'97 TDi 110 (AFN) not boosting?

[BadgerBoy]

Update - The problem is now sorted and turned out to be a lot more simple (and a hell of a lot cheaper) than originally suspected. If you're having similar issues, might be worth your while reading the whole thread to get some different ideas as to what your problem might be and how simple the solution could be.
BadgerBoy




Hi all, hoping you can advise!

I have a '97 TDi 110 with 150,000 that has suddenly lost power. It has seemed a little down on power for a while and just put this down to general wear and tear but there was sudden big drop in performance yesterday. Seems ok'ish to maybe 2000rpm but then, just as turbo would normally really be starting to pull, there's nothing. The engine is running as smoothly as ever and will rev cleanly when not under load but not when driving.

I've searched these threads until my eyes are square and concluded it was likely to be either the Air Mass Meter or vacuum hoses. Have checked hoses as best I can and they all appear in good condition and I tried a new Bosch Air Mass Meter but this made no difference.

Thing is, mine is doing something slightly different/not mentioned in all the other threads I've seen and I wondered if this might give any ideas:

If starting from cold, starts fine and idles at 800rpm immediately but if I start from hot, revs immediately jump to 2000rpm then drop to idle at 800rpm straight away, almost as if I'd started with my foot on the accelerator then removed it.

Also, I'm sure I used to hear a slight hiss/whoosh when I put my foot down (assumed this was just excess boost being dumped and can hear similar on my mates PD130) but can hardly hear this now and not at all after 2000rpm, just as the power drops off.

Oh, and my diagnostics socket does not work! Presently in process of removing centre console to check wiring but would really appreciate it if anyone has any ideas about the poor running?

Thanks
BadgerBoy
Getting greyer by the minute...

[calum]

First thing I can suggest is to sort the diagnostic socket . Do you have an aftermarket head unit in the car ? if so there's usually one wire that connects to a wire that it shouldn't , called the K wire , this results in the diagnostic socket not working . Do a search on this , it should come up with something , hope this helps you along the way ,

Other thought's , revs jumping when starting from hot but not from cold , have you changed the coolant temperature sensor yet ? Calum .

http://en.allexperts.com/q/Volkswage...-Wont-Smog.htm

[BadgerBoy]

Calum, many thanks for your quick response.

The car still has the original head unit though I've only had it 4/5 months (previously had another for 5 years that the cambelt went on after a cowboy supposedly changed it 8000 miles previously...) but judging from previous owners, I don't think it has ever been swapped.

Coolant temperature sensor has not been changed but could this cause the lack of boost/power? The revs jumping on a hot start has only just started happening, same time as the power loss, so the two symptoms do seem related but the temperature gauge is still sitting dead on 90c.

Thanks again, at least you’ve given me a direction to start looking in. Any other ideas appreciated though!

[calum]

On second thoughts , with the revs jumping up on hot starting but not on cold starting , could this be because of a split inlet hose somewhere ? My reasoning , a hot inlet hose will be much more pliable and more prone to leaking than a cold inlet hose . I'm referring to radiant heat from the engine affecting them , nothing to do with coolant temperature .

You could do a visual inspection of the inlet hoses but I'd recommend taking them off for a thorough check , flexing them against the bends to uncover any leaks / splits also check the o rings and of course the intercooler ,that's all I can think of just now , hope you come across something , Calum .

[ini]

When you hit 2000rpm onwards do you have excessive smoke?

Can you hear the turbo spooling up at all?

From your description it sounds like your turbo is not working.

Possibly the turbo variable vanes are jammed open in high boost position - check that the actuator rod moves freely on startup (needs 2 people), or by moving it by hand - 2cmish movement, its quite hard to pull against the spring.

Also suck on the control tube to the turbo actuator capsule to ensure the diaphragm is holding vacuum.

Or the N75 boost control valve is not functioning - test by blowing through it when energised and also when inactive, and lube with wd40 etc.

[hongkongstuey]

cheapest thing to try is do all the vacuum hoses with 3mm inside diameter silicone from demon tweeks or similar, the standard ones have probably been on since 97 and mine were cracked and perished. i had to change my coolant temp sensor on mine too, didnt turn out to be what i needed but was a pain to fit, right at the back of the engine bay, sounds like it may be that with the idle problem if it doesnt know wether its hot or not, whats the dash temp gauge saying?

[BadgerBoy]

Hi ini & hongkongstuey, thank you both for your posts.

ini’s comments first:
No smoke throughout the rev range and fuel consumption does not appear to have been affected. But I suppose I’m driving it on partial throttle and changing up quicker to compensate.

I’ve read about the vanes on the turbo becoming jammed as a result of carbon deposits but I’ve sucked (quite hard) on the control tube to the turbo actuator and the rod moves up 1.5/2cm then drops when suction is released. Not had a chance to observe it on start up yet and can’t say that I’ve definitely heard the turbo spooling up – all I can say is that it sounds pretty much as before apart from the absent whoosh/hiss after 2000rpm, as mentioned earlier. Is it worth trying one of these aerosols that you can spray in the inlet hose (down wind of the MAF I assume) when running to try and get rid of some of the deposits?

I’d also considered the N75 boost control valve but got the impression it was fairly rare for these to fail. Cost a lot more than a MAF too! Any chance you could advise a little more as to what exactly I’m looking for, what you mean by checking it when energised and when inactive?

hongkongstuey:
All the pipes look in much better condition than my previous TDi and I was therefore thinking they’ve probably been changed at some point in the past. I do have some similar size plastic tubing (possible washer tube) so I’ll try that in sections to see if it makes a difference though I’m not too hopeful. Actually, that’s wrong. I’m very hopeful it would be that simple, just not confident!

The engine runs at normal temperature and the idle is fine, it just blips to 2000rpm very briefly on start up when hot but not when cold.

I must admit I’m starting to feel a little out of my depth – I’ve happily worked on motors for years on most things mechanical, including engine and gearboxes swaps on older non-turbo cars, but my last TDi was so reliable, I never had to do more than normal servicing, suspension, brakes etc.

All your comments are really appreciated, many thanks.

[Izalman]

Easy to check the VVT vanes on the turbo are not stuck. Check for movement by having someone start the car (hot or cold) and you look at the movement of the vacuum chamber actuator linkage on the turbo. It should move approx 10mm up when started and drop down again when stopped. (or vise versa)
I changed N75 valve ( 4 in stock at local vw garage!!!!) to no avail. Ended up getting codes read at same place and they advised thrust sensor (MAP sensor) has intermittent fault.
This reads boost pressure / temp to the ECU - if duff shuts down turbo system
Part approx £50 - 2 screrws to fit - located in inlet ducting at the rear of the engine bay
Check this https://www.vwaudiforum.co.uk/forum/s...ad.php?t=58403

[ini]

If your turbo actuator rod is moving freely, then it may not be a jammed vnt mechanism.

Is the power loss constant, or does it only seem to suddenly occur under load?

Dos the car have an auto gearbox?

Has it ever been run very low on oil?

Have you tried swapping the N75 and EGR valves round (temporarily) to see if you get boost?

If the N75 is not the problem, you may have a more unusual issue causing reduced power mode, such as partially blocked exhaust/CAT or restricted manifold(generally a USA issue), pump problems, timing, multiple sensor failure etc.

Do not discount a faulty air mass meter, even if new, especially if not purchased directly from a VAG dealer. (also double check all pins/connector/harness on MAF and N75 etc)

You need to sort out the OBD fault code problem inorder to get a better idea.

The MAP sensor on a 97 AFN is onboard, inside the ECU, and is much less prone to failure than the boost pipe/intercooler mounted, later types.

Maybe some of these diagnostic pages will be usefull:

http://www.myturbodiesel.com/1000q_h...impmodetdi.htm

http://forums.tdiclub.com/showthread...hlight=3000rpm

http://forums.tdiclub.com/showthread...hlight=3000rpm

http://66.163.168.225/babelfish/tran...0a50a&.intl=uk

[BadgerBoy]

Hi all, thanks for all the advice so far. To answer a couple of points:

I was able to get someone to start the car for me whilst I observed the actuator rod - it rose by approx 10mm on starting then dropped back very slightly, maybe 1 or 2mm, whilst idling. When engine revved, the rod would drop slightly then rise as revs dropped off (think this is the right way round but it was a couple of hours ago). Rod dropped back to lower position when engine turned off.

Power loss is constant, feels like turbo is maybe boosting very slightly below 2000 but not at all after. It is driveable but just has no power as if the turbo is not working but no nasty noises and no smoke. Car is a manual and has not been run low on oil to my knowledge and doesn't appear to use any.

I've not tried swapping N75 and EGR valves yet. I did try removing the Air Mass Meter (AMM) wire and it did not alter the running at all - this is what led me to believe that may be the problem due to what I've read on other threads (though I was a little puzzled by the statement 'if running stays the same or improves, the AMM is at fault') but when swapped with a genuine Bosch AMM from TPS (who I gather now supply VW themselves) nothing had changed.

Timing belt and auxilary drive belts and pulleys all replaced around 3000 miles ago and ran fine since until the other day.