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Discussion Starter #1
Haven't installed Wayne's tune yet so has factory tune now.

I recently changed the intake around so it has a cold-air inlet behind the lower grille. Also, installed the CFM Throttle body and random cat. No other mods to intake or exhaust. I've put about 50 miles on it since these changes. It has stalled intermittently (3 times) which it has never done before and the idle has been fluctuating a bit too.

Today, it spit out the P0133 code after a quick run through the gears up to about 75 mph and probably not exceeding around 5000rpm, if that, as I opened it up a bit.

I read it's an issue with slow response to/from the HO2S - heated O2 sensor - correct?

Why might I have this code and which sensor is it - the front one or the rear one?
Any help - appreciated.Kevin
 

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Moved to ”Ford Focus Technical Chat”

Here's the full code description:
P0133 - HO2S Sensor Circuit Slow Response (HO2S-11)
The HEGO Monitor checks the HO2S Sensor frequency and amplitude.
If during testing the frequency and amplitude were to fall below a calibrated limit, the test will fail.
Contaminated HO2S sensor.
Exhaust leaks.
Shorted /open wiring.
Improper fueling.
MAF sensor.
Deteriorating HO2S sensor.
Inlet air leaks.
Access HO2S test results from the Generic OBD-II menu to verify DTC.


Did you reset the ECU after installing all the mods?
 

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sounds like the sensor went bad. and it's the one after the cat.
 

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O2's are like any servicable part of the car, they wear out. Plain and simple. I had to replace my primary. The 2nd O2 in my car is not an issue as I a) have it turned off via SCT tune, and b) my AEM UEGO Wideband O2 is in its place. If you undo the battery fora few minutes and put in Waynes tune, you should have no issues. 9 time sout of 10, the tuner turns off the rear O2 as a standard procedure.
 

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Discussion Starter #5
Unfortunately for me, we have state vehicle inspection in the wonderful state of NY. I will have to re-install the factory tune for inspection - yes? And, in that case, I'll probably have to replace the O2 sensor. I installed the HIA Street tune last night and drove it a bit - pretty happy with the tune except for some idle issues I'll have to discuss with Wayne - but I used the Xcal2 to clear the codes before installing the tune and the CEL didn't come back on - yet. Probably because the rear sensor is turned off.......I had actually requested that it be left on, maybe that didn't get through either. Sounds like Wayne is frequenting the boards again, I'll have to try and contact him too. Anyone have an idea, off hand, what the rear O2 sensor might cost?
 

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could something as simple as a drop in k&n filter (drop in - not an intake kit) cause the 133 trouble code to show up?

also, does the 133 code always indicate the rear sensor? i dont know what "Upstream heated O2 sensor circuit slow response" indicates. thx for any help.
 

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i have another question: if you get a cat back exhaust done at a shop do they just pop out the old sensors and put them into the new exhaust system?
 

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yoozer said:
i have another question: if you get a cat back exhaust done at a shop do they just pop out the old sensors and put them into the new exhaust system?
They don't pop out. They screw out. I don't see why they wouldn't.
 

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Somebody tell me if I'm wrong but isn't the heated 02 sensor the 'upstream' sensor? Upstream means at the start of the stream (which is before the cat) AFIK. The second 02 sensor is the 'downstream' sensor. The heated sensor (upstream sensor) is the sensor in the manifold and needs the heater to work properly before the engine warms up with the manifold temperature. Your car will run poorly without this because your ECU adjusts your air/fuel mixture based on this sensor's input. The second sensor (downstream) simply throws a CEL if your cat isn't putting out the right gasses but doesn't have any other effect on how the car runs.

As for the aftermarket exhaust question, I dunno about your SVT but the SPI has the upstream sensor in the exhaust manifold and the downstream sensor in the cat pipe after the cat so an aftermarket exhaust wouldn't need to have them moved.

NEway, the upstream sensor from Ford is $90 IIRC or a Bosch replacement from Autozone is $30 (but doesn't work as well in my experience....the sensor part is okay but the heater doesn't heat as fast as the Ford so the engine runs funny til it gets warm, maybe I got a bad one)

In summary, the second sensor, the downstream sensor after the cat, will not cause your car to run differently, it will just throw a CEL. The upstream sensor, before the cat, WILL cause your car to run poorly if it is bad.
 

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Both are heated, but you are correct. The downstream is just a check.

I think the Bosch is actually a better part and I have seen others on this forum say the same.
 

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I see, thanks for the clarification.

I hadn't read good or bad about the Bosch before I bought it. "In my experience" = 1 sensor [:)] I may return it and try another but it hasn't been acting up since the weather got warm so I had forgotten about it until just now.
 

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Discussion Starter #13
It's interesting that a MAF problem could throw the P0133 code - not sure why this would occur or why the electrical engineers have it set up this way. I did re-oil the filter and the induction tube is different from stock. I tried to use as little oil on the filter as possible while trying to get it coated all the way - I even blotted it with paper towel before installing to try and make sure it's even and not too much.

Even with Wayne's tune onboard, it still wants to idle kind of funny - when ever I kick it out of gear and coast to a stop for whatever reason, it'll idle at about 1500 rpm. Once I come to a complete stop, it will finally drop down to about 950rpm. And occasionally, it will fluctuate between about 950 and 500 too.

Any safe ways to clean the MAF? I know you have to be super careful with them and the wire elements. Maybe it's just the O2 sensor - the light hasn't come back on since installing the tune.......
 

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"It's interesting that a MAF problem could throw the P0133 code"

I agree, it sounds a bit odd to me, but I suspect they know what they are talking about.

"
Any safe ways to clean the MAF?"

There's a "How To" somewhere on this board. Try a search. I bet even a web google search would pop pop at least a couple of "how tos."
 

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Yup, it's happened to me a couple of times before. While I am typing something, someone else is already posting their response!
 

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Discussion Starter #18
I popped the MAF out just to visually inspect it the other day - is there a part number for the O-ring? Yeah, upon getting it out, I noticed that a 1/4-inch chunk of the O-ring was broken loose, probably when it was installed at the factory because I've never had it out before and I'm the original onwer. It was there, just no longer attached to the rest of the O-ring.

I don't think this is the cause of the idle issue, but it's got to be fixed I guess. It would result it the absoulte tiniest of air-leaks - seems inconsequential but hey, maybe it is enough to fool with vacuum..... I don't know.
 

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Nope, that leak would be before the MAFS. It would read that air coming in. Unless, there's an o-ring on both sides of the MAFS on SVT... I don't know. On my SPI, there's only one o-ring, before the MAFS.
 

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Discussion Starter #20
UPDATE

Been a few weeks now since the mods were put on. I ran Waynes Street tune first and of course, no more P0133 code - probably disabled rear sensor. With the street tune, damn thing had more idle problems than with stock. The most un-fun is a stall right as I'm beginning to navigate a turn. So, I ran Street for one week, no improvement with time so I loaded the Highway tune - at first, I thought it was better, but the bad idle business began again - this time stalling, spontaneously and intermittently, and at idle, it was missing and running poorly. The stalling is weird - if I disengage the clutch to coast to a stop, the idle will sometimes stay at 1500 until I come to a complete stop, only then will it drop to ~975; other times, under the same conditions, it will drop real low, fluctuate and mis-fire for a bit and then either stall, ot just run rough until I start up fromt he stop. Ran that a few days just it give it time, no improvement with time. So, said the h#ll with it - returned CPU calibration to stock. Have run it about a week now - no P0133 code and, although it might sound like an insult to Wayne, the stock tune is better than his for driveablilty. The typical SVT quirks are there but shifting between gears is smoother and at idle, it's not stalling or mis-firing.

As for the P0133 code - perhaps something about the header coating or cat temporarily contaminated it and it had since burned off cause there are no codes now, none at all.

Tried to get together with Wayne - still working on it........ He was supposed to call, must be busy....... Any other folks here with ideas as to why the HIA tunes would have such issues on my application? All I've modded is a CAI for the SVT airbox - creates some ram-air effect at a good speed, the CFM/Focus Central TB, and the Random cat. I'm baffled and I'm hoping my ~$380 inventment in the custom PCM calibrations will pay off - eventually. Could have done some brake worke with that cash.......
 
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