1992 Ford EXPLORER4X4 4.0 5MILES A GALLON DARNIT

Retrieving codes requires building a test light and connecting it to the test connector under the hood. I don't remember which terminals. You're better off having them read with a code reader. Many auto parts stores will do that for you for free. You're going to find they aren't as informative as on '96 and newer models. Start by looking for a misfire. When there is a misfire, unburned air and fuel goes into the exhaust where the unburned oxygen is detected by the O2 sensor. That tells the computer the mixture is too lean and it should add more fuel to all cylinders. Regardless how much fuel is added there will still be that unburned oxygen being detected in the exhaust. You can see this by viewing live sensor data on a scanner. The fuel trim numbers will be very high positive meaning it's adding fuel to the pre-programmed values. A similar problem can occur if there is an exhaust leak ahead of the oxygen sensor. Between the pulses of exhaust gas the momentum creates puffs of vacuum that draws in outside air where the oxygen is detected as a lean condition. If your engine uses a MAP sensor, check the vacuum hose for leaks. Fords use a MAF sensor to measure incoming air volume but a MAP sensor with a vacuum leak will tell the computer you're under heavy acceleration and the engine needs more fuel. A failing sensor can cause that too. As long as the MAP sensor's signal frequency remains within acceptable limits it won't set a fault code even though those values are wrong.

Doc, I have limited experience with a o2 sensor--I installed one right behind where my headers connect to my exhaust, At 1st, I used it with a voltmeter set on Millivolts, then I got me an Air/ Fuel Ratio Gauge (it's much EZer to see the Red, Yellow, and Green Lights bouncing around, than to watch a Digital Voltmeter)---I used this set-up to Jet My 4 bbl carb (looking at plug colors during "Plug Cuts", just wuttin'-a-working for me), as it all looked the same Between too Rich and Too Lean, YES I know a carb will not hold a candle to computer operated injectors, But this did get me THE BEST BURN I COULD HAVE AT 55 MPH!ON WITH MY STORY.I'm in the Ball Park saying.400--.450 MV, Or 14.7:1 Air/ Fuel Mixture, on a voltmeter is "Stoich" Or PERFECT BURN IN A PERFECT WORLD, "maCGOO's" EXPLODER, has a COMPUTER, Which really should keep his burn near this, CORRECT? If he were to shove a Open safety pin in beside his "SENDER" Connector/ wire at the O2 Connector (I'm sure his is heated, mine was is a single wire, not heated), then alligator clip a jumper wire to a voltmeter in the cab. Could he monitor his Burn to establish Too Lean (less than.400mv or Too Rich More than.450mv) This might confirm whether the O2's are working?---I have no clue, but maybe you could tell him what color the wire is to piggy-back on, in the O2 connector, and which O2 to get on, if not all, one at a time. The reason I mentioned this is My A/F Gauge really was designed to hook up to a computer vehicle.I guess just to watch the Yellow band of lights flickering at their lower end of the scale. If the burn was near perfect. NOW THEN, maCGOO, I'm stuck in the 80's on back, where real men own carburetors, IF caradiodoc SAYS---CJ MEDEVAC IS AN IDIOT, DO NOT DO WHAT HE SAYS. LISTEN TO HIM, HE'S GOT THE EXPERIENCE WITH THE NEW STUFF. I've fixed all of the JEEP CJs in the U.S, no more showing up in the CJ Forum yet, I'm sorta bored, that's why I came over here, to bother Ya'll---THE MEDIC. Tachometer top of column, Air/ Fuel Gauge on right of column, down from key switch----O2 sensor on exhaust, My Holley 390 4bbl on my 258--6 cylinder

The horns are bigger than the engine, ... Cool! It would be nice to see what the O2 sensor is reporting. If it's reporting a too rich condition, the computer can't control the extra fuel entering the engine. (That would be high fuel pressure or a leaking injector). If it's reporting a too lean condition, it is seeing the unburned oxygen that is entering the exhaust with the unburned fuel that is evident at the tail pipe. That would be typical of a spark-related misfire.