Okay, I changed my spark plugs on Friday. I used exact replacements [AC Delco 41-128 Iridium]. Last time was about 11 months ago right after break-in. I did not expect to see them so dirty. As you can see, there is a reddish-brown coating on both electrodes and center insulator. There's also a small amount of evenly distributed carbon deposits around the rim and inside the well. All 8 plugs looked identical.
[Possible Cause - Torco Fuel Additive]
These kind of deposits are usually caused by octane boosters, from what I've read. This might explain why I first noticed the anomaly after using the Torco for a few months. Still, I'm not sure that's the cause of the engine cut-out. After all, I added the Torco because I felt like the engine was producing less power at the time. It could have been caused by a latent issue and just happened to appear at that time.
I suppose this could have been a factor in the engine cutting out but
why only at 5500-6000 RPM in 4th (once in 3rd) gear? I would think that fouled plugs would manifest at a range of RPMs in all gears.
[Alternative cause #1 - Fuel Pump Supply]
This still feels like a fuel flow or ignition system issue, though. From the
Weapon-X detailed explanation of the fuel system I wonder...
Could the low-side pump be failing to supply the HPFP at high load?
AFM issues that Weapon-X describes in his excellent thread could account for intermittent failures in 3rd & 4th gear at 5500-6000 RPM.
Quote:
Originally Posted by WEAPON-X
The Dangers:
...
"If the line pressure isn't force feeding the HPFP, the entire system will falter."
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Quote:
Originally Posted by WEAPON-X
Followup post:
...
"A lot of the mishaps are simply inadequate fueling. Once the rail pressure falls, it cannot recover until a shift and then is depleted again as the gearing is smaller."
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[Alternative cause #2 - Dirty Valves]
Could my problems be the result of "dirty valves"?
Direct injection (DI) lacks valve cleaning benefits of port injection... Even though the ZL1 LT4 employs a clean side catch can, the dirty side still recycles combustion vapors and vaporized oil from the crankcase into the intercooler where they can coat cooling fins, compressor blades, and valves.
Quote:
Originally Posted by WEAPON-X
How it works:
"Another drawback [of DI] is the lack of the fuel cleaning the valves, which on a parasitic PCV system like the GM OHV engines use, they use the engine to draw the crank case pressure though it to maintain seal life and longevity, at the expense of future performance if proper care isn't taken."
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If it were a simple matter of inserting a catch can in the PCV line I might consider doing that. However, for the LT4 motor it would require a warranty-breaking mod. I'm just not ready to void my warranty yet. I don't see another way to clean the valves other than taking the engine apart.
[Alternative cause #2 - Malfunction of NLS]
Could this be a malfunctioning No-Lift Shift (NLS) system?
I got to thinking about how it was completely loosing power off and on. Normally NLS cuts fuel and ignition when you depress the clutch at WOT. If this system were activated intermittently without pressing the clutch, this is what I would expect to happen. Even though I almost always run with the nannies off, such a malfunction could still occur.
Does anyone have any thoughts on these ideas?
--Cal
P.S. The car feels like it's got more power after changing the plugs. If this engine cut-out issue doesn't rear its ugly head, I'm hoping to see some improved times at the drag strip tomorrow. We've got a weather window and I'm trying out a different track.