Hesitation and lack of power 99 2.5tdi tiptronic

[Phil G Watson]

This fault developed in the winter, I noticed a drop off in power on long hills - always used to go up like a train!. As the fault developed I noticed the engine bogged down, almost as though I applied the brakes and it happened at gear change intervals at 2000 rpm and 3000rpm.
The situation got much worse with fuel economy also dropping.
On a steady or even gently rising throttle the car made reasonable progress but any demand on power to overtake or accelerate dumped me in a powerless hole.

My local independent garage deduced it was transmission not engine related , checking the gearbox oil, it was black and burnt smelling. I have only changed it once during my ownership and it is now on 235,000 miles.
My independent changed the fluid and filter but without the correct pumping gear so some of the old fluid remained in the gearbox.

A trip to Bristol and back (200miles round trip) revealed that things had improved. I drove back in 'manual' tiptronic mode to try to isolate the symptoms. I noticed cruising at 80 ish and attempting to accelerate within the same gear, the hesitation was still there but less obvious. It is still however down on power from where it was before the issue began.I also notice the car smells rich (acrid diesel smell) on idle but there is no smoke idling, just a little if I accelerate hard (which it won't currently do)

Is this definitely a transmission issue?
Could it be also partially blocked injectors
I've replaced the narrow braided vacuum pipes visible as they were paper thin
I've checked the MAF sensor, gently cleaned it but this was replaced 70k ago.

Anything else?

I'd really like to sort this, the car is like 'Triggers broom' as most major ancillaries have been replaced over the years - Fuel dist pump, ABS pump and CPU, Alternator, Turbo, breather neck, heater motor, fuel pipes, MAF sensor etc etc.

Thanks in advance for any insight - help me save the old warhorse!

[Phil G Watson]

This fault developed in the winter, I noticed a drop off in power on long hills - always used to go up like a train!. As the fault developed I noticed the engine bogged down, almost as though I applied the brakes and it happened at gear change intervals at 2000 rpm and 3000rpm.
The situation got much worse with fuel economy also dropping.
On a steady or even gently rising throttle the car made reasonable progress but any demand on power to overtake or accelerate dumped me in a powerless hole.

My local independent garage deduced it was transmission not engine related , checking the gearbox oil, it was black and burnt smelling. I have only changed it once during my ownership and it is now on 235,000 miles.
My independent changed the fluid and filter but without the correct pumping gear so some of the old fluid remained in the gearbox.

A trip to Bristol and back (200miles round trip) revealed that things had improved. I drove back in 'manual' tiptronic mode to try to isolate the symptoms. I noticed cruising at 80 ish and attempting to accelerate within the same gear, the hesitation was still there but less obvious. It is still however down on power from where it was before the issue began.I also notice the car smells rich (acrid diesel smell) on idle but there is no smoke idling, just a little if I accelerate hard (which it won't currently do)

Is this definitely a transmission issue?
Could it be also partially blocked injectors
I've replaced the narrow braided vacuum pipes visible as they were paper thin
I've checked the MAF sensor, gently cleaned it but this was replaced 70k ago.

Anything else?

I'd really like to sort this, the car is like 'Triggers broom' as most major ancillaries have been replaced over the years - Fuel dist pump, ABS pump and CPU, Alternator, Turbo, breather neck, heater motor, fuel pipes, MAF sensor etc etc.

Thanks in advance for any insight - help me save the old warhorse!

Anybody at all? 100 views and no one has an idea?

[spartacus 68]

The 2.5 AKN is a fantastic V6 engine. I only have experience of it coupled with the manual 6-speed transmission. At 235k miles it could be any number of things. Have you pulled any codes via VCDS?

Couple of things I would try. If it is injectors, then try a can of Forte diesel conditioner straight into the fuel filter. Drive it hard through first to third gears and it should smoke like a chimney, but that will clear. Replace the fuel filter and top up with fresh diesel prior to connecting it all up. Check the fuel return pipes near the injectors. At this age, given the mileage and heat under the bonnet, they will deteriorate.

Have you ever cleaned the air intake manifolds, both sides? Could be the chambers are completely gunked up? Worth getting your hands dirty, to remove, thoroughly clean and re-fit. In addition if the turbo is reconditioned, can you rule it out completely? Try Mr Muscle on the vanes and check the actuator works as it should. The standard air filters on these cars are inadequate, so consider a lightly oiled K&N panel filter to improve airflow.

Finally, if you opt to clean air intake manifolds, then fit a blanking plate on EGR valve.

[Phil G Watson]

Thanks for the reply Spartacus, apologies for my delay in responding. That's very helpful, to start the process I've booked it in this morning to see if any error codes come up.

If we draw a blank I'll try as you suggested. A couple more questions.
To access the intake manifolds for cleaning, does the front need to be in the service position? Exactly how do I get at them. Secondly, how do I get access to the turbo vanes for cleaning? Do I need to buy any new gaskets if partial dismantling is required?
Thanks again for the help.

[spartacus 68]

Hi Phil, no the car doesn't need to be in service position to access air intake manifolds. Remove the V6 plastic cover insulation and you'll see both air intake manifolds and the alloy block that connects both that runs parallel with the radiator. I didn't have to remove injectors from memory, but take a look. I just removed the right hand air intake. With the connecting block removed you can see into both air intakes. The left hand side was okay on mine, so I left it. Pretty sure it's allen key bolts. On removal, scrape the gunk off, use a degreaser, soak in diesel, Mr a Muscle, whatever your choice of attack. It's a dirty job, so plenty clean rags, card or plywood as a suitable base, old toothbrushes, and lots of disposable gloves.

One the worst is removed, soap up with Fairy and rinse with warm water and dry thoroughly.

The turbo, I removed the elbow at the exhaust manifold to clean. I used Mr Muscle connected to a thin plastic straw (from a can of WD40) and flexible hose directly to the turbo vanes. Also check the actuator moves freely.

On reconnecting, the Mr Muscle in the turbo will be burnt off once you get the car to operating temperature.

[spartacus 68]

More pictures.

[Phil G Watson]

Thanks so much for the detailed reply Spartacus. Apologies for my late reply, after much soul searching I decided to part ways with my old warhorse.
From your explanation I think what you describe may well have been the cause of the hesitation. I took the car to an independent with full test facilities. The report that came back stated there were issues with manifold pressure caused by Turbo actuator malfunction.
Had this been my only problem I would have persevered, but also reported were a cracked engine mount, two leaking shocks, central locking leak, alarm malfunction and a few minor things. Nonetheless I put it through an MOT which was pretty good with a fail only on a sidelight bulb and a split CV boot. I've always wanted to change the shocks as the ride, while comfortable, was now quite 'wallowy'. Add to this old but non-urgent issues of a slightly leaking rad core, glow plugs needing replacement and some paint repair needed.
Time does not permit me to tackle the problems and garage bills would have been prohibitive so I started the hunt for a new (old) replacement. After much hunting and a couple of dodgy propositions (thats a story in itself) my focus polarised on something surprisingly different.
A 2006 2 litre tfsi A4 SE Avant 6 speed manual...Quattro!!. Don't ask me how I rationalised the slide from a lazy armchair of an auto diesel to this but I am working my way through the honeymoon stage and gradually growing into it. Handling is amazing, power more than adequate, fuel economy...er isn't. But the quality is fantastic, near perfect leather and black...yes blaaaaack! of the Phantom variety bodywork without a blemish. A full-size load liner for the Lab is on order!
It drives very well but I do have a noise issue to report, complete with the solution, but will switch to the B7 forum for that!.

Meanwhile, what of the old warhorse? I just couldn't bring myself to throw it to the wolves on e bay for a couple of hundred return... or put up with the associated eejits it would attract. So I donated the car to a Technology College I've done some volunteering for. They have their own MOT station and the good news is they are well on the way to getting the car roadworthy after which it will become their pool car. A much more acceptable retirement for what has been a fantastic vehicle for the last sixteen years of ownership. Thanks so much for all the B5 help, I hope I'll still be able to avail myself of that expertise now I've jumped ship for the Petrol Quattro world! Cheers.