P0174 - Out of answers.

[Facimeor]

so when I bought this 97 XL (sohc 4x4) it had the MIL on but I figured with my background it would be no big deal. Well Im at the point of asking for help because Ive simply run out of answers.

I have ONLY the 0174, not both banks, Ive reset it multiple times after attempting various repairs and it still comes back as only that code.

Ive checked every hose and every fitting for leaks. Ive cleaned the MAF, Ive replaced the fuel injector o-rings, installed a brand new lower intake (after trying new seals the first go round), and replaced the EGR o-ring. Somewhat related but incidental repairs have also included new spark plugs, new fuel filter and new front O2's on both sides.

Im beginning to suspect a bad injector or possibly sketchy wiring to one or more on that bank. Its kind of a stretch but thats about all I can think of left to try. A friend suggested I try swapping the injectors from one bank to the other and see if the code follows it. I plan to try that tomorrow but thought I would ask to see if anyone had any suggestions that I might not have thought of before I take this intake apart...AGAIN!

Thanks.

 

[pickupman6]

I got the same problem except mine is p0171. I've come to the same conclusion as u so I'm listening in on this one.

 

[SoNic67]

http://www.aa1car.com/library/ford_lean_codes.htm
DPFE sensor, fuel pressure regulator vacuum hose...

 

[2000StreetRod]

defective O2 sensor

P0174 System too Lean (Bank 2)

The PCM is not able to richen the mixture enough to achieve normal O2 sensor readings on the driver side bank. You seem to be confident that you have thoroughly checked for vacuum leaks that would affect only that side. If you had a faulty injector on that side the PCM would probably set a misfire code. There's a possibility that the pre-cat O2 sensor on the downpipe is defective. If your spark plugs on that side indicate a rich mixture, there is black smoke in the exhaust and your fuel economy is poor then I would consider replacing the O2 sensor. To save money you could swap the sensor with the other bank and see if the code changes to P0171 System too Lean (Bank 1). I would probably just buy a new sensor since the pre-cat Bank 2 is the easiest one to change.

EDIT: I just reread your post and noticed that you have already replaced the O2 sensors. Check the wiring to the sensor for shorts. Make sure the pre-cat sensor wiring to the PCM is not connected to the post-cat sensor.

 

[Facimeor]

DPFE and pressure regulator will not throw the single lean 0174. Those will both throw 0174 AND 0171 together as they will affect both sides equally.

From what Ive read a bad O2 or the wiring to the O2 will not throw the 0174 either. Also there is no possible way to mix up the wiring for the pre and post cats as they come from two different location on the harness entirely. Fuel mileage is great in fact. Took this rig 600 miles round trip to Seattle a couple weeks ago and averaged 20mpg loaded down.


_______________

So Ive ruled out the injectors themselves today. I pulled all 6 and ran them through a homemade injector test rig I built last year. They all spray a nice pattern and flow seemed consistent across all 6. Just for arguements sake though I went ahead and crossed them over, left to right...still throws 0174, bleh.

I also removed the ICV and the section under it with the diverter. I took that apart and cleaned the seals and everything looked fine, seals were soft, no defects. Put it back together and that too made no difference. I was clutching at straws since that should throw both codes as well, but its one of the few things I hadnt done yet.


The engine seems to run fine, I do think I have a bit a first start flare but RPM's settle down fine and idle is at a normal RPM but seems like it could be just a bit smoother like my 98. I have my 98 sitting here that runs perfvectly with no codes, so I was thinking about swapping some parts over one by one to try to find the issue, but thats not typically the way I do things.



So, Im still looking for ideas.

 

[Facimeor]

so just for argument sake I went and swapped the DPFE and the ICV from the 98 to the 97. No change, throws the code in exactly the same conditions.

If this helps at all, here are the exact conditions it throws the code, the same time the same way, every single time.

I live about 1.5 miles from a state park which makes a great turn around point for a test drive. The road there is rural highway so I reach 60MPH for about a minute each direction. Engine warm or cold doesnt seem to matter here, but If I reset the codes, then drive to the park, stop and shut off the engine, wait 30 seconds, restart the truck, return to my shop, I have to slow down to pull into my driveway which is uphill. The instant I give it throttle to pull up my hill the code triggers. This is repeatable and consistent every time.

 

[2000StreetRod]

cracked upper intake manifold?

In the past year I've helped two forum members correct their fuel mixture problems that were due to incorrectly connected O2 sensors. One member had the pre-cat left O2 sensor connected to the right O2 sensor PCM input and vice-versa. I think the other member had the left post-cat sensor connected to the left pre-cat PCM connector. In the second case the installed O2 sensors were aftermarket units that had been cut and spliced incorrectly.

There are a limited number of vacuum lines and hoses on the driver side that could result in a lean condition on that bank. Have you checked the check valve connection at the power brake booster? There is the hose that goes to the PCV valve "T". And finally there is the connection under the intake manifold that combines with the right side and goes to the fuel vapor management valve. Pay close attention to the slide locking type connector. All of the other connections would affect both banks or the right bank. You stated that you had replaced the lower intake manifold and I assume the gaskets above and below it. If there was a crack in the lower intake manifold I suspect it would only affect one cylinder and there would be an associated misfire DTC. What about the possibility of a cracked upper intake manifold? I believe at least one forum member reported finding one.

 

[Joe Dirt]

Is there a vacuum tree coming off the DPFE lines at some point on the SOHC? I had a cracked plastic line on one of those van "tubes" (the green one) that kept throwing a phantom code like that on my '95.

 

[2000StreetRod]

no DPFE vacuum connections

Is there a vacuum tree coming off the DPFE lines at some point on the SOHC? I had a cracked plastic line on one of those van "tubes" (the green one) that kept throwing a phantom code like that on my '95.

There are no vacuum connections to the DPFE. The two DPFE hoses connect to ports in the EGR tube. One port is upstream and one is downstream of the EGR tube orifice. The DPFE measures the differential pressure between the ports, converts it into an electrically equivalent signal, and passes it to the PCM to determine the flow thru the EGR tube.

 

[Facimeor]

Im not trying to argue with you and I appreciate you at least trying to help but a 0174 is the computer detecting a lean condition via a working O2. An improperly wired O2 will either throw a heater code like 0141 or a low voltage 0151. P0174 is NOT considered and O2 code (thought it is of course detected by an O2 sensor).

Also once again there is no way anyone with half a brain would cross wire the front O2's. They come from two different sections of the wiring harness. You would have to work very hard to even get the two connectors to reach. I do see how it might be possible to mix up the two post cat sensors, but that isnt relevant in my case. In any case, once again, that will NOT throw a 0174.


on more relavant possibilities: the Brake booster hose is good and that one way valve in the booster is also good, evidenced by the air that escapes as you try to remove the hose and brake booster function is normal.

For the PCV connections Ive tried several typical methods to check for leaks including a flammable spray (penetrating oil) and an unlit propane torch tring to expose a suction loss. I suspect thought that since I dont notice an idle difference and idle is smooth to begin with that if there is a loss it only occurs under certain conditions, and idling with the hood up is not one of them.

I pulled the plugs on that side today and I gotta say they look freaking perfect. They have a couple thousand miles on them and look like they just came out of the box, neither lean nor rich looking.

Progress? While I had the plugs out I thought maybe I should try to regap them. I had them gapped to the bottom end of the scale (.52-.56) and thought for giggles I would gap them to .56. After reinstalling them and doing my usual turn around test run, NO CODE! ? ...so I shut the truck off for a few minutes and repeated the test run...still no code!

Could the answer really have been as simple as a spark plug gap? I will report back after a little more complete testing.

 

[SoNic67]

What kind of plugs you use that you have to gap??? Copper?
I am using in all my cars only iridium ones (platinum and iridium are not supposed to be gaped by hand) so I know that those are perfect. If yours was dying in load, that means that the electric spark was not working right at that mixture. Regaping them is just a temporary sollution if they are copper, just use some decent ones! Ford engines require as minimum double platinum due to the ignition design.

 

[2000StreetRod]

waste spark system

Ford chose to implement a waste spark system on the Explorer. A plug in the right bank is paired with a plug in the left bank and connected to one coil in the coil pack. When a plug fires on its compression stroke its paired plug is fired on the exhaust stroke. Ignition current flow thru the right bank plugs is in the opposite direction in the left bank plugs. The current flow direction determines which electrode (center or top) wears. The Ford factory used to install different plugs that were bank specific. A single platinum center electrode only reduces wear in one bank. Most forum members purchase double platinum plugs. Many have had misfire problems with Bosch platinum plugs.

It seems unlikely to me that changing the gap from .052 to .056 would eliminate your lean code. If the plugs were misfiring you should have misfire codes and detectable driving symptoms. Also, there should have been indications when you examined the plugs. However, I have learned that theory is often unable to explain actual results. I hope that your problem is solved.

 

[SoNic67]

Well, probably it has just a partial burn of the fuel? Sure, misfiring completly is getting detected by the PCM.

 

[Joe Dirt]

There are no vacuum connections to the DPFE. The two DPFE hoses connect to ports in the EGR tube. One port is upstream and one is downstream of the EGR tube orifice. The DPFE measures the differential pressure between the ports, converts it into an electrically equivalent signal, and passes it to the PCM to determine the flow thru the EGR tube.

Not coming off the DPFE itself, it plugs into the hoses- I'll have to snap a pic of the tree I have when I get home. I know replacing it fixed my code... I can't figure the correct term I guess...

 

[Facimeor]

What kind of plugs you use that you have to gap??? Copper?
I am using in all my cars only iridium ones (platinum and iridium are not supposed to be gaped by hand) so I know that those are perfect. If yours was dying in load, that means that the electric spark was not working right at that mixture. Regaping them is just a temporary sollution if they are copper, just use some decent ones! Ford engines require as minimum double platinum due to the ignition design.

Sonic, I come from a high performance background. Ive been a small engine tuner since I was a kid. I can tell you with certainty that you have been misinformed on the nature, performance and hype regarding spark plugs. Put simply, Platinum and Irridium plugs are not...repeat NOT better spark plugs in terms of engine performance or driveability. What they offer is longer maintenance cycles, period. Quality copper plugs will almost always outperform a platinum or irridium plug head to head, just not for as long. Edit: Additionally, in extreme conditions such as with turbocharging, platinum plugs can "heat soak" and act like a glow plug leading to detonation.

Streetrod, spark quality and gap CAN and will affect the quality and completeness of a mixture burn. It is possible to have a poor burn that does not trigger a misfire code. As I said my plugs have a couple thousand miles on them and look like they just came out of the box, so I dont believe I was getting a misfire at all, just thinking its possible I had a quality of combustion issue? Its a stretch, I know. But like I said, Im about out of easy answers.


Now, having said that, do I think regapping my plugs was the whole issue and that Ive "fixed" it for good? Not really. Im hopeful my code doesnt come back quite as fast as it was though. Sometimes things like this are a combination of factors that lead the ECU to detect operation outside of its intended paramaters. Maybe I just found another piece of the puzzle. I also located an upper manifold in a nearby yard I will probably go pick up if the code returns. I will be sure to take the EGR hoses as well just in case.

The last thing to note I discovered yesterday is that the ECU is one from a yard to begin with. I pulled a hand written tag off of it that was dated a year ago, so I wonder if the ECU was the previous owners attempt to solve this issue, or if it was unrelated then, but related now? Seems possible, but I always consider an ECU the very last box in my flowchart.

 

[briwayjones]

Did you change the plug wires when you changed the spark plugs?

 

[Facimeor]

I did not, and that was another area I considered. Im opposed to just throwing parts at a problem and the wires ohm out ok, but Ive had wires ohm ok and still replaced them and had improvment. Again I would suspect a misfire code would get generated, but maybe they are just on the edge of needing replaced? Its possible. If the code returns today maybe I will swap the ones from my 98 for testing purposes.

 

[eazyasone23]

i ended up changing my o2 sensor post cat and the errors haven't been on for over a month. I also changed DPFE months before and did a tune up.

 

[Facimeor]

i ended up changing my o2 sensor post cat and the errors haven't been on for over a month. I also changed DPFE months before and did a tune up.

Not relevant to this discussion...

 

[SoNic67]

Sonic, I come from a high performance background. Ive been a small engine tuner since I was a kid. I can tell you with certainty that you have been misinformed on the nature, performance and hype regarding spark plugs. Put simply, Platinum and Irridium plugs are not...repeat NOT better spark plugs in terms of engine performance or driveability.

An I have high voltage engineering background. I know that a thinner wire will generate a higher intensity electric field when the same voltage is applied to it. Iridium 0.4-0.3mm fine tip will produce higher intesity electric field and higher ionization than a big, flat copper electrode.
Also, a sharp edge will produce a higher filed than a rounded one. A copper tip will erode and become rounded very fast compared with a platinum tip. Same goes for the grounded electrode in the ignition system used in Fords - one positive pulse on one plug and one negative pulse on the paired plug.

Sure, the advantage is not used/neded always, only on higher load conditions.
Also, reducing the gap you are reducing the electric arc energy - enegry that is used for initial ionization of the mixture. A lean mixture (like it is happen for 0.1-0.2 sec after you press the gas quickly) will suffer from low enegry of initial spark and will burn a little latter than normal (retard the timing).