BroncoCop

Ok...here goes.

I have a '96 with 5.8 with 205k miles. I know I have two upstream and one downstream O2 sensors. I know that the downstream O2 sensor is just a cat sniffer, but it is throwing a code and I'm going to change it anyway and have already purchased it, so it's a non-issue.

My question is regarding the two upstream O2 sensors. I checked the codes a week ago and the computer indicated that my two upstream O2 sensors were faulty. As is my habit, I cleared the codes when I checked it. I went into work the other day (part-time Advance Auto Parts) and checked my codes again (the light bulb for my CEL on the dash is blown so I just plug the computer in frequently). As expected my computer revealed that the downstream O2 sensor was faulty, but unexpectedly my upstream sensors did not show up.

Now, I'm getting horrible fuel economy (using about 1/8th of a tank of gas in a 6 mile round trip to work), and the engine seems to be running rough at times. I have already purchased the upstream O2 sensors to replace them this weekend. My question is have I spent unnecessary money by buying the upstream sensors, because my computer is not currently indicating a problem with them, or is it advisable that they should be changed anyway due to the past code and the current fuel economy?


Thanks in advance

fltdriver

As long as you get quality sensors it's never a "bad" idea to change them, especially if the ones you have look old/original. That being said it's possible to pull them and test them to see if they are functioning properly, other reasons for o2 codes are damaged wiring, bad/dirty/corroded connectors, etc..

I would check your vacuum lines as it sounds like you may have a leak, also cleaning the MAF screen with MAF cleaner, as well as hitting the throttle body blades/edges with some TB cleaner, is never a bad idea when it comes to a drop in MPGs. Other than that your basic tuneup, checking that the brakes are functioning properly, and ensuring your tanks aren't cross-filling are a good place to start.

BroncoCop

I have recently done a tune up, new plugs, wires, cap, rotor, etc. I know for a fact that there is a vacuum leak, as the dash vents will switch to defrost under acceleration. Chasing down that vacuum leak has been the bane of my existence thus far under the hood. I wish there was a more comprehensive vacuum diagram than I have been able to find thus far on line... You know, one that actually labels each line and shows you where they go and what they hook into, with pictures for us dumb red-neck Texans. Lots of those stupid, tiny, hard plastic vacuum lines that are a real pain to mess with cause they break so easily.

From what I have gathered looking at my engine, the only things the vacuum controls are the HVAC, the fuel pressure regulator, and the EGR valve. Have I missed something?

I have cleaned the TB and the MAF when I did the tune up, to include sea-foaming the engine through the brake booster vacuum line. I know it's not going to be a powerhouse engine due to the mileage, but it's still pretty sluggish.

A tranny filter/fluid, to include differentials and transfer case service is soon in the works too.

BLDTruth

^^^Change all the vacuum lines and then you won't have to hunt for it. It's a ~$25 fix that will take you less than an hour to do. After reading about all of the problems with cracked plastic vacuum lines and hearing guys like fltdriver stress the importance of replacing them, I finally gave in and ordered some high quality thick-walled silicone tubing.

A how to - http://www.fordtruckclub.net/forum/s...ad.php?p=48736

BroncoCop

I'm going to do the vacuum lines this weekend... looks like a fairly easy project. That should eliminate that issue.... hopefully.

BroncoCop

Those instructions for the vacuum lines seem pretty straight forward, except that my vehicle is not equipped with a smog pump, nor is it equipped with an air tube for the catalytic converter. My guess is that if it is not there then I don't need to worry about it. Is this correct?

Bonus.... got the little plastic T's and 20 foot of 5/32 vacuum line for $12, a good $10 cheaper than everyone else is posting.... makes a cheap fix even sweeter.

I'm hoping (crossed fingers), that between the vacuum lines and the O2 sensors I should see an increase in power and efficiency.... here's hoping for the best. When I get it done tomorrow and drive it I will post back and let y'all know the results.

Chris_1

iTrader: (1)

The computer will log a code, but if it goes through so many drive cycles without a repeat of the issue, it will erase the code. That's probably why you saw upstream sensors and then didn't.
I'd get the motor running right (vac lines and check the soup can reservoir for leaks) and see what happens before using the new O2 sensors - the old ones may be fine, and I'm presuming you can return the new ones if you don't use them.

BroncoCop

Ok....


Did the vacuum hose fix, glad to be rid of those stupid plastic lines, and it was incredibly easy due to the fact that my system had only a fraction of the vacuum operated equipment than they did only one year earlier. I guess OBDII has some advantages. But now I know I have no vacuum leaks what so ever.

Changed all three O2 sensors, and low and behold the vehicle runs pretty good, not to mention that I'm throwing no codes now. I have noticed a surging under light throttle, the engine revving up and down quickly when I have very light throttle, yet no codes..... any thoughts?

Now I have to tackle that pesky catalytic converter issue... it's starting to clog up, major performance issues when the engine reaches operating temp. I'm exploring different options in removing the existing 2 cats and just going to a single cat. My question with that is would going to a single cat cause the downstream O2 sensor to go haywire and throw a code?

Chris_1

iTrader: (1)

Maybe ? That system can be touchy.
Normally, the cats will clean themselves if you get them hot enough. Lots of short drives and/or a rich fuel mixture can clog them up.
A couple hours on open highway would do them a world of good.

BroncoCop

While under normal circumstances I would agree with you, however, due to the fact that they are the original units on a vehicle with 205k miles on it, with who knows what kind of driving done on it before I took ownership, I feel fairly safe in saying that the cats are well beyond cleaning.


Better to be safe than sorry with this one.