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1.8tdci smoking on overrun


paulh757
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Hi, first post on this forum

I'm after a little advice about my 09 1.8tdci. The turbo has been a bit whiney for a while. Just lately I've noticed when coming off the overrun (particularly after a long downhill) when I put my foot on the throttle there is a big hesitation and a puff of blue smoke out the back. Once its cleared itself it runs fine again. No loss of power. I pulled the turbo intercooler pipe off and there is a thin film of oil present. EGR is blanked off. Does this sound like the turbo on its way out?
Thanks

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On 27/10/2016 at 1:15 PM, paulh757 said:

when I put my foot on the throttle there is a big hesitation and a puff of blue smoke out the back. Once its cleared itself it runs fine again. No loss of power. I pulled the turbo intercooler pipe off and there is a thin film of oil present. EGR is blanked off. Does this sound like the turbo on its way out?

Hi there.

No, not really.

There is likely to be a little oil in those pipes, it comes from the crankcase breather system. There is a hose from the back of the cam cover, to the main air inlet to the turbo. Also a light throttle opening after over-run will not ramp up the turbo, so the hesitation is not likely to be caused by the turbo.

Blue smoke could be engine oil getting past valve stems or piston rings. A build up of oil in the cylinders on over-run could cause a hesitation, possibly. I think I would remove & clean out the whole crankcase breather system, with the oil separator unit (under the fuel filter) and its hoses. Then keep an eye on it to see how quickly it oiled up again. And check the engine oil level, of course.

Another explanation might be fuel related. Some problem happening while the injectors are shut down, and rail pressure is reduced, but the pump is still running. With all fuel problems, the first thing to look at is the fuel filter, the filter housing sealing, and the fuel pipes. Clogged filters or small air leaks into the pipes cause all sorts of problems.

Turbo related noise could be a leak in the air pipes from turbo to manifold.

I suggest getting a scanner, and using it. Most malfunctions will cause error codes (DTCs) at some time, and eventually the EML (engine light). The codes can often help.

If all other oil loss or fuel problems have been ruled out, or symptoms change, then it might be time to suspect the turbo, but not yet from what you describe.

Peter.

 

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  • 3 weeks later...

Hi,

So to update this thread, the turbo was on the way out, it seized on me last week:sad: According to the garage it sucked all the oil and blew it all down the exhaust/intercooler pipes, so I was lucky it didn't run up on itself and kill the engine!

Anyway its been replaced and I'm back up and running. The overrun thing is still happening though so its definitely a separte problem. I'm planning to take all the breather pipes off this weekend and give them a good clean, is it possible to clean the pcv valve on this engine? Also I can't understand why this only really happens after running downhill with the throttle closed?

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50 minutes ago, paulh757 said:

I'm planning to take all the breather pipes off this weekend and give them a good clean, is it possible to clean the pcv valve on this engine?

Sorry to hear about the turbo sad.png So I was only half right, or less, in my post above!

Diesels do not have the same sort of pcv that petrol engines have. There is something in the cam cover, under the round insert, but I have not been able to find out what it is. It is just open (no apparent restriction) on my car, when I tested it by blowing through it (via a non-oily hose!). So just make sure yours is also open. To clean it, I think you would need to remove the cam cover (not too difficult) and run some solvent through it. There is no access to it from inside the cam cover, as I recall.

The other important point is that oil can drain freely out of the oil separator, and run back into the crankcase.

I hope the intercooler was cleaned out after the turbo problem, to remove any oil or debris that may have got into it.

When these diesels are on over-run, the air flow remains high. When the accelerator is opened slightly as a hill flattens out, the fuel pump outlet pressure rises and the injectors start to open. The airflow is unchanged until ether the rpm changes, or the turbo boost pressure rises. The exhaust gas temperature will rise, so any oil in the exhaust manifold area will heat up and smoke. That is possible. The EGR valve also opens as the accelerator is opened, maybe this could do something, like letting any oil in the exhaust system, back into the inlet.

Sticking or faulty EGRs usually cause hesitations at other times, like pulling away. So I don't really suspect that, from what you say.

Have you had a chance to check the oil consumption after the turbo change? My 1.8 gets through only about 1 to 2 litres in 6000 miles. And that is on 155k miles.

 

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  • 4 weeks later...

This is really confusing me now.

I took all the breather hoses off and cleaned them through. I also removed the cam cover and tried to clean that valve but not with much luck. as you say its sealed and totally non-servicable. The car did seem better for a few days but the problem has come back again.

The egr is blanked off so that rules that out. Whilst he smoke looks blue in the mirror the car doesn't seem to have used any oil in 3000 odd miles so I'm not convinced, and still no errors on the computer. I'm starting to think some kind of airflow sensor issue perhaps, causing incorrect fueling?

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1 hour ago, paulh757 said:

the car doesn't seem to have used any oil in 3000 odd miles so I'm not convinced, and still no errors on the computer. I'm starting to think some kind of airflow sensor issue perhaps, causing incorrect fueling?

Have a look at the MAF (air flow sensor, on the air filter outlet). If it is dirty or oily, it could read wrong. Also check the hose to the MAP (pressure sensor on the inlet manifold). Like you say, over-fuelling on power start-up after being in over-run is a possibility.

Have you heard of a program called FORSCAN, or have you used it already? It can monitor live fuel pressure and injector signals, and log while driving for later analysis. On over-run, the fuel pressure should be cut right back, then rise as the accelerator is pressed. If is stayed too high, maybe that could cause over-fuelling.

When bringing power back on, is there a delay, then a bit of a surge before it settles? Your 1st post suggested that. In that case, either the injectors are not opening up when first requested, or the fuel is not burning properly at first, or ???. Bit of a mystery.

A log of fuel pressure, IMV & PRV valve commands, injector signals, and throttle position might yield some clues, or eliminate some possibilities. Below is a graph from my car fairly recently, showing pick-up after a brief period on over-run. APP is accelerator, FRP is fuel pressure, VCV is one of the pressure control valves. It picked up quite smoothly.

overrun.PNG

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Thanks, no haven't used that program. Think I'm going to let the garage have it for a couple of days and see if they come up with anything. Like you say, bit of a mystery!

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  • 5 years later...

Did you manage to sort out what was causing the smoke on overrun?

 

I have the same problem, new injectors and new hose from IC to EGR since it had a small crack, but still having this irritating hesitation and puff of smoke after a long downhill...

 

I also have the EGR blanked, thinking if it may be because of that...

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On 12/10/2022 at 5:40 PM, unofix said:

batman.JPG

😁 I know it's been a while since this was updated, I'm just desperate with my car since I have spent a lot of money with it and still have this problem, thought to give it a try and see if there is a reply 😉 

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