All is well so far. We got back yesterday evening after a little over 400 mile round trip to Ohio to get a rear seat for the Expy. She drove beautifully with no Check Engine Light
what so ever. THANX!

 

I started chasing this since my CEL has been on for the last 30 or 40K miles. A long time ago I took it to somebody and they said the "passages in the intake manifold" where clogged (back near the EGR) and charged me some money to take care of it. A few weeks later, the light was back. I had also noticed that right after a car wash the light would go out, and a couple of days later it would be back. But the car runs fine so just ignored it.

So reading this thread I went to look into it. Now, the first thing I notice is that my car hoses don't seem to match what you guys describe. (98 XLT 4.6L). My PCV hose comes from the right valve cover to the FRONT of the throttle body. The PCV is almost impossible to take out, and the hose seems fine. Behind the intake, running towards the rear is another vacuum hose. I can see and barely reach it, but it goes back towards the firewall, turns behind the battery hook up and I can;t figure out where it ends.

This connection seemed toasted. So I replaced the first part of it with 3 inches of new hose. The CEL went out. For about a day, then it came back. I then decided to use a clamp on it just to make sure it wasn't moving off or something. CEL persisted. Then, the next day, while driving, it went out for a few hours, then came back. This is all new behavior since before I used to stay on solid, only going out after a car wash.

So my plan is to go get the front hose (to PCV) and elbows, PCV valve and grommet and make sure that is all solid and new. At 149K miles I am sure it won't hurt.

But, what is this rear hose and where does it end????

 

I t-h-i-n-k that vacuum hose goes up behind the battery box. There it connects to a vacuum resevoir that is between the battery box and the inner fneder panel.

 

Codes: P0401, P0171, P0174
Hello, I have a 2000 Nav. with the same codes, same problems, and yes I tried all the same fixes. Before I found this forum I had a 02 sensor replaced which did nothing, replaced DPFE sensor for about $50 at auto zone. Old DPFE was aluminum but the new one was black plastic ( I heard this is normal to avoid corrosion). I cleaned the MAF sensor, replaced air filter, cleaned out the carbon buildup as suggested. I cleaned the throttle body pretty good. Reset the engine light and the light still comes on after about 65 miles of driving. I found this forum and found (2) pvc elbows that had small holes in the inside of the bend of the elbow. I am replacing these elbows today but used some electical tape as a quick fix to get me to work. The light is out after about 90 miles of driving with the electrical tap. Before I was getting 9.5 mpg and now I am getting 17.8mpg with the electrical tape temporary fix. I can't wait to replace these rubber elbows to see if my light will be out for good. Thanks for all your help and I'll keep you updated on this issue.

 

I'm having same P0171/P0174 codes appearing. '98 Navigator, 5.4 engine. The PCV and elbows are all OK, but the codes come on after being cleared only under heavy acceleration. I saw this may be a fuel delivery issue, and that makes good sense. Any other things I should check? Is the manifold leak issue a likelihood? I have a scan tool that will pull continuous or momentary data, what should I look for there? Thanks in advance!

 

i LOVE this board!

bought a new to me 99 last weekend. service engine soon light came on yesterday. first thing i did was log in and search. since it was sunday night all i could really do was disconnect the battery for 10 minutes to reset and see if the light triggered again. it did this morning.

had the codes pulled and i got the P0171/P0174. went straight to the computer and searched FTE. started up top with the PCV elbows and what do you know... the top one was so rotted that you could hear air whizzing in and out of the cracks! i hope the rear one isn't this bad because i can't even see it let alone reach it.

went back to advanaced and was looking for the part when an associate asked me what i was looking for. i told him, he reached right for it and proceeded to tell me he spent $1700 on his 98 a few years back tracking this problem down, only to find the rotted PCV elbow himself and fixing the problem for 7 bucks.

did i mention i love this board?

 

Hello Everyone. I've been lurking on this forum for some time and it has helped me out more than I can count. I am currently getting the codes for the "System Too Lean",
P0171, P0174 . I've replaced both PVC boots, as well as the PVC itself. I've cleaned the MAF 3 times now, and even went as far as to swap one from another expedition that is running fine. I've replaced the plugs (which were fouled becase of the running condition). I had the coil packs tested while they were out for the plug replacement. I listened to all of the injectors and they all seem to be working. I ran 3 tank fulls of fuel with Lucas injector cleaner in it. I've sprayed most of the engine with carb/TB cleaner to check for vaccum leaks without any success. I've visually checked all of the hoses that I could see/reach for leaks. I've even gone as far as to replace the TPS. Yet, I Still have this problem. It idles fine, and even runes "fairly" smooth if I "feather" the gas or very slowly bring it to speed. If I press the peddle even slightly hard, it bucks and hesitates like it's missing. It's actually not bad until it shifts into 3rd gear. As soon as it upshifts, I can feel it really badly. Most times, I have to turn off the Overdrive to force a downshift until the RPM's hit about 2200 and then re-engage it and it runs fair again. This has been driving me nuts for about 6 months. Inspection is due on this truck next month, and It won't pass unless I get this fixed. I refuse to get raped by the Stealership so I'm hoping maybe someone here can give me some insight into what else this could be. I was thinking the EGR, or the intake manifold gasket next but I really don't won't the headache of doing the gasket unless it definate. Anyone ??

 

~ bump ~

this seems to be one of the most common problems with this truck, and yet no one has any input for me on what I should try next?

 

You mentioned "listened" to the injectors. Have you visually inspected them? I know there was a thread here a while back that it ended up being a cracked injector that was the issue. exact same symptoms as you.

 

I didn't pull them to inspect them but thanx for the info, I'll look for the thread and do that next.

 

Add my 2001 to the list. One more hose burnt. This web site just save a butt load of money!!!

 

I had the same codes on mine and it eventually began to idle rough (although not right after getting the CEL)

survey

 

My uncle has a '99 Navigator that I am looking to purchase from him with the exact same driving symptoms. Runs good until you press the gas pedal just slightly hard, same code too, but I think his says only bank 2 is lean.

He has replaced the MAP sensor, both exhaust cats on the bank 2 side which included the O2 sensors. He has had two independent shops work on it and they both are stumped. CEL has not relit, but it still has the drivability issue during accelleration. I will have him try cleaning the MAF sensor next and double check the PVC system.

Considering that it idles great and messes up at highway speeds under load, I really doubt it is a vacuum leak of some kind. I guess after the MAF sensor cleaning or replacement, he will need to bend over and take it to the dealer. Any other suggestions I should tell him?

 

Problems only while under load, many times is an indicator of a weak fuel pump.

 

Ditto! I have an '02 Navigator with the 32-valve Intech engine and ONLY bank 2 is lean (DTC P0174). CEL comes on about every 300 miles or so. I found a pin hole in one of the PCV elbows but that didn't seem to make a difference - but I did make nearly 600 miles before the CEL came on.

Something is causing my bank 2 to run lean as the LTFT Bank 2 hovers around 15-19% while LTFT Bank 1 is around 5 to 6%. I'm suspecting it might be an injector o-ring on the bank 2 side, but I can't even see the injectors on this engine. I think the injectors are under the intake manifold?

Keep me posted on what the dealer finds on your Uncle's Navi.