MonteFord

Hello! I'm a new member and need help. With my truck that is LOL
I've got a 1998 Canadian-built 3-door XLT F150 4.6L 4x4 that's been pretty good to me but has recently begun running very sluggish. I'm looking for advice on what to do now after these symptoms listed below.
Symptoms: At first, maybe three years ago, my truck began running badly and the CEL came on the guy at O'Reilly told me it was my O2 sensor and that I had a misfire on cylinders 3 and 4. So I did the fun thing (not) and gave her eight new plugs, but I neglected the O2 sensor.
Then last week it had the blinking CEL and the guy said it's not misfiring, but my MAF sensor was bad. I replaced that and it runs a LITTLE bit better but is still running "weak", and acts like it's missing, so I ordered another set of plugs (from Evil Bay because here in my tourist trap town O'Reilly wants way too much) I'm intending to repeat the fun I had a couple of years previously. But I began to think about it after replacing the MAF sensor and went back to O'Reilly and was told that banks 1 and 2 are running lean.
Now I'm searching the internet and I found that a bad O2 sensor can set off those codes, including the MAF code. And to add insult to injury, it could also muck up my Cat. To save time and arduous effort, I'm opting to replace my O2 sensor(s). Which one? Should I do both? I have one near the manifold and one after the Cat. I have the kind that is by the driver side wheel well, not a Y pipe system, but it's still going to be a pain if my Cat is dead.
In the event that O2 replacement fixes my problem, I'll be happy. BUT if not, what am I to do next? My Cat replacement is very expensive even on Evil Bay and a serious pain in the butt to install. Naturally, I looked on Utoob for a workaround.
I'm going to check my fuel filter (when it stops raining) that was new a couple of years ago when I replaced the pump. Mama says buy a new truck with that whopping (not) SSDI check I get. LOL

JCR 56

Whenever you have codes read always get the actual codes and post on here, not what that guy at O'reilly's tells you they mean, which is usually wrong anyway.

MonteFord

Thank you for being so helpful. I unfortunately misspoke when posting. What I should have said was that the guy at O'Reilly's showed me the readings on the meter. Although I do not recall the codes I do distinctly remember it saying that bank 1 system running too lean, and bank 2 system running too lean.

F150Torqued

Boy, Paul Revere would have been in trouble if you, or the internet, had been around when he came screaming "The British are Coming". Sounds like you prefer to 'shoot the messenger' instead of deaing with the reported problem. Of course, bad O2 sensors can cause those codes. So can a bad PCM. But so can exactly what O2 sensors are designed to report on - LEAN condition being among them. Why not consider some of the numerous things that can cause the condition they are reporting just after the PCM has 'richened' the fuel mixture the maximum amount it can and the fuel/air mixture still appears too lean. You might have a vacuum leak - or a bunch of misfires going on. Or possibly an exhaust manifold leak upstream from the front O2 sensors.

Also @JCR 56 is spot on. Specific code numbers are far more helpful. There are several codes in the full list of codes that suggest mixture is too lean.

MonteFord

"Boy, Paul Revere would have been in trouble if you, or the internet, had been around when he came screaming 'The British are Coming' ".

Thank you for your comments. Unfortunately, since the dawn of internet thread boards, people have often assumed that other people are being facetious. I wasn't. But in yours and the op's defense, I've seen some very snarky and vulgar comments from commenters, even on this site. I'm here for help, not to create controversy. I'm handy, but by no means a trained mechanic. I've done my own tune-ups (and you know how fun that is on these trucks), replaced a few starters and alternators when working at an auto electrician's shop, my fuel pump and U-joints, brakes -both drum and disc, even done my own alignment. But my automotive knowledge is not as superior as that of others, hence my joining this group and asking for help.
That said, I've checked for exhaust leaks. None. Vacuum leaks, none. Fuel filter is good. My plugs are about two years old (although, I could get new wires). I've replaced my MAF sensor after seeing the code (which memory fails me on) saying it was the MAS. That didn't do the trick. I've ordered my Upstream O2 sensor and the handy specialty tool so I can give that a whirl. My truck has the small and larger cats on the driver's side, with one sensor by the manifold and the other behind the larger cat. Last resort, I'll delete my cat(s) and do the non fouler trick. My state does not have emissions checks. I just want to know if I'm on the right track here and would like suggestions. Should I have ordered both sensors despite seeing videos claiming that the "upstream" is the one that throws that code? Thank you.

JCR 56

Always replace the O2 sensors that are the closest to the engine.

Steve83

Never replace any part unless it's due on the maintenance schedule, or it fails a published test. Replacement parts are usually lower-quality than OE. Codes do NOT mean to change any parts, and they are NOT diagnosis. They only imply where to BEGIN diagnosis.

The first step in diagnosing a DTC is to confirm that the indicated condition actually exists. IS the engine running lean? If not, diagnose the hardware that generated the DTC (like the HO2Ss, PCM, & wiring). If it is, diagnose the engine, exhaust, fuel system...

F150Torqued

@MonteFord I didn't assume you were being facetious - and I wasn't trying to be facetious either. Tried to use a humerous analogy yes - but often the written word doesn't convey complete expression. I apologize for that failure. I see far too many instances of replacing a sensor that is reporting a condition the sensor is designed to monitor. And too many times respondents make that recommendation immediately - as though they are giving some professional diagnosis fix they know all about (like the parts counter person).

From the OP, I wasn't able to discern prior diagnosis - beyond replacing MAF and plugs, and suspecting CAT, mostly based on the atypical parts counter person's uneducated interpretation of some DTC (frequently ridiculous - ie: what is a MAF code?). And he said it wasn't misfiring when your CEL was flashing (which is the 'designed' meaning of a flashing CEL). But, as you put it, to add insult to injury, -- Your CAT's, nor downstream O2 sensors - which only monitor CATS efficiency, absolutely cannot and will not EVER produce lean codes. Cat efficiency yes, but lean no.

There is no shame in not knowing, nor asking, but the thread subject as well as original post gave the (non facetious) impression that some diagnosis explanation was in order to save a member from shotgunning away the SSDI check. (LOL) With these computer operated engines, one almost _has_ to have an OBDII reader tool to do better than parts swap. But with one - you can always figure out a way to 'challenge' a particular sensor to SEE if is working or not. Spray a little ether in the intake and watch your O2 sensor signals go solid "+" for a few seconds. This brings up another important question. HOW DID YOU check for vacuum leaks. You can't depend on idle quality or RPM changes. The computer will compensate way TOO fast. You need to monitor fuel trim values while checking for vacuum leaks by spraying ether or an unlit propane torch (my preference) around everything.

As for just replacing (Upstream) O2 sensors - the ones responsible for reporting Rich/Lean codes - they are so absolutely central to the proper operation of these engines, I'm actually an advocate of preventatively replacing them every 100k miles or so.

Hope this helps - that's the sole objective.

MonteFord

@Torqued: Hey, no harm, no foul. I'm grateful for the input. Okay... flashing CEL: I erroneously mentioned it flashing. It WAS flashing and I remembered that I'd gotten sidetracked and forgot about my #3 plug misfiring and has stashed said plug in my glove box. I installed that plug THEN went to O'Rilleys. BTW in my tiny town, those guys are all motorheads, but I concede that that doesn't mean that they're right all of the time. Anyway, that's when he -the manager, and Ford hecklers [wink]- said it was my MAF sensor, which I replaced. My next trip was after that, and was when I saw the banks 1 and 2 "system running too lean" on the LCD screen of the scanner. AFA checking for vac leaks, I did the old listening trick but not a chemical or propane test. BUT this morning, I was behind my truck with it running sipping my coffee and heard a "whistle". I just now looked -based on Youtube education- behind my breather. There's a big rubber hose running from the back of there and disappearing under the firewall. It looks worn and I can see a slight gap. I haven't sprayed carb or brake cleaner there yet, but I'm concerned nonetheless. The engine was off. I have to go to band practice or I'd check it further. I'm thinking of going and getting a screw type hose clamp until I can figure out what it its and how to replace it. My new O2 sensor arrived today so that's on my to-do list. The truck has 241K on the clock so it can't hurt to replace it regardless. I'll try to get down to O's by at least Friday when I'm freed up and get code numbers to pass on. Thanks so much for your patient assistance!
Cheers!

Steve83

Yes, removing a high-quality proven working part to install an unknown can certainly hurt. If it needed to be replaced after some number of miles or months, Ford would have put it in the maintenance schedule.