O2 sensor signal drooping out with MS

[Jtantare]

First I want to say that NAW_OEM has been working flawlessly with my MS1 conversion for the past 7000 miles through lots of hard driving. If it was still available I would buy another one in a a heartbeat. I popped open the laptop again last week for the first time in a couple of months to tweak some cold start and idle issues in MS. I noticed under sustained heavy load rich conditions (13.5-12.5 AFR) the O2 sensor signal from NAW_OEM starts to show full lean. It stays like that for about 15 seconds then the gauge starts working again as before. It only does this when the mixture is rich under load. It doesn't do it when the mixture is rich at idle or cold start. I suspect my Bosch LSU is toast. Is there any reason to believe that the controller is broken instead of the O2 sensor? Is there a way to check?
thanks for your help
Justin

[Noddle]

Is this when you first turn it on ?
I know it has a inbuilt test, when it's first powered up,  maybe it's losing power and going back to initial start up ?

During heatup, from 0-15 seconds, NAW_OEM is programmed to output 1.666[volts], MS should read 12.33 AFR
From 15-30 seconds, NAW_OEM is programmed to output 3.333[volts], MS should read 15.666 AFR

http://14point7.com/forum/index.php?topic=524.0

Nigel

[admin]

Is it only the output that drops? Does the LED display, if you have it, also show lean?

How often does this occur?

Regards,

Alan To

[Jtantare]

Is this when you first turn it on ?
I know it has a inbuilt test, when it's first powered up,  maybe it's losing power and going back to initial start up ?

During heatup, from 0-15 seconds, NAW_OEM is programmed to output 1.666[volts], MS should read 12.33 AFR
From 15-30 seconds, NAW_OEM is programmed to output 3.333[volts], MS should read 15.666 AFR

http://14point7.com/forum/index.php?topic=524.0

Nigel

No, this doesn't happen during start up. At start up goes through its normal routine where it will display 12.33afr for a few sec then 15.66 afr and then it starts functioning normally.

Is it only the output that drops? Does the LED display, if you have it, also show lean?

How often does this occur?

Regards,

Alan To

I haven't been able to look at the LED display on the controller yet. Its inside its own box. I would have to take it apart. From what I can tell 95% of the time it still displays the air fuel ratio perfectly. During cold start the engine idles between 12-13afr, displayed normally in MS and even hot idle is between to 13-14 afr which is perfectly normal for my setup. It happens EVERY time I accelerate (80KPA+). The mixture display goes rich as it should then after about 2 or 3 seconds it shows the mixture at 19 afr. It stays that way for about 15-20 seconds no matter how I drive after that. The car behaves perfectly normal because its going off the VE table. Since the engine is always running in closed loop (except for idle), even at WOT, MS will compensate for the lean feed back by adding 10% EGO correction (the maximum I allowed) above the VE table when the O2 sensor stops working. It ONLY happens when the engine is under load (80kpa +) with a rich mixture (12-13 afr). Turning the EGO correction ON and OFF didn't make any difference. I don't think this is a problem in megasquirt.

I had one incident while tuning 5 months ago where I accidentally messed with the ignition and left it extremely retarded where the exhaust manifold was glowing red hot after about 30 minutes of normal driving. I fully expected the O2 sensor to be damaged after that but amazingly it keep working fine for a long time after. Maybe the sensor was somehow damaged then and its only showing the consequences now? The problem only popped up a week ago.
cheers
Justin

[admin]

There are a few possible culprits, my best guess right now is that it has to do with the power and ground. I would try putting a 100uf 25v capacitor between 12v and system ground, close to the unit as possible.

[Jtantare]

I installed a new identical Bosch 17014 WBO2 and the problem went away immediately. I ran a new data log with MLV and found the AFRs were rich by about 0.5 AFR across the board. Also the AFR seems to switch more often in closed loop. So the O2 sensor can be damaged by excessive heat and stay partially functional. There were no wiring problems as far as I can tell and the NAW_OEM is still functioning great.
thanks
Justin

[admin]

Hi,

Was the O2 sensor new when you first used it with NAW_OEM, the sensor control algorithms are pretty tight and there should be no opportunity for sensor damage.

[Jtantare]

Yes, the original sensor was installed brand new out of the box. It worked perfectly for a long time until the glowing exhaust incident where I mistakenly drove the car with the ignition timing retarded. After that, whenever I accelerated to WOT and the AFR enriched below 13 for a couple of seconds, the O2 sensor gauge on the MS screen went full lean (19 afr). O2 signal started functioning again a few seconds after going back to normal driving. The new sensor I installed yesterday fixed the problem. No more dropped O2 signal.