EGR Woes

[davebrannigan]

Hi Guys,

Hitting my head against a wall with an EGR issue on my 1.9TDI 4 Motion with an AVF Engine. It all seemed to start with a refill of fuel from a certain supermarket but I've emptied it all and refilled with no improvement. VCDS tells me nothing. No error codes. I'm finding that at light-med throttle loads between about 1700 and 2500 RMP I get some hesitation and a considerable amount of smoke. Flooring it clears the smoke. Through substitution with my daughters car I've eliminated the N18 valve. The wiring to the N18 is solid. All the Vacuum hoses are sound - tested with a hand pump. I've reluctantly just put a new EGR on it to no avail. If I disconnect the EGR vacuum hose it runs perfectly but after 20 odd miles I get an emissions workshop light.

I've put a vacuum gauge in parallel with the valve and watched it whilst driving and the gauge is very erratic whilst this hesitation is going on. Something is clearly telling the N18 what to do and it isn't good.

I've done the VCDS 3rd gear acceleration tests to check the MAF sensor/ boost pressures actual-versus-expected and all look good.

I'm sure there are a bunch of you thinking "delete the EGR" but a) I'm not sure how you'd do that without getting the emissions workshop warning and b) I hate to let things like this beat me.

Anyone have any experience in this area? Id love to hear from you. Car has 210K miles on it, pulls like a train and uses no oil. I put 170 K of those on it and apart from a split turbo outlet pipe split I've never had any engine woes until now.

Suggestions gratefully received.

[Rob69]

Can you check the O2 probe output with VCDS - just thinking that must feedback to the ECU and operate the N18 / /EGR to regulate NOX.

[davebrannigan]

Yes I could check that, but what am I looking for and under what conditions?

I had a Lambda probe fail on my other daughters 1.6 petrol Bora and it gave me a distinct error code but no codes on this car. If you could advise what to look for under what conditions to highlight a problem that would help. I feel such a problem would show itself under all circumstances though, not just in light to moderate accelerations?

I just read up on the EGR delete options and have altered ch3 in adaptations to the maximum allowable 33768 (was 32768) with the vacuum line still attached and valve intact, no blanking plates etc. It may be just a tad better but it's certainly still there.

[Rob69]

Have a look at this EGR duty cycle info, maybe you've already seen it? I've just googled it over a cup of tea at work, VCDS AND PD TDI ENGINE HEALTH CHECK - PASSAT (https://sites.google.com/site/1810martin/vcds-and-pd-tdi-engine-health-check)
I think the mid range speed and load you get the problem at is the point that EGR valve is admitting gas into the intake, at full throttle or idle the EGR is closed off. My thinking is that the O2 sensor is giving bad reading back to the ECU about O2 levels and the ECU /N18 / EGR are all over the place during this part load, light acceleration running.
I don't know what other checks can be done to the O2 sensor, AFAIK it is not functioning like a 'Lambda' sensor on petrol engine, it is measuring O2 levels in the exhaust and trying to reduce them (and NOX) by adding exhaust at certain load conditions, and in a petrol it tries to maintain correct fuel trims, stoichiometric fuel air ratio, or 0% Lambda

[davebrannigan]

Thanks. The thought did cross my mind about the o2 probe (Still referred to in ETKA at least as a Lambda probe for the diesel) being used for feedback but wasn't sure if an O2 probe would be able to give closed loop control for NOX or just O2. I guess it's the only sensor that has a chance of such a task though, That said, going back to ETKA, I see lots of probes listed for various petrols and diesels, but not one for the AVF engine fitted to my motor. That and the fact that no motor factors seem to list one for it makes me wonder if it even has one? If it doesn't then what else could be having an influence? The EGR rate could simply be mapped against throttle position, MAF and MAP, but if that were the case it would never know when someone disabled the valve, whereas mine does. After about 25 miles of running disconnected I get an emissions workshop warning. More and more curious. More checking needed, but thanks for your input thus far.

[Rob69]

So can you physically see a sensor near the CAT, pretty sure my 2005 1.9 AWX has one (from memory)

[davebrannigan]

No I don't see anything pre cat. She's just been run so too hot to feel around just yet. Would it need to be pre cat? Don't have time for up on ramps again today so pre cat is as far as I can look for now once she's cooled a bit.. I've seen a write up on the net for someone changing one on a bhw engine but I don't see a probe where his image shows it or any connector in the receptacle on the bulkhead where his is. Given the problems locating on at ECP or GSF and the fact ETKA doesn't seem to list one (though I'm no ETKA expert) I think I'm going to say it doesn't have one. So... if it doesn't have one, how the heck does it control valve N18 proportionally?

Stumped!

[Rob69]

You and me both !!

[Rob69]

Been thinking about this one a bit more tonight and wracking my brain to think if my 2005 B5.5 1.9 AWX passat has a O2 sensor, I'm doubting it has now and I can't get to the car to check. As far as I can tell my engine is a Euro 3 emmissions standard and it seems to have open loop EGR control, with no O2 sensor. Like you said earlier, I can only think it regulates EGR flow by measuring intake MAF, MAP and opening the EGR based on the ECU map, throttle position etc, with no feedback. The EML light would ( or could ?) be thrown on by the ECU not seeing the expected intake MAF due to the EGR not being open at the correct or expected time.
That doesn't help you much - anyone else know any more?

[davebrannigan]

I happened upon a post on a VW forum that sounded exactly my problem. That guy started suspecting his coolant temperature gauge, then his MAF and finally cured it by finding a tiny split in his post turbo pressure hose. I myself has a split hose some years back but when that happened I had power loss and a whooshing noise under boost. I'm not going to rule it out though. I've since read that many cars do indeed look for a drop in MAF whilst the EGR is open and that is how it measures the EGR rate. Bit crude but obviously worked. Thing is though, if I'm loosing a fraction of my air out the boost pipe, then surely that would be measured as an increase in MAF which would have the opposite effect on what would be sensed when adding exhaust gas to the intake as that would cause a reduction in flow by displacing some fresh air.

Anyhow my next plan is to seal up the pipe from the turbo to the EGR valve and put a little pressure in it with a hand pump and see if it holds. If it doesn't, then maybe, just maybe that might be it. If not then a MAF sensor clean and if not that a new MAF sensor?

I thought cars were meant to self diagnose after Y2K. Clearly some holes in that if you'll excuse the pun. I'm surprised that nobody else has pitched in with ideas. There are thousands of these engines out there and I'm sure someone has seen this before.

Cheers

Dave

[Rob69]

I'm thinking back to a 2004 1.9 tdi touran we had a few years ago, which had a BKC engine IIRC, and I think that was a Euro 4 emmissions standard engine which had an electric modulating intake throttle flap upstream of the vacuum operated EGR valve to create a manifold depression at lower loads and draw in exhaust, assisting the EGR, that must surely have had an exhaust O2 sensor (???) , where as my current Euro 3 2005 AWX passat 1.9 sounds like it has the same EGR system as yours ie. open loop, non O2 sensor. Your leaking boost air pipe would have the effect of increasing air flow over the MAF but I would have thought it would have to be a pretty big leak and noticeable to be impacting on the EGR rates and as you say, the MAF would see a reduced air flow when the EGR opens.
Post up what you find!!

[davebrannigan]

Sure to Rob. Unlike my EGR system, I'm definitely keen to close loops and feed back!

As you can tell I like to maintain my own motors - I own a nice 1989 XR4x4 Sierra that I've owned for 28 years. It has 110k on it - about 1/3 through it's lifespan mechanically and lives in a heated garage. Needs to as its from that era of rust protection!

I've also just bought a lovely, nearly new Audi A6 C7 3.0 BiTdi. That's going to stretch me technically in a few years. Sooooo much to go wrong, but hopefully VAG have learned along the way and improved on reliability.

Thanks for chipping in and I'll be sure to post results, good or bad.

Dave

[davebrannigan]

The results are in. I looked into cleaning the MAF sensor but it was pointless. It was spotless after 210K miles! I made up a blanking plug for the EGR connection and an adapter to allow me to feed air at 10psi into the port that connects to the turbo outlet. This instantly revealed a tiny split on the hose feeding the intercooler. I removed that, cleaned it up and bandaged it with duct tape and Voila! no more hesitation. Great news. I still don't quite understand why this didn't show up on the 3rd gear full throttle acceleration tests, but I'm so pleased to finally nail it. Unlike my previous hose issue on the turbo connection hose, this was undetectable by ear.

I have ordered a replacement for that hose and pre-empted the intercooler outlet hose failure by buying one of those too. Hopefully that will be the end of boost issues for another 200K:D.

Case closed.

PS anyone want an almost new EGR valve for an AVF engine...

I guess I'll just leave it on there now. :(