Sluggish Misfiring TDI

So now you think the fuel side is ok what about the exhaust side? Restricted exhaust, blocked cat, split flexi joint? Is the compression good? Are you losing compression from a glow plug? Valves sealing? Cam wear? Or is it sensors cutting back the power? N75 valve?

Engine earth faulty? Battery faulty? Battery connections loose or corroded? Alternator faulty?
 
audifan said:
So now you think the fuel side is ok what about the exhaust side? Restricted exhaust, blocked cat, split flexi joint? Is the compression good? Are you losing compression from a glow plug? Valves sealing? Cam wear? Or is it sensors cutting back the power? N75 valve?

Engine earth faulty? Battery faulty? Battery connections loose or corroded? Alternator faulty?
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Thanks for the ideas.

Just whipped off the cam cover and it looks fine with very little wear on the cam and/or rollers at all.
There's no leaks on any of the glow plugs either.

Started up and checked Cylinder Deviations with VCDS, all are sitting at around 1.5 which is higher than expected , with one negative and the others positive. Looks like there's some compensation going on to try and balance the fuel flow across the cylinders. Does this point to injectors or is it a symptom of other issues?

Although there are no leaks on the N75 pipework, my thinking behind this is that it modulates the watergate, using the boost pressure for the signal, so as long as the wastegate actuator is not mechanically broken, ie stuck open, then the N75 will only come into play when boost starts to build. I do get some boost when revving it, but the response from idle is really poor, with very low power, almost as though it's in limp mode, but VCDS does not show any errors in the engine ECU.

Cranking is fast, with defined compression strokes, so I'm sort of ruling our any mechanical issues in that sense, but I don't have the ability to check pressures. The battery is less than a couple of years old, and earthing has been checked and cleaned.

There's only the exhaust to check now, is there an easy way or do I just remove the fixings to the turbo and blow down, or use hoover to check flow is not restricted?
 
Catnip64 said:
The front section is about 8 years old, rear box is original.
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You almost certainly need a new back box. I have no experience of owning any diesel vehicle, but my understanding is that mild steel exhausts still rust, albeit at a slower pace than the equivalent petrol vehicles. The back box is normally the first to go.

Rust and the accompanying scale is a fact of life; on the other hand carbon build up inside the exhaust can be cleared by some extended high speed running, preferably at motorway pace. So an 'Italian tune up' is probably your first port of call.

If you still have a cat, that can also block the exhaust when it fails, but that normally involves the cat developing a pronounced rattle before the core breaks up, so it's unlikely to be that.
 
steve_c said:
You almost certainly need a new back box. I have no experience of owning any diesel vehicle, but my understanding is that mild steel exhausts still rust, albeit at a slower pace than the equivalent petrol vehicles. The back box is normally the first to go.

Rust and the accompanying scale is a fact of life; on the other hand carbon build up inside the exhaust can be cleared by some extended high speed running, preferably at motorway pace. So an 'Italian tune up' is probably your first port of call.

If you still have a cat, that can also block the exhaust when it fails, but that normally involves the cat developing a pronounced rattle before the core breaks up, so it's unlikely to be that.
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An Italian tune up would be good, if I can get up those speeds!
It's seriously underpowered, takes 2-3 seconds with foot flat to floor in neutral to reach 3-4k rpm.

I'll try disconnecting the back-box to see if there's any improvement at all.
 
Have you already tried actual vs expected boost on the turbo? Via VCDS? Apart form the smoking which maybe somehting else seems like turbo lag.
 
Catnip64 said:
An Italian tune up would be good, if I can get up those speeds!
It's seriously underpowered, takes 2-3 seconds with foot flat to floor in neutral to reach 3-4k rpm.

I'll try disconnecting the back-box to see if there's any improvement at all.
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Is this in standstill or in motion. I assume in standstill. Maybe strange question, but if in standstill all diesel rev slow if the clutch pedal is not depressed.

just a thought.
 
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