Hey everyone. My 1998 ford expedition is throwing a p0171 code system too lean. Now I googled it and it seems like a common problem. Well I cleaned the maf sensor and no vaccuum leaks. Any other ideas? Engine is the 5.4l. Also spark plugs have never been changed !! 130,000miles
ford expedition p0171
- Thread starter finalyzd
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If you can put a live data scanner on it (or better, oscilloscope on the main O2 sensor) you can find if the O2 sensor needs to be replaced. But before doing that, I would do standard tune up and put a bottle or two of *good* cleaner in the tank (blocked injector can lead to P0171 too).
Also get the freeze frame data from the scanner. Comparing the data from the two banks of cylinders can provide valuable clues. If the problem is common to both the cylinder banks vs only to single bank, you can rule out some possibilities.
- Vikas
Also get the freeze frame data from the scanner. Comparing the data from the two banks of cylinders can provide valuable clues. If the problem is common to both the cylinder banks vs only to single bank, you can rule out some possibilities.
- Vikas
Those plugs don't owe you anything at 130k miles. That's a cheap maintenance item and well worth it in this case, IMO. A good injector cleaner like Redline SI-1, Chevron Techron Plus, Gumout Regane, etc. could help also, as Vikas suggested. If it's been a long time since you did anything like that, you can use 2 bottles in the tank no problem. The P0171 code means it's bank 1, which is the side that has cylinder #1.
You could have an exhaust system leak, bad O2 sensor, intake manifold leak, or the problem might have been fixed with the MAF cleaning but hasn't gone away yet due to not enough drive cycles. Have you cleared the code and it came back? When you switch the climate system from blowing out the defroster to blowing out the floor vent, does it change pretty quickly?
You could have an exhaust system leak, bad O2 sensor, intake manifold leak, or the problem might have been fixed with the MAF cleaning but hasn't gone away yet due to not enough drive cycles. Have you cleared the code and it came back? When you switch the climate system from blowing out the defroster to blowing out the floor vent, does it change pretty quickly?
I ran a seafoam treatment. Threw gas tank and vaccum line. I cleared the code 30 minutes later it came back. Before it would take a while to come back. I will hook up snap on scanner I have at work. Before I start throwing money at parts. Would a intake manifold leak cause a rough idle? Car runs smooth
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Check for a vacuum leak. Check the PCV hose; follow it through to the TB. And check the breather hose on the other valve cover.
It is probably the primary O2 on the right bank if you can't find a vacuum leak.
It is probably the primary O2 on the right bank if you can't find a vacuum leak.
I remember a PITA TSB on those early ones where tha AC evap drain would drip on the right O2 sensor and cause codes and driveability problems.
It was always nice to have the proper scan tool to look at fuel trims when diagnosing an O2 code. There is always one sensor weaker/slower than the other. If there is a vac leak/MAF concern/fuel pressure concern, that weak O2 sensor will code first.
It was always nice to have the proper scan tool to look at fuel trims when diagnosing an O2 code. There is always one sensor weaker/slower than the other. If there is a vac leak/MAF concern/fuel pressure concern, that weak O2 sensor will code first.
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