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MG MGF Technical - Emission Test
Today my MGF1,8i -97 fail the Swedish MoT emission test:
CO=6,8% HC=500ppm Lambda=0,75
|Those figures are pretty high - looks as though the cat wasn't doing its job for what ever reason.|
1. the cat wasn't properly up to temperature when the test was performed (or it might be fouled up with carbon deposits - depends on how the car was used prior to the test)
2. the catalyst has failed.
The latter is expensive to rectify - but happily doesn't happen all that often. Is there a rattling noise from the exhaust system that may indicate that the matrix inside the cat has broken up?
The cheapest option if to take the car for a quick blast in the countryside. Once the engine is warm, accelerate through the gears, taking the engine revs to the red line. 10-20 minutes should be enough. Then retest soon after. If the catalyst was fouled up, this should clear all the unwant gunk.
Fingers crossed that the cheap option works!
|Tanks. I will try the countryside blast and keep my fingers crossed.|
|voltmetereck that the labda sensor is connected by it|
|Definitely a catalyst problem. I got mine back today with 0.01% CO (0.2% pass level) and 28ppm HC (200ppm pass level)|
The UK lambda pass level is 0.97 - 1.03
|I'm sure someone will be along to correct me if I'm wrong - but those figures look pretty high even for a car without a catalyst? |
The presence of high levels of carbon monoxide and unburnt hydrocarbons shows incomplete combustion - either over fueling or insufficient air. In which case you probably get quite a lot of soot, which would foul up the catalyst, as Rob describes. Taking the car for a blast might clean off the deposits long enough to get through the MOT, but I think I would still want to check the tuning.
Possible that a fault with the lambda sensor, as Carl describes, would lead to the engine management system being confused and over fueling?
|Sounds like time to give the air filter a good clean!|
|My money is with Carl on the lambda sensor.|
With luck it may just be the wiring - mine had broken through rubbing against exhaust manifold heat shield.
Replacing the sensor itself is a bit of a challenge.
|Tank you all. I’m going to check the lambda sensor and then go fore a blast.|
Carl, what should a measure on the sensor?
go to the "Archive " and look for "CO/lambda". You will get a thread from 7/11-01 where further down I do describe where to attach a voltmeter to measure lamda value.
As noted a healthy sensor will fluctate between approx. 0,2 to 0,9 Volt several times/ second when using the throttle. A defect one will be almost stuck around 0,4-0,6 Volt regardless of engine revs.
Well worth cheching before someone starts to try to remove the sensor. Such work usually means that the whole thread on the downpipe gets damaged = both new sensor AND mainfold ;O(
|Carl, your *how to* is aswell on|
|Yeah, won't be a catalyst failure. You could remove the cat fully and let lower readings. A dirty air filter wouldn't make readings that high either. A lambda sensor is the most likely part to cause this, chaeck it and make sure it's switching as it should. Lucas do universal 4 wire sensors that cost about £30, you just have to remove the plug from the original sensor and crimp to the new.|
|Wow !! My MGB GT didn't have emissions that bad. If the cat's not rattling then it is more than likely the sensor - as it's fairly exposed it may just be corroded connectors, give it a quick squirt of WD40.|
Andy damaged the manifold boss thread before the Treffen and fitted a new manifold. He recovered the old manifold and considers that he probably could have fitted a Helicoil. Dieter tells us that it is M18 x 1,5.
MGR Sensor is £120. Ouch.
Dieter gives Bosch 0258 003 229 for Mk1 to 522572
I nearly passed the UK emissions without a cat on at all! Yeah I know from working at Volvo that in Sweden the tests are more stringent but try the following, clean the sensor connectors, and then take the car for a good long run. The take the retest, I presume that the engine is running ok and not too rich.
If you need to get a new cat they are frequently available on ebay.co.uk.
This thread was discussed between 07/09/2004 and 10/09/2004
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