Another TDI90 limp mode sufferer

Kennedy

A2OC Donor
Hi all. I am aware there are many current and old threads relating to limp mode related problems but my TDI90 is now displaying slightly different symptoms. I thought better to start another chat rather than hijack/resurrect somebody else's.

The car is a well cared for 2004 TDI90 on 140K. I've had it for a couple of years and done about 24K trouble free miles.
The other relevant bit of back story on the car (as we'll definitely wander into turbo talk) would be that the car had a brand new factory fresh turbo fitted at 83K along with extensive engine work costing a previous owner nearly £2400.00 in parts and labour so there's really only about 57,000 miles on the current turbo.
I have to say it has always driven really nicely with great power delivery until it started having 'limp mode' problems last year...

To start with it was just the usual story - if going up hill or accelerating hard for prolonged periods of time it would lose power and the engine light would come on. Switching off the engine and starting would immediately resolve the problem, although the engine light would usually stay on for a bit longer. I had a bit of a look around the hoses and pipework last year and considered that the intercooler was a possible source of the problem as it was slightly oily at the bottom but not too bad, but it was still driving really well most of the time so I left it.

I have a new intercooler and I'm planning on fitting that next weekend all being well, at which point I'll get a better look at hoses etc.

The bit where this is different to most is on the way back from MOT last week, I gave it a really good blast on flat roads and the engine light came on and went into limp mode... but it never went off :oops:. It's been parked up for a week almost and I can't get the light to go out, and the turbo's permanently disabled - the car is obviously picking up a problem as soon as the key is turned as the light is off for maybe half a second on start up and then comes on and stays on.

I disconnected the MAF this morning and went for a drive, and did a few cycles of starting and switching off the car but that hasn't had any effect.

What are the likely causes of the engine light on start up, would it be possible to have a big enough air leak that the engine management senses this immediately? - maybe absolutely booting it last week finished something off that was causing my more common limp mode issues, or damaged something.

I've read another possible problem could be with N75 valve - is that a likely culprit for triggering a permanent engine fault?

Is there a guide/s that help illustrate the removal of components to better access the turbo and pipes? - it's not easy getting a view of this side of the engine!

The current state of play is that the car is up on axle stands with covers and undertray removed ready for me tackling the intercooler change next week. Is there anything else I should perhaps be looking at?

Kennedy
 
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Scan codes from about a month ago as follows:
- 17057 'Cylinder 3 Glow Plug Circuit (Q12) Electrical Fault PO673 - Intermittent
- 19463 CAM Position Sensor - G40 No Signal P3007 - Intermittent
- 17964 Charge Pressure Control Negative Deviation P1556 - Intermittent
(it's worth mentioning at this point also that the battery is very weak and I suspect some 'events' may have been triggered by systems being interrupted on start up when only just cranking over... dunno)


Kennedy
 
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just a thought but I would think worth checking electrical connections at engine multiplug , the fact at no signal g40 intermitant could suggest poor connections especially if power not the strongest on start up
regards mark
 
A possible cause is a stuck Turbo VNT mechanism. This is more likely if the car spends most of its time on short journeys. Check if you can move the operating rod connected to the vacuum actuator, with a cold engine. If not, the mechanism probably needs cleaning.

RAB
 
My MAF sensor was faulty but replacing it made no difference. I have had the silver metal intercooler pipe which runs across the front of the engine ceramic coated. After removing this pipe and turning it upside down there was a clear area of soot under the MAF sensor (near the rubber pipe joint) were there was obviously a leak in the join. I think this may have had something to do with my limp mode.....photo to follow......
 
Under turbo pipe....
1516619160761-1543147067.jpg
 
I think that the Cam Position Sensor is the likely culprit at the moment.

If that fails the system reverts to the crankshaft sensor and that is just a "get you by" thing.

I would clear the errors, go for a run and then rescan to see what is going on.

The loom on those sensors can be the cause too.

Steve B
 
A possible cause is a stuck Turbo VNT mechanism. This is more likely if the car spends most of its time on short journeys. Check if you can move the operating rod connected to the vacuum actuator, with a cold engine. If not, the mechanism probably needs cleaning.

RAB
Yes this is the first easy diagnosis RAB
If its stuck then its Turbo removal time and strip and clean it
Ive done 5 of these VVT,s and all cars were cured
9 out of 10 times it wont need a new turbo
 
Hello Chaps, thanks for the points above, obviously a few checks I need to run through if I can get at things. On the possibility of the VVT being stuck I would really hope not as that's going to be more of a job than planned, but if it is that then I'll be looking for tips and advice on the strip down or knowledgable folks/recommendations who can do the complete job for me.

The car gets some really good miles in, I drive it 2 hours a day during the week and a lot of that is motorway, so it shouldn't be anything caused by frequent short journeys. With the turbo having covered only 57,000 miles from brand new could it really be coked up that badly? - anyone else had filthy turbo issues at circa 50K miles??

I think that the Cam Position Sensor is the likely culprit at the moment.

If that fails the system reverts to the crankshaft sensor and that is just a "get you by" thing.

I would clear the errors, go for a run and then rescan to see what is going on.

The loom on those sensors can be the cause too.

Steve B

...Regards the CAM Position Sensor, what sort knowledge is needed to do that job, anyone know what the garage bill could be on that one?

Another little question, I noticed on the bottom inner face of the intercooler there is a small pipe or breather (near to the main bottom hose), I've got nothing attached there is that right or is pipe missing?


Kennedy
 
I believe that it is a DIY option.
You just replace it and no need for any coding etc. But even though I believe that it is I a slightly awkward position it is still doable (happy to be corrected)

But do clear the errors and rescan, if the sensor is mentioned again then check the loom to it before spending on the (not cheap) sensor.

Steve B
 
Okay Steve nice one.

I've got a basic code reader that I think I can clear the codes with but anything further I'll have to get another proper scan done.

Luckily I've got another car in the form of a mk1 jetta, and although it's not practical or comfortable it gets me about just fine, so I won't be rushing out buying sensors and parts for the Audi until I've done all the more simple checks on it! - going to be a fun weekend... :cool:

Kennedy.
 
Are those turbo cleaning kits from ecp @60 quid of any real benefit (assuming that means turbo can clean without removal)?

Seeing this does makes new think that a precautionary clean every so often might prolong the life of the turbo
 
Had a pretty good afternoon getting the car stripped and the oily/leaky intercooler off - now I see it up close it definitely looks a bit past it's best so I'm glad it's off the car... new one to go on tomorrow. Quick one; Should there be anything coming from the thin pipe on the bottom of the intercooler? - assuming this is some sort of breather?.. but then with the turbo system being reliant on tolerances of pressure surely an open airway should be restricted by something?

Before doing that I reconnected the MAF, connected the OBD scanner I have and deleted the codes and then started it... on start up there is no engine lights which I'm happy about but can't road test as the car is in a few bits now...

Everything looks pretty good, I've been trying a number of things on other components, one thing as highlighted below...

A possible cause is a stuck Turbo VNT mechanism. This is more likely if the car spends most of its time on short journeys. Check if you can move the operating rod connected to the vacuum actuator, with a cold engine. If not, the mechanism probably needs cleaning.

RAB

How easy should it be to move the rod to the vacuum actuator? - I can get a small amount of movement on it but is the test to remove the vacuum actuator and then see if the rod movement is full and smooth i.e. that it's operating the VNT correctly? Is it a case of taking out the two bolts holding on the vacuum actuator and unscrewing... point me in the direction of a relevant post if possible.

I noticed that the lower plastic pipe bracket to the right of the sump has broken so the lower sections of pipe are free to bounce around, will need to order a replacement for that before I button things up so it stays where it's meant to.

Kennedy.
 
How easy should it be to move the rod to the vacuum actuator? - I can get a small amount of movement on it but is the test to remove the vacuum actuator and then see if the rod movement is full and smooth i.e. that it's operating the VNT correctly? Is it a case of taking out the two bolts holding on the vacuum actuator and unscrewing... point me in the direction of a relevant post if possible.

There's no need to remove anything. You should be able to move the linkage downwards towards the actuator by about 10mm. If you can't, try doing it with the engine hot but with some leather work gloves. Take care! If not, then there's a problem.

RAB
 
I may be wrong (I frequently am) but that looks like muck that has come from something else?

My theory being that if it was from the pipe the black would be there on the join too and that is perfectly clean. Not only that but as you can see there is a good strong lip there that forms a good seal?

But who knows, it would be great if it resolved your problem.

Steve B
 
The intercooler is now fitted and all hoses looked okay apart from being a little pinched by the Jubilee clips which have been used in place of the original type, but no splits or holes. Cleaned out the oil before refitting and made sure the hoseclips lined up un the impressions they had previously made on the hoses. Fired it up seems okay...

Ticking over nicely and no engine light and start up so all looked in order. I did try to move the vacuum actuator but it is awkward to get at when the engine is hot so couldn't be sure if it's moving freely or not, so I'll test drive and see what the drive is like now.

Once heated up a bit more I revved to about 3000 rpm a couple of times, then the engine sound changed and a distinct knocking sound started and stayed on tick over and when revving. Is this a possible symptom of the G40 Cam position sensor/connection being faulty?... that's one of the intermittent error codes that flagged up when it was last scanned.

While we're on the subject of the G40 Camshaft Position Sensor, how easy is that to change, is it just a case of getting the cam cover off the engine and unbolting from under the pulley on a TDI90? - links to relevant posts welcome.

Kennedy.
 
Make sure that you have not disturbed the large air tube. It can often rattle against things under the bonnet. Leave the car ticking over and rattling with the bonnet off. (It may even be the bonnet but you will soon find out if it stops when you take it off.
Then try holding the large air pipe to see if it stops the rattle. It may be hitting near the inner wing or under the brake reservoir.

Steve B
 
Make sure that you have not disturbed the large air tube. It can often rattle against things under the bonnet. Leave the car ticking over and rattling with the bonnet off. (It may even be the bonnet but you will soon find out if it stops when you take it off.
Then try holding the large air pipe to see if it stops the rattle. It may be hitting near the inner wing or under the brake reservoir.

Steve B

Thanks for the suggestion Steve, unfortunately everything appears as it should and I think the sound is definitely in the top half of the engine. It does it from cold now, so whatever it is, it's not affected by the engine temperature.
I'm not hugely worried yet as it's not a violent sound like the engine is eating itself, and I'm thinking it's some sort of timing issue... unfortunately I don't fully understand the relationship of the sensors (G40 Cam sensor, Crank sensor) on the running of the diesel engine so I need to do some research. I may or may not be on the right track.

Kennedy.
 
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