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Emissions help for nct

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minimike
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Emissions help for nct

Post by minimike » Sat Aug 11, 2018 12:49 pm

Hi,

I've a 91 city that failed nct on emissiosn (amongst other things....).
The other bits I can sort easily enough but I don't know anything about carb tuning etc.

It passed on CO: 0.014% ( 3.50% threshold)
but failed on HC 1228ppm (vs 750ppm threshold)

Seems a little odd as if it was running rich it would fail on CO I assume so why am I getting a high hydrocrabon level?

It did seem to hesitate a little when idling just before test (but is running smoother now) so maybe it misfired a bit and a load of unburnt fuel triggered the high HC?

It hadn't been driven in a few years so it had probably done all of 50 miles. I've done a few more miles now and seems a little smoother.

My only other thought was maybe oil but it's never smokey, even on start up. She starts very easily too.

So, my questions is: should I adjust the carb to lean it out a little for test temporarily? Or maybe put some dipetane in the tank?

Any ideas? Thanks



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Re: Emissions help for nct

Post by woody » Sat Aug 11, 2018 1:10 pm

Although not smokey the hydrocarbons would suggest burning oil.
Your CO is too low and a lean mix will cause ring ware, the correct mixture also lubricates the rings.
Since the car has been sitting the valve stem seals could be hardened allowing oil to pass through.
What I would do is set the CO about 2.5% and take the car for a long hard ( not cruse at 70 down the motorway) drive up the mountains with plenty of high revs to blow the cobwebs off the engine. Allow a couple of hundred miles before testing again.
Also check the crankcase for excess pressure and if there is high pressure remove the pipe into the carb and block the tube before testing
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Re: Emissions help for nct

Post by minimike » Sat Aug 11, 2018 11:32 pm

Thanks woody.is 0.014% co definitely a sign shes running too lean? I thought maybe itbwas adjusted really well... :P I was thinking she was burning oil with due to low co with high hc. Hopefully it clears...

How would I check high crank case pressure? Try find the pcv and see if there's loads of air coming out of it?

I've already driven it a bit since it failed, a little enthusiastically at times... And it seems to be running much better (it used to kinda hesitate at idle with choke off). Fresh petrol through it might be helping too.

How would I go about setting it to 2.5% co? I was reading up and not sure how to do it. Some guides suggest cutting hole in exhaust and welding in a bung to allow a lambda sensor to screw in which would allow adjustment of the carb then.

Others say colourtune but supposedly its not great. What's the best thing to buy?

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Re: Emissions help for nct

Post by woody » Sun Aug 12, 2018 1:34 pm

A quick pressure test would be to remove the oil filler cap and place your palm over the hole as you rev the engine. If you feel a lot of pressure on your hand it could mean that your breathers are blocked.
Old petrol won't help your emmisions as unleaded loses its octane after about a year. Any local garage should have a co2 meter to set the carb or go to Minifix in Santry.
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Re: Emissions help for nct

Post by minimike » Mon Aug 13, 2018 10:49 pm

woody wrote:A quick pressure test would be to remove the oil filler cap and place your palm over the hole as you rev the engine. If you feel a lot of pressure on your hand it could mean that your breathers are blocked.
Old petrol won't help your emmisions as unleaded loses its octane after about a year. Any local garage should have a co2 meter to set the carb or go to Minifix in Santry.
Sweet, thanks very much woody! Seems to be running totally different with fresh petrol. Might throw it into nct and see what happens. I'll look into getting co measured afterwards as don't want to do damage as you mentioned by running lean.

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Re: Emissions help for nct

Post by minimike » Mon Oct 01, 2018 10:13 pm

Well i passed the NCT yesterday pretty much.... :D
HC was 215 so well within the limit which is good. I didn't change anything but it had fresh petrol and took it for a few enthusiastic drives which seemed to do the trick. Thanks for that advice, worked a treat!

It still read a low co% at 0.35% but that was with the choke all the way in. I wonder with it out a bit is it running ok? Must get it checked.

Separately the brake lights are on constantly and rear fog won't work so need to dig into that but shouldn't be too bad hopefully.

Cheers for all the advice, glad to have it nctd ...nearly!

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Re: Emissions help for nct

Post by The Marcos Graveyard » Mon Oct 01, 2018 10:53 pm

For the brake lights, check the switch on the brake pedal for a possible short.
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Re: Emissions help for nct

Post by woody » Tue Oct 02, 2018 9:59 pm

The brake light switch is on an adjustable bracket that sometimes works lose. The fail safe on the switch is to stay on rather than have no brake lights,
The fog lights usually let in water and corrode.
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Re: Emissions help for nct

Post by minimike » Wed Oct 03, 2018 10:05 pm

Thanks guys. I took a look at the brake switch. I was replacing the accelerator cable and when i replaced the flexible pipe from the wing to the heater unit it was pushing on the brake pedal slightly triggering the switch! (There isn't much space there!) I'll see if that bracket is loose though as that might help.

I took a look at the fog light. Shorting the positive wire to the battery shows its working and earth is fine obviously. The in line fuse in engine bay had broken on one side so there's now a feed to the switch but seems like there's a bad connection or something as it's not giving enough voltage to the light. The light in the switch only lights up a little and isn't constantly on either. Anywhere in particular to try? I'm going to try sand the fuse and contacts a bit to ensure it's not a bad connection there.

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Re: Emissions help for nct

Post by woody » Wed Oct 03, 2018 10:46 pm

The inline fuses are a known problem and if its corroded at all you should replace it.
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Re: Emissions help for nct

Post by minimike » Fri Oct 05, 2018 8:40 pm

woody wrote:The inline fuses are a known problem and if its corroded at all you should replace it.
I'll give that a go. It didn't seem badly corroded but I'll give it a bit of a sand and hopefully that'll do the trick

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Re: Emissions help for nct

Post by minimike » Sat Oct 06, 2018 6:08 pm

Hey guys, I pulled apart the inline fuse and gave the fuse, spring, and contacts a light sanding and hurrah, the fog light is working! Now all I've to do is pick up my NCT cert :D
Cheers for the advice!

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Re: Emissions help for nct

Post by The Marcos Graveyard » Sat Oct 06, 2018 6:50 pm

8)

Job satisfaction 100%.
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Re: Emissions help for nct

Post by minimike » Wed Oct 10, 2018 7:55 pm

Pretty sweet alright! Thought I'd never get there at one point! :D

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