Mot fail

[iborguk]

Yes a smoke machine would help nail it if it’s a vacuum fault.
 

Stumbled across an OBD reader (which can read live values) and a couple of vids which may also be of interest.

https://www.amazon.co.uk/Autel-AutoLink-AL319-Universal-Diagnostic/dp/B007XE8C74/ref=sr_1_1_sspa?keywords=al319&qid=1637441691&s=automotive&sr=1-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyVDRRVUNIQVM1NVBWJmVuY3J5cHRlZElkPUEwMTQ2OTQ0MTNNNDZYMkEzQVZXQSZlbmNyeXB0ZWRBZElkPUEwNzQ2OTA0SFZUWDgzUldJSkVGJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

 

Edited November 20, 2021 by iborguk

[iborguk]

 

[Chukkieegg]

12 hours ago, CRC said:

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

AOS was replaced when first bought car but it was the cheaper one d911 do codes come back after about 5engine starts watched both videos the paul1962 video issue was same as mine sooty exhaust tips except his was left bank for error codes and mine is right bank will try tightening up clamps on the hose this afternoon but good place to start

[CRC]

The fact that your codes come on after 5 or so drives means that it's almost certainly not a mega problem with the variocam system.

The misfire codes are generated by the ECU timing how long the crank shaft sensor takes to be triggered after the cylinder fires. If it takes longer than it should, it increments a counter in memory and when those count values get to a threshold value (not sure what the value is) then it triggers the check engine light and the codes that your seeing.

The word RANDOM is key here. Those apparent misfires happen randomly, not constantly, if they were constant, you'd know about it.

One thing I would say about Paul's video is that individual bank fuel trims are as a result of the ECU looking at the results of it's actions by reading the results from the O2 sensor on each bank.

Given that the hose he tightened up is common to both banks, logic says that it's a good chance that his O2 sensor or maybe the cat on that bank might be the issue.

Your emissions results suggest that you have a gaping hole somewhere in the vacuum system and the fact that you can hear it suggests something has come completely off somewhere.

It's unlikely to be a slight leak solved by tightening clamps.

[Chukkieegg]

I don't have the time or space to remove the inlet manifolds so will check the clamps and see if I can see anything obvious but beyond that would need to get booked in at porsche specliast which defo can't afford this month

And as I said before I am at that point how much more money do I throw at it before I say enough is enough

[Chukkieegg]

And know one of the roof boden cables has snapped so more parts to order

Managed to tighten clamps a bit and has quietened the air down a bit but still can hear air being sucked in so guess leak is elsewhere will get it on gas aynalser tommorow and see if there is any change

[CRC]

I can appreciate your frustration and the despair we all feel on occasion.

Have attached a link to the Pelican AOS details. Those hoses / connectors shown on the photos look like possible culprits to me.

Good luck.

 

 

https://www.pelicanparts.com/techarticles/Boxster_Tech/09-ENGINE-Air_Oil_Separator/09-ENGINE-Air_Oil_Separator.htm

[Chukkieegg]

So I did take pipe off aos to throttle body there is some oil in it but what would you call an excessive amount? 

But not getting clouds of white smoke so that has thrown me a bit

[CRC]

It's just the external condition of the tube  that's important and how air tight the end connections are, as you're looking for a place that air can get in. If the tube is airtight, it's fine.

There's a  large bore rubber bellows down at the bottom where the AOS connects to the crankcase and the bottom clip is notoriously difficult to get on properly. Just wondering if that bellows is correctly seated and sealing property, but I think it has to looked at from underneath and much easier on ramps.

 

[CRC]

I thought this was quite interesting for a very cheap homemade smoke generator. Would like some sort of pressure regulator on the air inlet though ...

[iborguk]

https://www.amazon.co.uk/SDT-106-Automotive-Testing-Machine-Motorcycle/dp/B07MGL3MSL/ref=sr_1_25?crid=3GV58UXHHKD22&keywords=smoke+leak+detector+car&qid=1637517431&sprefix=car+smoke+detectors%2Caps%2C160&sr=8-25

 

Edited November 21, 2021 by iborguk

[Chukkieegg]

54 minutes ago, CRC said:

It's just the external condition of the tube  that's important and how air tight the end connections are, as you're looking for a place that air can get in. If the tube is airtight, it's fine.

There's a  large bore rubber bellows down at the bottom where the AOS connects to the crankcase and the bottom clip is notoriously difficult to get on properly. Just wondering if that bellows is correctly seated and sealing property, but I think it has to looked at from underneath and much easier on ramps.

 

Well I  couldn't feel any air coming out of the plastic pipe but it Could have pinpr*ck holes in it

[CRC]

I'm probably learning more from this thread about how these cars work and how to fault find than in all the rest of the time I've owned mine, so thanks for that.

I realised that I didn't really know how the AOS worked ( other than what the words say) so looked at a Youtube video that showed an owner replacing his AOS (fiddly job) and, at the end,  cutting the old one open to see what was inside.

The tall part of the AOS is a simple "cyclone" (think Dyson vacuum cleaner), but at the top, there was a spring / diaphragm / valve arrangement that puzzled me (and him for that matter)

More research and it turns out that the AOS function in life is to vacuum "oil vapour" from the crank case and burn it in the engine by letting the inlet manifold suck it into the engine where it can be burnt. This is not meant to be liquid oil droplets, but oil particles that have picked up enough energy to enter the "gaseous state".

However, the vacuum in the crank case and hence the air flow through the AOS  needs to be regulated, and that is the function of the spring / diaphragm / valve arrangement at the top of the AOS. This is designed to automatically regulate the vacuum in the crank case to between 4 and 6 inches of water column. ( In a complete vacuum there are around 33 ft of water column, or around 360 inches of water column.)

By regulating the amount of air being sucked into the inlet manifold to a fairly small amount, the air flow is slow enough to allow the separation cyclone to do its job and any liquid oil is spun out and drains back down into the sump though that convoluted rubber connector, and only a small amount of air and  gaseous oil goes into the engine and the  life is sweet and the engine doesn't smoke.

However, if the AOS diaphragm valve fails for any reason, then the valve goes wide open allowing the engine to suck way more air than it is supposed to from the sump, increasing the vacuum in the sump to around 40 inches of water column, pulling actual oil droplets with it and passing through the cyclone so fast that the oil separation can't happen and the result is the plumes of smoke coming from the exhaust that let you know it's happened.

So that's how it works, but it also gives a clue as to how to test "leak tightness" of the vacuum lines in this case, and it's as simple as attaching a sensitive vacuum gauge to a small bore hose that's been connected to a modified oil filler cap allowing the the gauge to measure the vacuum in the crankcase.

Reading 4 - 6 inches water column would indicate that the vaccum lines are tight and the AOS is fine

Reading 40 inches water column would indicate that the vacuum lines are tight and that the AOS is shot (but by now there would probably be so much smoke that you'd already know that)

Reading 0 (or very small)  inches of water column would indicate that the vacuum lines are letting in air elsewhere.

I'm woffling on a bit, but am intrigued by this problem and it'll probably happen to me one day, so all good preparation for that day.

Please let us know what your latest gas test readings show.

Thanks

 

[iborguk]

One of the things I like about this forum, everyday is a school day for me.

[Chukkieegg]

Didn't make it to garage tonight went for a drink with a mate but will get there 1day this week thanks for the tech on the aos very interesting

[CRC]

Did you ever manage to get the car for another emmissions test after replacing the MAF?

Would be interested to know if that solved the problem if you did.

Thanks

[the baron]

15 minutes ago, CRC said:

Did you ever manage to get the car for another emmissions test after replacing the MAF?

Would be interested to know if that solved the problem if you did.

Thanks

He think he gave up on the car and is trying to sell if hasn’t already, however I maybe completely wrong 😑 

[Chukkieegg]

Not been back for gas analyser test week after mot waterpump and drive belt failed so that was another £303 to get sorted still running it at moment but looking to try and partx in new year or sell if anyone wants it as a project lol

On a plus note did get me to Anglesea and back in a day last week and it will be replaced with another boxster

[CRC]

OK, thanks for that. What year and engine size is your car?

[Chukkieegg]

4 hours ago, CRC said:

OK, thanks for that. What year and engine size is your car?

98 2.5 base 986

[Rev Ken]

On 11/10/2021 at 10:20 PM, Rev Ken said:

I always give it an 'Italian tune up' (2nd gear around a bypass at around 70mph for about 4 miles) before taking it in for its MOT - hasn't failed on emissions yet.

But this year it has failed for Lamda (plus a universal joint torn boot - that makes two over the last four years, probably the other side. Also getting 'advisory' brake pipes replaced and a service. doesn't sound cheap!

[Rev Ken]

Well Lamda OK. All brake pipes replaced, serviced, gaiter replaced (splitting the universal joint was a problem) MOT Getting and fitting my 'special' number plates + one for my motorcycle. Total £823.31.

I'm happy.🙂

[Chukkieegg]

1 hour ago, Rev Ken said:

Well Lamda OK. All brake pipes replaced, serviced, gaiter replaced (splitting the universal joint was a problem) MOT Getting and fitting my 'special' number plates + one for my motorcycle. Total £823.31.

I'm happy.🙂

Great to hear

[CRC]

Well, the dreaded day arrived and this morning I took the car in for the annual MOT test, expecting the worst but keeping my fingers crossed.

Few hours later I got a call to say that it had passed, just a slight oil leak on the advisories (as noted on last years MOT) and perhaps rear brake discs might need doing sometime (have those in the garage already so a job for the Spring.)

He also said that an engine light was on but that the car was too old for that to be taken into account ...... wasn't aware that that was the case, but good to know for the future.

Even with the cheapo EEC cats on, it flew though the emmissions test - 0.088% CO (max allowed 0.2%), 7 ppm HC (max allowed 200)and a Lambda value of 0.998 (must be between 0.97 and 1.030).

So during the test the car was obviously running fine from a combustion point of view, and obviously not misfiring, though, of course, when I got home and checked the codes, just as I expected, random misfires on cylinders 1,2 and 3 !!!

These haven't come up for months now and they decided to show themselves during the emmissions test!!

It makes me more and more convinced that engine bay temperature is a factor in causing these codes - 15 minutes or so of stationary idling and then revving the engine during the test would have raised the engine bay temperature to a value not seen for quite a few months - need to find that earth point that the coil packs for 1, 2 and 3 connect to and clean that up a bit for starters.

[½cwt]

At least you have a 12 month ticket while you work on it now.