Chasing lean codes

[numbnuts240]

ok, this isn't for a nissan. but problems and codes are generally universal.

my 99 explorer with 4.0l v6 (vin x/ohv) 188k miles, is throwing lean codes for both banks p0171 and p0174. i'll provide some background info:

the exhaust terminates with a turn-down right after the downstream o2 sensor after the cat.
the codes originally came one leaving a scrap metal yard, which was wet and muddy.
at the time, the exhaust pipe was maybe an inch long after the o2 sensor.
the sensor was sprayed with cleaner and a turn-down end welded on.
i've experienced hesitation from time to time. there was one day when it was prevalent on the highway, 4hi engaged during a rather crappy commute. beyond that, maybe once a week. feels like a big jerk.
i cleaned the maf to no avail.
i sprayed carb cleaner around the intake manifold and didn't get any change in idle.
i've hooked up a scanner on 3 different occasions. 2 out of the three showed higher than normal fuel trim levels.

the 2 higher readings at idle:
long term bank 1: 5%
long term bank 2: 3%
short term bank 1: 0%
short term bank2: 0%

at 2500rpm:
long term bank 1: 9%
long term bank2: 7%
short term bank 1: 0%
short term bank 2: 0%

long term values increase when i step on the gas sharply. they also increase letting off the throttle after holding at 2500rpm

o2 sensor values at idle:
o2 bank1 sensor1: 0.7v
o2 bank2 sensor1: 0.7v
02 post cat: 0.2

o2 sensor values at 2500rpm:
o2 bank1 sensor1: 0.7v
o2 bank2 sensor1: 0.7v
o2 post cat: 0.13

my next test is to test voltage at the maf. i don't have a fuel pressure tester, which i can get, but i want to rule out everything else before i go that route. i'm hoping someone here has some insight of things to look for or check.

[numbnuts240]

oh yeah, fuel filter and pcv are new. seafoam treatment was done as well (oil, fuel, and vacuum)

[frapjap]

Did you clean/replace the plugs after running seafoam through your engine? That stuff fouls them out like crazy. Same with your 02 sensor. In my experience you can clean the 02 sensor, but a new one is better since if the problem persists, you can rule out another variable.
Plus, they're not all that expensive.

[numbnuts240]

plugs were replaced after seafoam, same day. all the tune up stuff was done back in november. the codes have just popped up within the last month. i'll be putting a multimeter to the maf tonight and testing voltage.

[PapaSmurf2k3]

You typically want a good bit of exhaust piping after your O2 sensor so it doesn't pick up regular air and read lean. I'd suggest you either move your O2 sensor up the exhaust pipe, or extend the pipe after the sensor.

When you pull the plugs, does it look like they are actually running lean, or rich? Is your gas mileage better or worse?
You could also try hooking up to an exhaust sniffer and see if you're running lean (higher NOx values), or rich (higher HC values).

[numbnuts240]

i have not pulled any plugs yet, but i will tonight tonight. i was able to test voltage on the maf and everything checked out. i hooked up a fuel pressure gauge yesterday and here's what i saw:

koeo: initial pressure around 45psi, steadily dropped to just over 20psi over the course of a beer.
koer: pressure steady at 60psi, loses pressure with throttle application.

[numbnuts240]

btw, gas mileage has been failry consistently in the 14-15mpg range. i'm not gentle on it

[PapaSmurf2k3]

Weird, usually fuel pressure regulators work the other way - they add pressure as throttle is applied.
Who the f*** knows with that candy van though.

[numbnuts240]

'tis very strange, indeed.

[PapaSmurf2k3]

Ever get a chance to pull some plugs?

[numbnuts240]

i have not. weather and other obligations (gf) have kept me pretty busy this week. i'm "single" tonight and tomorrow night, so possibly then.

[numbnuts240]

plus, i'm a little apprehensive about touching the plugs. it was a spark plug change that required me to dump the last exploder.

[PapaSmurf2k3]

Oh. Spray them with PB now and wait a day or 2, then pull?

[darylzero]

ok, this isn't for a nissan. but problems and codes are generally universal.

my 99 explorer with 4.0l v6 (vin x/ohv) 188k miles, is throwing lean codes for both banks p0171 and p0174. i'll provide some background info:

the exhaust terminates with a turn-down right after the downstream o2 sensor after the cat.
the codes originally came one leaving a scrap metal yard, which was wet and muddy.
at the time, the exhaust pipe was maybe an inch long after the o2 sensor.
the sensor was sprayed with cleaner and a turn-down end welded on.
i've experienced hesitation from time to time. there was one day when it was prevalent on the highway, 4hi engaged during a rather crappy commute. beyond that, maybe once a week. feels like a big jerk.
i cleaned the maf to no avail.
i sprayed carb cleaner around the intake manifold and didn't get any change in idle.
i've hooked up a scanner on 3 different occasions. 2 out of the three showed higher than normal fuel trim levels.

the 2 higher readings at idle:
long term bank 1: 5%
long term bank 2: 3%
short term bank 1: 0%
short term bank2: 0%

at 2500rpm:
long term bank 1: 9%
long term bank2: 7%
short term bank 1: 0%
short term bank 2: 0%

long term values increase when i step on the gas sharply. they also increase letting off the throttle after holding at 2500rpm

o2 sensor values at idle:
o2 bank1 sensor1: 0.7v
o2 bank2 sensor1: 0.7v
02 post cat: 0.2

o2 sensor values at 2500rpm:
o2 bank1 sensor1: 0.7v
o2 bank2 sensor1: 0.7v
o2 post cat: 0.13

my next test is to test voltage at the maf. i don't have a fuel pressure tester, which i can get, but i want to rule out everything else before i go that route. i'm hoping someone here has some insight of things to look for or check.

This guy is really good, knows his stuff. here is one video about a lean code. he may have other just have to search through.
maybe this will help

[numbnuts240]

well after doing some research and comparing my test results, i decided that fuel pressure was obviously an issue. the pump was priming and holding the correct pressures according to factory specs, but that drop of pressure upon throttle application was not normal. model year 99 and newer got fuel pressure regulators attached to the pump and level assembly in the tank, with a fuel pressure damper on the rail. i swapped out a new damper because it was easily accessible, cheap, and didn't require dropping the tank. if i'm wrong, my fuel level sending unit needs to be replaced as well, so i'll go for a full assembly change.

about 275 miles later, and the light remains off. i'm going to fill up again with a bottle of fuel system treatment and see how it goes.

[frapjap]

Hope its an easy fix!

The 02 would be easy, too. I still think its worth a shot.

[PapaSmurf2k3]

Or you could just hook up the pressure gauge and see if you still get decay.

[numbnuts240]

just an update, i hooked up the fuel pressure gauge last night and the loss of pressure with throttle application is gone. well it does dip for a quick second at first before going right back up to normal pressure, but that's to be expected.

lean condition: solved.

[numbnuts240]

update:

lean codes returned. swapped out the fuel pump/fuel pressure regulator/fuel level assembly over the weekend. also cleaned out the tank while i had it out. so far only 90 miles after new parts so we'll see.

after taking out the pump, it was obvious why the fuel level wasn't reading at all. the ;level sensor was just dangling there, only attached to the assembly at one of the two attachement points. it's a bittersweet fix. on the bright side, i can actually watch the needle drop as i burn fuel. on the downside, i can actually watch the needle drop as i burn fuel. part of me misses the days of a perpetually full gas tank.

[szh]

part of me misses the days of a perpetually full gas tank.

On the other hand, I think it would be better than getting stranded after running out of gas. I had this happen to me in my 2003 M45 - issue was taken care of by a recall - where the fuel gauge read high even though it was close to empty.

I ran out of gas in the fast lane during commute traffic - was doing about 40 to 45 mph at the time. Car started stumbling and then the engine shut down - had to put the car into neutral to be able to "coast" across three busy lanes to the shoulder! Kinda unsafe!

I had been driving on a freeway the prior day on a longer trip, so my mileage was high enough and I thought I had gas left! Yikes ...

Z

[numbnuts240]

I did the math based on the size of the tank and actual mpg after a fill up. I knew I could get slightly more than 300 miles per tank, so I made sure to fill up anywhere between 250 and 275 to be on the safe side.

I totally didn't stop driving it at that mileage and waited until someone asked to borrow it only to inform them it needed fuel