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First time posting, need some advice. We have a 2002 lx with 126k miles. Got it from my parents and it has been well maintained by the original dealer. I'll give all the history I can as concise as possible.

1) - Noticed a black residue on the rear of the van (dry black powdery, like charcoal) accompanied with the check engine light coming on. Local shop replaced O2 sensors and gave it a tune-up. (NOV. 2010)

2) - Immediately after service developed a new problem: Mostly on cold starts within 1 block of driveway, the engine stalls(?), loss of power, only temporarily for 4-7 seconds. Reminds me of an old jeep when you pull the manual choke. Sounds like the engine is going to die, van decelarates, then comes back and accelerates (late response) and then continues normally. Happens about 80% of the time, cold starts only.

3) - Took it back to local shop, no error codes present. Did notice a front broken engine mount. No "soft" codes either.

4) - Contacted dealership about problem becoming more frequent and sent it in. They could not re-create problem #2, but replaced the engine mount and did a timing/drive belt service. (DEC 2011)

5) - Got van back and problem still occuring but noticed a significant drop in gas mileage. Lowest was 13.5 mpg, highest since is 15.8 mpg.

6) - Drove it for two tanks worth and sent it back to the dealership. This time problem #2 occured with them while it was reversing. (We've never had it happen in reverse) The technician said he thinks it is the beginning of a transmission going out. No error codes at all, not even "soft" ones. Also said that didn't think it would affect gas mileage that much... Warned us to get ready to replace the transmission. They also put some fuel treatment in the tank and it helped a little. Attributed the the gas mileage problems to winter anti-freeze additives in the fuel supply ... Sounded like guesswork to me though.

So, that is where we are. I have some theories but curious to what others may think. I see on this forum some folks replacing tranmissions with less miles than this. The thing is it doesn't shift hard, or clunk at speeds. I will say that problem #2 usually occurs at the top end of 1st gear, after backing out of the driveway and accelerating on the street.

We have no problems out of it until last fall, been a great vehicle. Lately it's been getting expensive to drive though.

Thanks for any advice you can give, I'll check back soon.

Greg
 

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Welcome, I'll only comment on one item - I'm guessing that the fuel mixture is way too rich, this would account for the black residue on the back.

Changing O2 sensors may not have solved the root-cause issue. You could have something else going on, from a bad coolant temp sensor (if it goes bad, computer will default to cold and thus a richer mixture) to a stuck-open or leaky fuel injector (or shorted-out injector driver).

Find a shop that is good at troubleshooting to have a go at this one. They should be an emissions-certified repair shop, they will have an exhaust gas analyzer which they can use to verify the issue. Your new O2 sensors may be all carboned up now too (they can clean those using the proper cleaner). Oh, a large leak in the exhaust system upstream of the catalyst can confuse the O2 sensors too and make it run rich. This rich condition would also explain your poor gas mileage. Something definitely going on there that you need to get corrected.

The same shop should be able to duplicate and fix the stalling after a cold start issue (may be related to issue above as well), but you may need to leave the vehicle with them for a few days so they can have a few shots at it (they will need to have a scantool and other items hooked up when they start it cold to see what is happening real-time).

Hoping the best for your tranny too!
 

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My guess is you ran way too rich to cause black residue out the tailpipe and this then fouled your o2 sensor and gummed up your cat converter. A clogged or broken cat will glow red if it's bad enough and low mpg is a symptom
 

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Discussion Starter #4
Good information, but I've got more questions... Everybody that's worked on this is very quick to say there is no error codes to work from. Wouldn't most or all of the things mentioned above cause a check engine light and some error codes?

I'm located in central Arkansas, not even sure we have a "emission-certified" repair shop. I've had limited success with the dealership too. Does anybody recommend going to Midas or any of the national chains for a problem like this?

By any luck does anyone know a good shop in the Little Rock, AR area??
(I know that's a long-shot)

And again, thanks for sharing the knowledge you have.
 

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Does it ever stall or cough under acceleration or just when idling? What brand are the o2 sensors? I ask because I had a bad upper o2 sensor on my truck that would make it buck badly about 1/2 mile from my house when cold. Per my Scangauge, it happened right when the system went into closed loop mode. Took me a long time to figure it out because it did not throw a code. I proved it by unplugging the o2 sensor which makes it stay in open loop and uses a base fuel mixture setting and at that point did throw a code but it ran correctly. I wonder if one of the replacement sensors is bad, most likely the upper one.
 

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As mentioned find a reputable repair shop that will analyze the problem, not just throw parts at it at your cost. The dealer just deals in codes and parts, not diagnostics. That said the O2 sensers, converter, most engine sensers can be analyzed with a good OBDII tester and a compentent mechanic.
 

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Discussion Starter #7
ODYinNH - The stall I described has only happened to us while under acceleration. The O2 sensors are described as "Genuine Honda Parts", not sure if that answers the question.

William - I've learned that about the dealer. It's also true of a couple of shops I've already tried. They seem to put alot of trust into the computer to know what's wrong.

If someone knows of a reputable repair shop near Little Rock, AR - Please reply.

Thanks

Greg
 

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Well, it seems suspect to me that things went down hill after the sensor was replaced even though you do not have a code. I asked about the brand because after market ones seem to be crappier but maybe you got a bad Honda one.
 

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Why did the "local shop" replace the O2 sensor in the first place? Find out. All the problems seem to relate back to this -- so there is something suspect about this work. Check their work. Loose/unconnected wire(s), EGR, power steering wire, etc.
 

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Discussion Starter #10
UPDATE:

This Odyssey in the shop currently, with trusted guys that I thought only did tires. I was informed yesterday they also do engine/service work... They’ve taken a printout of this forum and been checking it since yesterday afternoon. Here’s what they’ve found:

The coolant temp sensor was checked , the catalytic converter seems to be fine too. New spark plugs are not fouled and are the better NGK brand.

The technican does not think it is transmission related, and says the engine is not running rich.

The original problem of black soot on the rear of the van was fixed by replacing the upper O2 sensor with a Bosch brand. The lower sensor was not replaced and appears to be original stock equipment.

So – my question -- Will Genuine Honda O2 sensors make a difference? Is it worth a try? I’m considering having them replacing both of them. That's the direction I'm leaning after reviewing some of the posts above.

Thanks
 

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I don't see how a tranny is going to make the engine stall or get that much of a drop in gas mileage without some crazy sounds coming from it. If it were me I would unplug the upper o2 sensor and drive it for a week. The engine will run on a predefined setting instead of relying on the sensors. If it runs better then the o2 is crappy. Yes this will make the CEL come on.
 

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Discussion Starter #12
So, got BOTH O2 sensors changed with Honda brands. First tank got 20.4 MPG. Seems to have fixed the stalling problem too. Didn't want to post until we got a second tank thru it on good driving. Got 24.5 MPG on freeway. The shop I took it too had a mechanic that read this forum entry and called with more questions. All in all turned out great. Lesson I take away is make sure both O2 sensors match and don't change out just one.
 

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Great miles per gallon!

So, does this mean you should change your O2 sensors once you accumulate high mileage in order to restore MPG?

Will the sensors throw a code when they degrade and need replacement?
 

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Great miles per gallon!

So, does this mean you should change your O2 sensors once you accumulate high mileage in order to restore MPG?

Will the sensors throw a code when they degrade and need replacement?
Yes, replacing O2 sensors is normal maintenance. They won't throw a code when they are sending an inaccurate signal to the computer - only when they outright fail.
 

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Yes, replacing O2 sensors is normal maintenance. They won't throw a code when they are sending an inaccurate signal to the computer - only when they outright fail.
So, when is it prudent to to replace -- 50,000 miles, 100,000 miles, decreasing MPG?
 

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So, when is it prudent to to replace -- 50,000 miles, 100,000 miles, decreasing MPG?
I'll Dispute that as all the specs of the O2 sensers are monitored by the PCM. If any get out of spec a code is generated. There is no maintenance listed for the O2 sensers. I run a scan on mine and graph them about once a year and compare them. So far I se no drop in the output of the sensers. A good scanner will show the output switching levels and also show the limits for failure.
 

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Yes, replacing O2 sensors is normal maintenance. They won't throw a code when they are sending an inaccurate signal to the computer - only when they outright fail.
+1 from my experience. With gas prices the way they are, replacing old O2's with OEM sensors is worth the cost. Maybe WW should try it on his wife's Ody. :DD
 

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Is there any "maintenance" you can do on O2 sensors to prolong their use? Like cleaning them?
Only if they are contaminated, like with oil. Normally, they wear out as the catalyst depletes.
 
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