996 Turbo - intermittent BOOST ?

[charandhindsa]

I thought I had stepped into the wrong car on the way to the gym yesterday. Unfortunately I had not..

Turbo normally kicks in at 3-3.5K rpm on the porker, welcome growl and thrust...this time, it just didnt Took a reading at 0.4 bar at best

On the way home however, different story. Normal service was resumed..0.7,0.8...0.9 bar readings.

Something is up...? Any takers?

[kayc]

charandhindsa said:

I thought I had stepped into the wrong car on the way to the gym yesterday. Unfortunately I had not..

Turbo normally kicks in at 3-3.5K rpm on the porker, welcome growl and thrust...this time, it just didnt Took a reading at 0.4 bar at best

On the way home however, different story. Normal service was resumed..0.7,0.8...0.9 bar readings.

Something is up...? Any takers?

Maf sensor.

[LeighB]

Could also be a sticky actuator rod on one of the turbos. I've recently had one snap and boost was down to 0.3/0.4 as a result.

Other culprits, if it's not MAF or actuator related, could be diverter valves or a split/loose hose to the turbos/intercoolers.

[charandhindsa]

Great - thanks gents.

No one has mentioned knackered turbo's yet...let's hope that's the case. Can't see how if the car performs as it should intermittently.

Any idea on the parts/labour required for the fixes mentioned?

Many thanks

[kayc]

charandhindsa said:

Great - thanks gents.

No one has mentioned knackered turbo's yet...let's hope that's the case. Can't see how if the car performs as it should intermittently.

Any idea on the parts/labour required for the fixes mentioned?

Many thanks

Maf sensor from memory around £300 and you can fit it yourself in 5 mins and is an intermittent fault based on temp,load,fuel etc..thats why im fairly sure its that..

[Moosh]

kayc said:

Maf sensor from memory around £300 and you can fit it yourself in 5 mins and is an intermittent fault based on temp,load,fuel etc..thats why im fairly sure its that..

^^^^^ As like the man says, most likely to be the MAF sensor.

[EvoSlayer]

Could be any number of reasons incluing faulty boost control valve causing car run in 'safe mode' limiting boost to .4/.5 bar I believe. If this is the case than it's a cheap/simple repair. If 'normal service was resumed' this is one of the first things I would look at plus sticking wastegates, and as mentioned could be a failing air flow sensor.

Have you got the standard airbox in? The wierd and wonderful aftermarket jobbies can cause all kinds of headaches.

Edited by EvoSlayer on Tuesday 6th November 15:30

[davek_964]

kayc said:

Maf sensor from memory around £300 and you can fit it yourself in 5 mins and is an intermittent fault based on temp,load,fuel etc..thats why im fairly sure its that..

It's quite a bit less than that. I had to replace mine a few weeks back (permanent ABS / PSM failure light, but actually no boost issues) and I paid £175 from here :

http://www.emissioncontrols.co.uk/page.php?domain_...

ETA : Assuming it becomes a repeatable problem, I guess you can rule out the MAF by unplugging it. It will give you immediate ABS and PSM lights until you plug it back in (and obviously, no ABS or PSM) - but it would prove whether dodgy readings from the MAF are causing the problem.

Edited by davek_964 on Tuesday 6th November 15:38

[charandhindsa]

Thanks guys, great advice.

The car is completely standard as it came out of OPC warranty earlier this year.

I intend to take the car into RSJ Sport Cars / BodyTechnics - both Slough based.

The only other thing to note is the battery in the car is very weak....on the way to the gym (cold start) it just about cranked, but got going. Im just wondering if this caused some synch issue with the ECU in some way? One the return journey, engine was warm and it cranked as normal & it drove 'normal'. Perhaps just a coincidence?

..just a thought.

[Homer J]

As mentioned could be any number of things.

I had a similar problem, turned out to be DV's. However to be be safe, replace your Turbos with some nice hybrids

It the only way forward!!!

[stup]

Potentially could be N75 valve that is faulty which is situated top side of the engine,if you can confirm turbo actuators are free and operate correctly this could be worth checking next as this is what controls the pressure to the actuators.. Boost pressure varies when this is faulty and on occasion puts the engine into a safer ecu map

[AndrewMontgomery]

If its the N75 they cost less than £20 I believe. Fiddly self-fix.