Wideband accuracy vs. Narrowband sensors

Hey all,

I have been mostly lurking on this forum, I think this may be my first post.

I have a 70 chevelle with an LQ4, 80lbs injectors and an ebay turbo. I have been able to tune it to the point that it is 100% drivable and working great at WOT.

The problem that I have been chasing for a little while is that while sitting and idling. The Wideband tends to slowly read leaner and leaner, usually to a max of around 16:1. When the car is up to operating temp, but recently started (within 10mins) the wideband will read closer to 13:1 at idle. I have compared the reading on the gauge and what HPT is seeing, they are within .1 of each other.

The weird part is, everything seems to say constant.. except the AF reading.

Everything mentioned above was while the car was operating in full Openloop (STFT and LTFT turned off.)


Today, I decided I would turn STFT back on and see where the car wanted to idle. I noticed that using the narrowbands the car seems to want to idle in the 15.7-16.2 area (on the AEM wideband.) Even though the narrowbands are programmed to target 14.7. Please see the attached logs.

My question is: Which is more accurate? The narrowbands or the wideband. The narrowbands tend to read pretty close to each other, and the VE table can't be far off of what the narrowbands are reading since fuel correction is less than 5%. Does anyone see anything weird about my log? I let it idle until the car was good and warmed up.

Please take a look and leave any insight or criticism you may have! I appreciate it all.

Attachment 44672Attachment 44673

Somebody will be along to answer some of the other stuff but the narrow bands are only able to work at stoich i.e. 14.7, then there are modifier tables for idle and full throttle etc.

Thanks Cosmik,

I have a pretty good understanding of the modifier tables, be it PE or BE and the 14.7 stoich. What I'm mostly curious about is whether my wideband is reading wrong or the narrowband sensors are reading wrong. You will see in the log that the NB sensors are behaving properly and bouncing up and down around the perceived 14.7:1 AFR. However, if you look at my wideband reading it is no where near 14.7. This is concerning to me because in Open loop (where the car is normally ran) I have used the wideband to finetune the VE table. If the wideband is reading wrong I am worried the engine might be running leaner than I had thought, which obviously isn't good!!

Go see what it does while cruising. Say in the 2000-3400 range.

My WB agrees with the NB at all points. Although I did have to add a smidge of offset to the WB in the HPT config.

My WB is the AFX with NTK sensor and I'm tuning in Lambda.

Ron

Thanks Ron,

I may have jumped the gun a little bit. I went for a cruise and the wideband lines up with the NBs most of the time. It seems to be the furthest off at idle, reading 15.2 or so instead of 14.7. I'm not too worried about it though.

I figured out that a lot of my problem is to do with the IAT sensor. I think it is getting heat soaked. Weirdly, the warmer the car gets the leaner the wideband reads.. But, the IATs never really go over 80 degrees. I have been messing with the IAT to ECT bias. But, I think I will try to move the IAT sensor into the pipe right next to the intercooler.

Cool, er hot!
Your trims while idling are good. Id say maybe the WB is just off at low exh heat, maybe too far away from the turbo?
Anyway, the trims say its pretty happy!

Go make some boost.

Ron

look at your OPENLOOP table is it all set to 1 or parts of it .90?

14.68/.90=16.3xxx AFR I have seen this before

don't worry about heat soak on the iat sensor it is sensitive enough to read accurate once air is flowing past, because of my blower mine is mounted on the manifold just before the head and i still have correct readings...