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FAILED MOT!

GAFTON

GAFTON

New member
Just collecting my car from OPC, realized the mot was due in April so might as well get it done... OPC not doing mots but arranged it and to my shock/surprise, etc., etc., after approximately 2 hrs and 4 tries(to warm it up) it failed because of high emissions!!! Almost the end of the day by then so OPC could only do a quick test/look : not the cats or anything else obvious, but guessing at a failed o-ring causing an air-leak resulting in a richer mixture, higher emissions..... OPC needing the car for a full day to investigate and the date fast approaching....
Any thoughts anyone?
Thanks and all the best,
 
Hi Gene :)

A failed O ring causing an air leak would give a leaner MIXTURE....SO ITS NOT THAT..

Did they even try and set the mixture ?? Its only a 3 mm allen key to turn...awkward to get at but the OPC will have the special tool....to make it easy...takes around 2 minutes with a gas analyser stuck in the exhaust...

What EXACTLY were the readings??? CO and HCS ???

If you can get me those readings , I will probably be able to tell you whats causing it...

All the best Brett :)
 
Hi Brett!
No, I think they just run their test gun on it; like I said the end of the day, etc. Will try to get the readings tomorrow and post them. At the time he said it was probably running rich, but no problem, just slightly higher gas consumption. When last I spoke to him he did admit that he really did not know what the problem was. I do not know if it is in any way related and (unusually) it was noticed by the OPC as well, the engine (it's taken me a long while to really get to hear/feel it) does not run smoothly (it doesn't just purr along), once in a while (and it is a regular cycle - at a guess no mare than 5 secs, probably less, between cycles) there is a faltering, a slight kick and then it picks up again (this is at idle - I don't know at higher revs). I queried the OPC - the spark plugs maybe? No, not that, but no other suggestion either.....

I'm surprised you have time or interest for any side-issues, keeping in mind the 200MPH RUN.

Thanks.
 
Hi Gene :)

Ok normally there are 2 important readings for an MOT fail on emissions...

CO and HC

CO should be under 3.5% (to pass MOT) and in real life your 928 should be running at around 0.5% maximum !!!

HC should be under 400 ( I think from memory) and yours would normally run at around 100 ppm (parts per million)

Now...if its failing on HIGH COs ...thats mixture or sensors playing up...

If its failing on HIGH HCs thats lack of basic servicing....(something is probably missfiring) when were plugs last CHANGED....when was distributor cap last CHANGED....when was rotor arm last CHANGED...???

And I dont mean checked....(as on a service) ..I mean actually CHANGED !!!

Hope this helps :)

All the best Brett :)

p.s. Its my job here to help :)
 
Hi Gene :)

Thinking about this some more....if its HIGH HCs ....assuming plugs were changed within the last year....Id put money on it being Distributor Cap or Rotor arm missfiring....tell them to change them...unless you can actually SEE an invoice saying they have been done within last 2 years...(I change mine yearly.......)

All the best Brett :)
 
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