Mot fail

[Chukkieegg]

They got the fast idle emissions down but Lambda still high they are the hydrocarbon emissions and ubends have been resealed don't sound like it's sucking in as much air so going to get a new maf as opposed to secondhand and see if that makes any difference and i can drop past and they will stick the gas analyser in and see what readings are like 

At least now I got time to find a replacement although it now has a squeak on os rear sounds like a bird squaking do don't know with coffin arm being replaced both rears if something else has now failed

[CRC]

For info, I've added a link to a video that I took when I was having problems with mine .... you can see that the problem on mine was that the CO values were higher than they should have been and the lambda values were also going high (indicating a lean mixture).

As it turned out, there was a large chunk of mesh missing from one of the cats, meaning that the exhaust from one bank was effectively going straight through and, as the function of the cat is to nudge the carbon monoxide molecules to pick up  spare oxygen molecules (in the excess air) so that they become CO2 molecules, the hole in the mesh  was almost certainly causing the problem.

With the cats replaced with two £70 EEC brand after market versions, the next test showed 0.068% CO and a lambda value of 1.005 on the fast idle test - well in spec.

HC values (unburnt hydro carbons) actually measured higher with the cats changed  -  125 ppm as opposed to around 80 ppm on the video, but still within the allowed limit of 200 ppm.

How high were your HC levels on the test?

If I was you, I think I'd first try cleaning the MAF either with a good quality electrical contact cleaner (must evaporate and leave no residue ) or a dedicated MAF cleaner spray.

The MAF works by allowing the ECU to measure the current that it needs to send to a small heater element in the MAF and maintain that temperature at around 200 degrees C. It must also have a small temperature probe built into the MAF to sense the element temperature. The theory is that the more air that is passing over the probe, the quicker the element will lose heat, so, by knowing the inlet air temperature and the current and temperature feedback from the MAF, the ECU can calculate how much air must be passing by it to give those conditions.

If either the heater element or the temperature probe on the MAF has failed, then you could expect some codes as the ECU will know that there is a problem, however, if it is coated in anything then that will act as an insulating layer and false air flow readings will result.

I'd also stick some Redex system cleaner in and hope that it might refresh the spray patterns on the injectors (who knows?), have a peek at the air filter and make sure that the clamps on the air inlet hoses are tight. Cheap things first .....   

 

https://imgur.com/a/TY0O4aE

[CRC]

I also did some resarch at the time, and am pretty sure that the actual allowed CO% values for the 2.5 engine are 0.5% at idle and 0.3% at fast idle.

 

[Chukkieegg]

OK got the emissions paperwork out

Cocor 0.28

Lambda 1.643 should be 1,030

Co 0.17

Co2 8.9

Hc 89

O2 8.54

[CRC]

Well, there's a huge amount of excess air getting into that gas analyser somehow .........

The results show CO2 and O2 values as well as the more normal CO values, so that's very helpful in analysing the results.

The function of an engine is to burn a hydrocarbon ( contains hydrogen and carbon atoms) fuel completely using the correct amount of to produce carbon dioxide (CO2) and water (H20).

In a theoretically perfect (but unobtainable in practice) engine there would be no carbon monoxide produced as all the carbon would be converted to CO2 and all the hydrogen would be converted to H20. The nitrogen that air contains would go through the engine and out again with no chemical reaction.

A well set up engine running at a stoichiometric ratio of 14.7:1  (Lambda =1 )would give the following gas analyser results (on a v/v basis):

Oxygen (O2) <1% - (Almost all the oxygen in the air has been burnt to create CO2 and H2O )

Water vapour (H20) - 13% - (Visible on cold days as it condenses to water as it leaves the car)

Carbon Dioxide CO2 - 13% (All the carbon converted to CO2, therfore negligible CO)

Hydrocarbons (HC) < 100 ppm (Equivalent to 0.5%)

Nitrogen - 74% (It came in and now it's gone out in the same form)

However, your figures are showing a Lamda value of 1.634 which is equivalent to (1.634 x 14.7) = 24:1 Air fuel ratio, or 63% more air than the engine needs.

Your CO2 value of 8.9% is a lot less than the expected value of 13% and your O2 value 8.54% is massively more than the negligible O2 value that would be expected. Both indicate that a lot of excess air is diluting the exhaust sample somehow.

Your HydroCarbon value is what would be expected.

All this points to the fact that the gas analyser is measuring a gas that has much more air in the sample that it should have, and that air has to get into the system somehow. Possibilities might be:

1. The garage gas analyser has a leak in the connections somewhere allowing it to suck in air along with the exhaust sample. (Unlikely as they would be failing every car they tested on high Lambda values, but possible)

2. There is a massive leak on your exhaust system that is allowing massive amounts of air to be sucked in, but as that equates to 63% of the air that the engine is trying to use, I think you'd notice that gaping hole

3. Combustion not happening in one or more cylinders, allowing neat air and neat fuel to pass straight through, though I would have thought that your exhaust would be making one heck of a noise in that case as the mixture ignites in the exhaust, or that the HC values would be high, which they're not, and you would definitely notice misfiring to that extent.

4. MAF reading incorrectly and thinking that a lot less air is going through than is actually the case? Maybe, but surprised that the car would even start with such a weak mixture.

5. Gaping hole on the inlet air ducting or a vacuum hose allowing a lot of air to be sucked into the engine that the MAF doesn't know about.

Short answer is that I don't know, but somethings amiss .... and it could be quite a simple fix.

 

 

 

[bally4563]

1 hour ago, CRC said:

Well, there's a huge amount of excess air getting into that gas analyser somehow .........

The results show CO2 and O2 values as well as the more normal CO values, so that's very helpful in analysing the results.

The function of an engine is to burn a hydrocarbon ( contains hydrogen and carbon atoms) fuel completely using the correct amount of to produce carbon dioxide (CO2) and water (H20).

In a theoretically perfect (but unobtainable in practice) engine there would be no carbon monoxide produced as all the carbon would be converted to CO2 and all the hydrogen would be converted to H20. The nitrogen that air contains would go through the engine and out again with no chemical reaction.

A well set up engine running at a stoichiometric ratio of 14.7:1  (Lambda =1 )would give the following gas analyser results (on a v/v basis):

Oxygen (O2) <1% - (Almost all the oxygen in the air has been burnt to create CO2 and H2O )

Water vapour (H20) - 13% - (Visible on cold days as it condenses to water as it leaves the car)

Carbon Dioxide CO2 - 13% (All the carbon converted to CO2, therfore negligible CO)

Hydrocarbons (HC) < 100 ppm (Equivalent to 0.5%)

Nitrogen - 74% (It came in and now it's gone out in the same form)

However, your figures are showing a Lamda value of 1.634 which is equivalent to (1.634 x 14.7) = 24:1 Air fuel ratio, or 63% more air than the engine needs.

Your CO2 value of 8.9% is a lot less than the expected value of 13% and your O2 value 8.54% is massively more than the negligible O2 value that would be expected. Both indicate that a lot of excess air is diluting the exhaust sample somehow.

Your HydroCarbon value is what would be expected.

All this points to the fact that the gas analyser is measuring a gas that has much more air in the sample that it should have, and that air has to get into the system somehow. Possibilities might be:

1. The garage gas analyser has a leak in the connections somewhere allowing it to suck in air along with the exhaust sample. (Unlikely as they would be failing every car they tested on high Lambda values, but possible)

2. There is a massive leak on your exhaust system that is allowing massive amounts of air to be sucked in, but as that equates to 63% of the air that the engine is trying to use, I think you'd notice that gaping hole

3. Combustion not happening in one or more cylinders, allowing neat air and neat fuel to pass straight through, though I would have thought that your exhaust would be making one heck of a noise in that case as the mixture ignites in the exhaust, or that the HC values would be high, which they're not, and you would definitely notice misfiring to that extent.

4. MAF reading incorrectly and thinking that a lot less air is going through than is actually the case? Maybe, but surprised that the car would even start with such a weak mixture.

5. Gaping hole on the inlet air ducting or a vacuum hose allowing a lot of air to be sucked into the engine that the MAF doesn't know about.

Short answer is that I don't know, but somethings amiss .... and it could be quite a simple fix.

 

 

 

Exactly what I thought, when I did the maths😂

[Pordave]

With my maths, I would have it running on diesel😀

very impressive maths sir 

[Chukkieegg]

So in essence it's broke

New maf will be fitted this weekend weather permitting unless @bally4563 will let me use his garage lol and as stated before when I put secondhand maf on it August time car instantly stopped smelling of fuel and the porsche specliast I had maf off had it in stock for some time and had no idea why it was swapped so maybe I will get lucky with new maf

[iborguk]

What's the latest set of fault codes from the car ? What are the live values for the MAF sensor - do they look ok ?

In no way related to your issue , I had an intermittent PDK Emergency Transmission Run error , which initially looked like MAF and turned out to be a failing AOS, which caused the ECU to go nuts and argue with the MAF, pulling the actual live values (voltage and kg/h from memory) from the MAF turned out to be the key there.

My point, in my case only pulling the codes/live values and seeing them in context nailed the root cause and what needed fixing, it could have been one or a number of things in conjunction (MAF, Vacuum leak etc)

Good luck with getting it sorted.

Edited November 19, 2021 by iborguk

[iborguk]

This might be useful reading

https://rennlist.com/forums/attachments/996-forum/914198d1424791769-log-graph-of-maf-output-via-durametric-dme-actual-values.pdf

https://www.pelicanparts.com/techarticles/Boxster_Tech/27-FUEL-Mass_Air_Flow_Sensor/27-FUEL-Mass_Air_Flow_Sensor.htm

 

 

Edited November 19, 2021 by iborguk

[Chukkieegg]

Don't have a reader that produces live results I can clear codes and rest stuff so bit hard to get live readings

A new oas was fitted when first bought car 2.5 years ago

But it was the cheaper one d911 sell so something to think about unless someone local to me has a reader that gives live stats and would be happy to test with me otherwise I think back to porsche specliast which after the £533 mot bill this week am a bit strapped for cash at mo 

Once again Thankyou all for the input and advice I wish I was more mechinal minded but at least I can swap the maf myself

[iborguk]

1 minute ago, Chukkieegg said:

Don't have a reader that produces live results I can clear codes and rest stuff so bit hard to get live readings

A new oas was fitted when first bought car 2.5 years ago

But it was the cheaper one d911 sell so something to think about unless someone local to me has a reader that gives live stats and would be happy to test with me otherwise I think back to porsche specliast which after the £533 mot bill this week am a bit strapped for cash at mo 

Once again Thankyou all for the input and advice I wish I was more mechinal minded but at least I can swap the maf myself

Yes I think getting it back on a reader which can do live values may help you.

Durametric and PIWIS can both do that, I think others like iCarsoft can too but it also needs someone to interpret the results to give that important context.

If you look on the members map there maybe someone who can help re the code reader access.

Good luck.

[CRC]

One thing I would say about the Rennlist PDF is that there is a difference between American and UK spec 2.5 cars.

American spec cars appear to have two O2 probes per bank while UK cars have just the one.

Also, American spec cars have a secondary air injection pump which is designed to pump fresh air into the exhaust upstream of the cat for a short time after start up. Presumably the idea of this is to allow the rich mixture needed for a cold engine to receive more air after it has combusted so that it "re-burns" in the cat.

This would be a good place to look for the leak in this case, but unless it's an American spec engine, it won't be there.

The AOS is a good shout as the air from it will be sucked into the engine after the MAF so an incorrectly fitted vacuum line or one with a hole in it could allow unmetered air to enter the engine.

[Chukkieegg]

So. Would that be the convultaed plastic pipe that connects to side of aos when you say vac connection? 

[iborguk]

15 minutes ago, CRC said:

One thing I would say about the Rennlist PDF is that there is a difference between American and UK spec 2.5 cars.

American spec cars appear to have two O2 probes per bank while UK cars have just the one.

Also, American spec cars have a secondary air injection pump which is designed to pump fresh air into the exhaust upstream of the cat for a short time after start up. Presumably the idea of this is to allow the rich mixture needed for a cold engine to receive more air after it has combusted so that it "re-burns" in the cat.

This would be a good place to look for the leak in this case, but unless it's an American spec engine, it won't be there.

The AOS is a good shout as the air from it will be sucked into the engine after the MAF so an incorrectly fitted vacuum line or one with a hole in it could allow unmetered air to enter the engine.

Good shout re the US stuff , thanks.

[Chukkieegg]

11 minutes ago, iborguk said:

Good shout re the US stuff , thanks.

Defo not a US import was built in Stuart according to vin plate

[CRC]

I've never actually looked which pipes they are, but they almost certainly connect into the crankcase breather system, theory being that any air likely to have oil droplets  in it needs to be connected to the air inlet so that the oil can be burnt in the engine.

It would always go in downstream of the MAF to avoid coating the sensor in oil. Normally it would be under vacuum with very little air flow, but if open to the air, then unmetered air can be sucked in.

A mate of mine had a very low tickover on a Passat once due to a hole in the vacuum pipe to the brake servo. Thus, unmetered air was entering the inlet manifold meaning that the MAF was only reading a small airflow and only squirted a small amount of fuel in accordingly.

If your brakes seem to require more effort these days, that would possibly indicate a hole in the servo vacuum hose, another place for unmetered air to sneak in.

My old BMW K75 bike once ran very strangely until I realised that I hadn't screwed the oil filler cap back on, meaning that unmetered air was flowing through the crankcase and into the engine by the breather hose that was connected to the inlet manifold.

 

[½cwt]

27 minutes ago, Chukkieegg said:

Defo not a US import was built in Stuart according to vin plate

They were all built in Europe, either Stuttgart of Finland....

[Chukkieegg]

And I can't spell lol

[Chukkieegg]

About to swap maf codes are 50 current missfire emissions revelant

Cylinder 1 missfire emissions revelant cylinder2 missfire emissions revelant and cylinder 3 missfire emissions revelant same codes I always get clearing now

[BBB]

Misfires on one complete side of the engine will certainly affect the emissions as not all the fuel is being burnt correctly.

[usman10316]

Just now, BBB said:

Misfires on one complete side of the engine will certainly affect the emissions as not all the fuel is being burnt correctly.

misfires on one side of the engine... it could be the variocam solenoid? I had that issue on mine... expensive fix 😕 

[Chukkieegg]

I think its sucking In air

Was listening to car after changing maf and you can hear air being sucked in but not idea where from

[CRC]

Air being sucked in is exactly what the emissions test is suggesting. 

I've heard of people spraying Easystart fluid onto suspect areas when the engine is running. If it finds the hole, then the revs will rise as the vapour is sucked in and burnt ..... Not quite so easy on a Boxster engine though, but suspect the AOS.

There are smoke injection machines out there that will show holes in vacuum lines by emitting smoke. Tends to be a garage tool though ......

Once you've cleared the misfire codes, how long does it take for them to come back again? Every drive, every few drives, every week ..... etc

[iborguk]

https://www.pelicanparts.com/techarticles/Boxster_Tech/21-FUEL-Vacuum_Leaks/21-FUEL-Vacuum_Leaks.htm