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Discussion Starter · #1 ·
My car failed its MOT last week on the emmisions. Both the hydrocarbons and co2 were both too high. I dont know the specific values, but apparently one of them needs to be at 1200, and it was at 2000 :confused:

The general impression is that they are way to high!

My engine is a C16XE with TB's and Piper BP285 cams. Its obviously the overlap causing the hydrocarbons.

I had already adjusted the fuel map in preparation, from

750rpm - 4.0ms
1000rpm - 3.5ms
1250rpm - 2.9ms

to
750rpm - 2.8ms
1000rpm - 2.8ms
1250rpm - 2.3ms

I also changed the lambda target map from 14.0 afr to 14.7, and when lambda is on, its chucking in a lot of fuel. Im not too sure on the accuracy of the lambda values we have though.

With these changes it didnt idle as well and did stall a few times. I asked the guy at the mot place and he said it doesn't matter how well it runs, as long as it does.

Should I turn the lambda off and just try with the low values?

I wont be able to damage the engine just by leaning off the idle and low throttle/rpm values will I?

Is it worth making any changes to the ignition?

What sort of RPM will the test be done at?

What are my chances of getting this through the retest? I can take the laptop and adjust the fuel.

Anyone else had similar problems?

Thanks,

Miles
 

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you would only need a small change
try 3.4, 3.2, 2.9. i would just have it on livemap and press pagedown 1 at a time till the hc dropped to legal levels, but then again my mot guy knows me.
 

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Discussion Starter · #3 ·
It was on

750rpm - 2.8ms
1000rpm - 2.8ms
1250rpm - 2.3ms

when it failed, but I get the idea.

I hope it is just a case of trimming until it passes hoping it will still run. Just wanted to get a better idea of things before I go back.
 

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That's a cat test report, yours is being tested for the non cat one I think?

http://www.motuk.co.uk/manual_730.htm

Note: If a vehicle meets the CO requirement at its normal idling speed but fails the HC check, re-check the HC level at a high idle speed of 2000rpm. If the HC reading is 1200 ppm or less, the vehicle will meet both the CO and HC requirements.
. the CO requirement must be met with the engine running at its normal (low) idling speed
. do not use a cold start/cold running mechanism to achieve a high idle speed. Instead, apply light pressure to the throttle pedal.
. HC not applicable to Compressed Natural Gas (CNG) fuelled vehicles.


2. From 1 August 1992 onwards Basic Emission Test (BET)
a. Carry out the test using the flowchart.

b. ensure that the engine is hot by checking for example - temperature gauge, cooling fan cut-in or hot coolant hoses. If the engine is not at normal temperature raise the engine speed to between 2000 and 3000rpm and maintain this speed until normal temperature has been reached.

c. attach engine speed measuring device. It is permissible for the purposes of this check to use the vehicle tachometer.

d. ensure the engine is idling normally.

e. perform a HC hang-up check and ensure that HC<20ppm before continuing. Insert the analyser sample probe.

f. fast idle test: Raise the engine speed to a fast idle between 2500 and 3000rpm and hold steady. Note the readings for CO, HC and lambda, and
record the results.

g. Idle test: Allow the engine to idle. Note the CO reading and record the result.

h. remove analyser sample probe.
 

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if its a non cat one the test should be done at tick over so that test certificate is no good to you miles they should not rev the car at all for a non cat test miles have you changed your number from when you gave it to me
 

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results i got for a standard cav gsi...
0.02% CO - allowed 3.5%
80ppm HC - allowed 1200

just thought it was more likely to be near the limit if it was running the best it could
 

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That's the non cat test, which are far from strict as old carb cars have that test so yours being a 20XE will pass it easy.
My C20LET got:

Actual - Limits
Fast idle:
0.05% CO - 0.30% max
14ppm HC - 200 max
1.009 Lambda - 0.970-1.030

Idle:
0.01% CO - 0.50% max
 

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it passed that anyway :D
just wondered cos the readings are so low if it could mean something could be done to get them nearer the limit + give more power, was just kinda thinkin out loud :)
 

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Must be the cams mate, as TBs don't cause high HCs. Mine failed on lambda being too high (on the cat test) but HC was 4 and CO was zero at idle and fast idle. I had to put a bit more fuel into the map at 3000rpm to bring the lambda down and it passed OK after that. I can pass the cat test without a cat (0.3% CO at idle) but I do fit a sports cat at MOT time to be sure. I tried to use a lambda sensor with MBE, but could never get it to run closed loop so gave up. I do run std cams however. Stick with it mate, I am sure you will get through once the map is adjusted as the non cat test is pretty easy for a well maintained car.
 
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