'94 4.0l running rich

[RonD]

My 1994 Ranger 4.0l 4x4 manual has been using more gas than usual for the last few months and it seemed to be getting worse.

Checked the usual suspects, cleaned MAF and checked Fuel Pressure regulator(FPR).

Plugs looked good, a little rich looking though, a little browner than normal.

It has 300k with original O2s so I bought a pair...............without actually checking them.

Changed the drivers side, wasn't seized, tight but came right out(22mm wrench).
Went to do the passenger side.............damn thing was 1/2 way unscrewed, lol, took it off the rest of the way with my fingers!!!

So there was the MPG drop, the loose O2 sensor would allow air to be sucked in, right next to the sensor itself, computer sees this as higher oxygen content(lean) so adds more fuel, the more it came unscrewed the richer the mix got.

If it finally came out I would have heard the exhaust leak, lol, but I would have gone broke putting gas in it until then

So I have 2 new O2 sensors installed and 2 used with only 300k

And hopefully better MPG

 

[Andy D]

Good news, The Rat doesnt qualify for emissions because it is OBD1 . It starts great and runs fine. Highway mpg is about 21. But I mostly putt around town in it.O2 sensors can be checked with a voltmeter. .9 is rich. .2 is lean. .45- .55 is the null state. the meter should dither between .2 and .8 rapidly. I did this dance a decade ago. and haven't needed it since, so I'm hazy on the details I pierced the wires to the O2 with a needle and clipped to that with a jumper.Other wire to ground, IIRC. It was a 4 wire, 2 whites were the heater,1 wire was the signal and the other was a drain. This was on a 528e back in '03 when it flunked dyno smog with too much NO2 So I did some on line research and found a Bosch site that tediously explained how to test with a torch. I thought of the sewing needles and live testing on my own. I had previously used needles to find a blown fusible link even further back. If your OCD about it there are all sorts of goo to cover the holes. I replaced the original 4 wire sensor which sold for 110 bucks on order or a 3 wire for a 93 Mustang 5.0 for 45$ out the door at the nearest store. I cut the wires off the original and the the new one and butt spliced the it to the BMW molex type plug. The drain is German overkill. If the exhaust isnt grounded, then neither is some much more essential stuff. But it was no trouble to clamp it to the body of the sensor either. A little bit of cut and paste to save 60$ after I spent some time learning. After this, I lost all fear of EFI in the 528e. The EFI in the 4.0 is very similar, the injectors won't match the impedance of the Ford, but the pintles and O rings fit the Bosch injectors and the big 6 guys use 5.0 injectors as an exact replacement. So I'm pretty much happy with that stuff, because it is a very bullet proof system. EFI is so much better than carbs because it doesnt need much for hundreds of thousands of miles . Carbed engines didnt last that long because they were carbed. Less is better with EFI maintenance. They're no big deal to work on, but they rarely need anything.

 

[RonD]

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