L29 Tuning help?

[n0dih]

Sorry, I know this isn't Gen III (Mark VI actually...) but I have a tuning problem no one seems to have a clue on.

Engine is a 99 Chevy Suburban, K2500, 454 (L-29) and I have a consistent problem with at cruise, LTFT's are at 18% rich. ALWAYS 18.0%. It varys some on decel, but 97% of the time it stays on 18% rich.

What we know: MAP is good (verified with my laptop reading the PCM and a vacuum pump), MAF is good (put it in my LT1 car and verified BLM's are good with proper MAF tables), TB is spotless, no air leaks after MAF (that actually that HELPS things...), knock sensors both ohm the same, but do not agree with resistance in the 96 FSM (parts books says same sensors, but I can't easily buy in that both sensors would fail the exact same resistance), CTS is good, IAT is good, crankshaft learn is good, FPR is good, fuel pressure is good (no leak down when engine shut off), EVAP good, EGR is clean.

I still can't seem to nail down why this thing runs rich consistently. It gets into closed loop fine, and then eventually settles on 18% rich once it is warmed up to operating temps, and the STFT seems to run between 5% rich to 3% lean, hanging more on the rich side, so I get a P0174/P0175 fault that I can't make go away.

PCM is tuned by Wait4MePerformance. Old PCM (untuned) and new PCM (tuned, yes, I have 2) both do the exact same problem. Tuned PCM runs worlds better, but problem remains.

Can anyone give me some thoughts on what else it would be? If this was my LT1 I would just tune the VE tables and be done with it.

If I didn't know better, I would guess someone put in larger injectors that look identical to the stock ones (L29's and LT1's share injectors, 24 lb 3 bar, 28 lb 4 bar which is where my truck runs).

[Russ K]

P0174 is for bank 2 lean, and P0175 is for bank 2 rich. Positive fuel trims mean the AFR is too lean. Check to see if the fuel trims are ok on bank 1. I can't see how your getting a rich & lean code for the same bank.

Russ Kemp

[n0dih]

Ok, I worded it improperly, -5% to +3%. It varies. This is STFT. LTFT is staying at -18.0% most of the time, save PE mode and decel, else, -18.0%. Never -18.1%, or -17.9%, always -18.0%. On Decel you might see it as high as -24% momentarily, and it will most commonly come down to -14%, but never anywhere close to where it should be.

Bank 1 and Bank 2 read fairly close to the same, while Bank 2 is slightly richer, maybe 1%. With the eyeball averaging device engaged...

Bank 2 typically sets the code 1 min before Bank 1. But AFAIK, that is the same.

[Russ K]

Ok, then what bank 1 code are you getting? If both banks have negative fuel trims, then check for an over fueling problem. If larger injectors were installed, then you need to change the injector flow rate table in your tune. I use Tuner Cat for tuning the Vortec trucks.

Russ Kemp

[n0dih]

I don't have access to PCM tuning software for this PCM. I have TunerCat OBD1.

Is there anything in the code that might shift that much in the fueling? I don't have a 99 FSM, but my 96 FSM lists the Knock Sensor resistance as 100K. ACDelco.com shows the 96-2000 L29's all use the same knock sensor. My knock sensors BOTH measure 8.5K. Can a knock sensor program cause this large of a % enrichment to protect from knocking? Can both KS fail at once? Any chance you have access to an actual L29 .bin file? Can you see if there is anything you can think of that might cause a blanket shift of the fueling to rich?

Else everything SEEMS in line. I don't have $100 to toss into parts to troubleshoot with (I don't do that, I preach heavily against tossing parts at your truck/car to troubleshoot....), and I just don't do that. My background is component level repair of cell phones, prototypes, and radars. I know my electronics and don't just do something unless there is data to show me that I should...