Excess fuel consumption and check engine light on '92 4.0L Ranger

['92Custom]

1992 Ford Ranger 4.0L OHV

For the last year or two I've been getting 17.5 MPG almost every tank (mixed city/highway). Lately I've had an intermittent check engine light that shows up after the engine is hot, and fuel economy has plummeted to around 10-12 MPG, which is bad enough to make me miss my old 460.

Yesterday I ran diagnostics key on, engine off, by jumpering the connector under the hood to get the codes to flash on the dash. I also tried to get the codes to flash with the engine running, but for some reason that wasn't working (ran the engine for 2+ minutes, shut off the engine for 10 seconds while adding jumpers, then restarted the engine - no flashing CEL).

KOEO, I got code 173 and 179, both of which relate to the O2 sensor which to my knowledge has never been replaced (~132k miles). I replaced it with a direct-fit Bosch unit from Auto Zone and went for a test drive. Apparently nothing changed because the light still came on.

Now I'm headed out to check the codes KOEO again and see if they are the same. In the meantime I have two questions if anyone can help.

1) do the codes 173 and 179 point to a different problem than the O2 sensor that I may have overlooked?

2) what am I missing to get the KOER codes?

 

[straycat]

When was the last time you did a fuel system cleanning/fuel filter replacement? Did you disconnect the battery for a few min. to see if that would reset the warning light? If not, try that.

 

['92Custom]

Just ran KOEO codes again and got 522 and 173.

I should mention I had a 522 the first time as well but disregarded it because it says I am not in neutral even though I am (manual transmission). So I always get a 522 code.

Code 179 seems to have disappeared, or maybe has not had time to resurface.

Tried KOER again with no luck. In case anyone is wondering how I jumpered it I'll attach a picture. This jumper arrangement works on other OBD1 Fords I've worked on, but for some reason the dash light won't flash the codes with the engine running still.

It still seems to be sucking gas, I drove 30 miles after replacing the O2 sensor and could practically watch the needle moving.

 

['92Custom]

When was the last time you did a fuel system cleanning/fuel filter replacement? Did you disconnect the battery for a few min. to see if that would reset the warning light? If not, try that.

I did an seafoam induction clean and fuel filter replacement last summer, about 8,000 miles ago. Yes, I had the battery disconnected for about half an hour while I swapped the O2 sensors.

 

[Andy D]

What do the spark plugs look like ? If it running rich, the plugs will show it. A week spark caused by a coil shorting when heated up ? Just a wild ass guess.

 

[RonD]

CEL after warm up could mean ECT is not working correctly.

The ECT(engine coolant temp) sensor is the "choke" for fuel injected engines.
The ECT is a TWO wire sensor, not to be confused with the ONE wire sender used for the dash board temp gauge.

The computer sends the ECT sensor 5volts, it then reads the return voltage from the ECT to determine if engine is cold(run preset rich mixtures with advanced timing) or warm(use O2 sensors to set mixture).
The computer has a timer for cold engine start, if ECT hasn't changed voltage after 5-10minutes of running then CEL will come on.

ECT problem would show up in two different ways.
1. good cold start and running but lower MPG as engine remains in "choke" mode after warm up
2. Poor cold start and running, but runs fine when warmed up, no "choke" mode is being run by computer.

ECT sensors rarely fail, not never just rarely, but they are easy to test with a volt meter or ohm meter.
Good read here on the ECT sensor
http://oldfuelinjection.com/?p=28

 

['92Custom]

Andy D,

I pulled a spark plug and it looks pretty bad. I'll go ahead and order a set, they looked new when I got the truck but that was about 22k miles ago.

RonD,

I will look into the ECT issue next.

 

[Andy D]

Change the plugs before throwing anymore parts at it , those are shot. Burming pretty clean otherwise though.

 

['92Custom]

Replaced the plugs with OEM Ford Motorcraft gapped at 0.053 and drove 3 miles to get gasoline to start a new tank for tracking purposes. 11.8 MPG on that last fillup, ouch!

Anyway, no CEL yet but I'll see what it does over the next couple days and what the new fuel economy is. If I still have problems, I may have to play "where was this connector supposed to go?" as I managed to find a few things under the hood which apparently have been disconnected since before I bought it. But then again, if it ain't broke...

 

[ZMan]

I had a similar problem last summer, I can't remember what codes I was pulling, but it was running really rich, I ended up replacing the MAF and it fixed it.

 

['92Custom]

Okay, after changing the plugs and putting 20 miles on the truck, both codes are back (173 and 179). Anyone have any experience with these codes? And I still haven't figured out how to read codes with the engine running.

 

[RonD]

I would clean the MAF:
http://www.therangerstation.com/tech_library/CleanMAF.html

MAF tells the computer how much air is coming in and at what temperature, so a big factor in fuel/air mix.

The 1992 might also use a MAP sensor as well as the MAF, check its vacuum line and connection, usual location is on the passenger side firewall, follow the vacuum line to find it, if so equipped.


Fuel pressure, computer doesn't read fuel pressure, it assumes it is 30-40psi.
If the Fuel Pressure Regulator(FPR) is not working then pressure can be higher so more fuel is coming in than expected.
Also check the FPR's vacuum line, if it smell like gas then the FPR's diaphragm is leaking and unmetered fuel is being sucked in to the intake.

There are three O2 sensors, the two that monitor lean/rich are on the exhaust manifold, one on each side, the 3rd, if so equipped, is after the cat converter, it monitors the Cat's efficiency in burning unused fuel, using levels from the front O2 sensors.

 

['92Custom]

I'm pretty sure mine only has one O2 sensor - it's at the Y-pipe upstream of the cat. I will clean the MAF and report back later today.

 

[RonD]

Yes, my bad.

Thanks to AllenD for this:
90-92 NON-Cali have only a single HEGO in the Y-pipe.

ALL 1993's (and 1994's) have dual-HEGOs one in each downpipe.

all '95-up have THREE (a cat monitor behind the cat)