I've had a wideband 02 setup for years, but a recent dialogue with Paul Abbott of Performance Oriented and a review of his excellent web site prompted me to try the old Gunson Colortune setup I purchased a couple of years ago. For those unfamiliar, a Gunson Colortune consists of a spark plug with a quartz window in it through which the combustion event can be observed. Blue= stochiometric, yellow= rich, spark only= so lean you've cut the fuel off.
I think the nice chaps at Gunson designed this for the Spitfire or something, where it was simple to install and observe the plug. For a 911 engine it is the bloody devil.
The kit consists of:
-The plug itself. Rather than having a 21mm head like our normal plugs, the head is like 17mm. I suppose this is for compatibility with virtually every internal combustion engine on the planet, from an F1 car to a hit-or-miss Maytag engine. This means you can't use the elegant Klein articulating plug wrench to directly install the plug. . . instead they supply you with a. . .
- Plastic adaptor. This is a piece of conical plastic that the plug fits into, with a 21mm hex on the outside. You fit this over the plug to install it with the Klein plug wrench. But wait, there's a catch. If this adapter is installed, you can't see the quartz window in the plug, so you have to remove it. Except that in a 911 engine, it's down inside the fins of the head, and you can't reach down in there to retreive it, unless you have fingers like ET or something. (Note to our Millennial members: ET was this funky dude from outer space with HUGE freaking fingers that featured prominently in the 1982 film epic of the same name.)
Yep there it is all right, stuck on the plug with no way to get it off. Somehow I flicked it off there and it fell into the valve cover and I retrieved it. So I drilled a couple of holes in the perimeter and ran some safety wire through there, which was able to be fished through the Klein wrench at the joint and then out through the spring, so you can remove it when you have to install the NGK plugs. This seemed to work fine.
The adaptor does NOT prevent the plug from falling into the engine when the wrench is inverted, however. For that, I turned to the old Standby. . . Bosch Distributor grease. If the Apollo 13 guys had a tube of this stuff the mission would have been over in half the time. A copious application of grease to the hex of the plug stuck it into the adapter long enough to get the threads to bite.
-HV lead. Of course you have to get high voltage to the plug, so this is a fairly thin, plastic-coated wire that screws to the tip of the plug. This is installed AFTER the plug is in place. One would think you could use it to seat the plug, and in fact you can, but once you go to unthread it, you end up unthreading the plug. So practically, you must seat the plug with the Klein/Adapter combo, then thread this on. Unfortunately you are trying to match up about a 2mm male thread protuding from the top of the plug with a similar 2mm hole in the end of this six inch plastic-coated wire, and you can't see what you are doing because as I mentioned before all these operations take place INSIDE THE HEAD. Paul says you should gently countersink the end of the wire in order to make fitting it easier. That is a VERY good piece of advice that I will heed the next time I do this.
-Copper sealing washer. Unlike a $1.98 NGK BP7ES, the Gunson plug does not come with an integral, captive, steel washer. Instead you are issued with a 14mm copper washer that goes between plug and head. Can you see where I'm going with this? Being copper, it's not magnetic, so you can't retrieve it. Being separate from the plug, the first thing it tries to do is assert its independence and separate from the plug. Of course all this happens. . . wait for it. . .
. . . INSIDE THE HEAD. Gunson recommends that you use some "high melting point grease" in order to adhere the washer to the plug. I tried this, it separated. I tried distorting the washer into an oval, which worked going in, but when the plug was tightened down, the washer went round again, and fell off the plug, into the recesses of the head.
I would like to thank Steve Jobs (RIP) for having the foresight to put the camera on the corner of the iPhone so you can take photos like this to figure out what is going on:
This wandering washer resulted in removal of the starboard valve cover, just to retrieve it. Mmm, hot valve cover, should have brought some silicone hot mitts. I took the washer off an NGK plug and used that, and it worked perfectly. Over the side went the copper washer!
- Plastic tube and right-angle mirror. This can be discarded, crushed beneath your heel. Instead, use the iPhone. For a nanosecond I worried, "Should I be operating my iPhone this close to a 48,000V ignition source?" The Phone didn't seem to care, and after fighting with the Gunson I was about ready to buy a new phone if I zorched the current one, caution be damned.
-Cleaning Brush. The Gunson people thoughtfully include this if your mixture is about 6:1 and you fog over the quartz window. For now, I ran out of time and patience long before the view was obscured.
That is it for the kit. Once it's installed, it looks like this:
You start the car as normal and observe the flame in the plug. I was skeptical, but it actually works. You use your smartphone camera to look down there, and take videos and photos like this:
Where it gets interesting is once the engine is warmed up and you have established an idle, you can turn the idle mixture in quarter turn increments and observe the flame. You turn the screw all the way in (careful don't break it!) and all you can see is the spark, no flame. Turn it out a bit and you can see a white flame. Turn it further for blue, and even further for yellow.
(Remember the guy who, when school film strips were being screened, used to shout "Focus?" Don't be that guy, I did the best I could with these photos, on a hot valve cover, with 48Kv a centimeter away, with the engine fan trying to make Wurstsalat out of my sternum. The videos actually came out great but I can't post them here.
My understanding is that you want an alternating blue/yellow for "lean best" - it was fun to approximate "lean best" with the old, turn clockwise until RPM falls off, then turn back 1/4 turn-- that is pretty close to when the tester tells you you're in the blue/yellow region.
I need more practice, but was able to get things dialed in more closely. I still have lean popping at times, particularly under part-load, and have some rich surges (which show up as HUGE yellow flares in the video) that need to be figured out, but generally speaking, it's a worthwhile exercise to get cylinder-specific AFR information.
AND the springs on my idle screws are bottoming well before the cylinder cuts out. . . I may have the wrong ones. . .
Stay tuned for more. . .
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