I am getting poor mileage (about 13mpg), and was told by a mechanic friend to replace my 02 sensor and PCV valve. Would appreciate any guidance on doing this--where are they located? any tricks to doing this?

Thanks!

 

For anyone to be able to help you we'll need to know what kind of truck you have.

The basics:
-model
-year
-engine

You'll need to help us help you. This applies to just about any question you might ask here. You could even put the details of your rig into your signature block so you don't need to remember to tack it on every time.

Calvin

 

true true....however I don't think you can get a sig on your first post

Itch

 

You know, I'm closing on 200 posts and I still haven't bothered to do my own. So much for taking my own advice.

 

hahaha....I did notice, you didn't take your own advice!

 

The PCV valve is at the rear of the passenger side valver cover under the upper intake.. hard to get at. The O2 sensor is in the exhaust Y pipe.. passenger side right about paralel with the back of the front wheel. The O2 sensor requires a special socket or a large box end wrench(and often some elbow grease) to remove. However.. these components may or may not be causing your poor milage. Along with the general info the others requested, tell us the general state of tune of the motor.. like when the plugs and wires were last changed, and if the Check Engine light has ever been on.

 

You might want to check for any stored codes first...eventhough you CEL might not be on.

I was able to remove my O2 sensor without a special tool, I did cut the wires, but if you're replacing it anyways it's no big deal. Works best if you run the truck for a bit to get the pipes warm...careful not to burn yourself! Put some anti-seize on the threads of the new O2 sensor, if it doesn't come with any applied to it.

Itch

 

Thanks guys. Sorry about not including more information. I have a '94 Ford F-150 with the 5.0L V8. I replaced the plugs last year, but not the wires. The truck has 160K miles on it--I have put 70K on since I bought it. I haven't replaced the plug wires, O2 sensor, or PCV valve in that time. Just had the fuel filter replaced. Truck runs good, although a little rough at idle. I haven't seen the engine indicator light come on. I don't have an OBD tool.

 

Wires, immediately, and if the firing order is 15426378, WATCH OUT with the routing of #7 and #8. Keep #5 and #6 between those two as long as possible, or you'll get the proverbial 7/8 crossfire, even with brand spankin new wires. Don't ask me how I know this. You said plugs, but didn't mention cap and rotor. Grab those while you're at it, and get a set with copper or bronze electrodes. The caps with aluminum electrodes just won't last, even the Motorcraft caps. MSD has a pretty good set that I'm getting good service from. Neither did you mention what brand of plugs you put in it. There should be an underhood sticker that gives you a Motorcraft plug number. DO NOT USE AN EQUIVALENT OFF BRAND. DO NOT USE SOOPER DOOPER WHIZBANG TURBOENCABULATED GIMMICKY PLUGS. Stick with the Motorcraft. Bosch Platinums will disintegrate. Again, don't ask me how I know.

To verify the need for wires, put the truck in a dark garage, and start it. Look under the hood and see if you see ANY spark at all. You should NOT. If you do, something is leaking (electrically), and all the spark intended for the plugs is not making it. You'll usually get some misfire, detonation, and possibly backfire from this. A good set of Motorcraft wires is recommended. I put a set of MSD 9mm racing wires on mine, and the Ford TFI ate those in about 5000 miles. Went with stock Motorcraft 8mm wires, all is good again. You can use the 9mm Motorcrafts if you want, but I don't think you'll be able to justify the additional cost.

Dunno how many basic tools you have, but add to your arsenal a fuel pressure guage, a vacuum gauge, and compression gauge. Wouldn't hurt to have a vacuum pump too. You'll spend about as much on these four items as you will for some fancy schmancy code reader. You won't regret it, especially when the EEC isn't throwing codes, but it's running like poopy. If you can count from 1 to 9 and the bulb isn't blown on your CEL, you probably DO have an OBD-I tool. Office Depot calls it a paperclip. See www.fordfuelinjection.com for good info on pulling codes and how to interpret them. They've got both 2-digit and 3-digit code lists posted on that site. Depending on your engine/powertrain setup, you may have either. I think most of the manuals and AOD's had 2-digit code sets, where E4OD and 4R70W had 3-digit codes. 94 model may have had 3-digit codes across the board, dunno. GREAT site for EEC help.

These steps may save you a pile of money by preventing you from taking your truck to a stealership if you just get a few basic diagnostic tools and do the diagnostics yourself. And dealerships don't even provide the Vaseline when they rape you. Gotta bring that yourself too, or they'll get you for shop supplies whether they actually do anything to your truck or not. There's lots of brain power in here that can help with actual repairs and walk the most novice mechanic through most of the procedures, even with some of the most complicated repairs. You've come to the right place, and we'll pitch in and help you learn how to work on your own truck.

If this doesn't help your mileage, chances are you have some other issues. Post back if you have any codes, and some of us may be able to lead you in the right direction. Oh yeah, btw, an O2 code does not always mean the O2 sensor is dead. Sometimes, it means the exhaust is always rich or always lean. The exhaust content has to alternate lean and rich causing the O2 sensor to switch on and off for the ECM to know it's working. Dunno who's brain storm this was instead of using an averaging type sensor, but I wasn't asked when the EEC-IV was designed.

Oh yeah, btw, welcome to FTE!!

 

Well said Old_Paint. I've got to tell you....every single one of your posts, long winded as they may be, are very informative and helpful. You're a great asset to the forum.


Thanks
Itch

 

Yes, thanks a bunch "Old Paint". I managed to get my sensor, pcv valve, and plug wires changed yesterday. It seems to run better. Time will tell on the mileage.

 

I'm not surprised the wires improved it. The first time I replaced my wires, I did 'em one at a time, and put them back EXACTLY like they were routed from the factory in '92. I know, I've owned it since 16 miles on the clock. While this improved driveability, it didn't elminate misfire and pinging. Turns out, in '92, they were running 7 and 8 side by side at assembly plants, which is BAD on the 5.0 SO motor (15426378 firing order). When I took it to a dealership because I didn't have time to work on it, they basically tied my wires up in all kinds of nifty knots, and in the process, pinched and nicked them in several places. Talk about P.O.'d ..... Those wires had about 200 miles on them when the dealer destroyed them, and the real kicker is, they didn't have wires to replace them. $800 later, I finally gave up and fixed the truck myself. Talk about a learning experience......

Follow up the wires with a good cap and rotor too, at your earliest convenience. You won't regret it, and you can't go wrong cleaning up the ignition system. I'm still liking my MSD cap and rotor with copper electrodes. (about 15,000 on 'em) If the looms are broken/missing, it won't hurt to replace them to keep the plug wires neat and appropriately spaced from things they can arc to.

Then, later, when time/money permits, get a good vacuum gauge and check the vacuum on the intake at idle. If you don't get at least 18 inches vacuum without pulsing, start hunting leaks. Unmetered leaks into or inside the intake will cause all kinds of driveability issues from surging idle, pinging, missing under light load, poor throttle response, you name it. It doesn't take long to yank the TB and upper plenum for a good cleaning and fresh gaskets. I disassembled one afternoon, spent the next morning cleaning, and reassembled the following afternoon. WOW, what a difference in an engine I thought was on it's last leg. While you've got the TB off, put a new TPS on it. It's a cheap added maintenance fix that will save you pulling the TB off again later. You can't replace the TPS with the TB mounted on the intake.

As long as the engine isn't smoking or knocking, it's probably in pretty good shape mechanically, particularly in the long block. Poor performance will typically be an age related problem, and face it, 10 years or more is OLD age for any mechanical system. I liken it to "dog years", about a 7:1 ratio. Since we're in the '86-'97 forum, any truck in here is 70 years old in dog years, minimum.