High hydrocarbons on MoT
Discussion
I think it's pointing to a cylinder not firing properly on idle, although it seems fine under load.
This would pass though extra unburnt O2 and the unburnt fuel as HC's.
When I yank out the plugs I'll see if any are fouled/black etc, hopefully the new set will sort that out.
So I have a nice list of things to do, and no work on the underside of the car, so I won't be getting too oily!
0. Check CO before doing anything to make sure CO meter working OK.
1. Check for air leaks
2. Check for oil in intake
3. Check crank breather for blowby
4. Set up CO for 1.75%
5. Pull each injector plug one at a time and observe effect on idle rpm (shows misfires)
6. Pull plugs and save on numbered card, take photo, gap and put in new plugs.
This would pass though extra unburnt O2 and the unburnt fuel as HC's.
When I yank out the plugs I'll see if any are fouled/black etc, hopefully the new set will sort that out.
So I have a nice list of things to do, and no work on the underside of the car, so I won't be getting too oily!
0. Check CO before doing anything to make sure CO meter working OK.
1. Check for air leaks
2. Check for oil in intake
3. Check crank breather for blowby
4. Set up CO for 1.75%
5. Pull each injector plug one at a time and observe effect on idle rpm (shows misfires)
6. Pull plugs and save on numbered card, take photo, gap and put in new plugs.
Well I found one major problem and a few minor ones.
Major one is that some of the ignition leads had gone quite high resistance. These are suppression leads. The spark must have been quite weak at the plugs.
Luckily I have a spare set that tested out OK between 3000 and 4500 ohms although number 3 is 6000-ish, so they are on.
Also there's a very slight air leak maybe from a rocker cover, and the breather pipe was a bit gunky, so tightened the rocker cover bolts and cleaned out the breather, pipe and junction into the throttle body.
My CO meter disagreed with the garage, it said 2.0% so I might go up a bit but not much.
Major one is that some of the ignition leads had gone quite high resistance. These are suppression leads. The spark must have been quite weak at the plugs.
Luckily I have a spare set that tested out OK between 3000 and 4500 ohms although number 3 is 6000-ish, so they are on.
Also there's a very slight air leak maybe from a rocker cover, and the breather pipe was a bit gunky, so tightened the rocker cover bolts and cleaned out the breather, pipe and junction into the throttle body.
My CO meter disagreed with the garage, it said 2.0% so I might go up a bit but not much.
Did a bit more fettling and investigation this evening and now I stink of fumes! But the mixture screw is now fully in for as rich as possible. Also there are no air leaks that I could find in the inlet system.
As the CO limit is now 3.5% I'm hoping a nice rich mixture will reduce the HC number further. Let's see what happens in the test tomorrow.
As the CO limit is now 3.5% I'm hoping a nice rich mixture will reduce the HC number further. Let's see what happens in the test tomorrow.
Thanks Zig your good wishes didn't jinx it this time! ;^)
IT IS PASSED!
The MoT ratchets another week later this year.
BTW I found my purchase of the last set of ignition leads £12 and lasted 4 years so not too shabby.
I am thinking of converting to copper leads as the resistive ones just seem to wear out. I now have plenty of ends to make a set with!
IT IS PASSED!
The MoT ratchets another week later this year.
BTW I found my purchase of the last set of ignition leads £12 and lasted 4 years so not too shabby.
I am thinking of converting to copper leads as the resistive ones just seem to wear out. I now have plenty of ends to make a set with!
Edited by adam quantrill on Tuesday 23 October 17:33
...Enjoyadam quantrill said:
Cheers!
And now adjusted back to sensible CO, revs back to 800 and the breather pipe back into the intake (it was a bit smelly).
Paradoxically this will result in less emissions, the ppm may rise but the absolute value will be lower.
Well done adam ...8OO the stuff of dreams i'm lucky if ours drops to 1000 when warmed.And now adjusted back to sensible CO, revs back to 800 and the breather pipe back into the intake (it was a bit smelly).
Paradoxically this will result in less emissions, the ppm may rise but the absolute value will be lower.
IIRC a 350i should idle at around 950-1000rpm..400se around 800-900rpm..450se around 700-800rpm...
Check your breathers Martin including the little mushroom on the N/S rocker cover...its best remove when warm and with a 10mm open ended spanner ..using a cloth under it as not to damage covers and gently prise out in a circular pattern.
Check flame trap and associated hoses, you can rinse the gauze in the flame trap with petrol but I would use some contact cleaner/brake & clutch cleaner, or buy some new gauze...check the small airways in the plenum intake mouth and associated air hoses.
Ziga
Check your breathers Martin including the little mushroom on the N/S rocker cover...its best remove when warm and with a 10mm open ended spanner ..using a cloth under it as not to damage covers and gently prise out in a circular pattern.
Check flame trap and associated hoses, you can rinse the gauze in the flame trap with petrol but I would use some contact cleaner/brake & clutch cleaner, or buy some new gauze...check the small airways in the plenum intake mouth and associated air hoses.
Ziga
Good news it passed the test! Assume you continue to enjoy your daily TVR drives 
Science (chemistry in this case) still works for our old wedges.
My CO is standard at 4,0%, a bit more at 4,5% seems to be the best on the 350i for max bhp/torque etc
Always needed to set it lower as MOT required 3,5% and an Italian workout to get at it.
Now registered as an historic car in Belgium, no exhaust gas tests to pass, even the MOT was not required temporarily.
Next historic MOT now in 2020 and that is from 2014 when putting it from Dutch on Belgium plates, so no complaining from me
Love the smell of petrol TVR fumes
(in the morning, springs then as an addition to my mind)
Rob
Science (chemistry in this case) still works for our old wedges.
My CO is standard at 4,0%, a bit more at 4,5% seems to be the best on the 350i for max bhp/torque etc
Always needed to set it lower as MOT required 3,5% and an Italian workout to get at it.
Now registered as an historic car in Belgium, no exhaust gas tests to pass, even the MOT was not required temporarily.
Next historic MOT now in 2020 and that is from 2014 when putting it from Dutch on Belgium plates, so no complaining from me
Love the smell of petrol TVR fumes
(in the morning, springs then as an addition to my mind)Rob
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