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Thread: 2.5TDi sudden rough running, vibration, no power, poor starting then no starting :-(

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  1. SOLVED - 2.5TDi sudden rough running, vibration, no power, poor starting then no starting :-( 
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    Morning all, hoping for some help and advice ! So the old A6 (BAU engine) had been going great; parked up then on re-start there was a rumble, engine vibration, very little power and inability to rev. Switched it off and towed it home. No MIL light or other idiot lights, no fault codes detected by my cheap little OBD reader. Oil level is good, belts are intact, fuel at all 6 injectors when cracked open at tick-over. It started reluctantly a few more times (to manoeuvre into garage) but now just cranks with puffs of black smoke (unburnt fuel?), almost catching but not quite. Turbo vane spins freely with no shaft wobble.

    Research here suggests maybe a belt jump, injector pump issue, injector issue, turbo failure, valve train failure..... I guess the next steps are compression test and trying a better diagnostic tool, then rocker covers off to check valve gear, and verifying timing?

    So does anyone recognise these symptoms and can point me in the right direction? Many thanks, Andrew
    Last edited by andrew shepherd; 21-09-2018 at 07:28 AM. Reason: Update
     
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  2. Re: 2.5TDi sudden rough running, vibration, no power, poor starting then no starting :-( 
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    Get a proper scan and report back.

    Ian
    A4 B6 Avant Nogaro Blue
     
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  3. Re: 2.5TDi sudden rough running, vibration, no power, poor starting then no starting :-( 
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    A friend came over with an older version of VAGCOM, all it showed was 01375 bad engine mount, and P1570 engine start blocked by immobiliser. We cleared the faults, and after a bit of cranking it reluctantly fired up again. It ran the same as before, very lumpy and noisy, grey smoke, inability to rev, in fact touching the throttle makes it stall. After this only the 01375 returned.

    I guess it threw the P1570 during one of the failed starts so can be ignored? Surely a bad engine mount can't produce the rough running? Should I change it first just to be sure, I'd much rather go after the real cause of the engine problem and not lose a couple of weeks waiting for parts and finding the time to change it. So none the wiser after the scan, where do I go from here please?
     
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  4. Re: 2.5TDi sudden rough running, vibration, no power, poor starting then no starting :-( 
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    Thought I'd update this for others. I pulled the cam covers and the nearside bank had thrown a few valve followers (lesson learned, CHANGE YOUR OIL ON TIME!). Not knowing if repairs would be worthwhile (mostly on here people say the head is bricked if this happens) I decided with nothing to lose (prepared to scrap it) to do a quick-n-dirty fix and hope for the best. One of the slave-cam lobes was detached so ordered a chinese cam on eBay for 110 quid. The cam sprocket had also spun on the shaft so the valve timing was all over the place. Most of the valves were not sealing (compressed air and liquid soap test) although didn't look bent to the eye. Anyway, having kept the old engine I blew up 8 years ago (see my old "run without oil" thread!) I had spare valves and followers, so switched various valves around and lapped them in until I had them all sealing. Put it all back together with all the old gaskets and seals (with new belts, pulleys and water pump which needed doing anyway). It's done another 10k miles since then, so all good! Total cost of repair (cam and oil) 150 quid. No doubt it won't last another 200k miles, but should hopefully see out it's lifetime with me. Changing oil every 4k now .
     
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  5. Re: 2.5TDi sudden rough running, vibration, no power, poor starting then no starting :-( 
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    Were these roller finger cams that had worn? I have seen the lobes detach, induction hardening failure.
    Dark was that day when Diesel conceived his grim engine that begot you, vile invention, more vicious, more criminal than the camera even, metallic monstrosity, bale and bane of our culture, chief woe of our Commonweal. How dare the Law prohibit hashish and heroin yet license your use, who inflate all weak inferior egos? Their addicts only do harm to their own lives: you poison the lungs of the innocent, your din dithers the peaceful, and on choked roads hundreds must daily die by chance-medley. Nimble technicians, surely you should hang your heads in shame. Your wit works mighty wonders, has landed men on the Moon, replaced brains by computers, and can smithy a "smart" bomb. It is a crying scandal that you cannot take the time or be bothered to build us, what sanity knows we need, an odorless and noiseless staid little electric brougham.

    W.H. Auden (1907-1973), A Curse:
     
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  6. Re: 2.5TDi sudden rough running, vibration, no power, poor starting then no starting :-( 
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    My guess was that the valve guides must be the weak point for lubrication failure (and I was well overdue an oil change), causing a valve to stick open, allowing the follower to jump out, which then gets pinballed around by the cam lobes, smashing a few roller fingers, allowing a few more followers to pop out, something eventually jams between a lobe and the head cracking and detaching the lobe, the cam drive gear spins throwing out the valve timing and most of the valve-train disintegrates with accompanying valve-piston contact. This would happen in a few revolutions of the engine, quicker than you can stop it or it stalls.

    However, now you mention it, perhaps the lobe did fail first as you suggest, setting in motion the rest of the havoc. None of the parts looked particularly worn, other than a bit of pick-up on some of the lobes commensurate with the mileage. You have far more experience and knowledge than I, I'll go with your suggestion if you think it likely (and it lets me off the hook about the oil-change!). It seems strange that they use the pressed-on lobes and gears (the chinese cam is billet steel), but perhaps it's an engineered-in weak point to protect the drive cam, cam bearings and head etc.?
     
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  7. Re: 2.5TDi sudden rough running, vibration, no power, poor starting then no starting :-( 
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    Roller fingers were supposed to stop this, taking away the Zinc additive (ZDDP) caused flat tap pet wear so roller fingers were used.
    Dark was that day when Diesel conceived his grim engine that begot you, vile invention, more vicious, more criminal than the camera even, metallic monstrosity, bale and bane of our culture, chief woe of our Commonweal. How dare the Law prohibit hashish and heroin yet license your use, who inflate all weak inferior egos? Their addicts only do harm to their own lives: you poison the lungs of the innocent, your din dithers the peaceful, and on choked roads hundreds must daily die by chance-medley. Nimble technicians, surely you should hang your heads in shame. Your wit works mighty wonders, has landed men on the Moon, replaced brains by computers, and can smithy a "smart" bomb. It is a crying scandal that you cannot take the time or be bothered to build us, what sanity knows we need, an odorless and noiseless staid little electric brougham.

    W.H. Auden (1907-1973), A Curse:
     
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  8. Re: 2.5TDi sudden rough running, vibration, no power, poor starting then no starting :-( 
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    Quote Originally Posted by Crasher View Post
    Roller fingers were supposed to stop this, taking away the Zinc additive (ZDDP) caused flat tap pet wear so roller fingers were used.
    Are you not afraid from damage to the catalytic converters because of the useing ZDDF ?
     
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  9. Re: 2.5TDi sudden rough running, vibration, no power, poor starting then no starting :-( 
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    Yes, that is why I do not use it on cars with catalytic converters, instead I use the highest grade oil possible and change it every 5k. Cars with roller rockers (e.g. BAU) don’t need ZDDP, only flat tappet engines (e.g. AKE), as below







    Having said that, engines with zero oil consumption like my 1.8T could use higher ZDDP levels but they don’t need it for the tappets as they don’t seem to fail even with abuse; on these and similar engines it is the chains that wear.
    Dark was that day when Diesel conceived his grim engine that begot you, vile invention, more vicious, more criminal than the camera even, metallic monstrosity, bale and bane of our culture, chief woe of our Commonweal. How dare the Law prohibit hashish and heroin yet license your use, who inflate all weak inferior egos? Their addicts only do harm to their own lives: you poison the lungs of the innocent, your din dithers the peaceful, and on choked roads hundreds must daily die by chance-medley. Nimble technicians, surely you should hang your heads in shame. Your wit works mighty wonders, has landed men on the Moon, replaced brains by computers, and can smithy a "smart" bomb. It is a crying scandal that you cannot take the time or be bothered to build us, what sanity knows we need, an odorless and noiseless staid little electric brougham.

    W.H. Auden (1907-1973), A Curse:
     
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