NFB: What would cause both banks to show running lean at once?

[Dave M]

My mom's 2000 Ford Ranger (4.0 V6) is showing codes for Bank 1 and 2 running lean. What is the most likely cause to have these two codes at once?

[Joe 1320]

Abnormally low fuel pressure, faulty throttle position sensor, faulty MAF, faulty coolant temperature sensor, severe vacuum leak or any combination of the above.

[Jeff_in_Atl]

Abnormally low fuel pressure, faulty throttle position sensor, faulty MAF, faulty coolant temperature sensor, severe vacuum leak or any combination of the above.

I read this earlier and because I am really tired I didn't think of anything but Joe just jogged 1 brain cell loose. I have seen many fuel injected Ford to have fuel starvation problems from a clogged fuel filter. I know a guy who carries a spare filter with him.

[Dave M]

The truck seems to running fine, except for bad gas mileage. I suspected fuel filter too. If it was the MAF or a vacuum leak I would think the truck would be running poorly.

[Christopherrr]

I worked on a 4Runner with a lean code in both banks...

Obviously, I started out filter...didn't work. Did a nitrogen smoke test, found a small vacuum leak at the TB...didn't work. Finally decided on a MAF...fix it. I tried cleaning the MAF first but didn't work either. Other than the SES, the 4Runner ran like champ...so eh.

I would definately start out with the cheap fixes first...

How many miles do you have on the Ranger?

[FTA1995]

I;m guessing both indicated lean at the same time?

Its probably one of what Joe said, someting to do with fuel delivery.

[Dave M]

There are about 123,000 miles on it. I don't know off-hand its maintance record. I might have the records somewhere.

[FTA1995]

Maybe the O2's are contaminated. use any rtv sealant on anything recently?
anything else that could damage the o2's at the same time?
Check those sensors I say, but just go with fuel pressure/volume for now. It still could be something else though.

[Wild Willy]

My first guess would be fuel delivery, clogged filter, or, at that mileage, clogged injectors-

Next would be an air leak- you're correct in that a vacuum leak would probably make it idle poorly, what about an air leak in the exhaust? That would make the O2 sensor see excess oxygen, thinking that there was a lean fuel condition-

How does it idle? Steady, at low RPM's, or does it surge and hunt?

[Jeff_in_Atl]

Now that I have had some sleep the brain is going a little better.

Another problem Fords and that engine specifically have is the idle air bypass valve gets carbon in them and get stuck. Usually they stick closed and cause a rough rich idle but I don’t see why they couldn’t stick open and make it run lean off idle and still idle ok. I guarantee if you took it off and cleaned it that a ton of carbon crap would come out.

[Trash man]

Dave - its the MAF sensor, for whatever reason they get dirty, happed on my dads 96 3.8L Thunderbird and now has happened on my moms 02 Explorer Sport (4.0L) they make a MAF cleaner, and you will need tamper Torx in a 6point to get the sensor off. almost every ford i worked on that had this problem was the sensor


the one exception is when my dads headgaskets blew on the thunderbird

[Dave M]

It seems to idle and run fine, and I can't detect any exhaust leaks with my highly calibrated ears. I'm leaning towards fuel filter/injectors, or MAF. Nothing has been added that could have contaminated the O2 sensors. I'll definately try cleaning out the throttle body and IAC too, as that's the cheapest fix. My mom doesn't drive the truck much, especially in winter. So it'll probably be a spring project to track down the problem.

[Trash man]

It seems to idle and run fine, and I can't detect any exhaust leaks with my highly calibrated ears. I'm leaning towards fuel filter/injectors, or MAF. Nothing has been added that could have contaminated the O2 sensors. I'll definately try cleaning out the throttle body and IAC too, as that's the cheapest fix. My mom doesn't drive the truck much, especially in winter. So it'll probably be a spring project to track down the problem.

go to napa, get MAF cleaner (CRC makes it) and clean the maf and crack open a beer and enjoy