BLMs say rich, but WBO2 and NBO2 and surging all say lean - what gives?

Oh, interesting. A couple LOW VE cells at 1200 low map. Tweaked the numbers to make more sense, and re-uploaded.

Good to see you are making headway its lots more fun when you are seeing results and everything starts to gell

Went for a drive yesterday, 100°F heat. There was still some noticeable surging 20-30kPa from 2000 to 2500 rpm, so I fattened the table up there.

Also increased O2 Proportional Gains at the low end because I'm not seeing a lot of saw tooth pattern here. I may, at some point, go back to the stock gains, but baby steps. I'm still not exactly sure how these gains exactly work. Anyone? Anyone? Bueller?

With fattened tables, my BLMs are saying pretty darn good, but there is still surging, especially 25-35kPa now. So, I fattened the table up more, and will test again in a day or two.

Attachment 13228

I haven't figured out yet if you cam specs are at .050" or advertised. If those specs are at .050" that's a big bump stick.

Just for reference, I have an LT1 with a 224/224 @.050 cam in it, which I think was 286 advertised (supposedly, sounds more rowdy than that), and I could not ever smooth out the cruise using the NB02. I tried several things, but as the O2 voltages would swing, you could actually feel it in the car. Going to open loop solved all that, and I've been much happier overall now with OL. I'm using the $DA3 and ECM from a '93 F-body which isn't as well documented as the later PCM and $EE, so I was somewhat limited in what all I could try.

Used the NB02 to get the VE tables close though, which seems to be where you are stuck, not sure how to help there. I think I had to tweak just a few VE cells after changing over to OL, but man it's so much better. Also, the car likes to be 13.9 or so at idle (can't do in CL), and it likes 14.3 or so at light cruise (can't do in CL), and then on the highway cruising which uses a bit more throttle, it leans out to like 14.7-15.0, and is plenty happy there.

Too much timing will of course also contribute to the surging feeling. I had to tweak both to get it liveable. Just sayin' - you can go down that path, and always easy to go back to CL tune if you wanted. For me, trying to hit 14.7 all the time just didn't work. OL is maybe less than ideal for engines that have to pass emissions or something, but I'm not sure. Might still be OK

My cam is 213°/219° @050, 112LSA. Pretty mild. Mild avoids the "snowball" of tuning issues and required support (gears, converter, etc). My daily driver ('77 Squarebody) runs a 231°@050, on a 108LSA - still carb and HEI, but it runs stellar (after a lot of old-school carb & ignition tuning).

Hmmm.... your comment regarding timing is an easy check. I may try that.

In a way, tuning with a carb and a distributor type device can be easier, but depends on the carb. I bought a Might Demon when Barry was still making them. Boy what a mistake. I burnt a set of MT drag radials off the car at my favorite testing spot before I got it figured out. THey used to put like .032" bleeds in the mains, so it would be good at 3000 RPM, but by 6000 it would be like 16:1 and fall flat on its face. Lots a few street races after I put the "magic" carb on too - look of WTH on my face as it consistently just layed down. What a piece HAHA.

This LT1 project I'm working on was my first FI controlled motor. I like it though, it's neat to have so much control and real time feedback.

just wait till you try a real ecm, that one is pretty limp in every respect

I'm just after "good enough to sell it." I want the money out of it, to put into a different project. I thought I had it close, but I will get it sorted (or restrict it to run with zero INT or BLM change and leave it at that).

Slight change, but only a small drive for testing. I changed BOTH the O2 Proportional Gains AND the INT Delay O2 Error Multiplier to be 75% of stock. Brief drive feels really good with zero surging, but I have a longer drive tomorrow for more analysis.

Oh golly. Still more surging. Very light throttle cruise.

This was also an inspirational read: https://www.thirdgen.org/forums/diy-...int-delay.html

Looking at datalogs I could see the mix slowly drift rich, then slowly drift lean, then slowly drift rich, as if it was looking for results before the changes actually got there, just like the article says.

In testing, I put the Proportional Gains and INT Delay O2 Error Multiplier back to stock, but added 25% to the INT Delay Base. My O2 is AFTER the collector of long-tube headers.

Massive surging right into closed loop.

So I looked at the line graph of the O2 Prop's and INT Error again, but since I wasn't sure exactly what part of the graph was light throttle cruise at 2000-2400rpm, 30kPa, I just picked a low number and made them ALL that, both.

Much better. Then I added another 25% to the INT Delay Base, no other changes. Even mucher better.

Also added back some spark timing I had taken out chasing this. It was feeling more and more lazy as I took spark out.

As far as I think I understand, if the O2 is reader farther than it ought, the INT Delay O2 Error Multiplier alters the INT Delay Base by its multiplier to shorten its delay time?

I don't have to pass emissions, and I don't have to feed cats, so I'm not sure if it matters if I get this perfect or not, but it sure runs a whole lot better than before. More mucking around, but I feel like I'm on the right track.

One issue I want to try is I've had the P/N wire grounded so the ECU thinks I'm parked. I may disconnect it so the ECU can try and control idle in closed loop. As it is, it's not a consistent idle speed when I am actually IN park (the IAC seems overly active; I have no actual P/N switch).

Usually it's been "I think I got it" only to discover more surging the next day, and repeat and repeat.

Except I drove it last night to pick up my sweetie from work, and it was fine. No surging.

I re-grounded the P/N wire, as I didn't like how it was closed-loop idling. Also the Throttle Follower for D wasn't as fine-tuned as I had it for P/N, so back to the way I had it for now.

I'm going to be taking it to work every day now, at least until the snow gets close, and see if I can't refine this even more. Pleased so far.

Drove pretty good today. Pleased.

Faintest of surging the other day, so I added 10% more INT Delay Base, but it became ever so slightly worse, so I put it back and took 10% out, and it was a lot worse. I put THAT back, and then added 2%. It looks like I'm narrowing in on where it wants to be.

Also tweaking the Accel Enrichment because I'm not sure the fueling is expecting the large bore Holley TBI unit. I needed less at slow TPS change, because I'm running a vacuum-referenced fuel pressure regulator which goes to 18psi at zero vacuum (lose vacuum and you get MORE fuel than you were expecting). Certainly needed more at higher larger MAP Delta since the throttles are so big, which I added. Hopefully get rid of this occasional lean "POP" through the intake when I snap the throttle.

Fixed a surging idle in gear (a tick more fuel, but really the IAC was too active) and I suspect the Idle Fast Adjust Threshold was too sensitive, so I increased Underspeed to 125rpm (stock is 50), and Idle Minimum RPM Error to 75 (stock is 12.5). Seems better. I will likely be proven wrong.

Either the tune is a lot better, or the tires are going off - I'm getting more wheelspin. I like that.