SScully,

CEL came on in truck about a month ago (98 F-150, 5.4). Took it in to the shop (local garage not Ford Dealer) and they said it was returning codes P0171 & P0174, system too lean, banks 1 & 2 respectively.
They pulled upstream O2's which checked good, reset PCM and drove truck for 50 miles with no CEL. I picked up truck drove it approx. another 70 miles and CEL came back on. This pattern continued for about the next month. I would reset PCM (Neg battery cable disconnect procedure), CEL would stay off for about 120-130 miles and then pop back on. Took truck back after about 4 of these cycles and received same report (same codes, but good O2's). They seem to think it has something to do with aftermarket exhaust system (I disagree 'cause it been in about 2 1/2 years now) or worst case PCM may have to be reprogrammed. Any ideas or things I can check would be greatly appreciated! Thanks in advance!

Redeye

 

Not too sure about the '98, but the '97 had a TSB for something linke this. Apparetnly on the '97s the AC condensate drain dripped onto the O2 sensor and threw a code periodically. The TSB gave detailed drawings.

Hope this helps.

Tony

 

Before you do anything else clean the MAF sensor. Reset the PCM and see if you srill get the SES light.

Regards

Jean Marc Chartier

 

First thing i would think it was is a PCV tube elbow way at the back of the intake behind the throttle body has sucked in and is a vacuum leak. Surely the shop you took it to would have been able to diagnose this though.???

 

Well I'd have to say you have been given a bunch of good advice so far from JMC and jefflaws.

Both the MAFS and the PCV are listed in the manual section ( will list after my pontifications, just so you have them ).

Another one to look at depending on what has been done.
Are both the hoses attached to the intake ? i.e. if you have replaced / cleaned your filter lately, installed a FIPK, or the likes.
Last time a member saw this, I think it was one of the 2 hoses up by the throttle body cover, specifically the PCV hose.

As for the O2 sensors testing good, that can be. The custom xhst system you put on, did this include changing out the cats ?
The only reason I ask is if you have a weld that was marginal when it was installed, did the weld finally let loose and now it could be causing a leak near the O2 Sensor ??

All these are just things that seem to come to mind as the more common reported cures for similar symptoms.

I would start with the intake myself ( it is on top and easiest to check ).

So far you seem to have real good input from others ( that even know far more then myself no less ), so any of these are good to start with.

Odd question, has someone messed with your gas cap as of late ? ( i.e. brother in law borrowed the truck, and cross threaded the cap putting it back on, and he is the type that if it don't fit right the first time, force it harder )
Maybe the low fuel pressure part is a craped up gas cap ? I would put this down the line after checking the PCV hose, MAFS and other hoses in the intake, but just keep that one in the back of your mind. I can't say if this is the specific DTC for that, but it could show up under the low fuel pressure part..maybe ?? ( just a big swag there ).

Here is the run down from the service manual just so you can see the list. The ones that sound real nasty, just don't concern yourself with them, unless we do every other thing. Cyclinder compressions, and fuel injectors are the ones I am refering to.

Good luck hunting for cracked hoses, or dirty MAFS / loose IAT sensors, let us know what else you need help with. We're open 24/7

DTC
P0171 - System to Lean (Bank 1)

Description
The Adaptive Fuel Strategy continuously monitors fuel delivery hardware. The test fails when the adaptive fuel tables reach a rich calibrated limit.

Possible Causes
Fuel system
Excessive fuel pressure.
Leaking /contaminated fuel injectors.
Leaking fuel pressure regulator.
Low fuel pressure or running out of fuel
Vapor recovery system.
Induction system:
- Air leaks after the MAF.
- Vacuum Leaks.
- PCV system.
- Improperly seated engine oil dipstick
EGR system:
- Leaking gasket.
- Stuck EGR valve.
Leaking diaphragm or EVR
Base Engine:
- Oil overfill.
- Cam timing.
- Cylinder compression.
- Exhaust leaks before or near the HO2Ss.

Diagnostic Aides
A SHRTFT-1,2 PID value between -25% to +35% and a LONGFT-1,2 PID value between -35% to +35% is acceptable. Reading beyond these values indicate a failure.

 

When I was having a CEL and the code was bank 1 lean I would re-set my computer and the CEL would come back after 30 to 50 miles. Sounds like what you are having.

Finally, I cleaned my MAF sensor by spraying some brake cleaner on it and reset the computer again and my pinging and CELs went away.

Now periodically when the pinging starts to come back I clean the MAF again and reset the computer. (I've only had to do this once since)

Let me preface this by saying I first tried changing my fuel filter and running fuel injector cleaner thru to no avail, although I'm sure it helped some.

Good luck!

 

ps - I have a K&N filter too and I think the oil from it was putting deposits on the MAF sensor wires. It's no big deal to clean them periodically.

 

Thanks to everyone for the quick reply!! Sorry I couldn't get back to you sooner, but a leaking hot water heater last evening prevented me from getting on line.

Sounds like I've got some hoses & sensors to check out! One other question I do have is the exact location of the MAF. Is it the one just a little less than midway (if you start from the fender well) that protrudes down inside the air cleaner to throttle body hose assembly? Looks maybe like it might be a miniature thermometer with a little protective cage around it.

Also, I asked the shop about a possible vacuum leak when I took the truck in and they said if I had a vacuum leak that my engine would be running badly. To this point, I haven't felt any difference in performance (from behind the wheeel) at all....CEL on or not. Any thoughts?

Thanks again everyone for your quick response!!

Redeye

 

Redeye, The one that you describe is the IAT ( intake Air Temp ) sensor.

The MAFS is actually inside the stock air cleaner housing.

Here are some pictures of the MAFS, from my K&N install directions. Sorry about the poor quality it is a picture of the paper directions.

The start of them is the same as if you were changing the air filter on the truck.

https://www.f150online.com/galleries...2028-48036.jpg

https://www.f150online.com/galleries...2028-48035.jpg

This last pic, shows removing it from the plate. You do not have to do this in order to clean it. This is only here to give you a closeup of what it looks like.
https://www.f150online.com/galleries...2028-48037.jpg

Let us know how it all goes. Good Luck !

 

Thanks for the pics SSCully!! Will keep you posted!

Redeye

 

Here's a picture of the MAF sensor when you open your filter canister. Spray the little squiggly wires inside the "barrel" on the left with some cleaner.

Then reset your computer by disconnecting your battery for 20 minutes or so.

 

Thanks for the additional pic, hapynzap! Just to let everyone know, I have cleaned the MAF and checked for possible cracked hoses and other vacuum leak possibilities on the top of the engine. Have her back on the road......drove the 30 miles to work today and so far so good, but if the pattern holds true it will be a few more miles before the CEL tries to come on. Will keep ya'll posted!

Thanks again to all for your help!

Mike

 

Well, I don't want to be too premature, but I've put close to 140 miles on my truck and to this point NO CEL!! Guess cleaning the MAF was the ticket. A big thanks again to SSCULLY, JMC, jefflaws, hapynzap, and F150tony for your help and quick replies. If any of you are ever around Las Cruces, NM give me a holler and the suds are on me!

Regards,

Redeye

 

We'll keep our fingers crossed for ya!

Now, when was the last time you had your fuel filter changed?

 

Here's what you saved...

1998 F-150 XLT 4x4 4.6L with 107,266 miles.
Check engine light went on a couple of weeks ago.

A code reader displayed the following codes:
code 01, P0174 System too Lean (Bank 2)
code 02, P0171 System too Lean (Bank 1)
code 03, P0171 pending
code 04, P0174 pending

Job description Total
Perform EEC test, replace MAF sensor and decarbed intake $611.91
Oil and filter change $24.05
Fuel injector service $169.95
Fuel Filter $87.48
Replace Serpentine Belt $147.46

Environmental fee $2.99
Shop supplies $47.00

Total labor $650.15
Total parts $390.70
Total misc. $49.99
Tax $17.58
Total $1,108.42

Enjoy your savings!