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things to look for - old 2.5tdi


luke1135
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Looking at buying a 1998 A6 2.5tdi v6 quattro avant. Its cheap (under £1000) a bit rough, and high miles (220000). Just looking for a cheap runnabout with a bit of poke and lots of room in the back for a mountain bike.

What should I be looking for - I hear the cams are a bit crap and can wear which worries me as theres 4 of them. I'm guessing I can inspect at least 1 lobe through the oil filler hole? Is any visable wear acceptable?

If I buy it I'd probably replace the cambelt myself + normal servicing stuff cos don't think theres any recent service history. Anything other then the ordinary worth doing or checking?

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On something that old, with that sort of mileage, I wouldn't worry too much, if it starts, runs and drives without any untoward noises, it'll probably be fine, and even if it only lasts six months, for that sort of money it doesn't really matter, and it's not really worth spending good money on to fix it either.

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Clutches on the V6 and V8 quattros are not cheap to fit!! Not sure if one that age will have the pricey dual mass flywheel - and if it does whether it needs to be changed with the clutch like mine for example.

Edited by Ian_C
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What should I be looking for - Another car.

You can either take the view that Tipex has suggested or steer clear. If the cams have gone, then it might only run for a short while. They are not cheap to fix, about £2-3K. depending in what else is worn. Everything else is very expensive on that car. Turbo, fuel pump etc. But then if you broke it and sold the parts, i guess you would get your money back.

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Hi Luke!

What to look for? I bought one last year - Y-reg, manual 180 BHP with 130K on the clock. Goes very well and returns 45+ onmy commute. So far, utterly reliable. But then again it was a bit more than £1K! Mine's now got 160K.

Check the thing warms up properly. A duff thermostat costs £700 (belts off job) or eats fuel when it's cold (your choice!)

The 180 BHP ones have the solid cams. The early 150s have the soft cams. If it's 180, you might be OK with that mileage.

Pretty easy to change th eoil and filters. However, any timing issues need a proper VAG indy visit. Also the fuel pumps can be pants, but at that mileage, it should be fine. They usually go much, much earlier than that.

If it's an auto - drive it carefully, slowly, quickly, fast, use the Tip function, kickdown and test it thoroughly - it should be smooth. If not, avoid.

Go have a look, there's plenty out there! Good luck! Let us know.

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thanks for advice - I brought it. I got it down to £800 as it appears to be in limp home mode with no power. The engine is smooth and runs nicely apart from the lack of power - so I think its fine mechanically. Very good fuel economy suggests the electronics is restricting the amount of fuel it puts in. Will run a fault code reader on it tomorrow at work. Are there any common faults I should be checking first?

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Hopefully a fluid change will sort that. What is it like in Tip mode? Does it go into Limp mode straightaway or after a few mins/shifts?

You could try a new MAF to start with anyway. The MAF is very important as it sends info to the ECU and gearbox.

Its a manual - so no problems with the shifting. Best way to describe the engine performance is that it runs perfectly til you get the accellerator halfway down and then you don't get any more. Turbo is winding up properly and just starting to push you forward but then it thats it. Was thinking MAF but would have expected a bit of jerking and hesitation from faulty MAF? Its still smooth. Couldn't get any fault codes but I was using a tester for all makes not VAG specific.

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Before you change anything, you should examine the cams. At this mileage and lack of service history, the law of averages points to the cams. You need to take the cam covers off. Looking through the oil filler tells you nothing. Remove the fuel pump pipes, fuel return hoses and some other bits and get the covers off. You will then see how badley the cams are worn. In some cases the cams can wear over 1mm, greately reducing power by starving airflow getting into the engine. This is the same as a maf sensor registering too much air and reducing the fuel supply. Spending money on parts using guesswork can be a big waste of money.

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Before you change anything, you should examine the cams. At this mileage and lack of service history, the law of averages points to the cams. You need to take the cam covers off. Looking through the oil filler tells you nothing. Remove the fuel pump pipes, fuel return hoses and some other bits and get the covers off. You will then see how badley the cams are worn. In some cases the cams can wear over 1mm, greately reducing power by starving airflow getting into the engine. This is the same as a maf sensor registering too much air and reducing the fuel supply. Spending money on parts using guesswork can be a big waste of money.

I think the cam wear item was an issue with the 150 BHP V6 TDi engines. Not sure which engine the OP has bought.

Also, removing all those gubbins will take time and money (replacing gaskets) anyway, so could still be a waste of money.

A new MAF will never be wasted.

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I think the cam wear item was an issue with the 150 BHP V6 TDi engines. Not sure which engine the OP has bought.

Also, removing all those gubbins will take time and money (replacing gaskets) anyway, so could still be a waste of money.

A new MAF will never be wasted.

Looking at the first post, its a 2.5tdi v6 so its an early model (150bhp) and likely to have a fair bit of wear. When I took the cam covers off, I used the existing gaskets and no parts. Given that Luke was thinking of changing the cam belts, this job of removing cam covers would be very easy for him.

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Yes it is the AFB engine known to have cams made of cheese. If the cams are worn they're not worth the £ to replace. I think it would be more obvious if they were worn with a rough idle etc anyway. No real benefit to getting in and checking (I presume the tappets are hydraulic and not adjustable?). Have ordered a MAF sensor so we'll see what that does when it arrives. Was also thinking could be a boost leak to atmosphere - but can't hear any sucking at idle. Had to replace a control arm and cv boot to get mot today but nothing major.

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Luke. I wish you the very best in getting the car sorted. Just keep a tab on the money you are spending.

Regarding worn cams, its not just the cams that wear but also the valve stems and the followers, so mutiply the cam wear by 2 to get the total wear. When wear happens, the valves do not open as much, so the engine is starved of air and fuel which is more noticeable at higher throttle openings.

If you have a boost leak after the air mass meter, you get the right amount of fuel, but less air causing a rich cmbustion and black smoke from the exhaust.

I hope this helps.

Regards

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Luke. I wish you the very best in getting the car sorted. Just keep a tab on the money you are spending.

Regarding worn cams, its not just the cams that wear but also the valve stems and the followers, so mutiply the cam wear by 2 to get the total wear. When wear happens, the valves do not open as much, so the engine is starved of air and fuel which is more noticeable at higher throttle openings.

If you have a boost leak after the air mass meter, you get the right amount of fuel, but less air causing a rich cmbustion and black smoke from the exhaust.

I hope this helps.

Regards

Yeah, seen many a TDi/diesel looking like a WWI smoke screen laying destroyer with the black soot!

Presume the air filter is clean(ish).

Does your engine still have the undertray? If that has gone, then it can let all sorts knock pipes and stuff.

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I had exactly the same symptoms on my old A8 2.8 sport on my way to Cornwall a few years back...stately acceleration, no misfiring etc etc just gentle acceleration whatever the throttle inputs.The ABS light was also illuminated. After a journey back, with a view to getting it fixed it cleared itself.Dont know whether driving rain or whatever cleaned a sensor or what, but in the subsequent 3 years of ownership the problem never manifested itself again..could be electronic?

I wouldnt have believed a fault break switch on the pedal of my A6 would render the anti skid, EBL and cruse control inoperable but it did...funny things car electronics

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Might be a while til I get to the bottom of it - had the alternator belt break and get chewed up (and the AC belt fly off intact) Fortunately not expensive but a bloody hassle getting the whole front end seperated to get at it. Looks like the plastic cover has been rubbing against the belt - whether it was the cause or the result of the belt breaking I'm not sure. Haven't been able to see if any idlers have seized yet. I'm tossing up whether to do the timing belts and tensioners while I've got the front off. Bloody frustrating!

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Removed the cam covers and had a good look at the cams - no obvious excessive wear. Didn't have anything to measure them with or indeed any specs to compare to but looked ok to me. Replaced my alternator belt too - all idlers/tensioners were ok. Have replaced MAF sensor now but no improvement. I'm back to where I was to start with. Runs fine but no power. I almost feel it might be the throttle position sensor - thinking I'm only putting my foot halfway down when the go pedal is firmly on the floor. It runs exactly as I'd expect til the pedals halfway down and then no change as I put it right down. Even revs up slowly in neutral. Manages about 65mph top speed and gets there slowly. No smoke black or otherwise and pretty reasonable fuel economy (starved of fuel).

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I think with duff cams, you can physically see the deep groove in the middle of the cam.

Can you hear the turbo? Could be a lack of vacuum?

I am not sure how the throttle works in these, but try to play with it as it runs.

Try some injector cleaner and also some Carb cleaner liberally sprayed in (to the intake after the air filter but with no gasp!!) with someone revving the engine.

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If there was no obvious signs of wear then the cams are good. That's great news. I am now thinking of the turbo. The variable vanes are actuated by a rod situated just beneath and to the front of the turbo. Check that when the car is started and revved, the rod moves, if stuck then possible turbo has sticky vanes or faulty parts which creates the vacuum to actuate the rod. You can test it by using a vacuum pump. Let me know if you need more info.

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got some fault codes off a reader -

00546 data wiring faulty implausable signal

00575 intake manifold pressure (map sensor?)

00523 air intake temperature

00553 MAF sensor (but has been replaced now)

1440, 1441, 1442 (fuel level related)

Provides more questions then answers. No idea what the data wiring one is refering to. Is the IAT sensor the one on the left side of the intercooler? And where would I find the map sensor? I think the fuel codes ones might be related to me cracking open the hp fuel lines while running to make sure no air in them after having them off.

As for the turbo - it seems to spool up normally sometimes and give the associated bit of extra power (still pretty modest) and sometimes doesn't spool up at all presumably engine not pumping enough exhaust out to spin it. The vnt linkage can be moved about 10mm by hand easily enough but I haven't had a chance to observe it while someone else revs the engine. Will I be able to test it with a vacuum by sucking on the hose or do I need a serious vacuum.

Also the intake manifold was caked with a pretty thick layer of tar and carbon - don't know if this is normal but maybe issue with the egr valve. Is it possible to just make blanking plates and get rid of it?

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PM me with your email address and I should be able to send you some instructions re testing vnt actuator.

I can look at this problem 2 ways assuming that the maf sensor is ok, but you should use VCDS to check readings. Either insufficient fuel or insufficient air enterring the cylinders. If insufficient air, this means too much fuel then black smoke will come from the exhaust and generally this is turbo problems or a leak in the induction pipes post turbo. Given that this is not the case and no black smoke is comming from the exhaust, I am looking at insufficient fuel, so fuel filter, or fuel pump or related items.

Have you cleared the codes to see if they re occur? Sorry, getting sleepy, so will continue another time. But please look at te following forum.

Audi A6 - C5 Forum - 1998 - 2004

There is plenty of posts oj the subject.

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I would second the suggestion about clearing the codes and starting again. You don't know how long the codes have been stored for.

try to remove all the crud in the intake. Alcohol and/or Wynns Carb Cleaner liberally sprayed in and left for a while. Then lots of rubbing to remove the crud.

It's possible the crud could be covering a vacuum pipe inlet? etc etc

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Changed my fuel filter hoping that was the problem. Didn't fix anything but I think I'm on the right track. watching the clear section of hose just before I can see that it is full of fuel at idle. When the engine is revved however it becomes aerated with bubbles. I'm seriously confused where the air is getting in from because the hoses are clamped nicely and not obviously dammaged but I can only guess that they are a bit porous with age and letting a bit of air through when the FIP sucks hard. (Brand new T-valve and o-ring on the fuel filter so no air getting in from there. I'm sure cavitating fuel like this can't do the FIP any good so hopefully its not harmed it. Halfords didn't sell thick enough fuel hose so I'll try to find some tomorrow. Also having erased old fault codes I only got the IAT and MAP sensor codes.

Slightly different subject - whats the proper procedure for changing filter? Cos I got air in the system and had to suck it all out through the fuel return line along with several mouthfulls of diesel! Got it all out ok but don't want to have to do that again when I change the fuel lines.

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