So this morning I replaced my spark plugs as part of my preventive maintenance routine prior to the DGRR road trip. No issue with misfires, or anything else that persuaded me to change them out. Plugs are all standard NGK BUR 9's in leading/trailing holes, 2200 miles and just shy of 1 year of usage on them, primarily street driving with a bunch of short road tuning 3rd/4th gear pulls thrown in. This is a single turbo 13B-REW, running with a Link G4+ EMS, and I'm running pre-mix lube from a gravity feed tank, via the RA OMP adapter and the FD's OMP, managed by the Link. My pre-mix oil consumption rate as managed by the Link averages 1 ounce of pre-mix burned per gallon of fuel burned. This is based on long term direct measurements that I've been tracking.

Anyway, here's a picture of my plugs - I'm no expert, but it looks to me like perhaps I'm either running too rich on fuel and/or pre-mix? Though they still fire off well with my IGN-1A coils, there's more carbon there than I'd expect for such few miles? What do you all think?

 

How is your fuel economy?

They are a LITTLE dark, but IMHO spark plug color reading is kind of an old voodoo practice. If the car runs well, gets decent fuel economy, and AFR's are good where they should be, I don't see any concerns.

Dale

 

Fuel economy I've seen on a long highway cruise is between 20~22 MPG. Most of my driving since DGRR last year was much shorter runs though, with more stop & go - and those tanks will burn anything from 13~17MPG, depending on how boost happy I get with it.

 

the porcelain looks dark to me too, but the color is some kind of average weighted on how the engine was running in the last little bit.

the old timey guys would turn the engine off right after a run, so they (try) and get the color of like WOT

 

care to share an AFR datalog? they seem a little too dark for my liking. i can see why you would want to investigate it further.

 

Definitely not an expert, but they look a tad rich. You could have just been idling for awhile or so. I would just look at the logs. What is your idle afr?

 

Complete waste of time on a rotary engine unless starting with new plugs and doing the WOT shutdown, and even then you can only judge the plug heat range by the grounding strap discoloration per Howard Coleman’s comments on it.

Otherwise O2 and EGT sensors are required
.

 

Sure, here's a screen shot of my Lambda target table, and a snippet from a log that shows target lambda vs actual measured lambda from the WBO2 sensor along with a bunch of other parameters while cruising in 5th on the highway.





Measured lambda's generally stay pretty close to target while cruising, and I've got closed loop lambda (CLL) control active in this log. Still working on tuning the PIDs for the CLL control to get a bit less oscillation/better response.

 

Probably right, I'm just concerned by the amount of carbon showing after such a short plug life. Though like I said, the plugs were firing off just fine and I wasn't experiencing any ignition misses or breakup. I've got WBO2 fitted to the ECU, but no EGTs unfortunately.

 

not me; Daryl Drummond

IGN-1A was still firing this one at 30 psig @ 3.5mS dwell, installed by the previous owner and (shockingly) discovered when swapped out to NGK 7420-105


.

 

I cant say its too rich from your target λ, i mean .73λ the richest spot being 10.7AFR does not seem overly rich. My target λ is very similar actually but my plugs appear to be cleaner. Also a picture can be deceiving.

how old are the plugs? Where they used for initial startups prior to tuning?

 

Interesting. Looking at your datalog, if I am reading it correctly, you are running 1 bar of boost which is .84 Lambda or 12.3 AFR?

 

Nope, the Y axis here references MAP (Manifold Absolute Pressure), not manifold gauge or boost pressure (MGP), so that row you noted with 0.84 Lambda is basically the transition from vacuum to boost. 14.5psi MAP = 0psi MGP/boost = 1 bar (i.e., = typical barometric pressure @ sea level). But yes, for gasoline fuels, stoic = 14.7 AFR, so 0.84 Lambda = 12.3 AFR.

 

Plugs were just shy of a year old and had 2200 miles on them. These plugs were not used for my initial startups and road tuning, and I haven't made any significant changes to the lambda targets or timing tables over these plugs life. Though I have had to tweak the secondary FI staging parameters & acceleration fuel enrichment a bit to improve on the primary/secondary transition behavior over these plug's life. I was getting lean dips at the transition initially, made some changes that made it too rich at transition, and after a few iterations of tune/road test, I got the transition point to track target lambda reasonably well - at least well enough where CLL can add/subtract 1~2% it wanted to stay right on target.

 

Shifting gears on this topic a bit... After deep diving my logs to determine where my car spends the majority of it's time while cruising steady state and at idle, and considering the amount of carbon I'm seeing on the plugs after just 2200 miles, I'm thinking I can stand to lean out the lambda's a bit more in those regions. The question is, how much leaner would be safe, given that I have no means of monitoring EGTs?

Here's my lambda target table again, annotated to show where my FD target lambda's are at idle and steady state cruise. My idle is set to 900RPM warm, so that blue box is the idle region. I can get it to idle at a more OEM-like 750~800 RPMs, but I've found that the DBW setup I have doesn't like that - so I set a higher idle for drive-ability reasons. The yellow box is the region where my FD finds itself in a steady state cruise most of the time.




I'm thinking I can bring the 5.8psi MAP row in the yellow box up to stoic, (1.000 Lambda), and do the same with the 8.7psi MAP row in the 1500 to 3000 RPM cells. Don't change anything in the 5000RPM column & above, and don't change anything in the 14.5psi MAP row & above (i.e., boost). Then do a vertical linear interpolation for the 11.6psi row cells from 1500-3000 RPM, and a horizontal/vertical linear interpolation for the remaining idle region cells and border cells adjacent to the 5000RPM column

 

I think that should be fine. Here's the lambda table I've been using on my mostly-stock car for about 7 years, 7000 miles including a few autocrosses, a few long drives, and an HPDE day. I don't have an EGT sensor, but I've heard that hot EGT numbers aren't as much of a problem at light load because there is less airflow. In other words, high heat and high flow would be more of a problem than high heat and low flow.

 

Thanks, that puts my mind more at ease. You're even running a little bit leaner than I am at the 100kpa/14.5psi MAP row (0.88 vs. 0.84 lambda), where it transitions from vacuum to positive boost.

Even though I don't have EGT sensors fitted, I had a thought on a simple test I could run to estimate if my EGTs are increasing or decreasing after making the lambda changes. Idea is to use my cheap IR non-contact digital thermometer to measure the same spot on the down pipe or the turbine housing before & after changes. If you setup your test procedure so the before & after samples are taken over very similar conditions (e.g., drive at steady 70MPH over the same stretch of interstate for the same period of time, pull over & quickly take your measurement), you can infer if the EGTs are going up or down by measuring the relative temps of the DP or turbine housing. Could do this on the way to DGRR this year.

 

the stock ecu would run 1.0 from ~1100rpm to 3200rpm OR 1psi of boost, so you should do that for sure