Got a 99 e-350 with v10. Check engine light came on during smog test, and
I've checked the 02 sensors, they all say it's lean (.115v) , and the error
code was 0171 (lean). Tossed in fuel cleaner, disconnect battery to reset code,
and 60 miles later, check engine light came on . Need to get it smogged without
going bankrupt. Anyone?

 

Did the test show the O2 sensors were giving a bad reading? If so it means the sensors are bad and need to be replaced. I'vd had sensors go bad and it always creates a lean condition. When you run the diagnostic to check the output from the sensors the readings are not stable and fluctuate indicating the sensor(s) are bad.

 

After a little warmup, the sensors put out about .115 to 125 volts (all three I could find) and it seemed like a fairly stable reading. The vehicle runs a little rough at idle, and when I covered the air intake with a block of wood, the vehicle still runs, although runs even rougher. There was no error code produced during the session that indicated that the sensors were faulty, but they did read lean. I don't know how to tell if the vehicle is running lean for some reason, or the sensors just say it is.

 

Here is where obdII can fool you.But first you need to chk out the following
Make sure there are no exhaust leaks in the system.
fuel filter
fuel pressure
no vacum leaks (chk elbow to pcv system)
Intake gaskets leaking.
Bad wiring to the o2 sensors.

Now the pcm can fool you here,I've seen it many times before the first code sent to the pcm can be a rich dtc and the pcm adjust fuel trims far enough the other way to go lean.Just be aware of this when looking for causes to the code.

Rich

 

Are you showing lean codes in both banks? I've had that happen - cheap FRAM fuel filter failed. Replaced, reset, no problems... might be worth a shot if its been a while for your F/F.

 

I tried replaceing the air filter a week or so ago, I'm not absolutley sure that there's no air leak, but I don't think so. I had the fuel filter replaced in October, and it appears they got the arrow going the right way. I replaced the O2 sensors just for kicks today ($200 of fun), and that wasn't it. Checked the PCV valve by pulling it off and seeing the the ball rattles. Sure would like some more ideas. Thanks again!

 

Clean the MAF (Mass Air Flow) sensor!

Then, check for cracked elbows/hoses on the PCV system, and then the rest of the vacuum hoses.

The MAF is the most likely culprit, after unmetered air (PCV system leak) ...

 

I had a mechanic claim he checked the Mass airflow sensor last week, but I'm not totally sure he did a good job. I've not tried it my self, but I may recheck his work if I get some instruction. I'm also on may way to check to see If I can hear any leaks with a sthethescope, but I've never done that before so we'll see. Thanks again!

 

To really do the MAF right, you need a set of "anti-tamper" Torx bits, they're the ones with the hole in the center to match the pin in the middle of the Torx screw.

Take out the two Torx screws and gently remove MAF (after unplugging it).

Clean with brake-cleaner. If it's really dirty, you might have to knudge it with a q-tip, but do so GENTLY.

But before you do anything, take a good careful look at it and see if the filaments are dirty on the side facing the air-cleaner.

Clean it, and if it still happens, you have un-metered air entering the system.

 

you reset the chk engine and it came back on instantly or did it take awhile after changing 02's?
you chkd fuel presure at the rail while running?(fuel pressure reg)
Does this truck fall on its face when given the go pedal?
What kind of air cleaner being used ?
What kind of scanner are you using to watch the 02 switching?
A maf could be it also as art suggests
could be intake o-ring gaskets also or a cracked intake.

Don't forget what I said about being fooled by the pcm.but too really see it you have have a good scanner that records more that the last dtc code being stored .

Rich

 

Thanks guys, here's an update.

After replacing the o2 sensors, it took about 40 miles before the check engine light came back on. That's been a typical delay between disconnection of the batter cable and the check engine light coming back on.

2) haven't yet checked (re-checked the MAF)
3)haven't yet checked the Fuel pressure at the rail
4) This things a beast and runs great when I step on the gas, there's no hesitation or stalling when I "put the coals to it", but it doesn't have all the kick it once did. I runs just a little rough at Idle.
5)Air cleaners a Fram, just replaced. I'm reasonably sure it's the right one. Engine stalls when I try to run without the air filter on (is that a clue, possibly?)
6) I had two separate guys with scanners tell me that it gives 0174, 0300, an 0171 in the log, but I didn't ever see a code that states the sensors themselves are damaged, anyway, the sensors were replaced today.
I checked all three of the old sensors by "back probing" while the vehicle was running, and they all seemed to give a steady reading of around 115 mV when warm, although this was a difficult test, and I got some readings that I didn't completely trust. I don't understand "open loop" mode of the sensor. Does that meen that when PCM doesn't trust the sensor, it ignores it, or shuts it down in some way?Anyway, I'm very confused about how the O2 sensors should behave, so I replaced them and the problem persisted.
7) I think I hear a hissing but It's not real loud, and it seems to be coming from somwhere not obvious( it's a van and its hard to get to anything). I'll have to try and figure out where the intake o-ring gaskets are and go after them next, since I don't have access to a guage for the fuel pressure, yet.

Thanks again

 

Okay A p0300 is a misfire counter,bad cop bad boot or plug.Thats a seperate problem from the lean condition.

Lean condition could be :
Look for the hose of the back of the throttle body thta goes to the pcv valve common is the elbow cracks and causes this problem.
Rich

 

Thanks, Rich, I'll check it out!

 

Thanks Fortyfords (Rich) that was awesome. It took me a while to find where the elbow from the PCV valve was, but when I got a sheild off for the throttle lever area, I was able to sneak my hand down there and feel a crack (big engine, the throttle body is amost touching the dashboard on this van). I've got a feeling that's it.

 

Can you take off the cowl inside? (the doghouse, some people call it)

That makes things SO much easier in a van...