Error Code 306 - `97 Explorer

The techs flip chart is lacking...... I can't see a catalytic converter affecting one cylinder only (one bank, perhaps, but not one cylinder). Other things... faulty fuel injector or wiring, compression, coil, valve spring....

I'd start with inspecting the plug wire.... check inside the boot for carbon tracking, pull off the coil end and inspect the inside of the boot and the coil tower for carbon tracking. Test the wire with an ohm-meter...... I would expect to see 4000ish to 9000ish ohms. Remove the spark plug.... look for fouling, carbon tracking - especially on the outside porcelain. Test the compression... without compression, nothing else is going to matter.

Once we know the basics are good, we can start looking further afield. I wish I had a dollar for every time someone has thrown vast amounts of money at something only to find out that there wasn't enough motor left to fix....

Jim,

Not to argue with your expertise, which is a thousand times superior to mine, I have to point just one thing from my experience (and possibly training as an electrical engineer): Obviously, out of range resistance indicates a problem, but an OK resistance reading is nowhere near a guarantee that the wire is good. All kinds of 'interesting' things can happen at 20,000 Volts that this measurement can't tell you about. In my case (a failure at 35,000 miles, and another one at about the same age, of a replacement wire; both OEM), the problem was not an open connection, but insulation failure. This apparently caused arcing somewhere, but I could not see any evidence. The 'proper' way to diagnose this is to scope the ignition, and if a problem is found on just one cylinder, replacing that wire and retesting. A short cut for someone who has no access to an oscilloscope could be to swap the wires between two cylinders, and check if the failure follows the wire (last digit of the code matches the cylinder where the suspect wire was moved to).

I guess I could have been a bit more clear on the "inspect wire" part..... What we're looking for, along with cuts and abrasions, is "lightning strikes" - some of these are very obvious, some aren't. Using a scope is no guaranty of finding faulty insulation. At idle, required voltage (the pressure required to ionize the spark plug gap) is much less than required voltage at a wide open throttle romp. The first gap to ionize will be the gap requiring the least voltage. At idle, this may be the spark plug gap - under load, it may be an "unauthorized" gap somewhere else in the system.

A "poor mans" insulation test is to have someone perform a brief stall test on a dark night while watching the engine compartment (disable the underhood lamp, first). Bear in mind that there are no transmissions that enjoy stall testing. The heat built in the torque converter is astounding...... Any stall test should be followed by a couple of minutes of high idle in neutral to remove heat from the converter.

Jumping into the wayback machine with Prof Peabody (if you can remember that, you're in trouble), we return to my youth. First I must point out that we are talking breaker point ignition, here, and available voltage was much lower than what we see now. We took a 100 foot roll of bulk spark plug wire and ran it out to the parking lot and back leaving several feet between the two lays to avoid any EMF induced activity. The wire was the usual Hypalon insulated, carbon impregnated cotton core wire that we used then. Good quality connectors and boots were installed at the distributor cap and plug. I can't recall what we measured with an ohm-meter (other than we did indeed have continuity), but the scope pattern looked exactly like the other cylinders in the motor. Bear in mind that a resistance indicates some kind of continuity where a gap is a gap and no resistance can be implied.

Without specialized equipment, we are reduced to other methods. Admittedly, some of these methods aren't as good as what's available but they suffice. Some of the testing available isn't going to mean much to most observers without specialized training (good ol' Catch 22). We have to remember that there are those coming to the NG because they are cash strapped and shop time can mean the difference between Kraft dinner and hamburger. Others are trying to save money now in order to prepare for their golden years. For whatever reason..... I can't see overspending on a repair nor can I understand underspending on a repair.(what with the chance of repeat failure).

I realize that many don't have experience in my area of expertise (but I'm smart enough to know that they have expertise that I can only dream of in other areas) and I try to keep stuff simple. One big problem involves those actions that have become "unconscious"..... I do them without thinking about them and forget to tell people that I do them.... I document everything on the back of my RO..... if I don't think real hard, I can "perform" the diagnosis and repair in a half-dozen lines of text. If I itemize every operation, I can produce reams of paper....