No Turbo Effect - 406 HDi 110

[andydorset]

The turbo effect was produced at higher and higher revs - then not at all. It still drives, but as you'd expect - sluggish. No warning lights; no oil used; no horrid noises; no smoke from exhaust. The car drives normally until the point - around 1800rpm I believe - where the turbo should actuate, but nothing happens. It just struggles through to 3000 rpm and beyond without turbo assistance.

OK so thats the fault. Now I have some questions that I so hope someone on this board will have experience of! What I know so far is that the two leftmost vacuum solenoids seem to be OK. I have swapped the electrical connectors and the vac out tubes - makes no difference. When idling, the leftmost (turbo wastegate?) solenoid applies a good vacuum at the vac out side -
Question oneis this going to the wastegate? Is it 'suck to close'?

Question twoHow can I locate the fault to ?turbo unit ....?Throttle position sensor...... ?vac solenoids ?EGR.... ?air mass thingy...

Question threeI wondered if I got a vacuum tester in the solenoid-to-turbo tube and drove the car through the rev range with foot quite hard down could I see if the turbo wastegate was being TOLD to close?
Question fourIs there a thorough detailed explanation of turbo operation/controls/dependencies available online?

I connected a large syringe, about 200ml, to the vac tube going to the wastegate, and sucked hard - when released, the plunger returned to the start position, about halfway up the syringe. I pushed, pressurising the tube and again the plunger returned to start position. I'm thinking the tube/actuator integrity is OK...

Thanks!

Andy

[legoless]

A few tests may help you narrow down the problem..
Grip the big hose that goes across the top of the engine from the intercooler to the inlet manifold and rev the engine .. it should bulge noticeably in your hand to confirm if indeed the turbo is boosting.
Remove the front vac pipe from the egr solenoid (the middle one) and block the solenoid with a small piece of hose and a tight bolt etc so you still maintain a vacuum for the rest of the system. If the car feels alot better after a drive suspect the egr system/valve. ( low down torque will feel improved even if the egr is ok but a big difference is a egr fault)
Remove the connection from the mass air flow meter and drive it a short distance it wont generate a fault light .. if it feels the same as when connected suspect the maf and try to grab another from scrappers or around 90 quid from the main stealers

Al

[andydorset]

Thank you Legoless.....

Here we go:

The large flexible boost pipe does indeed swell when revs increase. I can feel it pushing if I squeeze it. Hmmmm.

I disconnected and blanked off the EGR solenoid as you suggested - very little difference if any.

I removed the MAF sensor connector - big difference. No turbo effect but much livelier, less accelerator pedal required, pulls up hills much better in higher gear. But still no turbo feeling. Would a bad MAF sensor prevent the ECU from allowing higher fuel input required for turbo boost? Or am I way off the mark?

Thanks
Andy

[andydorset]

Posting to my own thread again!

Before swapping the MAF sensor with one I located at the scrapyard I thought I'd dismantle the current one, save time struggling in the mud at the scrappy - took the sensor off, and it looked OK, but obviously not sure what I'm looking at. Nothing to lose by giving it a clean, I thought, so gave it a good hosing down with carb cleaner spray, refitted it without the screws - waddya know, it goes much much better. I'd say it's working properly now, lots of power, low end torque like I remember>

I guess the MAF sensor could still be faulty but I'll leave replacing it till the weather improves.

It's probably not recommended practice, but I'd say it's worth trying a good spray for the sensor before replacing it.

Many thanks Legoless

[Doggy]

Depends on what kind of MAF sensor you have, but I'd heard one version responds well to brake cleaner

apparently it destroys the other kind though

[Welly]

Could be a dodgy throttle postition sensor, very common although usually flags the Engine Light.

Somethings telling the ECU to dump the boost.

[andydorset]

I'm very grateful for all the help I've had on this. To round it off, this is what I think has been happening - I bow to experience so please correct me if I'm wrong!

I think the MAF sensor was unable to tell the ECU the actual amount of air passing it. I think that because it was dirty it under reported the amount of air, so the ECU sent accordingly less fuel. This resulted in the engine being underfuelled and sluggish. Cleaner now, the MAF is telling the ECU there's loads of air going in - send more fuel!

Or something like that.......

I did wonder about the Throttle Position Sensor and tried to test it, just on resistance. The readings didn't make sense. I think it's a 4 wire system with 2 used to power an LED, probably infra-red, the other two for an infra-red receiver. Between the two moves a graduated disc which increases or decreases the light passed according to throttle position. This system has the advantage of no parts in contact, not susceptible to dirt etc. That's how I'd design it anyway.

Cheers y'all

[steve_earwig]

You have to use two, the other for sideways movement, and a couple of buttons on your bonnet...

[teamster1975]

You have to use two, the other for sideways movement, and a couple of buttons on your bonnet...

What'choo talkin' 'bout, Mr Earwig?

[steve_earwig]

Sorry, I thought he was describing a mouse...

[Doggy]

Is it that cold in your manor, Steve?

[steve_earwig]

Not yet, but it's in the pipeline