P0171/P0174 Fix Procedure

Legal Stuff

The information shown on this page is for informational use only. The information provided is not endorsed or recommended by the Ford Motor Company. All brands mentioned belong to their respective owners. I do not guarantee that the information here will fix your vehicle's problem, so I cannot assume any liability for your mistakes or misfortune.

Please do not link to these images without notifying me first.

I am providing this information to my fellow F150 owners with the hope that we can continue to enjoy these great American built trucks. Feel free to link to this page as you feel necessary.

This page was originally designed at the following URL: http://sites.google.com/site/fordf150p0171p0174fix/Home/

Contact Information

I enjoyed working on this project, and I think I understand the frustration that other V6 F150 owners feel. If you have any questions, comments, suggestions, clarifications, or additions, please contact me.

My email address is wchong4 [at] gmail [dot] com. (Sorry, but spammers are just too smart nowadays.)

Update [3/12/2009]

Well, I am glad to report that 1.5 months later and over 3,000 miles after this fix, I have not had any check engine lights appear. We have had weather fluctuations from below freezing to mid 80s, and it appears that the new isolator bolts are holding strong and nothing has warped. My driving conditions are about 70% city, 30% highway, which I think is a common ratio for most of us. If anything, more city driving means more stress on the engine, so the fix is definitely holding up.

I have had the pleasure of talking with some of you who have performed this procedure, so it seems that word is getting around. Please continue to refer your friends to this page if they come across the dreaded code. These are great trucks, so it would be a shame for someone to get rid of theirs because they could never get the code fixed.



Update [6/17/2009]

It has now been almost half a year since I did this procedure and I can confidently say that I have NOT had the P0171/P0174 codes come up. (or any other codes, either)

I have received lots of feedback regarding this article, which I really do appreciate.

Keep on truckin'


Update [1/8/2012]

Well folks, it has been 3 years and still no codes! The truck is still running as well as the day it was repaired back in 2008. Since that time I've had the opportunity to become aware of how to keep the engine running in factory new condition. Based on my experiences, the following help the most:

  • Stick with OEM Motorcraft for anything powertrain related. In particular, I've found that Motorcraft spark plug wires and spark plugs do an excellent job of keeping the engine running smooth. The cost difference nowadays is very minimal against aftermarket parts. The Motorcraft spark plugs come pre-gapped at .054" and that seems to work the best.

  • Replace the fuel filter often! I've been replacing mine yearly, at a cost of about $12 for a Motorcraft fuel filter. You can't even change the oil for this cheap.

  • Replace the belt drive idler pulleys if you notice any noise. I battled this one for a year or so and found that Motorcraft idler pulleys (2 of them, one is on the tensioner (which is bolted on using a reverse-threaded bolt!)) and a Motorcraft serpentine belt made everything very quiet again.

Hope that helps!



If you've stumbled upon this site
, you probably own a 2001-2004 Ford F150 with the 4.2 liter V6 engine. Anyone who owns/drives one of these trucks is very likely to come across the dreaded P0171/P0174 service engine soon light. A Google search for either of those terms will return thousands of pages since OBDII codes can be ridiculously vague, so drivers are left wandering in circles searching for a solution.

Foremost, if your F150 recently threw one of these codes for the first time, do not view the procedure shown here as your first fix. Again, OBDII codes are just stupidly vague, and your code could be due to a leaking vacuum tube or a million other things. I recommend that you perform the procedure listed here (http://www.aa1car.com/library/ford_lean_codes.htm) for cleaning the MAF since that is a very cheap fix. Other fixes include new O2 sensors, EGR valve replacement, PCV valve replacement, and so forth.. Ultimately it is your money, so you have to decide how to spend it.

Before we get to the actual procedure, I think it is important that we find out why these codes pop up on these trucks. Ford Windstar owners who have the 3.8 liter V6 engine have been victim of these codes for just about as long as us F150 owners, but because of the way that Ford handles TSB (technical service bulletin a.k.a database of common problems that dealerships can check to find repair information) information, Windstar owners had a TSB that actually states OBDII codes P0171/P0174 (http://leckemby.net/windstar/windstar01.html). The reason why the Windstar throws these codes is twofold:

  1. First, a poorly designed valve cover allows excessive oil to be sucked into the intake manifold via the PCV (positive crankcase ventilation) valve.
  2. Second, the intake plenum uses "isolator bolts" to hold it down to the intake manifold. These isolator bolts have a sleeve that is essentially designed to allow the bolts to retain tension (keeping the plenum stuck to the manifold) and to block off any debris or oil that would enter the intake manifold via the PCV system. The original "black isolator bolts" that Ford put into millions of Windstars were not oil resistant and actually would harden after constant exposure. So, the badly designed valve cover allows oil to be sucked into the PCV system, which then introduces oil into the intake plenum, where it settles on these isolator bolts and weakens the sleeves and reduces the bolt tension.
OK, so why are we discussing the Windstar minivan? Well, the 3.8L V6 in the Windstar shares engineering with the 4.2L V6 in the F150. It just happens to be that the 4.2L V6 uses the SAME isolator bolts (8 of them) and the PCV system on these trucks allows a measurable amount of oil to enter the intake manifold. Unfortunately, this wasn't really caught by Ford, in the sense that they issued a TSB that addresses OBDII codes P0171 and P0174. Instead, they have a TSB that addresses OBDII codes P1131 and P1151 (http://www.justanswer.com/questions/1nslx-2003-f-150-4-2-4x4-codes). The procedure it mentions to fix these codes is to replace the intake plenum port gaskets and isolator bolts.

This is where I draw my own conclusions. Since my truck threw the P0174 code in August 2008, I have searched the ends of the internet for a fix. Only recently (February 2009) did I realize the similarities between the Windstar's P0171/P0174 and the V6 F150's P0171/P0174. I can't recall how many internet discussions I read where F150 owners had these codes and didn't know what to do. Some just went on living with the code, as you really aren't going to notice any driveability issues. Others went to the dealership and paid $500-$700 to have a technician diagnose and repair the problem. My truck did not seem noticeably different after driving around for nearly half a year with the codes, but I'm not one to pay dealership cost for repairs and I refuse to simply "live with" something that could be fixed.

So, I decided that I would attempt to replace the isolator bolts and intake plenum port gaskets on my F150. The total cost was less than $100 and the procedure doesn't require any special tools or even a 2nd person to help out.

Refer to the following procedure on how to replace the isolator bolts and intake plenum port gaskets on your V6 F150. I have added my tidbits of wisdom so that you can have a streamlined repair and not make some of the mistakes I did.

Getting Started

Here are the parts and tools you will need to complete this job:

First, the replacement gaskets and new isolator bolts. I ordered these from www.rockauto.com. Prices are listed as follows (shipping not included):

  • Isolator Bolts (listed under "Engine" section of catalog) - DORMAN Part # 55164 {#3F2Z 9S479-AA, XF2Z 9S479-AA} $25.89
  • Intake Plenum Gasket Set (listed under "Fuel/Air" section) - FEL-PRO Part # MS94452 Overhead Valve Engine; Plenum Gasket Set; Upper set $31.79
  • *Optional, but highly recommended: Replacement IMRC Bushings - Ford Part F5RZ-9F955-AB (you need 4) or Dorman Part # 47099 (Total cost less than $20) See page: IMRC Bushing Fix

Next, the tools needed for the job.

  • Basic mechanic's tool set. You'll need various sockets, open ended wrenches, torx bits, screwdrivers, etc..
  • Hayne's Repair Manual for Ford Pick-ups (1997-2002) (or a later edition, if one exists?). You will need this for torque specifications and bolting patterns (I provide some of this information later).
  • Tape and marker. You will be disconnecting many cables and vacuum tubes, so you should mark off everything you separate.
  • Carburetor cleaner (not pictured). You will need at least 2 cans, but the more available, the better. I ended up using 6 cans of regular sized carburetor cleaner during this process (and I still didn't get everything as clean as I wanted).
  • Combustion Chamber Cleaner. This is similar to carburetor cleaner in that it is a solvent, BUT it is a gel consistency so that you can clean an area and wipe it away.
  • Electronic Contact cleaner (not pictured). This goes by various names such as CRC QD Electronic Cleaner, etc.. Basically, you want this on hand to blast any dirt and gunk out of the electrical connectors you'll be disconnecting.
  • Dielectric Grease (not pictured)
  • Shop rags, towels, q-tips (not pictured). These are needed when cleaning the oil/carbon gunk off intake parts. Have plenty of clean ones on hand. For the amount of work this procedure takes, you will want to clean everything well while you have the opportunity.
  • A spare/disposable cardboard box (not pictured). You'll see why later.
  • A torque wrench that measures in INCH POUNDS (not pictured). This is a MUST. Even if you buy a $20 one from Harbor Freight. The goal is that you get all intake bolts evenly torqued to prevent warpage and future leaks!
  • A large, sharp knife (not pictured). A kitchen knife works.
  • An old toothbrush (not pictured).
  • A dental pick, or any sharp pointed object (not pictured).
  • A shop vacuum (not pictured).
  • A small plastic zip-tie, or a small (1/4" diameter x 1/2" length) bolt and washer and nut (to be explained later)
A site reader, Pete, offered some good advice on some additional tools to make the job easier:

"You will need a both a deep and shortwell 8mm and 10mm 3/8" ratchet"
"You will need a 3/8" flex drive" (in order to get off the #10 long bolt off the top plenum cover) as it is a nightmare getting that out (such as: http://www.amazon.com/Danaher-Tool-Flex-Handle-Drive/dp/B000CD32Y6)

Thanks, Pete!

Let's Begin

  1. Wait for the truck to cool down. Ideally, you want to do this procedure early in the day so that you aren't dead tired when you finish up (like I was).
  2. Pop the hood.

  3. Disconnect the negative cable from the battery. Position the clamp so that it stays out of the way.

  4. Remove the air intake tube from the throttle body. Use a flathead screwdriver to loosen the ring tensioner.

  5. Disconnect the driver's side PCV tube from the intake. This pulls out fairly easily.

  6. Disconnect the Intake Air Temperature sensor connector. This connector is right next to the ribbed part of the intake tube.

  7. Remove the air filter from the filter housing, remove the annoying filter clamp and then set the intake aside.

  8. Remove the plastic cover for the throttle cable. If you have never removed this, you'll have to use considerable force to remove the stupid one-way plastic "screw" holding it on towards the top back. It pulls forward, then upward.

    At this step, I need to point out something VERY important: When you finish this entire procedure, and you put this box back onto the throttle body, you MUST secure it! If you end up obliterating the one-way screw that holds it in (like I did), throw it away, and use the small plastic zip-tie or the bolt+nut to secure it back on. I am currently using a small plastic zip tie to hold mine on.

    A reader emailed me about this and says if the throttle box is on loosely, it may work its way off and your throttle can get stuck in the open position while driving. If for some reason this happens to you, immediately put the truck into Neutral and then take out the key. Find a safe place to stop and service the vehicle.

    (Thanks Tony)

  9. Remove the wire for the throttle cable. To remove this, turn the throttle wing until you can loosen tension on the wire. The bar at the end of the cable sits inside of a channel, and the wire rests in that indention.

  10. Use some pliers to squeeze the retention piece so that you can remove the throttle cable from the plastic mount attached to the plenum.

  11. If your vehicle has cruise control, remove the cruise control throttle cable. The square end has a circular cut out so that it slips onto the round screw on the end of the throttle blade.

  12. Use pliers to squeeze the retention piece on the cruise control cable. When taking this one out of the mount, be careful as it is made of plastic and could easily snap if you force it too much. Take your time.

  13. Set these aside so they aren't in your face while you're working.
  14. Disconnect the electrical connector for the Idle Air Control valve.

  15. Remove the IAC valve. Plug the holes with some shop towels.

  16. Use tape + marker to mark off the spark plug wires at the coil pack (Front, Middle, Back). You want to mark the wires that connect to the driver-side plugs.

  17. Remove the plug ends from the coil pack and carefully route the wires to the driver side of the engine. If you still have the original wires and plugs, the wires will be held together at the back corners of the intake plenum in retainer clips on posts. Carefully use some needle nose pliers to pop the retainers off the posts. They come up easily, but it's that first centimeter that is difficult to move.

  18. Set the wires aside.

  19. On the left side of the plenum there is a bunch of vacuum hoses that connects to a port in the middle of the plenum. Pull this off and mark it with tape.

  20. In that same area, there is a bracket that holds the heater tubes up. Remove the bundle of wires that is plastic-fastened to the bracket. Set the wires aside. This bracket is fastened onto a post that sticks out of the plenum. You should be able to loosen the nut and pull up on the bracket. Leave the nut on so that you don't lose it.

  21. Now walk on over to the driver side.
  22. On the driver side of the plenum, there is a brake booster vacuum line that connects to the middle of the plenum. Mark this off. Use pliers to loosen the hose retainer clamp and then pull the hose off and set it aside.

  23. On that same side of the engine, but towards the front, there is a similar vacuum hose. This hose goes to the canister shaped device that sits above the master cylinder. Mark this off and pull out the hose.

  24. Disconnect the Throttle Position Sensor from the throttle body. Mark this off with tape so you don't confuse it with the IAC connector.

  25. Back on the passenger side of the plenum, towards the very back, there is a canister device (like the one above the master cylinder) that has an electrical connector and a vacuum hose. Remove both and mark them off. The vacuum hose has 2 inlets that are staggered. Do not remove the canister as this is unnecessary.

  26. Where the engine meets the firewall, there is a thick fiberglass heat pad. If you know how to remove this without dedicating half a day to the task, please let me know. For the rest of us, cutting the upper portion was sufficient for me to have room to work on the back of the plenum. Remove the two screws that hold the pad to the firewall.

  27. On the passenger side, the heat pad has a thin portion that can be cut with scissors.(Since this is fiberglass and it has been sitting there for years, it is going to generate LOTS of fiberglass dust. Try not to breathe in while cutting this stuff!).

  28. Now, to remove the rest, here's what I did. I tugged at the top part of the heat pad (that I had just loosened) to get an idea of how it wiggled. Then, I pulled on the heat pad from the top, while using a kitchen knife to cut into the pad towards the back of the firewall. You want to cut it so that you will have room to reach around the back of the plenum.

  29. Remove the bolts that hold down the top of the plenum. There are quite a few, so do not lose any. Also, I'm a bit of a stickler when it comes to bolts, so I used a spare box with a diagram to map each bolt to its original location. The two holes with lines in them are the bolts that the spark plug retainer clips slip onto. To get an idea of how tight the space is near the firewall, take a look at the 3rd pic.

  30. Carefully pull the top of the plenum off. The baffles are attached to the top portion, so you'll have to maneuver it out. Stare in shock at the amount of oil that made its way into the intake. Ridiculous, huh?

  31. Now that the lower portion of the plenum is exposed, remove the gasket that sits on the border. If you have a small dental pick, this will easily pull it off. You will probably notice lots of oil on the gasket.

  32. Now onto the lower plenum. There are various holes, but it's really a pattern. There are 6 sets of holes. Each set has 1 port with the EGR port inside and a separate port for the IMRC butterfly valves. The remaining holes in the plenum are for the (8) isolator bolts. Expect all of these to be cruddy and oily and carbonized.

  33. I sort of went in a roundabout way, because now we're going to remove the PCV valve from the throttle body. Use a torx bit to remove the 2 screws that retain the PCV valve. Leave the coolant hoses alone. Pull off the rubber elbow that connects the PCV to the hose that runs to the passenger valve cover.

  34. Remove the tube that runs to the valve cover.

  35. Now, use an 8mm socket with an extension to loosen the isolator bolts. Be aware that they are NOT fastened tight. The best thing is to loosen them, then use your hand to loosen them all the way. They will NOT come out as they are shouldered into the holes.
  36. Gently pull the lower plenum off the manifold. The isolator bolts may still be clinging, so keep the socket on hand to loosen any clingers. Carefully maneuver the plenum out, and do not bump or scratch the intake manifold because it is made of aluminum that can be easily damaged.
  37. Drop your jaw at the oil and carbon accumulation that is so obvious now.

  38. On the lower half of the plenum that you just removed, flip it over. The port gaskets need to be removed. Use a dental pick to pluck each one out.

  39. With the plenum still upside down, rest it on top of a soft, but firm object. I used a box with an old towel. Use a 3/8" socket extension and a 3/8" socket to hammer the isolator bolts out of the plenum. You should not have to do much hammering, as the first swift blow usually knocks it out. Just be sure to hammer straight down. What's holding these bolts in is the plastic/rubber sleeve on the old isolator bolts. Be sure you are hammering them OUT (as in, the bolt heads are facing down and will pop out first).

    Late Edit: In the picture I am using a claw hammer, but it would probably be best if you used a rubber mallet or a ball peen hammer (for the sake of your tools..and possibly to prevent any accidental damage to the plenum). [Thanks Gerry!]

  40. Click HERE to continue to the next page. (Google site editor ran out of memory after 40 steps! Too many images, I guess?)