erratic afrs under WOT
 

Hello,

I've been lurking here for a few years and this forum has been a wealth of information and helped greatly with settup my DIYPNP as well as installing a VVT engine into my 93 NA. I'm hoping someone here can help me get pointed in the right direction.

Ive had the ecu in the car for a few years now, and its been running great, once I got cold start and idle figured out. I had a tune based on other vvt tunes I've seen and used VE analyzer live and ran it that way as a daily driver that saw some track and autox use and it was running problem free, and I didn't even think about the tune until recently. I installed a Track Dog Rotrex kit in my car about a month ago and loaded a different spark and fuel table and the car has been running well with no apparent issues. I went to a dyno day a couple of weeks ago just to see what it would do (made 220hp/183tq on a dynojet) and saw a dip in power between about 5.5k to 6k, so I thought I would do some logging and see if there was anything obvious that would cause it. I was alarmed to find that my AFR's were all over the place under acceleration. I found a few threads talking about grounds so I decided to revisit my wiring, and moved the grounds from my LC-1 from chassis ground to directly to the ground wire on my ecu. Both the blue and white wires are grounded together as per the instructions for the LC-1. The instruction don't mention which one is heater ground and which one is signal ground. I also changed the response speed of the LC-1 analog outputs from instant to 1/12 sec. After I did all that, the afr gauge was swinging wildly from one end to the other, so I did a free air calibration and it seemed to stabilize. I went for a drive, and turned on VE analyze live and it added fuel all over my map. Not sure what to make of that, other than assuming my WB is reading leaner now than it was previously. I thought that was odd, since I though the car was running a bit rich to begin with.

My real concern at the moment is that in my log, the AFR would swing wildly up and down from max lean to target or below rapidly. The graph looks like a heart monitor. I've attached a pic to better visualize whats going on. What I'm not sure is if it is a WB controller or O2 sensor issue, or something in the tune. I do plan on eventually bringing the car to a tuner to get a proper dyno tune, but I would like to get my current tune as close to perfect as possible so the tuner only has to worry about tuning spark and fuel. I feel like I'm at the point where I know enough to be dangerous, and maybe have overlooked some simple setting. If anyone can take a look at my tune and make some suggestions that would be greatly appreciated. I'm especially interested in the WB controller settings and other setup type settings, as well as the overall tune, if anything looks way out of place. The screenshot from the log is a second gear pull. Thanks all!

Your VE table needs work. There are huge jumps from one cell to the next. Need to smooth it out.

While the VE table looks a little jacked up, it's definitely not going to cause what he's seeing on the AFR log trace. I would also bet that his VE table is jacked up because of the AFR log trace.

IMO your LC-1 is malfunctioning.

I think I remember reading on this forum once of a similar issue and it was an exhaust leak messing with the o2 readings.

Or you could just have a failing LC1 as mentioned above.

My first thought as well.

Make sure your sensor is still tight in the bung, and recalibrate the O2.

Thanks for the input. I have recalibrated the sensor again today, no exhaust leaks that I can tell and pretty much same result. At idle, the AFRs will spike every so often, but not with the engine off (ignition on). Could this also be symptom of a failing fuel pump? It's a new Walbro that came with the Rotrex kit, so only about a month old. I figured these things should be pretty reliable since the stock one was good for 250k miles, lol. I did notice today on my way home the car hesitated a few times, mainly when accelerating from around 3k RPM, 5th gear on the highway, feels like a misfire. Or could that be the EGO control trying to correct the fuel due to the wacky afr reading? I have the authority currently set to 5%, so I don't think it could make that much of a difference, and it is set to be active only under 75kpa, which should be well under actual kpa at 3k under load.

it doesnt look like any of htose things. it looks like a crappy connection or ground from the wideband, or faulty wideband

your wbo2 looks dead.

that or youre injecting too much fuel and washing everything out.

Well, I'm happy to report, all is well now. It ended up being the grounds. I picked up a new Bosch O2 sensor from my local Advance and gave that a shot first, but no dice. I decided to go all in, and ran new power and signal grounds directly from the board on the ecu straight to a bolt on the engine where I already have a 4 gauge ground to chassis, and connected the LC-1 signal and heater grounds separately directly to the new respective wires just before the ecu. Sooooo much better now! I should have done this first before changing the sensor, but I'm not mad about having a new one considering the old one was 4 years old. At least now I have a spare. Still need to work on the ve table, but I've made some manual adjustments to smooth it out in the WOT areas until I bring it to a real tuner. Thanks again everyone!