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Sooo... it's a third year in a row failing mot due to high emissions. This time it's running quite rich, lambda shows 0.6. Co% and HC about 10 tenfold past the limits. And can't seem to find the source. Here's my investigation so far:

 

- no vacuum leaks

- compression test ok

- no visible leaks in exhaust system

- plugs in need of change but nothing critical about their condition

- plug wires ok

- timing ok

- ecu reseted

- worn cap + rotor, a little bit of play in dizzy axle + dizzy a bit noisy = gonna replace distributor. But not in such a bad condition that would explain the richness.

- coolant reservoir was empty, only a bit of dark brown muck on the bottom. At first thought it was oil, but when i rinsed it turned out was (atleast mostly) dirt etc. Discovered a small crack on the reservoir lid, might be a cause. Besides the reservoir no other clues pointing to a possibly leaking head gasket.

 

Any ideas what to look for? One suggestion was that a faulty heat sensor etc. could be feeding the ecu wrong info and messing up the mix? Valve stem leak also one possible cause. In addition to the dizzy i'm planning on replacing the ecu with a p28 with Hondata to get better data about what's happening. And ofcourse once it's fixed, then it's tuning time 8-).

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it could be the coolant temp sensor, might be worth putting a fresh one in. Can't you slide the mot guy a few quid for a pass? 

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On 6/25/2018 at 10:35 PM, dmrichards said:

it could be the coolant temp sensor, might be worth putting a fresh one in. Can't you slide the mot guy a few quid for a pass? 

 

Luckily they're pretty cheap, i'll give it a shot. And i'd be ready to slip quite a lot more than a few quid to get a pass, this is getting a bit boring year after year! But on the other hand, otherwise the deck is working spot on i'd like to keep it that way. Been allready 9 years under my ownership.

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Mine failed emissions last year, but it was tested before it was serviced. 

I ran some injector cleaner through it, then had the service Inc plug change and went through okay. 

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Hmm been trying to sort this for a few years now. Changed the entire exhaust system, plugs, rotor, lamba and still shows above 0.6 %Co. 

 

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My problem got sorted by replacing the o2 sensor. It's become a yearly thing now, this fall i swapped it before mot and passed without any notifications. The old sensor was totally black.

But in your case it has to be something different. Have you checked compression and for vacuum leaks? Dizzy bearing?

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That's interesting.. I wonder why they're failing so often. 

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On 12/9/2019 at 11:05 PM, dr_broon said:

That's interesting.. I wonder why they're failing so often. 

 

I'm suspecting an oil leak somewhere inside the engine which causes the car to burn even more oil than a vtec honda normally would. It feels like i'm topping up more often than before. I've also had oil frequently inside one of the spark plug wells even after changing the gaskets, for a few years now.

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Oil in the spark plug hole can only come from one place. Clean the gasket up and use silicone.

 

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1 minute ago, KiNK43 said:

Oil in the spark plug hole can only come from one place. Clean the gasket up and use silicone.

 

 

You mean silicone the gasket to make a more secure fit? What kind of silicone? I've used hondabond when changing rocker cover gaskets.

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I've also had issues with emissions. This time it was broken distributor cap but there has been problems earlier too. Cat has been changed once. If anyone is having oil leak/consumption issues then it could be worth to change VTEC solenoid gaskets, all of them. Especially the big one with the filter gets bad in a long period of time. I've been wondering if aftermarket exhausts and manifolds can affect emissions? Stock ECU may not be able to handle it? Can't cope with the flow change etc.? Increased heat in the engine bay with aftermarket manifolds? Stock ones have heat shields and all that...

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On 2/6/2020 at 9:48 PM, MBFinlay said:

 I've been wondering if aftermarket exhausts and manifolds can affect emissions? Stock ECU may not be able to handle it? Can't cope with the flow change etc.? Increased heat in the engine bay with aftermarket manifolds? Stock ones have heat shields and all that...

That's a really good point mate. Think the free-er flowing exahusts will deffo raise emissions due there being an increase in the fuel being delivered. The cat plays a big part, as do the 02 sensor/egr valve. Either of those can dramatically increase the emissions.

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1 hour ago, Dave said:

That's a really good point mate. Think the free-er flowing exahusts will deffo raise emissions due there being an increase in the fuel being delivered. The cat plays a big part, as do the 02 sensor/egr valve. Either of those can dramatically increase the emissions.

Nah. The oxygen sensor is after the manifold and before the cat. So the o2 sensor feeds back info about output after the manifold and therefore whatever goes into the cat, the ecu/o2 sensor doesn't care/monitor.

This is unlike later cars that measure the output coming out of the cat and compare the output prior to and after the cat, and may adjust the mix accordingly. 

In my case, changing out the oem cat for a total new exhaust system front to back made b****r all difference. 

 

 

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Does chipped/tuned ECU make things better or worse with emissions and flow/back pressure of the exhaust?

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