P0171 + P0174 OHV Regulator or Fuel Pump?

[liquid217]

Hi Guys. I have a 97 explorer 4.0 OHV that has been giving me the codes P0171 and P0174. The odd thing is that it only occurs when the outside temperature drops below ~45 degrees F. The truck has a slightly rough idle, but nothing in my opinion to be concerned about. I have done a great deal of checking on this issue, ranging from looking for vacuum leaks, cleaning the MAF, etc. I replaced all of the O2 sensors last year, so I know they are fine. I have a fuel pressure tester and at KOER, I get a pressure of 30psi. With the vacuum line off of the regulator, it jumps to appx 38psi. (There was no fuel in the line, FYI) If I shut the engine off, it holds pressure for several minutes.
These DTC's seem to come back almost as soon as I clear them when the temperature outside is in the 30s. Also, my scanner tool can tell me if it is passing the readiness tests. It has been unable to perform the catalytic test for quite some time. This weekend, I decided to pull the vacuum line off the regulator, and cap it (Using PVC tape). I decided to drive around with it like that. To my surprise, not only did the DTC's NOT return, but it also completed the catalytic readiness test. So my question is this, does this sound like a fault with the fuel pump, or the regulator?

 

[steve6534]

Hi Guys. I have a 97 explorer 4.0 OHV that has been giving me the codes P0171 and P0174. The odd thing is that it only occurs when the outside temperature drops below ~45 degrees F. The truck has a slightly rough idle, but nothing in my opinion to be concerned about. I have done a great deal of checking on this issue, ranging from looking for vacuum leaks, cleaning the MAF, etc. I replaced all of the O2 sensors last year, so I know they are fine. I have a fuel pressure tester and at KOER, I get a pressure of 30psi. With the vacuum line off of the regulator, it jumps to appx 38psi. (There was no fuel in the line, FYI) If I shut the engine off, it holds pressure for several minutes.
These DTC's seem to come back almost as soon as I clear them when the temperature outside is in the 30s. Also, my scanner tool can tell me if it is passing the readiness tests. It has been unable to perform the catalytic test for quite some time. This weekend, I decided to pull the vacuum line off the regulator, and cap it (Using PVC tape). I decided to drive around with it like that. To my surprise, not only did the DTC's NOT return, but it also completed the catalytic readiness test. So my question is this, does this sound like a fault with the fuel pump, or the regulator?

I hope someone chimes in as I'm having the exact same problem with my 96 OHV! I just checked my fuel pressure after getting home and I'm seeing about the same - 32 running with the FPR and 39 without. The specs I'm looking at say this is in the range but I'm a little leery after reading your post. I capped the regulator line and we'll see what happens tomorrow.

FYI the specs I show are the following :

With FPR - 30-45
FPR disconnected - 40-50

 

[liquid217]

I have noticed that different sources say different things. The flowchart in my chilton's states that the idle pressure should be 35-45 psi. As I understand it, the haynes states 30-45 (I don't own a haynes unfortunantly).

I neglected to mention earlier that I have replaced the fuel filter as well, so that can be ruled out. Right now, from the individuals I have spoken to, I am leaning towards the fuel pump being the culprit. Of course, I would love to hear any one else's suggestions, if they have any thoughts.

 

[steve6534]

I have noticed that different sources say different things. The flowchart in my chilton's states that the idle pressure should be 35-45 psi. As I understand it, the haynes states 30-45 (I don't own a haynes unfortunantly).

I actually got my specs from the haynes book.

I neglected to mention earlier that I have replaced the fuel filter as well, so that can be ruled out. Right now, from the individuals I have spoken to, I am leaning towards the fuel pump being the culprit. Of course, I would love to hear any one else's suggestions, if they have any thoughts.

My fuel filter is also only a few months old. I replaced the pump about 3 years ago but unfortunately didn't take a pressure reading then.

 

[Rob0424]

I have these same codes coming on. I have a pretty good idea that it is the Intake Manifold gaskets. Can someone tell me how much I can expect to pay for this to get fixed at a shop? I can do the small things, but I don't think this is something that I want to take on myself.

 

[NHale623]

I have noticed that different sources say different things. The flowchart in my chilton's states that the idle pressure should be 35-45 psi. As I understand it, the haynes states 30-45 (I don't own a haynes unfortunantly).

I just looked this up in my Ford CD's.

For a '95 4.0L OHV engine (has a FPR on the fuel rail), the specs for fuel pressure are 28-45 psi with the engine running, and 35-45 psi with the key on and the engine off.

For a '01 4.0L OHV and SOHC (returnless systems), the specs for fuel pressure are 30-65 psi.

liquid217, P0171 and P0174 mean you're running lean on both banks. Since your fuel pressure looks good and the DTC's clear when you max out your fuel pressure, I'd start looking for a vacuum leak. Since the problem appears in cold weather, I would strongly suspect the o-rings in the intake manifold, both upper and lower.

 

[masospaghetti]

The fact that your throwing codes on BOTH banks means that its something common to both cylinders (and not O2 sensors, for instance). There was a post that I dont have the link to but apparently the intake manifold bolts work loose sometimes and can be a source for leaks. I used a torque wrench and two of the 6 bolts on my Ex were pretty loose.

 

[Eddie V]

Look at this post, replacing the Upper Manifold Gasket on a pushrod v6

http://www.explorerforum.com/forums/showthread.php?p=1555157

 

[liquid217]

Thanks everyone. After doing a little more troubleshooting, I believe everyone is right on track regarding the upper air intake. I plan to replace those o-rings in the near future. (Following the writeup outlined in the post directly above me). I will definitely post back with my results.

 

[liquid217]

Well last night, I decided to take a stab at replacing the upper intake o-rings. While the plenum was off, I also checked the torqe on the studs. As I followed the steps above, I quickly realized that I would also need to remove the egr valve to remove the plenum. Honestly, that was the hardest part of the job.
With that said, so far, everything is running smoothly. I have not had the CEL come back as of yet. I will be sure to post back if something happens.

 

[joe doe]

i just had the same thing done on my 2000 ex with ohv 4.0 ....its been a few days now and no cel light yet.i was going to chime in but you already figured it out.i did post up about my experience ...just look thru this area ..its not to far down.....

 

[steve6534]

I hope someone chimes in as I'm having the exact same problem with my 96 OHV! I just checked my fuel pressure after getting home and I'm seeing about the same - 32 running with the FPR and 39 without. The specs I'm looking at say this is in the range but I'm a little leery after reading your post. I capped the regulator line and we'll see what happens tomorrow.

FYI the specs I show are the following :

With FPR - 30-45
FPR disconnected - 40-50

Just as a followup my fix to the P0171 & P0174 codes was to replace the EGR tube from the EGR valve to the upper intake manifold. There was a vacuum leak here that was from the tube leaking at the seal in the upper intake.

Hopefully this can help someone else in the future through a search.

Steve