P38A [P38] MOT Fail - Emissions

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Just Japan and USA got 4 o2 sensors. Everyone else made do with 2 I think.

I think (think) the engine is OBD compliant enough to show what the o2 sensors are doing with a bog standard code reader. With the engine running they should show the voltage swinging up and down. If they're not doing that you know there's a problem with the sensors somewhere.... or something is causing the engine to constantly run rich.

I know where you can get some cheap CATs if it is them.....
 
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Just been to the garage - they reckon the cats have been cut out and replaced with straight pipes. Pictures to follow later.
If that's the case - please do share where I can get some replacement ones.

Should the O2 sensors be pre-cat or post-cat?
 
They should be pre. Just the two of them.

I went to Cats2U for mine…. £156 delivered.

You have to be careful you get the right one though. They changed a bit over the years. Biggest change is GEMS to Thor. The hole and thread size for the o2 sensors is different.

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Thanks , I'll take a look.

Here are the pictures, does this support what they're telling me?

1000007465.jpg1000007462.jpg1000007463.jpg1000007464.jpg1000007466.jpg
 
Failed on emissions I believe, no mention of cats in the results:

  • Exhaust carbon monoxide content after 2nd fast idle exceeds default limits (8.2.1.2 (b))
  • Exhaust Lambda reading after 2nd fast idle outside specified limits (8.2.1.2 (c))
  • Exhaust carbon monoxide content at idle exceeds default limits (8.2.1.2 (b))
 
ER1C said:
What is the logic on cutting them out ?
Click to expand...
LPG can kill them as can oil containing zddp.
The v8 sounds much nicer without cats.
They don't really do much for emissions on this old engine, just restrict the exhaust and decrease mpg

Mine had the cats emptied and refitted
 
That's good to know.
I'm back at square one then - assuming the MOT station won't fail it for missing cats, what's the usual process of diagnosing high emissions?

I'm going to have them check the voltages on the O2 sensors today to see if they're reasonable.
 
blue_cheese said:
That's good to know.
I'm back at square one then - assuming the MOT station won't fail it for missing cats, what's the usual process of diagnosing high emissions?

I'm going to have them check the voltages on the O2 sensors today to see if they're reasonable.
Click to expand...
The o2 values should swing across pretty much the full scale fairly quickly, like once a second.. when they let go, they get slow or stop completely.. i think the range is "-5v - +5v"
 
from the gov website;
removal of all or part of the emissions control system, may lead to significantly higher levels of harmful exhaust emissions which can then find their way into the vehicle’s interior
🤣🤣🤣🤣
 
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