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Exhaust pipes CO2 different


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Dear all

1970 PI

I have just purchased a gas tester and readings at idle are LH exhaust pipe + 6.2 and RH is +7.1 both seem high to me and can anyone shed light on the differences? At 2000 rpm they both read +8

 

I have also bought a vacuum gauge which reads -10 which is on the line between the yellow and the green part of the gauge, is this normal?

 

Many thanks for your advice in advance

Cheers

Smeggie

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Dear all

1970 PI

I have just purchased a gas tester and readings at idle are LH exhaust pipe + 6.2 and RH is +7.1 both seem high to me and can anyone shed light on the differences? At 2000 rpm they both read +8

 

I have also bought a vacuum gauge which reads -10 which is on the line between the yellow and the green part of the gauge, is this normal?

 

Many thanks for your advice in advance

Cheers

Smeggie

 

Hi, vacuum are correct for a 2.5 P.I. for a TR5-6 very high, maybe a bad cam? You mean CO not CO2, CO are not really important, In my opinion you had better ivest in a Lampda (CO2) gauge, it is very good possible to tune them between 12-14-1 AFR over the whole range.

Cheers,

 

Rien

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Smeggie,

 

~6.5% is too high @ 850rpm (or thereabouts) for a CP PI.

I was told (by Neil Ferguson) to aim for 3.5% at idle.

This assumes that the MU has been correctly calibrated across its range, something that can only really be done on either a rolling road or with the MU off the car and on test (you can DIY as the MU needs to be setup to deliver a set amount of fuel @ a specified vacuum).

Ken (Poolboy) is the master of vacuum tuning (from 6-pack fame ;-) ) and its a brilliant way to fault find, set and diagnose vacuum issues and timing of the engine.

Id suggest systematically going through the vacuum system first (blank off brake servo) and see if any immediate CO values change. If they do, then you have a vacuum leak. From the Lucas red book, you should see 7" @ 850rpm.

 

Hope it helps

 

Andrew

Edited by AndrewP
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This is the best forum :D

Ok if I have this right my reading of -10 vacuum is good although I read an article that suggests adjust timing for best vacuum and then reduce until it drops -1 to prevent pinking?

Any ideas on why one exhaust is richer?

Thanks for all who have suggested ideas

best regards

Smeggie

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Surely vacuum depends on whether this is a CR or CP engine. My understanding was that the CP should be 7 to 8" while the CR should be between 10 and 12".

 

Edit: oops, just spotted the 1970 car. However, that doesn't mean it has the CP cam - or even engine for that matter. Do you know?

Q

Edited by Quentin
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A very valid point Quentin, nothing stopping either of those changes happening in the last 42 years (engine change and/or cam change).

Also, the setup of the butterflies will change the vacuum values as well. Make sure they are barely open at idle and that they are returning to the same spot each time.

 

Worth emphasising that the only way to ensure that the MU is delivering the correct AFR is on a rolling road. This alone would take into account worn parts, slightly tired components etc etc. Don't just assume that because you have a 'correct' CO value at idle, that it will be correct over the rev range. This is true especially if your using an old MU with old injectors and/or not running the correct fuel delivery pressure. This is just my way of saying go careful. Any adjustments should be made gradually.

I used a good CO meter and regularly checked the plugs to indicate if I had things about right. I was lucky as I set the system up using a newly reconditioned MU and injectors, along with a recon PRV and healthy Lucas fuel pump (delivering 108 PSI).

 

As to why you are getting 2 different CO readings. Its probably just the butterflies that are not balanced at idle. I cant remember how the exhausts outlets are grouped, but if there is one or more butterflies in the set more open than the others, then to my way of thinking, this would make that CO reading on that bank slightly leaner (less restriction to air entering the cylinders).

How does the car drive? If its smooth and not jerky, then just accept that its very...I mean very difficult to get a perfectly balanced set of 6 butterflies balanced across its opening range. You can spend large amounts of money and time trying to achieve this with reconditioned throttle bodies, new spindles etc etc..even then theres no 100% guarantee.

 

If it were me..Id check the plugs first...what do they look like? black/sooty or brown or white? Generally speaking the rear cylinders (5&6) can suffer from air starvation if your using the standard plenum. These sometimes look black/dark brown compared to the rest. Use maybe plugs 2,3 and 4 for a better overall indication as to how your fueling is across the range.

If you think that you can wind the fuel back a bit, then you can adjust the MU 1/4 turn at a time to reduce the CO. Then, give the plugs a quick wire brush and go for a drive (not just round the block, but a decent drive) and check the CO and plugs again. If the CO has been reduced, then the plugs should look a lighter shade of brown.

Rinse and repeat.

If the plugs start to look white or get a glazed look, then reverse the last adjustment as your going too lean. Remember that although you can adjust various points along the MU fuel delivery curve, its a job for a test bed and/or rolling road. What you are simply trying to achieve is to not meddle with the curve as such, but simply move the relationship between vacuum and fuel delivery up or down.

Finally, remember that this is a 60's English sports car. It eats fuel for breakfast. Youd be hard pressed to get it near the current MOT values using the standard equipment. If you want efficiency and controlability then look at the fuel injection and elec ignition solutions people have installed.

 

Wow..went on for a bit. Hope it helps anyway.

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I remember, many moons ago, my father coming home with this marvelous tuning tool called a Red Ex Robot I think which was actually a vacuum gauge with coloured segments on the scale and a printed sheet which detailed all sorts of diagnostic tests which this one simple instrument could perform.

We had a Triumph Herald at the time, 948cc's of raw power!! we spent hours under the bonnet with this magic gauge clutched eagerly tweaking this and that to get the desired results.

Happy days when life was so much simpler than today!!

Graham.

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I would not worry about discrepancies at tick over - the engine is developing maybe 5hp. Its far from the best load condition to tune it. Its breathing air at perhaps 3% of max power. So as Andrew said it could be the butterflies are tiny bit different, and the screw air feed on front manifold will weaken the front cylinders more than rear.

 

The 2000rpm readings agree, and thats what matters. Thats still not under much load - to do full load tune involves the expense of a rolling road ( and the likely ignorance of the operator on Lucas PI) . But you could fit wide-band exhaust oxygen sensor and DIY.

Edited by Peter Cobbold
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Hi

Plenty to go forward with here, how much and where do I get the parts needed in the message above?

regards to all

Smeggie

 

Smeggie,

I bought this:

http://www.efi-parts.co.uk/index.php?productID=204&sent=yes

The boss has to welded into the exhaust - roughly near the starter.

The meter reads as Air/Fuel Ratio (AFR) by sensing the residual oxygen left in the exhaust flow. A rich mixture will be around 12, and very lean 17.

Peter

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Hey up prof's we are talking a twin exit exhaust ?

 

Well one is better than no AFR measurement at all.

If its a problem swap the sensor one to other, buy second boss and blanking plug. Or fit second Bosch sensor and switch between them.

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My opinion are, is it only to make mixture adjustments (and you are sure your engine don't have any fault) the single sensor type are perfect but yes if you are looking for a fault the Innovate dual channel LM2 by example are a very fine tool.

 

Regards,

 

Rien

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I think what Rien is saying is that this product :-

 

http://www.innovatemotorsports.com/xcart/product.php?productid=16293&cat=0&page=1

 

(the LM2) comes with a dual channel option so your able to have a sensor in each branch of the dual exhaust system...

Looking at the price though..you REALLY have to want to monitor your exhaust gasses :o

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  • 8 years later...

Hello everyone,

I wake up this thread. On my 69 Pi fitted with standard exhaust manifold, standard exhaust lines under the car (so 2 separate lines) and twin box exhaust system (so 2 different silencers), MOT indicated a couple of years ago 2% CO value. The measurement was made with the sensor in 1 silencer, of course. So is the total CO value 4% (2 silencers * 2%)?

Thanks,

William

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No.

The measurement is the percentage of CO  in the exhaust gas, not the total amount.  If you measure both pipes you double the amount of both exhaust and CO so the percentage should stay about the same at 2%,  provided the mixture in all the cylinders is set up correctly. 

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