Bad gas?

Get a code reader to find out what item(s) the computer is seeing as wrong. Or get someone you trust to give you a readout.

Or that wirey haired kid from the next street is siphoning your gas. Good luck.

thanks, bob!

The guy who changed the oil may have accidently damaged/disconnected the O2 sensor wire or some other signal wire with his elbow.

When the O2 sensor is out the injection defaults to a rich mix to keep it running.

Mr. Gee

All the other guys have sent you excellent info. that should solve your problem .

The only other thing i can think of is a blocked catalitic converter.?

This is very unusual but i have seen it happen on low miliege vehicles , due to faulty cat. converters from the factory . We are now recieving many, to most of our automotive parts from China and they do not have the same quality control as we used to have .

99% HEGO sensor. If the HEGO is faulty, the vehicle will default to rich fueling to ensure that the air fuel mixture does lean out and damage the engine.

you may find you got the cheap cut gas it seems in canada we have that problem they are cutting it with wood alcohol just like the winter fuel due to refinery shortages. i saw a tank just like that and changed stations all better now

It does sound like the O2 sensor under the car. Does the car run ruff and or put out a lot of black smoke when you accelerate. One other thing could be a damage vacuum line could make it run rich.

Also like another said alcohol mixed gas. You haven tried to use E-85 blend? The car will run on it, it just won't like it like low power. Also if the cat is stop up the car won't rev fast and it could run hotter than normal.

Some thoughts

metalSmith's

A good post, but it would be better if he let his wife or a friend drive the problem car and he watched from another vehicle for the black smoke, there is usually not enough for a driver to look for safely anyway.....

It sounds as though the Oxy sensor is either disconnected or broken, it would give the same type of problems he describes......

Good suggestion Andy Germany, I typically have to do my own trouble shooting, I usually find a safe place and adjust my mirrors to help me see with. If the fuel is to rich you usually will see a large puff of black smoke on hard acceleration from a stopped.

metalSmith's

Absolutely correct.....

Might be difficult to see, if the cat-con is working properly.

If the Oxy sensor is not working (as may be true) then the kat will (even if in good working order) become "overloaded" by the subsequently rich mixture. Which will eventually damage the cat anyway.....

If the cat is working well, then as you say, once it has got to its working temperature, it will tend to remove more of the black cloud, but when cold, I feel that most probably the black cloud will be visible to anyone following.....

I have to admit that this is all theory on my part, but hopefully close to reality enough.....

I would get the Oxy sensor checked and if needed, replaced, it could be done in a shorter time than it takes to post on CR4....

Read the codes first. In the past, I have had a speedometer drive cable fail. Didn't think much of it. A few days later, the engine went rich. I didn't connect the two (who would think!) and spent the next month disconnecting and reconnecting the battery to reset the computer fault mode (you get ten starts before the fault mode kicks in again) as I rebuilt the carburetor, replaced the O2 sensor, exhaust recirculation valve, plugs, wires, coil, ignition module and all the vacuum hoses (they needed changing anyway I found out). The problem still didn't go away so I temporarily gave up and decided to change out the speedometer cable. Fixed the problem. The speed sensor located at the speedometer was now able to send correct information to the computer relative to engine speed. I would have found this out had I checked the codes first. With all the new parts, it ran better than ever to 279,000 miles before I gave it to a friend and he kept running it.

Gas Thieves???????????????????

Yes, get a lockable gas cap.

What is size of your gas tank. I'm sensing that the 325 was the abnormal . . . and is what may have led to exhaust system code. That could have been damage to CAT from overlean mixture . . . implicating the HEGO among other things such as clogged or sticking EGR pipe/valve. However, 55K miles seems low for failed or sluggish exhaust sensor. I don't see any connection between oil changes and the problem you describe.

What we need is to know you MPG so we're all on the same page. Without knowing tank size . . . no way to know which is normal and which is not, if either. Also, did you check the warranty? Also, did you take the car in for free evaluation (in US) of the engine code? In US, the emissions controls (engine fault codes) are warranted for five years, 50,000. I would check with the selling dealer who sold you the car.

I don't see any connection between oil changes and the problem you describe.

Rule #1 The last one that touched it screwed it up. Has anyone else ever found this to happen?

anyone else ever found

Yup. All the time. The car is driven onto the lift, elevated, worked on, de-elevated, driven off the lift. Wires and vacuum hoses get nicked, broken, and pulled loose during these various steps.

You will often find tools left behind under the bonnet. Perhaps the phone rang or he broke for lunch; forgot his place when he returned to the job.

Sometimes stuff has to be moved out of the way to accomplish a "job" (i.e. a signal wire or vacuum tube). But then, it doesn't get replaced.

Check this.

But oil change? Really?! I suppose it might be possible to have a temporary problem (other than a little smoke and smell) if oil was spilled outside the filler tube; or that the oil was overfilled (most unlikely at a commercial service). But such a scenario does not fit with the sequence of events OP describes: where before any oil change) the (supposed) problem arose; oil was changed; the problem re-arose; etc. To me, this would be sufficient to eliminate any suspicion or oil change, or oil change-er. (All this assuming that the car in question is not one of those where the engine is pulled to change oil . . . or was that spark plugs? )

I was thinking the oil filter. May not have spun off quite so easily. Or the mechanic didn't have the right filter wrench then went in and broke the O2 wire or loosened it in some way. (Jiffy lube or Sears might do something like this, no offense)

Thanks, eriew, now it's clear what you were "driving" at. Yes, that's a valid possibility; but, if I read correctly, it would not explain the owner-perceived existence of a problem before any oil change was done.

In OP-er's place, again, my first instinct would be to take the problem first to a dealer in hopes of getting the (premature) problem taken care of (or eliminated) under vehicle or regulatory warranty on the low-mileage vehicle. Even if a $75-100 (typical) diagnostic fee could not be avoided, it's probably a price worth paying . . . in order to establish a documented record for the vehicle . . . just in case . . .

With Sears and their fondness for repeating service and replacing non-defective parts . . . I certainly don't take offense; neither do I take vehicles to that company for repairs. No experience with Jiffy, since I do my own oil changes.

Thanks again for the clarification.

Reread the OP's description.

1: poor millage one tank

2: oil change

3:first tank ran good

4:Now engine code

I don't think he asking about the millage thing but about the code.

Just that the millage was the first problem.

It is of course possible that the person who replaced the oil, helped himself to two working sensors, by replacing them with ones already defective......or am I being too un-Christian when I say that?

Andy

As good a guess as any. It is difficult to diagnose this problem over the internet. Stranger things have happened than the one you suggest.

I heard that sometimes on ebay someone will put bad parts on an item and take the good parts off before selling. Anything is possible. We just don't know.

Have other problems been reported concerning this specific service provider? That is a question that one might ask.

Are you implying that some of the mechanics here in the states might not be honest? I never heard of a dishonest mechanic. That seems impossible.

Yeah yxeah yeah!!! (Beatles refrain!!)

Before joining the RN many years ago, I worked in such a place and the bits that got replaced first were still charged and left on the bill, with todays complicated car electronics, does anyone think that it has got any better?

You mean, like putting oil in the radiator? Water in the engine? Things like that? That would indeed reduce MPG . . . considerably. Thanks, I didn't take that into account.

My experience: Engine light came on. Two error codes indicated that both O2 sensors failed. Thinking that the likelihood that both sensors would fail a the same time was remote, I spent hours checking all the connectors and wiring, reset the codes and still it came up with both sensors failed. Replaced one O2 sensor (the parts store only had one in stock) and the associated error code did not reoccur. Replaced the second O2 sensor and it also cleared. I spent too much time over-analyzing the problem and wasted gas driving with the failed sensors and making multiple trips to the parts store.

Recommendation: Do a quick visual on the wiring. If no problem is found, replace the sensor.

29 reasonable responses, here's #30, hope it is too. Yes, it may be any or several of those things. Or, it could have been a tank of "bad" gas. A bit too much alcohol in the blend, a slug of water from condensation, some debris riled up by the refueler truck that left 10 minutes before you got there fouling an injector temporarily, etc. Question is, does the mileage problem recur? I've had a "check engine" signal for too lean an exhaust before, but it didn't affect my mileage.