Strange power loss 2.5TDi - help please!

[Teflon]

Can anyone out there help with some advice on my power loss problems (2002 A6 2.5TDI Multitronic, 62k, FSH)?

I've searched the threads and there are lots of similar problems, but nothing that fits the bill.

Ok, here goes...... Everything was okay, except that sometime the car would accelerate up to about 3000-3200 rpm, say 40mpm on the flat and then just go flat for a few seconds, no further acceleration, just like good old fashioned fuel starvation. No oil smoke, no other symptoms. Next thing everything was okay for another week.

Slowly it got more frequent, but still intermittent. Had it looked at and a faulty MAP sensor was diagnosed (it's located behind the front bumper, plugged directly into the intercooler).

MAP sensor replaced, went like a rocket for 1/2 a day, then occasionally back to its old ways. Diagnostic then said an intermittent wiring problem between engine and gearbox. oooh er Missus!

Last week I got overtaken by a bus going up a steep hill as the speed just bled off to 20mpm.

Today, I've finally managed to get a huge cloud of blue smoke out of the back when I started her up.

Now, if I try to rev the engine (with car in neutral) it will go all the way up to the redline but seems to be "notchy" in several places from about 2000 to 3000 rpm. If I hold the pedal stationary at about 2400rpm, the engine drifts up and down between 1900 and 2400. If I press a bit further, it will hold steady at 3000rpm all day.

At least it confirms an engine problem, I was getting worried that the multitronic was banjaxed.

So, I know for sure it's not the MAP sensor. It's also not the MAF sensor, this has been well checked out. Pretty certain its not any vacuum leaks or split hoses - these have been thoroughly inspected.

At this stage anything short of a new turbo would be a good result.

Anybody out there with any good ideas?

[ronmcintosh]

It sounds like it might be a problem with the way the car is breathing.

especially since it seams to be intermittent. When you say you got black smoke at start up did you get it at all when you were driving the car after that ? (eg either hard acceleration or easing back off the throttle)

Ron

[Teflon]

It sounds like it might be a problem with the way the car is breathing.

especially since it seams to be intermittent. When you say you got black smoke at start up did you get it at all when you were driving the car after that ? (eg either hard acceleration or easing back off the throttle)

Ron

Ron,

No, just a big cloud of blue smoke on starting after it had been stood there for a couple of days. Never a problem either pedal to the metal or on the overun.

Turned the key this morning and all was like normal. It drove smoothly enough, but in traffic and no steep hills or dual carriageways where I would need to plant the pedal to find out if the gremlins are there or not.

Last service was August, complete with a new air filter, so if it is a breathing problem I reckon it is control based, not any physical restriction.

Does this help?

Teflon

[dandam]

I've a 99 2.5 TDi quattro, manual, and very occasionally I get a situation where the car goes 'dead', won't give any acceleration but will continue down the road ok. If you are at 70mph on the motorway it will continue until you hit a hill. A friend of mine had the same situation in an A4 tdi 110 quattro.

So far I haven't managed to find out what is wrong, but if you switch off the engine, then switch it straight back on (easier when you can just drop the clutch on a manual car admittedly) full power is back again. Alternatively full power comes back after a few minutes of driving....

[RobDob]

I've a 99 2.5 TDi quattro, manual, and very occasionally I get a situation where the car goes 'dead', won't give any acceleration but will continue down the road ok. If you are at 70mph on the motorway it will continue until you hit a hill. A friend of mine had the same situation in an A4 tdi 110 quattro.

So far I haven't managed to find out what is wrong, but if you switch off the engine, then switch it straight back on (easier when you can just drop the clutch on a manual car admittedly) full power is back again. Alternatively full power comes back after a few minutes of driving....

I've got a standard 2.5 V6 TDI and occasionally have the same problem but only in 4th gear.........................

[Teflon]

Thanks for the feedback. Problem still not solved, but at least it is now permanent, so the chance of finding the root cause is high. It's going in this week (to an independant), for a more thorough diagnostic check and fault finding session.

For the record, I've found the following possible causes by scanning through the threads here and elsewhere:
MAF sensor...................... - No. Cleaned it. Ran without it and get same symptoms
MAP sensor..................... - No. Changed it. Still a problem.
Leaky vacuum hoses....... - No. That's the one thing I can check without any electronic gizmos.
Blocked air filter.............. - No. it's new
N75 Valve
EGR valve
Turbo acutator rod sticky
Turbo stuffed

One smart Alec even suggested that that the ECU software is set up to make the car a complete pain in the RRRRSS after 5 years, so that you go back and buy a new one. Can't see it somehow, but anything is possible.

Because the first diagnostic showed up a manifold absolute pressure fault, I'm suspecting that it is something boost related and that the turbo itself is still okay.

If anyone has any other options or possible causes, I'd like to know.
I'll report how the problem solving goes.

[Teflon]

Okay, car went in for a good session of plug-in fault finding.

Just for a laugh, it drove absolutely perfectly on the way in. First time in 3 weeks. I wondered if it was because I'd had the battery disconnected earlier in the week.

Anyway................

This time the diagnostics pointed to a problem with the crankcase breather control valve that is closed off when the turbo spools up, to prevent the turbo blowing all your oil out of the engine. If it sticks open or flutters the boost varies and the ECU gets more confused than the England back 4. It can also cause the crankshaft rear oil seal to pop, meaning a big job to replace it.

It was stripped off and sure enough, it looked poorly sick. I considered myself lucky that there was no collateral damage. New valve installed. Car went like a rocket.

Drove home. Car went back into "Ha, ha, I'm still taking the psssss" mode.

I'm tempted to go at it with a can of parrifin and a box of matches. Or a sledge hammer. Or both.

Going back in next week for a serious sorting. Watch this space.

[RobDob]

I had a total power loss in my 2.5 TDi last week...........turns out one of the pulley's driving a cam-shaft broke causing £1000 worth of damage (including labour). Not a happy bunny at all! Was hoping it was the timing belt as that was all under warranty. Hopefully after this repair the car should go on for quite a while.

[Teflon]

I had a total power loss in my 2.5 TDi last week...........turns out one of the pulley's driving a cam-shaft broke causing £1000 worth of damage (including labour). Not a happy bunny at all! Was hoping it was the timing belt as that was all under warranty. Hopefully after this repair the car should go on for quite a while.

Yep, that sure counts as a power loss. you have my sincere condolences.

I'm almost jealous - at least you have a reason for the car being a dog. I'm thinking I might have racked up £1k by the time I get to the bottom of it.

What's the mileage & maintenance history? A cam shaft pully seems like a funny thing to fail, unless they have some design or manufacturing fault.

[RobDob]

It's a 1999 'V' plate with 111,000 miles on the clock. Full service history. I don't know whether to have it repaired or replaced now! The price I've had quoted doesn't include valves either......is it highly likely they're all screwed too?! The pulley is apparently aluminium and just broke causing the subsequent damage.

I wish I'd kept my Golf GTi now................