Well the title pretty much sums it up. I have a friend of mine that just recently purchased a 98 4.0 OHV with 207,000 on the clock. The truck runs great, but the CEL is on. The truck is throwing both the PO171 and PO174 codes. Bank 1 and 2 running lean. Well, for starters I jumped on the forum to see where we could begin. To start, we checked the vacuum lines. Everything looked pretty good. Then we replaced the upper and lower manifold gaskets. No change. Still throwing the codes. Then replaced the MAF sensor. What do you know, still nothing. I've heard some speculation that there could be problems with the o2 sensors or possibly a fuel pressure issue? I mean I have no clue.. What do you guys suggest we do next? He needs it to pass inspection, and as we all know, you can't have that done with a CEL on. Thanks in advance for any advice!!

 

Bump. Anyone?

 

Try the heater controls. Does the air only blow out the defrost vents?
If so, there is a vacuum problem. Probably a crack or hole in the vac reservoir .

 

Thanks! We'll give that a shot. Anyone else have any other ideas?

 

If you have a vacuum leak the idle will be very shaky, bigger the leak the worse the idle.


O2's are a maintenance item along with plugs and wires. If these parts have age they needed to be replaced regardless of codes.

Check the fuel pressure, could also be bad injectors with that mileage.

 

It does not shake at idle so i dont think it is a vacuum leak, but could the 02 sensors having alot of age on them cuase them to throw the cel on? oh yeah, this is the guy with the ranger, i just joined the forums