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CP Series PI Emissions Testing


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I've recently had my 1970 CP Series TR6 PI MoT tested, and the emissions results on the MoT test weren't as I would have expected of a carb-fuelled classic. Of course a 1970 car doesn't legally need emissions testing, in fact doesn't need an MoT test at all, but it's interesting to see the results:

Carbon Monoxide: 5%

Lambda: 0.9

Hydrocarbons: 5,000 parts per million, at idle dropping to 2,000 ppm at fast idle

The CO and Lambda values suggest the fuelling is quite rich. I'm aware that PI does normally run rich to compensate for the lack of acceleration enrichment, but do the test results indicate my car is running too rich?

The Hydrocarbon figure is very high at idle but the fast idle figure is more reasonable for a classic. Perhaps the high Hydrocarbon result is due to the duration and overlap of the aggressive cam profile Triumph used for CP series cars?

The car performs very well, nothing to suggest there's anything amiss, although idle and acceleration isn't so smooth after a period in traffic. This clears quickly once on the move again. Fuel consumption is reasonable, with over 30mpg possible on longer runs using overdrive.

Do the experts here see any reason for concern with these emissions results? Is it running too rich compared to other PI cars, and should I therefore weaken the mixture a little?

I'm inclined to the view that it ain't broke and doesn't need fixing.

Nigel

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I think they all run a bit rich when not newly refurbished, plus if the engine has wear, you'll lose vacuum and immediately get richer running. 

I have tweaked mine and it no longer soots up the plugs at idle. 

Gareth

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Hi Nigel

No expert but if she is running well with 30mpg I'd leave well alone.

Andy 

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Hi Nigel,

my CP engine (fully reconditioned and std) had

1.6% CO, 1630 ppm HC and lambda 1.1 when it was first tested for our “MOT”. Engine was warm and measurement at idle, if I recall correctly.

Your numbers are higher, but if you have no issues (fouling, smell), I would leave it tbh.

Waldi

 

 

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Thank you for your comments gentlemen.

The engine does start to run a little rough after crawling and idling in traffic for 5-10 minutes, which makes me think it's rich enough to start fouling the plugs. It does smell a bit rich but it's not so bad as to coat the rear bumper with soot, as sometimes seen on PI cars. When I've nothing else to do, I will try to lean the metering unit a little using a home gas analyser to aim for 3.5-4% CO. If the car doesn't run so well like that, I can always put it back.

Nigel

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1 hour ago, Nigel Triumph said:

Thank you for your comments gentlemen.

The engine does start to run a little rough after crawling and idling in traffic for 5-10 minutes, which makes me think it's rich enough to start fouling the plugs. It does smell a bit rich but it's not so bad as to coat the rear bumper with soot, as sometimes seen on PI cars. When I've nothing else to do, I will try to lean the metering unit a little using a home gas analyser to aim for 3.5-4% CO. If the car doesn't run so well like that, I can always put it back.

Nigel

The three adjustment screws are usually marked from when they were set so you should be able to return them back if you need to. I found that the best adjustment was the large one carrying along the other two and the returning the small one back as this is the one that limits the movement of the linkage and rollers at high vacuum conditions (high revs with no throttle) otherwise it will lean a lot causing popping (some will enjoy it sounding like that) in the exhaust. 

Gareth

 

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2 hours ago, Mk2 Chopper said:

The three adjustment screws are usually marked from when they were set so you should be able to return them back if you need to. I found that the best adjustment was the large one carrying along the other two and the returning the small one back as this is the one that limits the movement of the linkage and rollers at high vacuum conditions (high revs with no throttle) otherwise it will lean a lot causing popping (some will enjoy it sounding like that) in the exhaust. 

Gareth

 

Thank you Gareth.

I've done that once before, following the instructions of a retired Lucas PI Service engineer. His advice was the same as yours, plus he used a vacuum gauge to set the mixture at tickover for maximum vacuum. He used to tune up the 2.5 PI saloons for the police and apparently this technique always gave the best performance.

Nigel

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Good to know Nigel, I've simply followed the Lucas guide regarding the MU, they show fuel curves so you know what changes what. I used a Gunson colortune and my ear at idle, you also have an idea how it drives and performs, plus your plug colour to work out how it's going. 

Cheers

Gareth

Edited by Mk2 Chopper
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19 hours ago, Nigel Triumph said:

Thank you for your comments gentlemen.

The engine does start to run a little rough after crawling and idling in traffic for 5-10 minutes, which makes me think it's rich enough to start fouling the plugs. It does smell a bit rich but it's not so bad as to coat the rear bumper with soot, as sometimes seen on PI cars. When I've nothing else to do, I will try to lean the metering unit a little using a home gas analyzer to aim for 3.5-4% CO. If the car doesn't run so well like that, I can always put it back.

Nigel

Nigel have you got black smoke coming out of the exhaust when you boot it. If so so its running too rich. That is what I was told by a Lucas - CAV dealer local to me 50 years ago! But he knew exactly how to adjust the M/U to compensate as he had all the equipment.

Bruce.

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Hi Bruce,

There's no obvious black smoke on acceleration, and no soot stains on the rear valance or bumper, so it isn't very rich. But 5% CO and a Lambda reading of 0.9 does suggest it's a bit rich.

My 2.5 litre GT6 runs on twin SU HS6 carbs shows 3.5-4% CO and Lambda 0.95 at idle; it performs very well. I feel similar figures should be possible from the PI system on my TR6. Time will tell!

Nigel

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18 hours ago, Nigel Triumph said:

plus he used a vacuum gauge to set the mixture at tickover for maximum vacuum.

That's a new one on me Nigel. He would just wind the (largest) adjustment up and down for maximum vacuum?

<EDIT> Right, I've just looked it up and read about it - for carbs. If I knew it before I'd forgotten it. Thank you.

Cheers, Richard

Edited by Spit_2.5PI
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1 hour ago, Spit_2.5PI said:

That's a new one on me Nigel. He would just wind the (largest) adjustment up and down for maximum vacuum?

<EDIT> Right, I've just looked it up and read about it - for carbs. If I knew it before I'd forgotten it. Thank you.

Cheers, Richard

Yes, wind the largest adjustment ring on the metering unit up or down to get maximum vacuum. Idling speed will increase when the mixture is spot on, so the idle air bleed screw can be closed slightly.

Nigel 

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49 minutes ago, ntc said:

I take it you did clean the cars lunges before mot?

Don't understand lunges. Or did you mean lungs, as in drive it hard for a few miles first?

I drove it hard for about 15 miles before the test but had to crawl in traffic for 5-10 minutes before arriving at the test station. It doesn't idle so smoothly after sitting in traffic and needs a couple of quick miles to settle down again.

Nigel

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26 minutes ago, Rob Y said:

Looks like everything you need is here;

http://www.tr6pi.com/Lucas Petrol Injection.pdf

What is the “largest adjustment ring” you mention Nigel?

Cheers, Rob

Hi Rob,

I think from the diagram on p17 and list of components on p18, it's item 4 'outer calibration screw and locking ring'.

Nigel

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36 minutes ago, Nigel Triumph said:

Don't understand lunges. Or did you mean lungs, as in drive it hard for a few miles first?

I drove it hard for about 15 miles before the test but had to crawl in traffic for 5-10 minutes before arriving at the test station. It doesn't idle so smoothly after sitting in traffic and needs a couple of quick miles to settle down again.

Nigel

Sorry but you have answered your own question 

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The Pi mixture is a compromise. Comparing to carbs or efi is unfair and potentially detrimental. 

Triumph didn't produce data on the emissions so we have little info. 

Other factors might contribute to fluffy running after getting stuck in traffic. Timing, plugs, oiling, weak spark and so on.

 

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I ran my PI for years with a CO value from about 2.8%. Performance was there. Consumption was there. After many years I took the head off and everything was ok inspite of using Unleaded. Wherby the butterflies etc were in top conditon.

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