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'55 174 Caravelle Auto - B@stard Limp Home Mode . |
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Greggers 
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Joined: 10 Aug 13 Location: United Kingdom Status: Offline Points: 28 |
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 Topic: '55 174 Caravelle Auto - B@stard Limp Home Mode .Posted: 10 Aug 13 at 17:28 |
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Hi Guys ... Lurker coming out of the shadows ... I've been looking for some hope in a 'cheap' solution to my limp-home woes. The T5 dropped very occasionally into LHM a few months ago, so prior to my holiday to France I thought it would be wise to give the turbo a clean with Innotec after looking at an old thread with Chaufferdude... After much cursing and more than a drop or two of blood from the gash I got on the heat shield - saying nothing about dropping the stainless steel gasket - I managed to do the business and free the previously sticky variable vane actuator mech. The exhaust end of the turbo was still nice and free and showed no signs of bearing wear. In the days following everything looked rosy - the motor had perked up considerably and was a lot more willing than it had been for a while so I thought all was good. The week after we set off to the South of France with the trailer in tow and b*gger me if the van didn't drop into LHM at the first sniff of serious throttle! We'd only got 15 miles from home, and had another 600 to go FFS!! I stopped the van and restarted, but much the same happened quite soon - we managed to make Dover just in time for the ferry, but only by nursing the T5 at no more than 55-60 mph and nothing over 2-2500rpm. Likewise, I was able to limp - quite literally - to the camp site at the ridiculously sedate pace forced by not risking having to stop on the very narrow autoroute hard-shoulder. Dropping the trailer helps a little and with no huge load the van will go into LHM if booted, but otherwise drives normally - remembering it's an auto... I'm driving mostly in Sport mode to try and prevent low rev/high torque gearbox conditions which seem to provoke LHM. I believe my turbo is good and at 105k miles and a full VW service history it has been properly looked after so I'm less than willing to let VW charge me 1500 notes just to replace it and see if it resolves the problem so I'm wondering if anyone has found a workaround for this problem yet?? EGR? MAFF ?? any other random but critical sensor?? If VW do replace the turbo just because that's the accepted solution, is the problem really sorted out by an associated component or a software reset? I'm seriously p!ssed off with this as it is clearly not a condition which is properly potentially damaging to the engine otherwise it would always be in LHM or at least show some EMS warning somewhere...?? I've another week on the campsite before the tedium of 700 slooooooow motorway miles home! Hope someone can throw some light on this one... Greg |
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danny
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Joined: 05 Mar 06 Location: Surrey Status: Offline Points: 129 |
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Posted: 10 Aug 13 at 22:44 |
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Had the same problem and it alway came up as an inlet manifold boost sensor fault.
It's the sensor on the inlet pipe under the coolant bottle. It wasn't the sensor but the cable to it at fault. Only found this after a heap of new sensors it causes loads of fault codes but when the cable breakers it comes up as over boost and cuts the turbo. It could also be a vacuum fault but unlikely if it resets with the ignition key. I only found the break once the coolant tank was moved out of the way. Good luck |
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Greggers
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Joined: 10 Aug 13 Location: United Kingdom Status: Offline Points: 28 |
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Posted: 10 Aug 13 at 22:51 |
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Cheers Danny, I'll have a look in the, morning..
Greg |
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T5 TDI
Vanorak 
Joined: 05 Nov 05 Status: Offline Points: 3687 |
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Posted: 11 Aug 13 at 13:07 |
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You could try working the variable vane rod by hand to free it as a temopary measure but as you already know it's not easy to get at. It really needs to go on diagnostics which I know is difficult in the middle of France! It doesn't have to be the turbo again (although it's fairly likely) it could be anything.. You could also try unplugging the MAF. That works because the ECU will then use an estimated airflow value which is better than a dead MAF. It will cause a fault code though so you should mention this when you get it hooked up otherwise you may end up paying for a new one. Then they can just clear the spurious code and check that it doesn't return.. Have good look at the wires and small vacuum pipes on the turbo boost valve (N75). It's fairly accessible on the 2.5's. It's a small plastic thing with a vacuum pipes and a wiring plug on it under the bonnet near the back. Unfortunately it won't help to leave this one unplugged. Good luck anyway! .
Edited by T5 TDI - 11 Aug 13 at 13:15 |
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2004 2.5 174
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gregozedobe
Vanorak
Joined: 22 Dec 06 Location: Canberra, Oz Status: Offline Points: -998266 |
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Posted: 12 Aug 13 at 16:56 |
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It sounds like the variable vanes are not moving to reduce boost as the revs (and boost) comes up. So either the cleaning you did only made for a temporary fix, or there is something else wrong. I vaguely recall readin one how-to that put some thin washers under the vanes so that there was extra clearance for the vanes so they didn't get stuck.
To know what the ECU thinks is wrong you really need to find what error codes are being recorded. I don't know whether a basic non-vw OBDII code reader can extract them for you, or whether a VW specific set-up (VCDS or genuine VW dealer tool) is the only way to go.
Edited by gregozedobe - 12 Aug 13 at 16:58 |
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Greggers
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Joined: 10 Aug 13 Location: United Kingdom Status: Offline Points: 28 |
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Posted: 13 Aug 13 at 11:30 |
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Hi Guys ..
The variable vane mech appears to be ok as I can reach through and get a thumb on it to push it up and down - I did this throughout the Innotecking (!) as well, but used a short length of broomstick so that I didn't sh@g the end of my thumb! I've watched it while the engine starts too and the mech is actuated to what looks like full travel as soon as the engine is running. I'm doing to try and get the coolant bottle out of the way this afternoon and have a look at what Danny suggested, if only because it's the most accessible thing to do!! I'm assuming the EGR valve is the greasy and dirty gear just to the front left of the coolant bottle - with the vac controlled flap. That would be my next project whrn I'm home. If the MAF isn't functioning wouldn't that just 'flatten' the performance? I was amazed how much difference changing it on my T4 made. But - would disconnecting it just not make the ECU throw a code? All I'm looking for at the moment is a quick and dirty fix that's going to get me home without too many issues - I can fix things properly when I'm back in Blighty!! G
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gregozedobe
Vanorak
Joined: 22 Dec 06 Location: Canberra, Oz Status: Offline Points: -998266 |
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Posted: 13 Aug 13 at 13:47 |
That sounds like it is going into maximum boost position, but your problem might be that it isn't pulling back to control the boost as the revs come up (and the boost increases). A possible bodge to try out would be to disconnect the rod or restrict it's movement to the low boost position. The engine would be pretty gutless until you had 2,000rpm or more, but might stop it over-boosting and triggering the limp-home mode. Worth trying ?
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T5 TDI
Vanorak
Joined: 05 Nov 05 Status: Offline Points: 3687 |
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Posted: 13 Aug 13 at 13:54 |
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Taking the MAF wires off will cause a fault code but it won't do any harm. The code can just be cleared when you get home. It's true the MAF does normally cause flat performance rather than what you have. Yours sounds like a classic overboost fault- either turbo or control systems to it (like the N75 valve or the pipework to it I mentioned). Btw, you couldn't have reversed any vacuum pipes could you?
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2004 2.5 174
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Greggers
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Joined: 10 Aug 13 Location: United Kingdom Status: Offline Points: 28 |
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Posted: 14 Aug 13 at 17:24 |
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Thanks guys --- I've not disturbed any vac pipes (as far as I know at least) and the LHM is kicking is much as it did before. I'd thought about restricting the rod's movement and might try to see if I can do that wit ha bit of fencing wire or something (I'm stuck in an old french farmhouse right now!). I guess the N75 valve is what controls the movement of the vane actuator rod so restricting its movement against the vacuum pump isn't going to do any harm ... worth a try! Is there any kind of idiot's guide to how these systems work?? I've recently picked up an old Porsche with a K-Jetronic injection system - fooking complex in its entirety, but once everything's broken down and you can see what each part of the system does it's a lot easier to see how the whole thing works together. Cheers Greg |
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danny
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Posted: 16 Aug 13 at 00:26 |
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I checked my N75 in two ways
pulled the vac hoses of and butted them together to see the actuator working. Removed the cable and tested it with a simple volt meter to see if it changed when the van was revved up(it didn't change as it was in limp mode from a different wiring fault). If i pulled of the air mass sensor cable it didn't make any difference to the van when its in limp mode. My limp mode became more frequent until it was permanent and didn't reset by the ignition off on reset. Then after much swearing at the f*****g thing i found a broken cable assuming it was an intermittant break until it totally snapped. Good luck |
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174 caravelle
180 dsg 4motion van Both full of problems ........ |
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T5 TDI
Vanorak
Joined: 05 Nov 05 Status: Offline Points: 3687 |
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Posted: 16 Aug 13 at 09:24 |
This is handy
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2004 2.5 174
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Greggers
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Posted: 16 Aug 13 at 17:00 |
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Very interesting .... cheers!
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Greggers
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Posted: 16 Aug 13 at 18:19 |
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Well now .... I had a thought that I couldn't make anything worse ... well, I probably could if I tried harder lol... Anyway, overboost has been mentioned a couple of times, and Gregozedobe validated an idea I'd had about limiting the variable vane actuating arm, so with my trusty Leatherman under my arm I raided the wardrobe for an old steel wire coat hanger. Made a hook to go under the actuating arm linkage, and hooked the other end over the master cylinder casting. At a guess the arm has about 50% range - but is pulled tight as soon as the motor starts so the limit is within its previous operating range. With great trepidity I took the van out for a run, and ...... booting it up a hill took it to 4500 rpm .... kickdown - the same ..... three times and with no EMS lights!!! The proof of the pudding of course will be dragging the trailer tomorrow, but I'm keeping my fingers quietly and confidently crossed .... I'll let you knpw what happens when I get home - or if there is free WiFi en-route - but I hope this is the indicator for the solution ... watch this space!! Greg
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Greggers
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Posted: 17 Aug 13 at 20:22 |
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Ok, so after 350 miles of mixed roads I can report limited success with the coat-hanger cure ... I've had two LHM events today, one approaching 3k rpm going up a hill and the other at about the same rev point on slight incline going for an overtake. Both were on top (6th) and without too much aggressive throttle. Restricting the variable vane actuating lever's throw has certainly made a difference - as long as I don't completely floor it I can get reasonable throttle response and can cruise with the trailer at about 75-80mph, so not a huge problem to get home tomorrow, well - not to miss the ferry anyway! I think the fact that limiting the vanes' range indicates a problem with boost level control and I'm taking a guess at the N75 valve - what do you think?? G
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T5 TDI
Vanorak
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Posted: 17 Aug 13 at 23:22 |
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Greg, although what you are doing makes me nervous on principle, as far as I can see the ECU is still free to put the system into limp home if it sees boost levels too high. I still think in the end you'll find the VNT mechanism is the culprit but as you say it could be on the control side. The MAP sensor is another possibility in that case. You could really do with VCDS out there!
How great is this site?
 Coat hangers that get you back from France, welding stuff that's way beyond welding, fabricating special tools and even novel useage of chimney pots! |
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2004 2.5 174
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Greggers
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Joined: 10 Aug 13 Location: United Kingdom Status: Offline Points: 28 |
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Posted: 18 Aug 13 at 23:53 |
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T5,
Well, I got home albeit with a lot of gearbox/speed/juggling and as long as I left it below 2.5k it was ok - just 2 or 3 events... I'm going to have to take it to my indy to have a diagnostic done which will hopefully identify the culprit. I'm happy to have a crack at heaving the turbo off but suspect that it will be fine as the actuating lever seems to move quite readily through what I think is a reasonable range and there was no play or roughness I could feel in the bearings. I'm still puzzled by the fact that there's no dash indication of the fault, going into lhm without warning is in my book a significant event and is dangerous especially if -as I was - going for an overtake and expecting normal levels of acceleration. Anyway, the important thing was getting home so objective no.1 has been achieved. Now I just need to fix the leaky steering pump on my T4... More on the T5 later... G |
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gregozedobe
Vanorak
Joined: 22 Dec 06 Location: Canberra, Oz Status: Offline Points: -998266 |
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Posted: 19 Aug 13 at 02:13 |
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Glad you got home OK. If the turbo vanes are moving freely then the next obvious suspect is the boost control side of things (either electronic or mechanical). If you've got access to VCDS check out the log of actual boost compared with requested boost.
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T5 TDI
Vanorak
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Posted: 19 Aug 13 at 09:31 |
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It's possible to test the N75/MAP/ individually with VCDS. With the engine idling, it spookily picks up the revs on its own while it's doing the test and operating the VNT rod.
 . The VNT mechanism only has to stick briefly to produce LHM even though it appears to be free when you move it.
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2004 2.5 174
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Greggers
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Posted: 19 Aug 13 at 13:45 |
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I've got it booked for a diagnostic at a local VW Indy - it will be interesting to see what the results are. This VCDS (Vag Com Diagnostic SoftwARE?) ... is it available for public consumption in any form?? Not that I'm condoning SW piracy in any way you understand, but is it just a question of a laptop and a suitable interface?? G
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gregozedobe
Vanorak
Joined: 22 Dec 06 Location: Canberra, Oz Status: Offline Points: -998266 |
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Posted: 19 Aug 13 at 14:45 |
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VCDS is available to the public (it's a 3rd party product from ROSS-TECH, not VW product). I think the software is free but the cable (which acts like a dongle to give you full functionality) costs.
More info here: |
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Greggers wrote: