Okay, I just got into data logging and I am seeing some things that don't make too much sense. When I first started I think I had a bad o2 because the stupid thing would drop off to 0 mV for large blocks of time. After changing the o2 I no longer get 0 mv, but I do get many samples below 100 mv in the 70-99 mv range. after I get up to operating temp. As it warms up, my BLMs get up to 140?!

When I am heavy on the throttle, it seems that I am closer to 128, but in all other cases, the BLMs are always high.

I am running 43 psi on fuel pressure, and my only mods are a ported intake, 1.6 rockers, and headers. I think I have a small exhaust leak, but I am 90% sure that it is after the o2 sensor where the collector meets the y-pipe. I have read that headers can cool the exhaust down enough to throw off the o2 sensor? Would a heated o2 solve my problem? I am getting to closed loop no problem.

 

Have you done anything with the tune since adding the 6E swap/1.6 rockers/modified TPI or is it a stock tune? 305 TPI right?

The o2 during closed loop is suppose to switch back and forth from low values in the 100-300 range and then go to high numbers in the 700-900 range to establish stoich air fuel. BLM of 128. If its switching alot back and forth in your logs, then its working. Since it gets to closed loop it shouldnt have any issues with getting too cold so a heated sensor wouldnt help I dont think, but its a nice setup to have.

If you are in the 140's during some cruise spots and your on a stock 6E based tune, then you may need to tune this setup. With those mods, its gonna get more air flow and probably lean out some. I know my L98 seemed to lean out alot at WOT with 1.6 rockers but generally was ok during most cruise points. I cant recall what my idle BLMs were.

When on heavy throttle you may be hitting PE mode and if so, the BLMs will go to 128 anyway and sit there. Doesnt mean air fuel is 14.7 to 1 nor does it have to be depending on what load the motor is under and what rpm. A good heavy load may need 13's to 1 air fuel and when WOT, it will require 12.5-13.0 generally for max power.

If its in PE mode, watch the o2 milivolts. Blms/INT will force to 128 and o2 milivolts will hold at a certain value based on actual air fuel. From what I'm seeing on these cars, 900mv is about mid 12's to 1 air fuel ratio. 930-950's can be mid 11's to 1. In the mid high 800's, you probably in the 13's to 1 but I have never been there with the wideband to confirm. I believe 14.7 is around 450mv for most O2 sensors. The range is kinda funny. Further you are away from 14-15 to 1 air fuel the more the range drops off.

 

If the BLM is at 140 it is maxed out and the o2 sensor is still saying you are lean. Either you need more fuel or it may be the o2 sensor is not hot enough to give a proper reading. If it is the o2 sensor your plugs will probably show rich. If the plugs show lean, you need more fuel.

 

Today I look & realized why I made no attempt to answer.

Fix your exhaust.

It's not worth trying to figure out till you do.

I will say that adding a little fuel pressure has helped many, 43 is bottom barrel,
but let's face it you may have bad data w/leak.

 

Even if the leak is small and down stream of the o2?


Anyways, I swapped out the new Bosch single wire o2 for an AC Delco o2, and the thing reads even lower mV with lows in the 20mV range?! The only thing is, it seems to bounce from low to high with more regularity with this sensor than the unheated one. Am I actually lean, and even leaner than I thought? Seems the perception of smelling rich doesn't mean much.

I pulled the plug from #1, and it doesn't look black or anything, just light brown. Seems like I may be lean, seeing as my intake is ported upper and lower, I have SLP runners, and 1.6 rockers, I guess being lean at 43 psi isn't too far fetched. Perhaps I should raise my fuel pressure to 50psi and see what my o2 sensor says.

 

Well, seems I fixed the problem. I guess the mods I have were enough to make the stock tune lean, particularly at idle. I saw this post:

https://www.thirdgen.org/forums/diy-...or-0-00-a.html

I played with the #1 MAF table, and moved the g/sec up 0.11 in each cell. Now my BLMs at idle move around between 128 and 120. My O2 voltages now fluctuate in closed loop from ~50mv to 950mv rather than staying steady below 100mv.

The car idles smoother, and doesn't stink anymore. There was also a noticeable improvement on the butt dyno.

Tomorrow I will test how it does at cruise.

 

what about if you have longtube headers and the o2 sensor is really far down the exhaust cause of this? I mean, i like the way my car runs with the blm's a little on the high side. So, what would happen if i installed a heated o2 sensor? Would it bring the blm's back down because the o2 voltage would now be possibly higher cause of the heated o2? I mean i always thought the blm's were strictly based off of o2 sensor voltage?