A tuning tale: BLMs say lean, plugs say rich

[XfireZ51]

Originally Posted by Paul Workman

You may have significant carbon deposits in some chambers as result of the oil seepage issue. So, once the gasket issue is resolved, you may want to de-carbon the motor first before doing a lot of hocus-pocus (VE/SA manipulation).

Did both heads come off to inspect the motor as well as replace the parts related to the broken ring? - seems curious you'd have a leaking gasket(s) issue a year after they were (presumably) replaced, no?

Ah yes. Pete did the work. He replaced rod bearrings as well because they showed signs of wear.

[XfireZ51]

Due to the holidays, and waiting for gaskets, haven’t done much. However, I did take the opportunity to scrape some of the carbon gunk off the back of some of the intake valves. Some had more carbon build up than others. Driver’s side semed to more of an issue than the passenger side. Also, the primaries were clean while the carbon build up appeared mainly on the secondaries. That leads me to suspect that the carbon buildup occurs during idling situations since secondaries are off only during that time and primaries continue to spray fuel.
I’ve had these injectors for 10 years, so “while I’m there”, I’ve decided to have them flow tested and cleaned. May as well certify they operate at “nominal” levels before buttoning up the top end. We’ll see if any of them may be sub-optimal.

[Hib Halverson]

Couple of comments here...

1) NGK 5 heat range is too hot for any LT5 other than show cars which are only driven on/off trailers. Use the NGK 6 or Denso 20 for normal use and NGK 7 or Denso 22 for aggressive street driving or occasional track use. When I owned "Barney", for the first few years I ran an NGK 6. From the late 90s to early 00s on I ran the Denso 20. The last couple of years I ran the Denso 22. Densos worked great in an LT5

2) I would not use plug readings as a basis for making decisions on long-term fuel trim, ie: BLM. First of all closed-loop operation likely does not color the plugs enough to offer useful information and secondly, pump gas has so many additives which erroneously color plugs such that whatever color you see is useless. That said, if you have a case where, say...six plugs are one color and two plugs are so black they are near-carbon-fouled, then you don't have a BLM problem you have an injector problem.

3) If you trust your O2Ses and don't have a wide band, ignore plug color and use the narrow band sensors. While I don't calibrate LT5s, I do calibrate various '96-up stuff and I strive to get ± 3% on part throttle, closed loop tuning of LTFTs. Trying to get closer than that and you'll just chase yourself into frustration...and waste a lot of time erasing and burning PROMs.

[XfireZ51]

Originally Posted by Hib Halverson

Couple of comments here...

1) NGK 5 heat range is too hot for any LT5 other than show cars which are only driven on/off trailers. Use the NGK 6 or Denso 20 for normal use and NGK 7 or Denso 22 for aggressive street driving or occasional track use. When I owned "Barney", for the first few years I ran an NGK 6. From the late 90s to early 00s on I ran the Denso 20. The last couple of years I ran the Denso 22. Densos worked great in an LT5

2) I would not use plug readings as a basis for making decisions on long-term fuel trim, ie: BLM. First of all closed-loop operation likely does not color the plugs enough to offer useful information and secondly, pump gas has so many additives which erroneously color plugs such that whatever color you see is useless. That said, if you have a case where, say...six plugs are one color and two plugs are so black they are near-carbon-fouled, then you don't have a BLM problem you have an injector problem.

3) If you trust your O2Ses and don't have a wide band, ignore plug color and use the narrow band sensors. While I don't calibrate LT5s, I do calibrate various '96-up stuff and I strive to get ± 3% on part throttle, closed loop tuning of LTFTs. Trying to get closer than that and you'll just chase yourself into frustration...and waste a lot of time erasing and burning PROMs.

Thanks for the comments Hib. Appreciate u following this. I was using the NGK 5s based on the ground strap coloring. I’ve recently switched to the Autolite 3924 plug which has an extended nose relative to the NGKs. The extended nose actually is a “colder” plug than the 5 altho its about the same heat range. I can tell u the motor idled smoother and got measurably better mpg than the 5s. That could have been a function of the “new” plug, but the BKR5E-11s didn’t have more than 1k mi on them either.

I do use ZT-2 WB which is always in the car. So I watch that but only use the WB for WOT tune. I tune PT in C/L, so I datalog quite a bit, and agree that when shooting for BLMs I’m using a +/- 3 count window. So anything between 125-131 average is good. Of course the LT5 has the same issue as the LT1s did with right/left, Lean/Rich fuel distribution. Bigger cams tend to exacerbate that.

I do trust the O2s. They’re AC Delco, and they are new. Changed them out to make certain. Had ACs there to start. The cylinders I was concerned w mainly are 2&4 where the plugs were tending towards a shiny black, not sooty. That suggested oil to me, not injector. I did OHM the injectors, which of course is not conclusive but nothing overt was indicated. That’s why I decided to pop the top and look at the IHs and plenum. The pics I posted show oil surrounding the intake runner area and the trail leading back to the crankcase vents in the head.
Concurrently, I was also chasing a “random” knock issue at a steady cruise in the 1800-2200rpm range. Now I suspect the two issues are related, with oil seepage being the culprit for the knock.
However, as I posted earlier, I will be having injectors flow tested just because of the “while ur there” rule.

[Hib Halverson]

Even if you could read plugs accurately with today's pump gas, you'd absolutely not use the color of the side electrode as your benchmark. Also, you can't read plugs by driving around on the street mixed with WOT pulls.

To properly "read" plugs you need 1) a good spark plug viewing tool, 2) a fresh set of plugs, 3) a hard pull in third gear with a clean key-off (but NOT key-lock) at the top end and after you coast to a stop, pull some plugs and 4) look at the area down in the body of the plug...the insulator below the tip of the center electrode and the inside wall of the plug body. If you want to actually do that, you need to run some 100-oct unleaded race gas. That stuff will color plugs accurately.

You need to run a plug at least as cold as the NGK 6 or Denso 20 heat ranges.

As for data logging...I'm a little confused because you keep talking about BLMs. Are you tuning for part throttle closed loop or WOT open loop? If the latter, forget BLMs and use your WBO2S.

As for random detonation at part throttle...If you hear the engine rattling while it's in closed loop then either EST is f**ked-up somehow or your getting so much detonation, that KR is maxed. First thing to do is determine if what you hear is false knock or real detonation. The solutions to each are quite different. When the motor is rattling have you been logging data? If so, what is KR doing when that happens?

Spark plugs which look shiny black are from cylinders which are using oil and if the engine has some cylinders that are using enough for you to notice it shortly after a plug change, then there's a problem somewhere...as you apparently have decided.

Lastly, as you suggest, oil ingestion can cause detonation because oil is really low octane.

[XfireZ51]

Injectors are off to be checked. Meanwhile, I will be trimming IH gaskets and mounting on cylinder heads tomorrow. Then plenum gaskets go on to get trimmed if needed.
Installed new knock sensor from Rock Auto. Think I snagged the last one.

[XfireZ51]

Thx Hib,

Yes I’m datalogging because I do part throttle tuning in Closed Loop. So I use BLMs. Really can’t move onto WOT tuning until part throttle is nailed down. Besides, we spend 98% of our time in part throttle.
If u view prwvious posts u’ll see evidence of oil migrating from crankcase vents to intake runners.

[XfireZ51]

UPDATE:

IHs are bolted on. Waiting on injectors. Should hear something on them Monday/Tuesday. I did Permatex the crankcase vents on the cylinder head to stop oil migration under the gasket to intake runners. May be a PITA to scrape the gasket off next time but I’m hoping that’s a ways away.

[Ccmano]

Who’s testing your injectors? Local or did you have to send them off?
H

[XfireZ51]

Originally Posted by Ccmano

Who’s testing your injectors? Local or did you have to send them off?
H

Sent them off to Portland. One of the people from ThirdGen has a shop.