o2 sensor placed? I'm thinking it's a heat issue.
The O2 sensor is where the stock front sensor usually lives, well away from the turbo exit. I think it's heat related too, but I can't figure out what's being affected. If it's the sensor itself I would think that the pulse width would tank like the AFRs are.
The EGO Cor1 value is trending downward at the same time, but tops out at 90% (so +- 10% fuel max, dictated by the settings) - and that's when your AFR's become really unhinged. A quick google search doesn't show how an overheating sensor affects reading (reading lean or reading rich, but I suspect it's lean?), but tossing on ye olde wideband heatsink might help?
The EGO Cor1 value is trending downward at the same time, but tops out at 90% (so +- 10% fuel max, dictated by the settings) - and that's when your AFR's become really unhinged. A quick google search doesn't show how an overheating sensor affects reading (reading lean or reading rich, but I suspect it's lean?), but tossing on ye olde wideband heatsink might help?
By Jove I think you've got something here!
Yes, I'm limiting the EGO correction to +/- 10% and that's exactly what you're seeing with that pulling down. I think the key is that the EGO correction is pulling fuel and then getting into a weird condition when it gets to that limit and stays there. I was looking at something on YouTube a few days ago about PID loops and it described a condition where a poorly tuned control loop would cause the control signal to "jack down" - I can't recall the exact term used - into a totally uncontrolled condition. I think this is what's happening. I think that my EGO PID settings are causing the control loop to "jack down" the fuel and go into an uncontrolled state.
I'm going to re-tune the EGO control loop and see what happens. Also, I'm going to shift the resolution in the VE table to get a better handle on that cruise range of the table. Wish me luck!
More testing shows that it is DEFINITELY the EGO Corrections that are driving down the AFR readings during sustained cruise. After trying a bunch of different settings, I simply turned off EGO Correction and the AFR's remained steady(ish) during a sustained cruise. When I went back to EGO "on"...BAM! The "jacking down" condition returned. I tried a bunch of different settings for PID, but nothing seemed to make a difference, eventually it would come back.
That's good an bad. Good, because it means that it may not be a heat-related problem (with either the sensor, or the controller). Bad because I either have to give up EGO control, or find settings that won't cause this to happen. I think I'll choose the latter, so that means lots of experimentation...
I think the first step is to do a bit more tweaking to the VE table so that the AFR's in the cruising range better approximate what's in the AFR table in cruise (right now, they're about 1 point richer). Then I'll turn on EGO Correction again and see if the problem was that I was asking EGO to "do too much" in cruise and it went bonkers.
09-07-2020, 11:14 AM
Strange AFR readings at sustained highway speeds
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