1994 4.3L vin W surging. Service Bulletin recommend upgrade to BPLC.

After replacing the spyder fi, nut kit, and tuned VE tables because still too rich, my Sonoma surges at light throttle.
Found Service Bulletin 57-65-03A which recommend upgrading my old prom (BHRH) to new (BPLC).
Can anyone help me with a BPLC bin?
Or a BPLB might be of help. The same bulletin recommended upgrading a BHRJ to a BPLB. Maybe I could look inside the bin and figure out the changes made.
Or does anyone know what the changes made were? The bulletin says it is 'to change Emission Axle under S/T Utility'. (whatever that means)
Oh, mine is a 16196395 PCM, but my understanding is the 16197427 is a direct replacement, so might find the BPLC in one of those.

Any other ideas would be appreciated.
Other things replaced, for many other issues on this acquired headache, O2 sensor (was confirmed bad), distributor, icm, tp sensor, map, plugs, wires, cap, rotor, pcm, muffler, cat, exhaust leaks repaired, coil, air filter.
Other things checked/done during all the headaches, fuel pressure, compression, back pressure, temp sensor, vacuum, egr cleaned, iac, vacuum controlled evap canister bypassed, iat, scoped best I can (pretty good waveform, some end of fireline noise), battery voltage noise, grounds, engine clean done by pro shop (2 part, air intake and fuel additive).
I do get spark retard from knock counts (think other noise being sensed). But believe is not the current surge issue as I still have the surging with knock/retard disabled in the pcm (disable by over high temp requirement set for knock response).

Hmm, while I'm asking, after exhausting all I know for continuing to have my fuel trims too rich (the previous owner performed many, unknown repairs), any secondary effects known to result from having tuned my VE tables quite a bit to compensate for rich trims? I originally changed my injector flow rate to shift all my trims less rich, worked, but then found out my VE tables wanted to go above 100 for tune corrections (which wouldn't take in TurnerPro, go figure :) ), so I went back to original injector fuel rate to tune. The highest VE cell, before tuning, was 89.5 (4000rpm at 100 map), same cell after tune is 77.7. Other cells follow, with much lower values.

Warning, I'm not an experienced mechanic, but having way too much fun.
Why did I buy? My wife said, it just fits us (with big loving smile), and you can fix anything....

Thanks in advance.

It would take a lot of investigating before I altered VE tables to "fix" a problem if the engine was stock. You're saying that the exhaust readings are showing rich, and you've reduce the delivered fuel volume? Is it about 10% on average? Because that's not that much... But if I thought there was a problem I'd confirm the rich readings using a wide band O2 or a three or four gas analyzer. You have to prove the sensor is correct. And I wouldn't be afraid to run open loop for a time as a diagnostic step. We had a six liter truck engine here yesterday which was adding fuel at idle. It had the slightest misfire which was sending unreacted O2 past the sensor, but it was very subtle with the pcm adding fuel and the desired idle at 550 rpm. Forcing the engine into open loop and clearing the long term trims made it much more obvious. Next step is basic mechanic stuff; diagnose a misfire.

Quote:

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Originally Posted by 1project2many

It would take a lot of investigating before I altered VE tables to "fix" a problem if the engine was stock. You're saying that the exhaust readings are showing rich, and you've reduce the delivered fuel volume? Is it about 10% on average? Because that's not that much... But if I thought there was a problem I'd confirm the rich readings using a wide band O2 or a three or four gas analyzer. You have to prove the sensor is correct. And I wouldn't be afraid to run open loop for a time as a diagnostic step. We had a six liter truck engine here yesterday which was adding fuel at idle. It had the slightest misfire which was sending unreacted O2 past the sensor, but it was very subtle with the pcm adding fuel and the desired idle at 550 rpm. Forcing the engine into open loop and clearing the long term trims made it much more obvious. Next step is basic mechanic stuff; diagnose a misfire.

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I don't know if 'stock' as I don't full history, but I assume stock. The previous owner said he had put in about $2500 in parts is all I know.
So, ~10% change might not be of concern. If my math is correct, my 89.5 to 77.7 VE cell change is ~13 %.
When I first changed the injector flow to shift all the cells in the VE table for the rich issue, I changed from 119.4 gm/hr to 153 gm/hr to get most of the trims to average ~128. I think that was about a 28% increase.
See any worries from these numbers?

I don't have a wide band O2 or gas analyzer. I had LT trims maxed neg (2 O2 sensors produced same), rich smelling exhaust, plugs fouling black.
But, if I understand what you're saying, a subtle misfire might, cause my narrow band O2 sensor to not get proper reading of 'richness' due to the unreacted O2 (causing lean bias) with additional fuel add to compensate, thus my richness.
Is that correct?

On your truck with misfire, when you forced it into open loop with trims cleared, can you tell me what were the 'more obvious' symptoms you saw? Were they something I might observe without wide band O2 or gas analyzer?

Thanks for your help.

"More obvious" means the vehicle was noticeably shaking from the severity of the misfire.

Rich plugs and black exhaust are not acceptable. Are all the plugs turning black or just a couple? Where is the fuel pressure currently? If the regulator has been replaced it may be adjustable.

All the plugs were turning black.
I didn't record the fuel pressure, but I remember it was in spec and I think ~60psi. Leak down test passed.
No adjustment on the fuel regulator. 2 spider assemblies (1 new) both fuel pressures were good. The fuel regulator is replaced with the spider assembly.
I had the truck at a shop where the mechanic says he has had ~10 years GM experience. He said the engine is a little rough but is still within 'normal' from his experience.

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I have not tried to measure that O2 ground with the motor running. The sensor ground is through the threads.
My pcm ground to back of engine, which I can't reach. Have tested by running a separate ground from batt to pcm, no change.
I have cleaned all grounds I can find, except the 2 on the engine between it and the firewall. My hands do not fit. Testing, I have run a separate ground from the battery to the engine, and another time from ground to pcm. No change.
I have tried another pcm, no help.
Fuel pressure tested at engine off (fuel pump ran), engine idling, engine reved. All good. Not driving down road. Not sure how to do that, my fuel pressure gauge line too short to expose for viewing while driving.
Was using cheap autolite plugs during much of troubleshooting. Recently changed to CR43TS, gapped at .045. No change. Tried new Delco cap, rotor, wires, just to make sure. No change.
My O2 runs full time. Tried 2 different new O2 sensors, same results.
Current status is with it running with good looking trims, just the light surging around 2k rpm (+- 500rpm), at light to moderate throttle.

Watch scantool and correlate readings with surging. O2 swinging to lean or rich while it's happening? Timing advancing when it's happening?

O2 grounds to exhaust, ok, but what connects exhaust to engine? Sometimes you need a good ground strap there.

Rings OK? No oil usage? External oil leaks? O2 "compares" exhaust with fresh air. I once ran into a rich engine caused by oil dripping on exhaust and smoking. Smoke accumulated around O2 at idle and caused the O2 outside the exhaust to be less than inside and O2 sensor reported that as a lean condition to the ecm.

Also, silly question but check to make sure vent tube in valve cover is working. Vacuum in crankcase can draw hydrocarbons past rings.

Any chance you've got an older engine??

Stared at the scan readings for hours looking for any correlations. Can't see any correlation, positive or negative, other than rpm 2000 +/- 500.
No O2 correlation that I can see, spark advance can be going up or down.
Ground of exhaust has not been checked. Will do that.
Haven't run it enough to have data for any internal oil usage. Known, small oil leak from pan (leaving for future fun), not leaking onto or near exhaust and the O2 sensor.
Compression all within 15%.
No oil leak from around intake manifold, but the intake manifold gasket was replaced on forlorn hope, and just to check for possible vacuum leaks and any cracks. All ok.
Oh ya, the PCV was replaced on gp.
Previously tested for internal vacuum issue (at oil dipstick tube), none found.
Hmm, haven't checked for older engine. Suggestion on how to do that? If not original, I assume it can't be much older as it has the balance shaft.

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billygraves, thanks for you reply.
Both of the 2 new O2 sensors cycle hi/lo. The O2 to exhaust is clean connection as had to tap the hole after the bad original one came out hard (3 pound hammer and pound pound pound).
I just used the anti seize compound that came on the sensor.
Both the spider injector that was in it when I got (the previous owner said he had replaced it) and the one bought at Knechts produce the same results and both seem to work. I replaced his because I couldn't find why it was running rich and didn't trust his repairs (instead of replacing the nut kit, he put in rubber fuel lines with hose clamps. so i replace spider assembly and nut kit). Never found good reason for the running rich and bought a prom burner and changed tables so trims look good and no longer running rich. Now just the surging.
No problem asking about the gas. This problem has been around for several tanks of gas (76 gas).
The first of the two new O2 sensors was a Bosch and the second a Borg Warner. 3 wire, after exhaust y, just before cat.
WOT truck runs to high rpm. As never driven this truck without it having issues, I can't be sure of lacking power, but seems ok at WOT.
Looked over my saved logs and don't have any at WOT. I was always capturing low/med throttle logs for my surge problem. I will see if I can get a log file of WOT tomorrow.
No fuel leak seen with plenum off. Fuel pressure leak down, tests good.
Both new O2 sensors cycle hi/lo.
I recently have started with a 'original' copy of my bin file and 'retuned' it. No change.

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I took if for a run. At WOT the O2 is not cycling, ~969mv.
During 'normal' cycling it's low ~60 - 70mv. Lowest seen 31mv. So don't think have O2 ground issue.

I would love to try the New Prom, but where can I get the bin file? I can't find it.

I have previously block off the egr valve, no help. During tune runs I disable the EGR in pcm with coolant cal, no diff on surges.
The evap canister is vacuum controlled on mine, I have it disabled for troubleshooting. So no effect.

Carbon on the exhaust valve stem is something I have thought about because I has the history of running VERY rich for unknown periods.
What would this look like on a scope? My electronics bench scope died in the time sweeps I need, so I bought the cheap Hantek 1008C.
Slow and not enough memory, but I can get waveforms.

I haven't pulled valve covers and so haven't checked valve tension. Put on my to check list.
Thanks for the thought on the rear block grounds. On mine, they are grounds for the pcm. I have ran external ground wire to test, no help
Re the back half of the proms, I'm not sure what you mean. Compare of the code? The limp mode code/hardware?