1999 Ford ranger 4.0 throwing p0171 and 074 codes

[Matt1989]

Trying to clear these codes on my truck so I can pass my inspection and renew my registration asap so far I checked for vacuum leaks with no luck cleaned MAF sensor,cleaned throttle body , replace idle air control valve, replaced fuel filter, checked fuel pressure got a reading of 40 psi is it that to low? could I possibly have a bad pump ? Also noticed hole in my cat on the passenger side could this cause the code ? If anyone could help I'd appreciate it

 

[rhekman]

Trying to clear these codes on my truck so I can pass my inspection and renew my registration asap so far I checked for vacuum leaks with no luck cleaned MAF sensor,cleaned throttle body , replace idle air control valve, replaced fuel filter, checked fuel pressure got a reading of 40 psi is it that to low? could I possibly have a bad pump ? Also noticed hole in my cat on the passenger side could this cause the code ? If anyone could help I'd appreciate it

P0171 Bank 1 Lean, P0174 Bank 2 Lean

Those codes mean the PCM is sensing excess oxygen at both the left & right O2 sensors upstream of the cats. That could be caused by a lean condition from unmetered air (after the MAF) in the intake, engine misfires, exhaust leaks, or insufficient fuel (injector or fuel pressure).

1. I don't know how thorough your inspections are, but I'd suspect a visibly damaged cat is an immediate fail. I'd at least patch that if possible and see if the code recurs.
2. Does your scan tool show live data? Are the B1S1 and B2S1 O2 sensors constantly low voltage? Do they occasionally bounce up above 750mv under changing load?
3. Does live data show fuel trims? Is the PCM adding fuel to compensate for the lean condition? Like double digit positive short and long term%? Combined with #2, that could be faulty O2 sensors.
4. Is the 40psi fuel pressure with KOEO? Does it go up or down with KOER? 40-60PSI should be normal, but if it drops below 35 at all with the pump running, that would be an issue.
5. Does the truck run smoothly? Any smoke from the exhaust? Fuel smell? Misfires? Blackened spark plug boots?
6. Does the PCV valve allow you to blow through it only one way? If you can blow through both ways with lung pressure, replace it.
7. How did you check for vacuum leaks? Does the truck idle at a high RPM? Have you checked the condition of lines/spritzed starting fluid around:
- PCV tube
- EGR tube (particularly after EGR valve)
- Brake booster
- EVAP valve line (under throttle body and down to canister)
- Heater bypass valve line
- Fuel pressure regulator line
- Intake pipe (MAF connections, IAT sensor hole, valve cover breather)
8. Does the truck change behavior when the PCM switches from open loop to closed loop? If it gets worse once warmed up and in CL, that could be faulty O2 sensor(s).

 

[4.0blue98]

I guess when you change the cat to pass inspection you'll find out if that's the problem. If not I know a few years back I had the same situation in my 98 and had to replace the upper intake manifold (plenum) gaskets. Lower gaskets were okay so only the uppers in my case. This solved my problems and I guess it's pretty common for the 4.0 OHV.

 

[Matt1989]

P0171 Bank 1 Lean, P0174 Bank 2 Lean

Those codes mean the PCM is sensing excess oxygen at both the left & right O2 sensors upstream of the cats. That could be caused by a lean condition from unmetered air (after the MAF) in the intake, engine misfires, exhaust leaks, or insufficient fuel (injector or fuel pressure).

1. I don't know how thorough your inspections are, but I'd suspect a visibly damaged cat is an immediate fail. I'd at least patch that if possible and see if the code recurs.
2. Does your scan tool show live data? Are the B1S1 and B2S1 O2 sensors constantly low voltage? Do they occasionally bounce up above 750mv under changing load?
3. Does live data show fuel trims? Is the PCM adding fuel to compensate for the lean condition? Like double digit positive short and long term%? Combined with #2, that could be faulty O2 sensors.
4. Is the 40psi fuel pressure with KOEO? Does it go up or down with KOER? 40-60PSI should be normal, but if it drops below 35 at all with the pump running, that would be an issue.
5. Does the truck run smoothly? Any smoke from the exhaust? Fuel smell? Misfires? Blackened spark plug boots?
6. Does the PCV valve allow you to blow through it only one way? If you can blow through both ways with lung pressure, replace it.
7. How did you check for vacuum leaks? Does the truck idle at a high RPM? Have you checked the condition of lines/spritzed starting fluid around:
- PCV tube
- EGR tube (particularly after EGR valve)
- Brake booster
- EVAP valve line (under throttle body and down to canister)
- Heater bypass valve line
- Fuel pressure regulator line
- Intake pipe (MAF connections, IAT sensor hole, valve cover breather)
8. Does the truck change behavior when the PCM switches from open loop to closed loop? If it gets worse once warmed up and in CL, that could be faulty O2 sensor(s).

Thanks for all the info I did use starter fluid to check for leaks with no luck.few things you mentioned I'll try. unfortunately I just have harbor freight scanner that doesn't do live data and the inspections differ where you take it places care about the emissions codes when you plug it in it you can't beat the computer

 

[Matt1989]

I guess when you change the cat to pass inspection you'll find out if that's the problem. If not I know a few years back I had the same situation in my 98 and had to replace the upper intake manifold (plenum) gaskets. Lower gaskets were okay so only the uppers in my case. This solved my problems and I guess it's pretty common for the 4.0 OHV.

Did you truck idle high when you sprayed the intake manifold? I'm getting nothing from that so I figured I rule that out

 

[4.0blue98]

No I tried spraying around and it did not change idle. I figured it was leaking in an inaccessible area as far as spraying went. The intake plenum has a few spots that are not easy to get to. I think you can really only spray the outer areas efficiently. Changing the upper gaskets was sort of a last resort but not too bad to do. EGR was a pain. The lowers are a bit more involved.

I did see a couple suspect spots when I looked at the old gaskets. I seem to remember this being a fairly common issue with these engines. Some people just re-torqued the plenum and/or the fuel rail and fixed the leak (at least short term).

 

[moparownr]

Trying to clear these codes on my truck so I can pass my inspection and renew my registration asap so far I checked for vacuum leaks with no luck cleaned MAF sensor,cleaned throttle body , replace idle air control valve, replaced fuel filter, checked fuel pressure got a reading of 40 psi is it that to low? could I possibly have a bad pump ? Also noticed hole in my cat on the passenger side could this cause the code ? If anyone could help I'd appreciate it

Yes an exhaust leak can also cause these codes

 

[Matt1989]

Update So I put a fuel pump on it codes Cleared and after 100 miles came back I'm getting good vacuum and fuel pressure I suspect the ac vacuum line is damaged I was wondering if I could just plug that off the intake just to clear the code for inspection does anyone no if that would cause a new code and if it's not that I'm probably going to do upper and lower manifolds