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Hi all,

My Civic 2002 with the d16v1 engine failed the MOT in Sweden due to high CO under high rpm (They run it at 2500 rpm)
Lambda value was 0.97

High CO and Low Lambda indicates that the engine is running rich.

Any ideas of why it's running rich and what I can do to fix it?

 
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Check engine light on?
Any codes?

 
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CEL is not on and no codes.

 
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Did you put on an exhaust part on it right before the test?
​​​​​​Does it burn oil?

 
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most common cause on mine is O2 sensor (what caused the sensor to go is another story)

 
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Um.....cracked or otherwise leaking exhaust (manifold?) causing inaccurate o2 sensor value?

 
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The exhaust is just recently replaced since the old cat collapsed.
rear o2 sensor just replaced due to previous CEL.
I haven't owned the car long enough to say if it burns oil or not. But all spark plugs are black and the old o2 sensor was black.

Can it be the front o2 sensor that is malfunctioning? Or can it be that the exhaust is leaking after the manifold, I don't hear anything indicating this though.

 
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In addition to the previous I must say that it's producing a LOT of exhaust gases. It must be running really rich but still no CEL.

Anyone who can point me in the right direction?

 
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Cat has been replaced? With an OE cat, or was it an aftermarket cat?

There's a whole shopping list of parts that "could be" the problem.
Also consider possible mechanical problems such as low compression, low vacuum, cam timing error, valve adjustment out of specification, and more

 
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The cat was replaced with an aftermarket CAT. I doubt this is the issue since spark plugs all go black.

I haven't tested the compression but I'm planning to do it.

I think it's a long while since the valves were adjusted, can this really be causing the car running rich? Can it be ANY vacuum tube that might be causing this or is there any specific tube I can focus on?

 
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Tight valves can

Low manifold vacuum, does not necessarily mean it's caused by a vacuum leak. Mechanical issues can cause it too, such as incorrect valve adjustment or cam timing error.

 
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Can it be that I didn't manage to get a tight fit between the exhaust and the manifold?
How do I go about troubleshooting that?

I tried plugging the exhaust but wasn't able to hear anything at the manifold.

 
Rep Power: 517

Disconnect wiring from both oxygen sensors. Disconnect battery and open the doors and boot for 15 minutes, this should hopefully drain capacitors and cause the ECM to dump it's learned adaptive values.

Reconnect battery, do NOT connect the sensors.
Run the engine, see if it is still running too rich.

If it is still too rich the disconnected sensors are not causing the problem, something else is.

 
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Can I check this using the OBD2 scanner? If so how do I go about doing it?

 
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i would recommend doing what ezone said - scanner will not drain capacitors.

 
Rep Power: 517

Check what?

IMO if you already had a scanner connected displaying live data and you couldn't discern a root cause of running too rich before, the same scanner won't help you now either.

With no oxygen sensors input, the computer will stay in open loop, It effectively becomes a "Speed-density, non-feedback EFI" system.
NO fuel trim adaptive correction.
YOU will have to manually figure out if it's still running too rich.