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2006 147 JTDM 16v 137,000 miles.

For quite some time I've had a slight hesitation and then a sudden surge in power on hard acceleration. I put this down to the turbo actuator sticking and intended replacing it at some point. The problem however, was nothing much and easy to live with.

Last week I did an oil change and also decided it was time I fitted the air filter that I bought for the last service but never fitted due to it looking like a proper pain in the ass to fit - it was! I'm an ex mechanic and really don't miss the crazy design features on modern cars......................but I digress. Back to the problem - following the service I drove to Heathrow and back last Wednesday - 500 miles without a problem. Thursday I went to a nearby city and thought I felt slightly more hesitation than before but it seemed to clear. Friday, as I was pulling out of my drive the car was really sluggish, then cleared and seemed OK. After 10 miles I stopped for an appointment and when I came back and drove off the car was a nightmare. It lost all power and stuttered occassionaly - the slightest hill saw me in 3rd gear, I didn't think I would get home. Stationary the car hardly revs and misfires a little when revs are applied. There are no warning lights on at all.

A quick check showed that the turbo actuator was hardly moving - I thought that was the problem. No such luck - when I attached a pipe to the acuator and sucked on it, the actuator moved freely. I decided that the problem must lie in whatever controls the actuator and suspected I may have broken a vacuum pipe or something when I was fighting with the airbox during the filter change. I started the car with the actuator pipe disconnected and held it to my tongue whilst someone revved the car - there didn't seem to be an awful lot of suction but there was some.

So moving further back I checked the I pipe from what I presume is the boost valve to the inlet manifold (vacuum pipe) but left it in place at the manifold end as it looks a proper swine to get back on if its removed from the manifold. I wish I'd checked how much suction was coming there was in this pipe before I did any more dismantling (engine running) but I didn't. I have checked it as best I can with it in place and I can't see any cracks. Blowing through the pipe produces some resistance and I can't hear any air escaping so I'm guessing its OK.

I have now removed the airbox and the boost valve (I think that's what it is) attached to it. The valve looks like some form of solenoid and I have no idea how to test it. With it off I can blow or suck through the 2 connections freely - both ways so it seems to be open. To my thinking that would only be a problem if its the type of solenoid that closes when its off. In other words, if it is that type, I should not be able to blow through it when its off. I don't know if it operates at a full 12v so I'm reluctant to pass 12v through it to find out if it anything changes when I pass current through it.

I'm hoping this is the problem but I'm not convinced - does anyone know how to test these or have any other ideas? Does this valve actually close when the engine is running and open slowly as revs are applied? From what I've read - people say these (VNT?) valves are fairly reliable but I guess they do fail sometimes.

One thing that occured to me - I have not yet removed the swirl flaps from the car. Its the aluminium manifold type so should have plastic flaps. They don't come off and lodge somewhere where they can block the vacuum pipe do they? (No idea as I've never had one of these manifolds off).

I really need to check how much vacuum the pipe from the manifold is producing so I'm going to have to do some partial putting things together again. Will I get a warning light if I run it without the MAF connected? If so, can I clear it without a computer?

I live in the middle of nowhere and I'm kinda stuck at the moment - hope someone can help.
 

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The boost control solenoid should apply full vac at idle to move vanes to max boost position, as boost increases the solenoid starts to close off to reduce vac and bring boost level down.
As you can blow through I would say it is faulty as it should be closed when de energised.

if you have a vac gauge on idle the inlet to n75 from pump should be 20+hg and roughly same out to vnt on turbo. Arm on turbo should be at its max position

swirl flaps on ally manifold don’t give so much trouble as the other type they tend to leak boost or have the actuator pop off. The other type with metal flaps break off and cause damage, they can’t cause loss of vac as vac is from outside source
 

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Thanks for that - I suspected the solenoid should be closed when not receiving a current as most are.

I'm following you a little but not completely - bearing in mind that I don't have a vac guage these are my observations. Previously when the car was revved the actuator rod would move quite a lot - towards the ground. When this problem occured, I watched the actuator rod and it hardly moved when RPM was increased. Attaching a tube to the actuator and sucking results in full movement - which to my mind ruled out the actuator and pointed elsewhere. If I'm understanding you correctly the actuator arm should be fully pulled down on idle and then slowly let go as the VNT reduces suction - correct?

I'm guessing that at the moment the VNT must be operating but shutting vac down when energised (on idle) - if not it would be open and applying full vac? Something must be happening because if it was doing nothing it would remain open and allow full flow as it does when I blow through it?

When you say 'if you have a vac gauge on idle the inlet to n75 from pump' - I'm confused, I have never worked on this engine and its difficult to see because of the position below the inlet manifold but vaccum appears to be supplied from the a connection somewhere below the manifold which I presumed was on the manifold itself. Are you saying that vacuum comes from a pump?
 

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vac is created by a pump driven off the camshaft,diesels do not make manifold vac like petrols.

to trouble shoot you really need some diagnostic software and a vac gauge so you can actuate n75 on mes and also test vac amount.
 

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OK, thanks again, yes I know that most diesels use a pump for vacuum, unlike petrols.I just thought there was some form of inlet manifold vacuum because of the position. There are 2 or 3 pipes coming from the source of the vacuum - do they control anything else? I haven't noticed any other problems - brake servo operation is fine for example.

Diagnostic equipment is a not possible at this stage - dismantled and the cost for a 14 year old car. Been down that road before and gor bills for £££'s. I'm just going to have to soldier on.

Before I go further, I'll rebuild enough to start the engine and see if there is vacuum coming from the pipe that leads to the pump. If there is, that would, I believe, point to a faulty boost control valve as I suspected and you suggested.
 

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OK, had the car running again and the pipe from the pump that goes into the boost solenoid is producing an excellent vacuum. The strange thing is that when I connect everything up fully the vacuum going to the actuator is now pulling it down fine. I think my original suspicion was correct - I disturbed something when I changed the air filter.

I feel its a good bet that the boost solenoid was sticking or has some other intermittent fault - it could even be a dirty electrical connector - whatever, I don't trust it and I'm going to fit a new one.

Fingers crossed this is the end of the matter and I don't have to fork out £££'s in diagnostic fees.
 

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Well it was solved!!!

Ever wished you'd left well alone? I should have been a lazy git and left the air filter just as the previous owner's garage did!

The old boost sensor was deffo faulty but 300 miles after thinking I'd fixed the problem - its back. Well, something similar is back - intermittent loss of power and this time a fault message and eml.

This time I took it to a mate's place and had it plugged in to his Snap On diagnostic kit - which has pinpointed the Mass Airflow Sensor. Its a favourite as this problem began shortly after changing the air filter so it was disturbed.

I say favourite but I'm not 100% convinced - I've seen other things cause faulty readings before. I have a new main intake hose arriving on Friday as I did note some perishing when I was in there last - I'll check all the other hoses before ordering a MAS.

Just reporting really but I would like to give a recommendation here that could save other mermbers £££'s. If this is not allowed, please delete this section.

My car is fitted with a MAS that was only used between 03/2006 and 06/2007 - yes you guessed it - and is therefore very pricey (remember I'm used to paying trade prices). There's loads of cheap Chinese crap and copies on a certain auction site - some as low as £15 but there is no way I'm fitting one of those. Euro Car Parts quoted £230 + vat, even at my discount for a Hella unit. After a lot of searching I found YB Racing from Rossendale, Lancashire (Powersparks on Fleabay) who are an authorised Bosch distributor who have quoted £48.31 (+3.95 Royal Mail 24 Tracked) for a Bosch unit.
 

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If you disconnect the MAF (mass air flow) sensor (located in the fat hose by the intercooler) as a test, it will idle poorly but power should be fine if the MAF is at fault. If power is still poor, it probably isn't the MAF.

There is also the MAP (manifold absolute pressure) sensor, that as a single bolt fitting in the top of the inlet manifold. This is robust but gets blocked with oil and soot (turbo mist+EGR soot), and under-reads, causing the ECU to not supply enough fuel - hence reduced power. Cleaning the gunge (gently) out of the small protective plastic cage surrounding the pressure sensor element is usually enough,

Common other causes are, as you guessed, cracked or holed boost hose. The lower especially. It softens with age and balloons under boost, slowly rubbing a hole through the top surface (against a bolt on the bellhousing). This is difficult to spot, but can be felt as a dimple or small pit. Once you had full boost back, it may have given up and started leaking.

If you weren't absolutely certain that the skinny, 3mm ID silicone vacuum hose, that runs from the vacuum solenoid to the turbo actuator has no leaks, now might be a good time. Even a pinhole can mess things up, and they do deteriorate. 1m of new silicone is about £6 on eBay.

Other fun possible causes of lost power: clogged EGR valve, or (on your car with metal manifold and plastic flaps), boost leaks from worn swirl valve pivot bushes. This should be visible as an oily mess. Aftermarket repair kits are available, in two slightly different sizes.
 

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If you disconnect the MAF (mass air flow) sensor (located in the fat hose by the intercooler) as a test, it will idle poorly but power should be fine if the MAF is at fault. If power is still poor, it probably isn't the MAF.

There is also the MAP (manifold absolute pressure) sensor, that as a single bolt fitting in the top of the inlet manifold. This is robust but gets blocked with oil and soot (turbo mist+EGR soot), and under-reads, causing the ECU to not supply enough fuel - hence reduced power. Cleaning the gunge (gently) out of the small protective plastic cage surrounding the pressure sensor element is usually enough,

Common other causes are, as you guessed, cracked or holed boost hose. The lower especially. It softens with age and balloons under boost, slowly rubbing a hole through the top surface (against a bolt on the bellhousing). This is difficult to spot, but can be felt as a dimple or small pit. Once you had full boost back, it may have given up and started leaking.

If you weren't absolutely certain that the skinny, 3mm ID silicone vacuum hose, that runs from the vacuum solenoid to the turbo actuator has no leaks, now might be a good time. Even a pinhole can mess things up, and they do deteriorate. 1m of new silicone is about £6 on eBay.

Other fun possible causes of lost power: clogged EGR valve, or (on your car with metal manifold and plastic flaps), boost leaks from worn swirl valve pivot bushes. This should be visible as an oily mess. Aftermarket repair kits are available, in two slightly different sizes.
Yes, Cheers, I'm aware of most of that but appreciate the info. My vacuum hoses are hard plastic and as far as I know they are fine but its very hard to check them 100% as they are pretty inaccessible under the manifold area - if all else fails I'll tray a torch and mirror.

I'm waiting for a new turbo hose (turbo to filter) to arrive and will check the MAS by unplugging it once I get in there to replace that hose. The bottom hose looked fine when I removed it before but I will check it again.

Someone else mentioned the other sensor in the manifold and I said I'd leave it as I intend doing a complete manifold overhaul/swirl flap removal/EGR delete in the near future but as that sensor sounds easy to check/clean, I'll take your advice and have a look at it.

I don't know if its my imagination or not but I seem to think there is more induction noise than before so I would not be at all surprised to find a split in the turbo hose.
 
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