Hi!
I've read through several of the threads, and am hoping that I might be able to get some advice, and save myself some aggravation :-)
I've got a 2003 F150 XLT 4.2L 2WD, around 100k mi.
About a month ago, the "service engine soon" light came one, so I went directly to a local parts supplier and had the codes read, which indicated that both upstream O2 sensors were malfunctioning. It drove normally (aside from the hesitant start-up, which I was attributing to winter mix fuel). So about a month passes, and I'm driving home on the interstate again and I begin to feel a vibration, which worsened, and the dash indicator flashed for about a minute and then went solid on like it had been. Now it also throws codes for cylinder 1 and 2 misfire and idles rough and while it is somewhat less rough at speed, it's still noticeably having some issues going down the road.
From what I've gleaned from the collective knowledge on this site, the symptoms seem to fit the problem of bad oxy sensors. I am however suspicious that they are not the actual root of the problem though, because why would both HO2S's fail at the same time? I read here that there are a number of upstream components that can mimic bad oxy sensors, but didn't see any threads or posts where someone's had the same issue as me, involving both sensors. I know that the downstream ones throw codes too if the upstream ones do due to the effect on the mix management etc that they're involved with managing.

I'm a person that learns things and figures it out as I need to, so I have a decent base of automotive knowledge but not enough to be confident by any means regarding this issue.

Any help will save me a lot of a few things that I don't have to waste, so thank you in advance!

Also, I'm new here so I apologize if I'm putting this in an extremely wrong place. Thanks.



Update... since I first typed this out, I cleaned up my battery posts and checked fuses, and replaced my air filter which didn't seem too awful. This seemed to correct the mediator start and decreased the rough idle somewhat, but there's still obviously a problem and now no "service engine soon" light. Thanks!!!

 

I also checked the MAF and since it looked pristine, I didn't do anything to it.

 

And mileage is 87k

 

What codes exactly? The O2 sensors look for oxygen in the gas and can detect oxygen if the fuel ratio is less than 14.7 to 1 air to fuel. Missfires could give you a code from the sensors. Most of the time the issue is not the sensors but something else causing a rich fuel mixture.

 

Thanks for your reply!
Initially (when the ses light first came on) it was giving p0133 and whatever the corresponding code was for bank 2, as well as the codes for the downstream sensors. I apologize but I didn't write them down--just got the parts recommended to replace the sensors.
When the problem got worse the other day, I read the codes and in addition to the original ones, misfires were indicated in cylinders one and two.
Since I disconnected the battery to clean the terminals, the ses light is off and hasn't come back yet. My understanding is that if that light isn't on, no codes will be present. If that's true, I can't get the codes to give you currently.

 

Read this if you haven't already. One of the causes could be a vacuum leak

https://www.yourmechanic.com/article...-blake-griffin

 

Thank you. I read what you referenced and I think tomorrow the first thing I try (before limping it to somewhere to buy a multimeter with wire-piercing leads) will be to check for vacuum leaks. If there's a leak, it will allow carb cleaner or starting fluid in, which will result in the engine bogging down, right?

 

It may not be relevant, but earlier in the day when the problem got noticeably worse, I had to really lurch onto the brakes. Damn red light cameras with shortened yellow lights!

 

No. You need a helper, a scanner, and an unlit propane torch. When it finds a vacuum leak the fuel trims will go nuts.

 

Thanks...I assume you mean a scanner with live data? I'd really like to avoid having to buy one if it's possible to arrive at the same conclusions deductively with other methods. The one they pulled my codes with at the local parts place doesn't do that.
To see if I understand, using propane gas to "probe" for vacuum leaks, if one is present and sucks in propane, will cause a change in my idle that I'll be able to notice under the hood, correct?

 

This hose or tube is the only one that really looks bad, as it has some deterioration in the insulation.

Will try the propane vacuum test first tomorrow.

 

AKITE , your showing your a pretty naive guy from the responses your giving.
The motor is computer controlled, you have issues that need to be taken care of properly.
You will not notice a change in idle with a propane test.
The system is too fast in responding because the computer control will readjust to keep the same idle speed as it is designed to do.
Your not working on an old carbureted motor that has no such fast control correction.
You will either 'get lucky' or need a Scanner to look at the short term fuel trim tables for the reaction when the propane gets through the leak area.
Basically you have little idea how the systems work at this point.
You came here for help. it's time to listen.
If you feel a bit insulted, sorry but it's the real help you need..
Good luck.

 

No worries Bluegrass, a stranger typing in a thread on the internet isn't worth feeling insulted over. Thanks for the advice all the same. Also, me asking a question about something doesn't mean that I don't understand it, nor does the collective content of my posts here include everything I know and understand. I'm glad you're an expert, but no need to condescend.

Are you saying that this is wrong?:




To rephrase what I thought I rather plainly put before, to "get lucky" by trying a 5-minute test using things I already have is preferable to buying equipment that I might not need to arrive at the same conclusions.

 

The computer is too fast, you'll almost never discern any difference in the engine's operation. You MUST look at the short term fuel trims if you want to have a chance at diagnosing it.

 

If all you had was misfire codes P0302 and P0301 then you should have nothing to do with oxygen sensors. Or did I miss something here?