ULTM8Z

I had posted this in the DIY PROM section, but it may not be a calibration issue, so I"m putting it here. Admins feel free to delete the one in the DIY PROM section... Also some subsequent posts for the updates...

So I'm not sure if I did something to cause this and not sure how far back in time this has been occurring.... but I was datalogging and noticed that after about a half hour of driving, the BLMs shoot up from 128-130 to upper 140s, sometimes as high as mid 150's. But only in certain BLM cells, mainly the lower to mid ones, like 3-7. From 11 and up, it holds steady at 128.

Before this starts happening, BLM's are around dead-nuts at 128-130 everywhere.

It also doesn't do this all the time... on certain runs it holds steady at 128-130 everywhere.

What also happens at the same time is at idle, I'll get these momentary "glitches" where the AFR on the WB shoots up to 16-17:1 and get this drop out and surge before it recovers. It'll idle rock solid at 14-14.5:1, and then this random split second glitch. I idle in open loop, so assuming these two issues are related, it can't be the O2 sensor itself.

I was thinking the ECM is glitching out or something, I swapped ECM's since it was easy to do but that didn't help.

It almost seems temperature related, but I'm at full operating temperature within about 5-10 min of driving. So what could be changing after 20-30 min that would cause this? Everything that is affected by temperature has already been at full operating temperature for a while.

In the meantime, Is there something in the calibration I should be looking at?

If there was some fueling issue, why wouldn't I see it everywhere? I.e., If something was causing the engine to go lean at all these BLM cells such that the BLM's shoot up to ~150, I would think that I'd see a steady lean out at idle as well (since I'm open loop idle). But, except for the momentary glitches, the AFR holds steady at 14-14.5:1.

Also my Power Enrich will easily get to the 12.5:1 that I commanded even when the high BLM's start occuring. Again, if there was some fueling issue, I'd expect the PE's to be lean as well.

For reference, I'm running S_AUJP V7. Engine is a 383 with a Miniram and 7730 ECM. I've attached a datalog that shows what's going on.

ULTM8Z

Update...I swapped the WB and NB O2's to the opposite sides of the engine (NB was on the driver side).

With the NB on the passenger side and a couple of runs.... it's now doing the high BLM more quickly and consistently . But again, it's ultimately going up to the 150's and even 160 (I have the max allowed set to 160 in the tune).

But here's what I know so far...

1.) Not the ECM... multiple ECMs do the same thing
2.) Sensors all seem to be good - Tunerpro data
3.) I think it's unlikely I have a bad injector(s). They're all new. Swapping the NB O2 to the other side produced essentially the same results. If I had a bad injector on the driver side, the O2 now wouldn't be able to see it. And having a injector that's bad to the exact same extent on the passenger side as well seems awfully unlikely.
4.) Same story for the plugs and wires as in #3 above
5.) I thought about an exhaust leak, but again, moving the O2 to the other side... It'd be extremely unlikely I have leaks on both sides. Plus I don't hear anything and I don't see any evidence of soot anywhere.

The strange thing is above 50 kPa, it's not doing this. It stays at 128 above 50kPa no matter the RPM. Question: I have my PE MAP enable set to 50kPa, but the TPS% enable is upwards of 60%. When in PE, I have the tune set to lock to 128.

So does the PE come in if either the MAP OR TPS% meet the threshold? Or does it require both to meet their thresholds before PE engages?

Maybe I'll set the PE enable to say, 80 or 90 kPa and see if the high BLMs get up into that MAP range too.

What's also happening is that due to the high BLMs, the ECM is adding a lot of fuel because the WB O2 on the other side is showing very rich AFR's... like down into the 12-13:1 during normal driving.

Lastly, while driving today, I reduced the injector constant from 31 to 29 (trying to force it to run richer) to see if I could get the BLMs to go down, but they wouldn't budge.

ULTM8Z

Figured it out (I hope)....

Some sort of copy and paste error I think during a past bin update.

I back tracked all my O2 swing points, prop gains, lag filters, etc... constants and tables against AUJP and found that I some how screwed up the table at 0X4C6 (Slow O2 lag filtering coefficient vs airflow).

While AUJP ranges from .062 at 8 gm/sec up to .172 at 64 gm/sec, somehow I ended up putting .550 in all the entries. Don't ask me how I did that because I have no idea...

Any rate, I put it back to stock AUJP settings and the BLMs are back to normal, ranging from ~126 to ~134, and holds there indefinitely with only minor variation within that range on a given cell.

On my way back from work, I shut the car down and disconnected power from the ECM (I have a toggle switch hooked up for that)... three times. And each time when I started the car and drove it, the BLM behavior remained correct.

I'm not sure how that table works or how it contributed to this, but looks like that was the issue (again, I hope... don't want to jynx it).

On a positive note...

This issue gave me the impetus to switch O2 sensors side to side, which gave me a chance to see how the two sides compare when the ECM controls each one. I'll be damned if they aren't pretty much dead-nuts identical to eachother, both in the data and seat of the pants feel. For a Miniram with batch fire, pretty happy about that... putting those 10% bigger injectors on cyl's 1-4 was one of the best things I ever did.

Eightyninef

How do you have 2 O2 sensors ?

ULTM8Z

I have the factory narrow band that communicates with the ECM. But I have a wide band that I added for monitoring the air fuel ratio. The wide band is not used by the ECM.

In retrospect, I probably should have mounted them both on the same side, but I put them on opposite sides. So when I see things like lean BLM's from the NB side with rich AFR's on the WB side, I have to do some interpretation on what's actually happening since the two can seemingly contradict eachother.

Fred SS

iTrader: (3)

Let me understand this correctly. You have two different size injectors on one motor, 10% larger injectors on cylinders 1 - 4. What lead you to do that? Very interesting. I am considering going with a GM HT383 with a Holley Stealth Ram.

I have heard that intakes such as the Holley Stealth Ram tend to run rich on cylinders 5 - 8. Does that have something to do with what you did?

Fred

ULTM8Z

Yep....

https://www.thirdgen.org/forums/diy-...injectors.html

https://www.corvetteforum.com/forums...l-s-1-4-a.html

ULTM8Z

It has everything to do with it... lol

Fred SS

iTrader: (3)

Thank You ULTM8Z.

Fred

Fred SS

iTrader: (3)

Do you mind if I ask what cam you are running?

Fred

ULTM8Z

I'm running Crower's 00482LM. Pretty mild for a 383, but I wanted a very mild mannered car.

https://crower.com/camshafts/chevy/s...mshaft-64.html

Also running 1.6 rockers, which adds some lift and maybe a degree or two more duration.

But, it idles in gear at 650 rpm with ~16.5 inHg of vacuum and drives like stock... which is exactly what I was looking for. You wouldn't guess what was in the car by listening to it idling... lol.

I also re-used my AFR 180cc heads from my old ZZ4 350, so the 383 was never going to be a high-rpm power maker. Nevertheless, for my rpm range (which stays below 5500 rpm), it makes a ton of power. Plus with the gear vendor OD, I'm never out of the power band of the engine. So overall the car puts more than enough power to the ground for what I do with it.

Fred SS

iTrader: (3)

Great information. I was looking at that cam for the HT383. But I was looking at the reduced base circle version of that cam, part number 00482S.

Fred