EGR Cooler Problem

[snapdragon]

Thanks again Lee - looks a great bit of kit.

Only the EGR and cooler bypass flap are vacuum powered. The turbo VNT, intake flaps and throttle are all electric.
On 2008- models with 4 digit engine codes such as CABA, the EGR is also electric but the cooler bypass flap is still vacuum on those too.

I need to get one of those handy vac pumps - but in the meantime I found the one way checkvalve 046905291A allows air to suck and blow both ways I cleaned it out with IPA and some blackness came out but it is still not sealing inside so will order a new one.
I pulled a vacuum on the rest of the system with my oil extractor and it held pretty well but not perfect. It got dark but tomorrow I will pull a vacuum just on the cooler and watch the arm move and do the same on the EGR and see if I hear it snap shut when I pull the pipe off. It will be better when I get a handyvac with a guage.

Interestingly, with the vacuum blanked off after the brakes, I still don't get an engine light until part way through the second journey and the VCDS readings are the same EGR actual is greater than specified even though I know the EGR is shut tight and has a stiff return spring.
I have read in an SSP PDF that EGR flow is measured by lambda changes and only uses a drop in MAF reading as a fallback. My lambdas are always pegged at 99.9% as though they have been 'fixed' at that by ECU software that the previous owner did which may not help, but I had the car over 4 years before I got issues with EGR so I know it isn't the root cause.

[Mechcanico Lee]

On cars with no lamdas egr flow is measured with air mass difference only ..... it has no other way really , even if egr valve has built in tracking switch to monitor its position the real flow is measued by air mass difference .

But yes ,with lamdas it can use the difference in oxygen to monitor egr also .

Where you are getting actual egr flow more than desired is correct for your circumstance , because you have no vac to the egr the valve will be closed so egr flow will be higher

Doesn't sound right does it ....it's not measuring flow through the valve it's really measuring air mass difference , open egr lower air mass ..... closed egr more air mass .
So when you are driving on say light load ecm will be commanding egr to open let's say 35 % duty , but because there is no vac to egr it cannot open so air mass will always read as higher than actual or egr higher than actual ..... it's just the wording gets confusing as like you say how can egr be open with no vac and a strong Spring holding it back .

If you say your lamdas are fixed at 99.9 % for all the time you have had it , the ecm must be using the lack of air mass change to work out that egr is not opening thinking about it .

Does your car have dpf ?? lamdas on the diesels are very often used for regeneration control and ensuring pre dpf or oxidation cats are up there efficiency threshold as they assist in getting regen temps up .

Diagnostics is a field I enjoy doing in my job ...... specifically non intrusive diag ....pico scope , in cylinder pressure transducer waveform diag ..... something I'm just getting to grips with .

[tc4332]

You are the man Lee. Certainly in this area.
I remember being very interested the last time you started to discuss diagnosing with a scope. Waveforms are the way.

[snapdragon]

Thanks Lee.
Well... it did have a DPF when I bought it. The car was fine on a test drive and passed the documentaion and VCDS tests. It was a great price too from a used car foreourt (this was nearly 6 years ago). So I bought it and drove 120 miles home.
Over the next few days it lost more and more power until it was asthmatic and the turbo would get very hot and had started to leak exhaust gas from the gasket between the two halves (castings). I took it to Audi who said it looked like the turbo was faulty, I was annoyed and bought a new turbo and after getting a small VW indie to fit it - it was exactly the same. We scratched heads and eventually they disconnected the exhaust and went down the road and it was like a different car. They said the DPF or exhaust was - blocked but there were no warnings. They said I needed a new DPF for £1200 but I wasn't convinced as no warnings about regen, I though I will do a regen (the garage was a bit traditional and normally just does old lady's Polos etc..) and the option was greyed out in VCDS and the soot level measuring blocks were blank.

I looked more into VCDS and it said there was a flash of engine ECU 3 weeks before I bought it - it was under the Identification tab - no. of flash attempts =1 Sucessful flash attempts =1
Hmmm, it seemed like the DPF had been flashed-out in software but the DPF was still there and was now blocked. We found the pre-cat next to the turbo behind the engine had been cut in half and neatly welded back up. It looks like someone did a DPF removal but removed the pre-cat instead (as that is where the DPF is on later variants). So...they removed the soot and soot trap and everything was fine.

During the repairs, I called the seller who sounded sympathetic but the phone stopped ringing the second week. To cut a long story short they had gone bust and were struck off. Nevermind, I was still a few grand up all in all.
I don't know what software is on my ECU or who did it, whether it also gives performance boost but it has been fine for 5 years and the car now has 250,000 miles.

Aha- I think you gave me the lightbulb moment....Sounds like the measuring block 003 labels are wrong/misleading and are really MAF readings?
So 487 actual - 411 specified means 76 of EGR is being specified and the EGR should be opened until the actual MAF is brought down to match the specified MAF?
Attachment 14071

[tc4332]

Oh Dear Snap,
My 3.0 TDI is two years older than yours and I have been a little bit into panic mode with your current saga, then I read 250K miles.
Phew, scare over, mine is under 130K so my "man maths" tells me I should be OK.
Hope that with Lee's assistance you are nearing the end.

[Mechcanico Lee]

Snap ,Sounds like you have had a bit of a hack job done to delete dpf , that's why lamdas are held at 99.9 % .

We had a sprinter van t'other month dog slow ....no codes , no reading from differential pressure sensor , I un plugged loads of sensors off the engine ....still no codes , I knew something was off , read the file with our cmd unit and sent it to my chipping man ... he said the whole fault code library has been erased !!
Complete hack job on it for dpf deletion .

If you look at air mass values you will see there the same as the egr flow data blocks , the ecm knows from its scripted algorithms that when egr duty is say 20% that the air mass should drop by a certain value , so if you have vac loss at
the egr control solenoid the egr will not open as much so air mass will not drop enough . The ecm will drive the egr solenoid to get the actual to the desired if the duty goes out of its working window egr flow codes for to high to low will be
logged .
Did you rule out all the vac loss areas .... all the splitting / cracking vac pipes replaced , if you still get the code after that I would suspect egr control solenoid

Ray
Thanks for the support , yes still playing with the scope , we have got the pico 4 channel and just got the in cylinder pressure transducer kit

For complete diagnostic nerdyness here's a Audi a2 1200 fsi engine with jumped teeth on cam chain sprocket .






Green trace crank sensor ( digital )
Red trace cam sensor ( Hall effect )
Blue trace cylinder pressure transducer


You are looking for correlation between the green traces missing tooth effent .... the gap in the green trace , the missing gap is the missing tooth on the flywheel that the crank sensor references from , you just have to know what a good engine trace is like to know the correlation .












Here's the fixed engine , new timing chain kit and correctly timed up

All this diagnostic capability with even taking a rocker cover off or timing cover , just done from ecm wiring plug and a spark plug hole .


Told you it's for nerds ......Anyone still here Zzzzzzzzzzz hehe !!

[tc4332]

To be honest Lee, I never thought when I was playing with scopes that they would be used like this.
I was only using them on computers, modems and early disc drives.
I admire what you are doing, just wish that I was still young enough to be involved.