Howling Turbo

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stevieb
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Howling Turbo

Post by stevieb »

406 2.0 petrol turbo.

During the hot weather on Friday, my turbo developed a loud howl, part way through a journey. No popping sounds, and no other signs of problems, just a howl around 1500 - 2000rpm.

When I get home and check things out I realise it's also got a backfire, when blipping the throttle from tick-over (it was always slightly hesitant before), but I cannot repeat the turbo howl without placing the car under load. The backfire is only noticeable when blipping the throttle when the car is stood. It doesn't do it under normal acceleration.

Over the weekend I checked everything over, the weather cooled, and I diconnected the battery to reset the ECU in case that had anything to do with matters (I had my suspicions about possibly dodgy temp sensors upsetting the ECU). Starting from cold everything seemed fine.

Yesterday and today, now back at work, the howl hasn't quite returned, but has turned into a much louder than normal whistle, which dies out suddenly at around 2200rpm with a very faint jolt of the car (as if the turbo has suddenly woken up and started pulling), and a strange growl. From this point everything remains pretty normal except I have little boost until around 3700rpm when the car shoots off like a scalded cat. The backfire is also back. This time I can repeat all the noises with the car on the drive.

I have checked over all hoses, and can see no leaks/loose connections. The elbow connecting the pipe from the air filter to the turbo is slightly deformed, so has clearly been compressed by vacuum, but does not appear to be compressing when the noise starts.

Clearly there is something that is opening or closing at around 2200rpm (remember it's the petrol turbo), which is cancelling out the problem at this point in the rev range. I suspected the "Cut Valve" (I'll post a pic of this shortly), but this appears to be working okay, and bypassing it has very little effect.

I know some of the symptoms are typical of a leak on the inlet side, but surely with a turbo producing positive pressure (even at tickover), this shouldn't be a problem. A back fire is a sign of an imbalance in the mixture. Could it be the ECU is getting a false reading from somewhere and allowing over lean-ness at tickover (the engine does overheat VERY quickly at tickover or low revs)?

Any suggestions?
stevieb
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Post by stevieb »

Pic time.

Image

Item 11 is known as a "Cut Valve". The small pipe from it is a vacuum pipe and leads directly to the inlet manifold. At tick-over the vacuum in this pipe is quite strong and opens the cut valve.

This in turn, it would seem, allows inlet air to bypass the turbo, presumably when the turbo is creating too much drag at very low revs (more drag than a petrol engine could handle, where a diesel would cope with it better). At a given drop in vacuum the valve closes and all inlet air is that which arrives via the turbo.

Anyway, the cut valve seems to be out of the equation, as bypassing it completely does not eliminate the problem.

The noise appears to emanate from the turbo area itself, so this is where I'll have to focus my attention. There is a heat shield between the turbo and the lower UJ on the steering column, so the growl (half growl, half "whoop") might just be the heat-shield vibrating. But that still doesn't explain the extra noise from the turbo. It seems I may have some fun evenings on my hands while I look into this further.

Suggestions are still welcome though...

Edit - Forgot to ask - what are the tell-tale signs of a Cat letting go, or getting all bunged up? Mine seems to make a hell of a lot of noise - it's louder than either of the two silencer boxes (which sound as if they have little to do). It's also inconsistent - sometimes I have to turn up the radio quite loud on the motorway to drown it out, and other times I don't need to bother. But at tickover, it's definitely VERY loud.
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fastandfurryous
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Post by fastandfurryous »

Item 11 is also known as a "dump" valve, it's purpose is to dump pressure from the system when changing gear to prevent compressor stall. I doubt this is your problem.

I suspect you have the beginnings of turbo siezure, as this problem is fairly common with the 2.0turbo petrol engine in the 406. The turbo is jammed fairly solid until about 2200rpm.
Below this, the turbo will howl as exhaust gas has to negotiate the jammed turbine wheel, and above this, the pressure is sufficient to shift it, and suddenly you have a spinning turbo, and hence pressure in the inlet manifold, and the car goes faster.

What the mode of failure is, I'm not sure, but it sounds a lot like a gummed turbo shaft

When was the last time you changed the engine oil? and do you use a decent oil with additives to prevent turbo shaft gumming/siezure?
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stevieb
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Post by stevieb »

Cheers FandF, I had hoped nobody would suggest that the turbo was on its way out.

The oil was changed about 4-5,000 miles ago, after a damn good flush. Prior to that it was about 8,000 miles before. And before that I couldn't even hazard a guess as that was before I owned it.

I think I'll whip off the elbow pipe on the inlet side tonight and see if there's any stickiness in the spindle of the turbo. If you're right FandF, then I guess I'll be able to feel it quite easily.

One other thing I've noticed, is that on warm starts the "K" warning light is staying on quite a long time and I have almost no turbo at all until the light goes out. I've also noticed the engine pinks under load. This has only really started since last Friday. The warning light makes sense, but the pinking is a sign of excess air isn't it? The pinking goes off as soon as the "whoop" noise has passed at 2200rpm.

One thing that might change your opinion FandF, and something I've noticed more today, is that in say 5th gear at 1750rpm, when the whistling is at its loudest, if I blip the throttle (obviously with little effect on revs or at the wheels due to the gear I'm in), I can hear the turbo whistle rise and fall in time with the movement of my foot, even though no change in revs occurs. Obviously I'm adding more load to the engine, therefore higher exhaust gas temps, and a faster flow of gas through the turbo, but would this also apply on the inlet side? Would it draw gas in faster? If the airflow is being restricted, then would it not just run a little rich for that moment or two while I blip the throttle? Or is the ECU that quick to respond? This seems to oppose the pinking idea. Unless the head is just coked up anyway and I've never really noticed it before (it's never been warm enough to have the windows open as much before :) )

Edit - Another thought - the revs have always been slow to die down on this car, when changing gear etc. I suspected just because of the additional turbo - but maybe a turbo problem was on the cards all along.
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Post by stevieb »

Update - kind of...

I've had a thought since earlier FandF - whilst playing with the dump-valve yesterday I was getting positive pressure on the post-turbo side, even at tickover - so I guess the turbo must be turning and generating some airflow - though I've no real way of knowing if it's enough - I s'pose a sticky spindle/bearing could be slowing it down rather than completely seizing it.

Secondly, I've had a blast down the motorway this afternoon. From home in Sheffield to Long Eaton in Derbyshire (jct 31 - 25 of the M1). Outwards, there were no real changes, except the boost at 3700rpm, seemed nearer to 4000rpm and was a LOT more forceful.

On the way back I headed to Trowell services for fuel. At a steady 60mph behind lorries, and hardly touching the accelerator in 5th, the temperature would not drop below 90°C. This sort of confirms what I said earlier about the engine heating up much quicker at lower revs. The coolant is all in good order, and the system proeprly bled, so I don't have any reason to suspect that.

After stopping for fuel and returning to the motorway the car was very sluggish - feeling like the choke was on - for about five minutes. Getting anywhere near 3700rpm or more was a real effort, and didn't result in any boost at all. After the five or so minutes had passed everything returned to some normality, and the boost was back as ferocious as ever above 3700rpm.

I'm guessing this may be a dodgy temperature signal getting to the ECU and causing it to try and choke the engine, mistakenly thinking it's cold. Am I right in thinking this could be the case?

As far as I can tell this car may not have a MAP sensor, though there is an "electroswitch" which has hoses from the inlet manifold, the turbo, and the inlet piping. I guess this does the same job as the MAP sensor. The wiring from it goes directly to the ECU.
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Post by PowerLee »

I keep telling people NOT to buy a 406 or 605 with the 2 litre 8 valve low pressure turbo engine because its a well known fault with the turbo but I get told im talking crap :wink:

Another turbo seized :lol:
stevieb
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Post by stevieb »

PowerLee wrote:I keep telling people NOT to buy a 406 or 605 with the 2 litre 8 valve low pressure turbo engine because its a well known fault with the turbo but I get told im talking crap :wink:

Another turbo seized :lol:
But it's sooo much fun. :D

When it's working... :oops:
stevieb
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Post by stevieb »

Once again, the French Car Forum provides the answers.

I removed the inlet ducting, including the elbow pipe, and found the spindle of the turbo free, but loose. Initially I just thought "Ah well, it's not that", and was about to reassemble everything.

Then it occurred to me that the inlet air would be arriving via an elbow, and would therefore potentially cause a lot of disruption to the turbine blades, especially at low revs.

So, I levered the spindle to one side slightly, so it was not centred in its bearings, and lo and behold it sticks. It sticks pretty damn tightly too.

So it seems you two gents are right in your diagnoses. Many thanks for that.

Now, does anybody fancy paying for the recon job for me...??? :P

Looks like a couple of days holiday required, as my local factors can only get the original turbo reconditioned. No exchange on these b*gg*rs... :x
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Post by pug_owner2002 »

The Turbo on my 306 went a while back (sounded like a siren).
Anyway I had it reconditioned by Turbo Technics (www.turbotechnics.com) and they sent a courier to collect it and bring it bck to me (It was gone for about 5 days) and came back with 12 months warranty.
It's still working fine 35K later.
Maybe worth giving them a call.
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stevieb
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Post by stevieb »

pug_owner2002 wrote:The Turbo on my 306 went a while back (sounded like a siren).
Anyway I had it reconditioned by Turbo Technics (www.turbotechnics.com) and they sent a courier to collect it and bring it bck to me (It was gone for about 5 days) and came back with 12 months warranty.
It's still working fine 35K later.
Maybe worth giving them a call.
Cheers for that, I might give them a call in the morning. Along with various other places...

Ideally I want a cheap second-hand turbo with a few miles left in it while I get mine properly reconditioned.

Failing that, a good exchange option. I could do without being without the car for any length of time. No car = me not working.
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Post by stevieb »

Just in the middle of trying to swap the turbo now...

What a job!!!

Any ideas how to tip the engine forwards? This lump won't lift clear of the top mount so I can rock it forwards and get the heatshield out of the way. Without getting the heatshield out of the way, and can't undo all the bolts.... :x

Any guesses?

Edit - I should've said other than removing the mount/bracket completely. Which is difficult, as the Allen headed bolts are tight beyond belief.
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Post by Dave Burns »

I wouldn't expect the air arriving through an elbow to have any effect on the compressor wheel at all, I certainly would expect the shaft to jam if it were levered to one side.

If the shaft was stiff or siezed when you got to it then there would have been your culprit, but it wasn't so I hope what you've embarked on isn't an expensive wild goose chase.

Turbo bearings are of the hydrodynamic type, they run on a high pressure wedge of oil, what you have done to diagnose the fault without that oil in place and the turbo spooled up could prove fruitless.

Have you not got a boost gauge on the dash.

Dave
stevieb
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Post by stevieb »

No boost gauge on the dash Dave.

The turbo needs changing anyway, as it started bleeding oil into the inlet ducting on Friday - and creating lots of blue smoke. The turbo is definitely at fault.

I have everything undone to remove the turbo - it just needs all the miles of stiffness breaking now to release it. Then I have to work out how to maneouvre it out, as it won't drop out the bottom like my 405TD one did.

The engine mount bolts (the allen headed ones) needed the impact wrench to free them. Damn things.
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Post by stevieb »

Turbo now fitted and seemingly okay. What a stinker of a job though. :x

A motorway journey in the morning will be the telling time though. I'm praying for no leaks, as most of the joints a are in awkward places, and I'll definitely not be feeling up to it tomorrow. The aches and pains are already kicking in...
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Post by stevieb »

Well, after replacement of the turbo, and a reset of the ECU everything is fine (almost).

The car starts easily, with the "K" warning light extinguishing immediately (much quicker than before), and everything runs just fine. Acceleration is now consistent too, which is a bonus, and the overheating seems to have stopped too, though ambient temps have been a lot lower today, which have helped.

The only snag, which I think is related to something I mentioned earlier, is that under pretty hard acceleration (not necessarily high revs), the engine will momentarily lose all power, as if something has been stuffed into the air intake. A moment before this occurs, the "K" warning light appears. As soon as everything rturns to normal the light goes out. This is quite a violent experience, and does not appear at similar revs under less strenuous acceleration. Gradual acceleration causes no issues at all.

So, I'm firmly of the opinion that the elbow pipe on the inlet side of the turbo is collapsing. Probably "popping" under a certain amount of vacuum. This shows itself through this sudden loss of power, and a moment later the loss of boost causes the dump valve to open and thus releases the vacuum that has been created between the turbo and the inlet manifold. And the pipe returns to its normal shape.

The pipe looked like this last Wednesday...

Image

Image

Anybody else agree that this isn't the shape it should be? It gets very soft when the engine is warm too...

Lucky I ordered one last week, eh?
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