A tuning tale: BLMs say lean, plugs say rich

[XfireZ51]

Trying to dial in the tune on the LT5. Just when I seem to be close to finalizing based on BLMs, I pull plugs and they don’t indicate what the BLMs are saying. Specifically, my plugs are a very dark brown suggesting the tune is rich but the BLMs are reading in the 133-135 range. I’m tuning to within a +/- of 3 to 128. The heads and top end have been ported, larger cams, and 3” exhaust w headers.
Here’s a pic of the NGK BKR5E-11 I am using. They’re gapped at .044”. The darker one is from the passenger side bank, the lighter from driver’s side.

[jss06c6]

Dominic,

This is interesting.. I've got my '91 dialed in to 128 on driver side and 133 on passenger side. Haven't made any PE changes yet, but the first pull on our new Dyno showed the engine to be very rich. Raw fuel spraying out of the exhaust! Still made 359/405 on a loaded Dyno. There is a lot left in the engine, but I'm still intrigued as to why, after porting and the engine is so rich at WOT. BLM's we're running 138-145 after porting using un-ported tune.

Watching and learning!

Steve

Sent from my XT1585 using ZR-1 Net Registry mobile app

[XfireZ51]

Originally Posted by jss06c6

Dominic,

This is interesting.. I've got my '91 dialed in to 128 on driver side and 133 on passenger side. Haven't made any PE changes yet, but the first pull on our new Dyno showed the engine to be very rich. Raw fuel spraying out of the exhaust! Still made 359/405 on a loaded Dyno. There is a lot left in the engine, but I'm still intrigued as to why, after porting and the engine is so rich at WOT. BLM's we're running 138-145 after porting using un-ported tune.

Watching and learning!

Steve

Sent from my XT1585 using ZR-1 Net Registry mobile app

Steve,

If u enriched up the mixture to keep up w the additional air from the porting, the PE table is still set up for the stock VE tables. With more VE fuel, the PE multiplier are being used over a larger number. The VE and SA tables are the basis for practically everything else. Change them, and other parameters need adjustment because they”feed” off those tables.
One other modification that most don’t know about. The PE will be modified based upon the last Active BLM prior to going into PE mode. Anything over 128, and the ECM will add fuel beyond just what the PE muliple is. So if the motor is running somewhat lean based on the last BLM it sees, then the ECM will add a bit more cushion.
This is if u r tuning in C/L.

[XfireZ51]

The motor feels that it likes the BKR5E plug better than the 6E. I tried raising SA again but started to pick up some KC at a steady cruise as I had in a previous datalogs. The Knock occurs during steady cruise at about 1800-2000rpm and shows up when the road begins an incline. In the LT5, AE is based solely on MAP differential not TPS%, so I can maintain a steady foot on the throttle but MAP will change slightly and that’s when I will see the KC increment. So this is why I dropped timing. It was to eliminate the KC at steady speeds. Otherwise I don’t get KCs.
So my question is, did I drop timing to eliminate KC but in the meantime lower timing is giving me a more incomplete burn?
Am I creating s problem trying to solve a lesser problem?
__________________

[XfireZ51]

Been out of pocket for a bit so no progress. But, I'll be pulling the plenum here for two reasons: 1. Check to see if I am getting oil seepage into #2 cyl,possibly less in #4. If that proves negative, I will likely be sending injectors for cleaning and flow check. I'll be replacing knock sensor and tensioner since I'll be dropping coolant. Qjacks will be making this an easier chore Stay tuned.
Meantime, I have some new weatherstrip to put on doors.
LET THE WINTER BEGIN.

[XfireZ51]

So we move ahead. Before I start tearing into top end of motor, I thought I would first check the injectors thinking perhaps something obvious would show. I ran a resistance check on the injectors. The primaries ranged from 14.6-14.8 ohms, while the secondaries ohm'd out at 14.1-14.3. All pretty consistent. This does not definitively rule out injectors, but its a start. If I don't find evidence of a particular cylinder sucking in a bit of oil, I'll have the injectors cleaned and flow tested. This MAY have some relation to getting knock counts during cruise.
If I'm running rich in one bank, I would be tuning to balance that out causing possibly the opposite bank to be running a bit lean which, again, MAY induce knock on accelerator position change.

[Ccmano]

Originally Posted by XfireZ51

Trying to dial in the tune on the LT5. Just when I seem to be close to finalizing based on BLMs, I pull plugs and they don’t indicate what the BLMs are saying. Specifically, my plugs are a very dark brown suggesting the tune is rich but the BLMs are reading in the 133-135 range. I’m tuning to within a +/- of 3 to 128. The heads and top end have been ported, larger cams, and 3” exhaust w headers.
Here’s a pic of the NGK BKR5E-11 I am using. They’re gapped at .044”. The darker one is from the passenger side bank, the lighter from driver’s side.

Air leak before or near the O2 sensor?
H

[XfireZ51]

Originally Posted by Ccmano

Air leak before or near the O2 sensor?
H

No Hans. I logged before and after O2 sensor change. No significant difference.

[Ccmano]

Originally Posted by XfireZ51

No Hans. I logged before and after O2 sensor change. No significant difference.

Understood, but changing out the O2 sensor does mean you don’t also have a leak somewhere that hasn’t been resolved. That said a leak would affect one side or the other if it’s in the exhaust..
H

[mhobtr]

Are you going to check the injector housing gaskets also?