Volkswagen Passat Forum banner

1 - 16 of 16 Posts

·
Registered
Joined
·
29 Posts
Discussion Starter #1
Hi everyone,

Posting here as I'd like some input on a situation I'm having with my car. Its a Passat 2002 model running on an AWT engine 1.8T 20V. I have been noticing some smoke every once in a while that occurs during specific times: in the morning when I start up its very light. An inspection of the exhaust pipe shows black soot (dry), while at the same time some water drops right at the end of the tailpipe (I assume this means good combustion when starting up?). As the day wears on traffic jams are my worst nightmare. At this time there is blackish smoke every time we idle in the jam. Even moving forward the engine appears to be strained/choked. So with more acceleration than usual, it opens up and if I'm out of the jam the car will smoke for a few minutes then no smoke again; if I drive fast when I stop again it will smoke for a short while. My observations:
1. There is no CEL
2. We noticed some oil on one of the spark plugs and my mechanic believes we need to change the valve seals because of this; he also says the smoke is caused by this.
3. He also advises that we change the MAF (air mass meter). My car normally idles at 0.9 l/h but is currently idling at 1.3 - 1.4 l/h. Normally on the highway I get to 6.6 l/ 100 km when I'm doing about 100 kph. Currently, I get 10 - 11 l / 100 km which is clearly higher consumption. When I disconnected the MAF I encountered very slow-moving traffic and my consumption was at 2.6 - 4.0 l/h at standstill and as bad as 88 l / 100 km when moving slowly. I had to get into a petrol station and reconnect the MAF which resulted in idling going down to 1.5 l/h.
(l/h = litres per hour on the display, and l/ 100 km = litres per 100 km)

I have read all that I could find here on MAF and valve seals. I've also read a whole bunch of stuff online and I'm at my wits' end here. I am requesting some input from anyone here who has experience in these two areas.
1. Should I buy the seals and head gasket first and observe how the car behaves.
2. Should I change the MAF meter as well? Are these clear symptoms that it should be changed? This is because it's unclear as to whether it's faulty in the first place; I read on one forum that removing it without the car going off is a sure sign that is should be replaced; on another forum, they say the car can move, and consumption can even improve when the MAF is disconnected (clearly consumption did not improve in my case). Which is which?
Can the MAF meter be faulty without throwing a CEL?

Any ideas will be of great help.
Thanks.
Jay.
 

·
Registered
Joined
·
9,195 Posts
The valve seals might be worn, but they are not causing this issue.

It appears to be running rich, mostly at low revs.
The MAF Sensor might be faulty, but I would expect the fuel consumption to lower with it removed.
It looks like there could be air leaking into the exhaust, check for an exhaust leak forward of CAT.
Check the combi valve on the back of the head, if it doesn't close properly it could cause your problem.

Edit: A faulty front O2 sensor is another possibility.
 

·
Registered
Joined
·
4,932 Posts
Definitely sounds like valve seals need to be replaced.
FYI, if you're doing this yourself I would highly recommend at the minimum getting yourself the VAG tool to reinstall the valve seals.
The seals must be installed with great care as not to distort or misalign them. When reinstalling the valves, the valve keeper retainer grooves (on the valve stem) have razor sharp edges and can tear / cut the valve stem seal.

Other FYI, you'll need a special fixture to compress the valve springs.



I would wait on the MAF until after the valves seals are taken care of. I would guess you'll get slightly different readings after the seals are fixed.


Valve stem seal install tool
99637


Single station valve compressor

99638



This is the best one I've seen. Gets all the valves without repositioning the fixture. It's much easier to use and much quicker than the other one.
99639
 

·
Registered
Joined
·
29 Posts
Discussion Starter #4
Thanks for your replies. I notice I did not mention this in my first post. The mechanic said there is a leak between the turbo and the intercooler, I don't know if this could be what you're referring to @Tomvw . The mech said that this means there is less air reaching the intercooler and this affects the performance of the car in terms of less oxygen and hence also making the car burn rich (excess fuel). However, I will take your advice and hold off on buying the MAF until the leak has been fixed; interestingly as you have pointed out disconnecting the MAF resulted in a terrible upsurge of consumption, at least in traffic. I don't know the meaning of this yet, and after reconnecting it I haven't had the courage to disconnect it again. Also, I changed the post CAT sensor but not the pre CAT one. Let's see what happens after the leak is fixed. I'll probably have to have a scan done to see if anything comes up.

@AndreasPassat for sure the valve seals need replacement. I have seen this tool at the mech's garage so I think I'll let him do it right as he has the experience :) . I haven't developed that level of expertise yet. Sure he'll definitely charge me an arm and a leg but I'm sure we'll come to a mutually agreeable arrangement.

I will read up on the combi valve and have the tasks above done in the coming few days. I'll report back once the leaks and the seals have been done.
On another note how reliable are the diagnostic toolkit and scanner devices sold on eBay? I think I need to buy one for myself and learn how to use it. Any recommendations?
thanks a lot for your input guys. I really appreciate it.
 

·
Registered
Joined
·
9,195 Posts
There is nothing other than the mechanic's suggestion to indicate leaking valve seals.
If they are leaking, it would cause white smoke, and would not alter the air/fuel ratio.

Everything points to an air/fuel ratio problem.
This can be caused by air leaks, faulty pre CAT O2 sensor etc.
I certainly would not be wasting time and money on valve seals at this point.
 

·
Registered
Joined
·
29 Posts
Discussion Starter #6
Hi Tom, thanks for the advice. You are right on the colour (y) of the smoke as is it blackish. I was also thinking of the seals since I had noticed some oil on one of the spark plugs some time ago. However, I will go by your suggestion; I will have the leaks done on Tuesday (Monday is a holiday here) and see how the car behaves. I will post once the leaks have been fixed.
(y)
 

·
Registered
Joined
·
9,195 Posts
Any air leaks cause fuel ratio problems, they should be fixed ASAP.
The most likely cause of your issue would be a faulty pre Cat O2 sensor or the combi valve not closing/sealing properly.
A bad combi valve continually feeds air directly into the exhaust before the O2 sensor.

If there is no white smoke and/or excessive oil consumption, I would not consider replacing the valve seals.
 

·
Registered
Joined
·
29 Posts
Discussion Starter #8
Thanks for the insight, Tom. My analysis is that the smoke is black, as it leaves a black deposit on the exhaust tail. I found the following article informative too: Exhaust Color Diagnosis | White Smoke Blue Black might help others following this thread. Will have the leaks done between tomorrow and Wednesday. I will then have a scan done and hopefully, we shall see if any faults come up. I am thinking if the pre CAT sensor has a fault then the CEL will be on right? Same with the kombi valve? Thanks
 

·
Registered
Joined
·
9,195 Posts
If the O2 sensor is not reading accurately or the kombi is not closing properly, no directly related code would be produced.
Fix the air leaks first, but I think a gunked up leaking kombi is the main problem.
Do a scan and report the codes.
 

·
Registered
Joined
·
29 Posts
Discussion Starter #10
Ok, will do. I ordered a scan tool, and it arrived today. Seen some good review about it but will see how it works (mini ELM 327). The garage says the car will be ready for collection tomorrow. I will scan and share the codes before the weekend is over (assuming I figure out the right software to use with the scan tool 🤓, seen so many options to use though most reviews recommend Torque Pro).
 

·
Moderator/Administrator
Joined
·
24,165 Posts
If Android, torque or torque pro. If Iphone, OBD Auto Doctor is a good one.
 

·
Registered
Joined
·
29 Posts
Discussion Starter #12
UPDATE......UPDATE

Hello all.
I have been a busy body since I last posted relating to this problem. An update:
1. I had the leak checked and indeed there were two holes caused by the previous owner. He had a sump guard made and two of the anchor points were on the pipe running across the bumper from the turbo :oops:. So I had the customized bumper removed and the pipe was fixed. So goodbye leaks as no other leak were found.
Result: noticed more power and the whooshing sound I used to hear, which I thought was part of the turbo kicking in process, gone.

2. The smoke colour changed to whitish-grey/blue. This convinced my mechanic that the valve seals needed changing; it was done. He told me that I should expect the smoke to persist for a couple of days after changing the seals, but it would go away; it didn't. He's the expert and the change in colour convinced me he was right. I know. Don't say it.

3. I mentioned that I bought an OBD II scanner, right? ELM 327, comes with its own ELM scanner software. The software doesn't quite read everything you'd like but one thing that stood out like a sore thumb: "open loop fault". There were no other codes detected....at least not by ELM 327.

4. So I decided to go to another mechanic who comes highly recommended on a local Audi/VW telegram forum. I explained everything that had been done on the car and its current behaviour. He did a scan using VCDS software and a number of faults came up; the glaring ones involved the fuel injectors. He said he suspected it was electrical and not mechanical. After examining the relays under the steering wheel and the fuses he decided to...clean them. Previously the car was idling at 2.0 - 3.0 l/h. After cleaning them idling dropped to 0.8 - 1.0 l/h; this is the way I know it should be. After checking DTCs again, the injector codes were all gone. One code relating to the oxygen sensor was left. Strangely the upstream sensor read voltage and when I drove to his place it was fluctuating in response to driving needs (0.25 - 0.7) or thereabouts. I measured this using torque pro. Oh, one of the other faults was related to the MAF and this too cleared after cleaning the fuses and relays. I should mention that there was no fault detected on the downstream sensor using VCDS but using torque pro it gave a constant reading of 0; still trying to figure out what that means. 🤓So, he too, said that I should drive around and the oxygen sensor fault should clear by today. It did not.

I noticed as I was driving home yesterday there was no smoke for a distance of about 20 km when I ran into moderately heavy traffic. What I noticed is that when decelerating the smoke comes on, and when accelerating it disappears. I thought to myself, gosh don't tell me its now the rings. So I did some homework; I found this video
explaining differences between smoke from valve seals and smoke from worn-out piston rings. I am convinced the rings are ok. What I am still trying to figure out is why the car still stays in open loop when the sensor is working in what I guess is an ok way? From my understanding of open-loop, the car is not reading real-time from the sensors, rather it is using pre-programmed information to determine air/fuel ratios right? I also noticed no reading for short term fuel system, clearing showing its operating in open loop. I am guessing the current sporadic annoying smoke is as a result of this?

This week (probably tomorrow subject to his being available) I will go do a compression test with the second mechanic; he has software called ODIS which he claims does a lot more than VCDS! I am still thinking of how to get the car to go into closed loop as it should; should I swop the sensors (the downstream one is new), or what should I do? I am at my wits' end and any pointers will be highly appreciated.

I know it's a looong read; bear with me please 🤓.
 

·
Registered
Joined
·
9,195 Posts
You seem to be going in circles, I suggest you get it scanned with a decent VAG scanner and post all of the codes.

You could download the free version of VCDS lite, and see if you can set it up with your scanner.
 

·
Registered
Joined
·
29 Posts
Discussion Starter #14
Indeed. You are right Tom. I will report back on what I find on the VCDS asap. Thanks for the link
 

·
Registered
Joined
·
29 Posts
Discussion Starter #15
Alright, I am back with another update:

Spent the whole of yesterday back at the garage. These guys have a scanning tool that I'm not familiar with (not VCDS or any of the android ones I'm familiar with).

The faults were all related to short to ground on all the cylinders; electrician said this was due to poor insulation of the coil pack harness. I was sceptical about this as I had never heard of this before. So he added some more insulation. Well, this fault went away on re-scanning.

The second fault was an oxygen sensor bank 1 sensor 1 fault ("no activity"). We changed the sensor with a second hand one from the garage (new ones aren't currently available here) and then they went and did a test drive. When they came back there was just some very slight smoke from the exhaust.

They claim the fault codes are all gone; I did not see as they had disconnected the machine. They said with the sensor replaced I should drive around a bit for all the smoke to go away, the theory being that there must be some soot/dirt that had clogged the exhaust over time. Driving home in the evening it was impossible to get space to race it up coz of the evening rush traffic. What I did notice however is that the would be a puff of smoke whenever I stopped in traffic. When I got home and left the car in idle there was no smoke from the exhaust.

What I am also disturbed about is the fact that Torque Pro did not report these faults; it is reputed to be one of the best android apps for diagnosis. I have the mini ELM 327 OBD II Bluetooth scanning device. I also have the PC version of the ELM Scanmaster software; the only thing it reported was 'open loop-fault' but did not pick anything else. I wonder what the problem there could be? So I am thinking I will have to use the VCDS lite link that you sent me; the challenge here is, of course, getting the hex-can cable as I've only seen one place that sells it, and exorbitantly too I might add. But will do so all the same.

So I will drive the car around for a couple of days and report back on how it behaves. The picture below is the oxygen sensor that we removed from the car.

99912


I am wondering whether to clean this and keep it as a backup or is it totally gone?

Hoping the car will behave itself going forward.

Cheers.
 

·
Registered
Joined
·
9,195 Posts
Do a search on Ebay or Amazon, you will find plenty of suitable cables like below.

Download the VCDS software, DO NOT use the the disk that comes with the cable, these are often full of malware.
 
1 - 16 of 16 Posts
Top