po 171 and 174 stumped

[michaelwilson98]

Alright so I have had these codes keep rearing their ugly heads. I have replaced a few things first was just a regular thing when I buy a new one, replaced air filter and oil and oil filter then fuel filter. I also replaced the IAC to get rid of the howling sound (guy i talked to said it was intake " turbulence").I get the codes and I start searching around for an answer when I stumble on this site. Awesome site. So I become a member and start digging in. First I replace the MAFS, the throttle position sensor, then water temperature sensor, then the dpms switch which had rotten lines on it. And now the evil light is back. Anybody else have any ideas before I take it to someone to diagnose? The vacuum leak everyone feafears is not present tested for it three different ways.

2000 explorer sport 2wd 4.0 OHV

 

[chefduane]

Upper/Lower Manifold gaskets. (Ha Haa!! I was first!)

 

[michaelwilson98]

But wouldn't that be a vacuum leak?

 

[Turdle]

Just replace the gaskets. You'll fix the codes.

 

[koda2000]

you should also check your fuel pressure. i'm seeming more and more cases where insufficient fuel is causing these codes. when's the last time you changed your fuel filter?

 

[michaelwilson98]

you should also check your fuel pressure. i'm seeming more and more cases where insufficient fuel is causing these codes. when's the last time you changed your fuel filter?

When I bought it in September. Where would I test the pressure?

 

[koda2000]

When I bought it in September. Where would I test the pressure?

there's a Schrader valve (looks like a tire valve) on the fuel rail. you can borrow a fuel pressure gauge at most auto parts stores. Note: sometimes the gauge doesn't push the valve stem in enough and you have to remove the valve stem to get a good reading. a 2000 should have around 60-65 psi at the rail.

 

[BustedKnuckles24]

I second or third the intake manifold gaskets, upper and lower. Fel-pro offers them as a set for around $20. I had the same problem, checked vacuum lines, fuel pressure, cleaned injectors, changed filters, including the fuel filter, and the entire gambit. On cold days, it would shutter and stumble at start-up from stone cold for a few seconds, then smooth out. Then, the CEL lit up with those same codes. After checking all the above, I finally spent the time to do the gaskets. That fixed the problem.

 

[Dirt n Oil]

I had the same codes right after replacing the fuel filter. For a long time prior, I've had to turn the key a few times to build fuel pressure (which I'll check soon), so the pump may be going bad, the uptake screen dirty / crud in tank, etc. ..I disconnected the battery to reset the codes, and they haven't come back after driving over 100 miles, so I'm not sure if the codes were just triggered by the removal of the fuel pump relay fuse when I depressurized the fuel system or what.
... I've been swimming through this website, and it appears that MANY different things can trigger those codes, yikes!
...I hope that you keep us updated. I figure the more data points, the better, especially concerning these codes!

 

[michaelwilson98]

Thanks for the info might be a stupid question but I'm assuming you check the fuel pressure with just the key on or is it running?

 

[Dirt n Oil]

Check both. Running, it should be 55-65 lbs. Key forward/engine off should be lower, but i don't remember what it should be exactly, maybe around 30lbs.
...I'm a novice, but have been studying this website pretty hard this week. Do some digging, use the google search bar on this webite, it searches only this site. I remember reading a few posts regarding fuel pressure.

 

[Dirt n Oil]

...I just realized that we have different motors, so I don't know if my previously posted values are accurate for your particular application. It seems like I may have read that they have different fuel pressures... Oops?

 

[chefduane]

But wouldn't that be a vacuum leak?

Yes. I was in same the situation as you.. same codes, same symptoms. Went through the protocol, cleaned IAC, MAF, fuel filter, fuel pressure test... everything. Then finally tore the mani down and changed out uppers and lowers. Cleared the codes and been running great since. I did it about 2 years ago, hasn't thrown a P0171/4 since.

 

[koda2000]

...I just realized that we have different motors, so I don't know if my previously posted values are accurate for your particular application. It seems like I may have read that they have different fuel pressures... Oops?

which motor doesn't matter. return or return-less style fuel system matters. the older Expl's, with the return style fuel system, ran about 35 psi, the later ones around 65 psi. I think '98 was the first year of the return-less system.

 

[JethroBodine]

Just reading up on pcv problems. It mentioned those codes specifically.

 

[JethroBodine]

Double post

 

[brownbagg]

i just went through this, been fighting it for years. mine was the upper gasket. I change both but it wasn't needed, the bottom gasket is a beech.

there are two gaskets for the top, one is o ring, and in my valve cover gasket kit there was a solid sheet gasket. I used both, solve my problem.

tip, when you first start removing parts, take the egr completely off the vehicle, you need the extra room to get the manifold off. loosen the ac compressor and move off its mounts but don't disconnect any hoses. if you going for the bottom gasket, which i don't recommend , remove the alternator and watch out for the dipstick, that plastic t handle will break if you bump it

i recommend using both gaskets for the top manifold. orings and the sheet

 

[AppleWood]

My recent saga goes like this. First off, I have the "Job One" 4.0 SOHC engine. 144,000 miles.
PCV and three hoses check okay; replaced plugs, wires, and coil pack.
Plugs gap > 0.100" and one wire arcing to valve cover. No change.
Next verified MAF, TPS, and IAC all clean and proper voltages. Removed, cleaned throttle body and IAC valve. No change.
Then four days ago removed/replaced fuel filter. Erased codes, and, I hate to even say it, but no CEL since. Pretty sure filter was OEM so, jes sayin'...

 

[michaelwilson98]

I'll give the fuel filter change a shot. I think iI got mine from Napa. Where did you get your second one? Exact brand would be awesome

 

[michaelwilson98]

Double post

There's alot of these threads if someone posted this exact problem please provide a link I'd like to see what finally fixed it.