Turbo-a-huntin.

[tigran]

Using the 9000 fpt as my sensible economical daily at the moment. Have noticed a perculiar trait of the turbo. When it's boosting not at maximum but from low down in the power band the turbo seems to do a kind of hunting-idle impression. Where it's on off on off - it's not jerky and fairly smooth so i doubt its a fuelling thing and saabs with direct ignition either spark perfectly or not at all from what i understand.

Which leaves what? Shagged turbo accumulator?

The exhaust on the car is now totally grenaded (waiting for sale of sd1 before getting a turbo-back stainless sorted). But severly blowing exhaust wouldn't cause that kind of surging surely?

Also it's fine when under full boost.

It's a mystery.

[bstardchild]

May 25, 2008 3:54:35 GMT tigran said:

Shagged turbo accumulator?

What's one of them

[tigran]

May 25, 2008 7:26:17 GMT bstardchild said:

May 25, 2008 3:54:35 GMT tigran said:

Shagged turbo accumulator?

What's one of them

I'd love to know myself tbh. I blame sleep deprivation. What i meant was turbo actuator.

[cptsideways]

Could well be bearings on way, I'd inspect it for end play, if its wobbly it'll be running the blades on the housing causing it too stall & then its bye bye turbo. Catch it before it goes & it'll saveable

[dave21478]

yah, if the bearings are going, lower boost isnt quite enough to overcome the resistance, hence it doesnt spin smoothly untill you get higher pressures to force it round.

Also, check the wastegate is fully closing and the actuator is moving smoothly.

[Fiat Daft]

could be the electronic boost controller

[xbo11ox]

Doesnt sound like a 'mechanical' probem in the turbo to me, almost certainly not the turbo bearings or actuator. Is the actual boost fluctuating? or is the actual power delivery on-off-on-off? If so it sounds like a fueling/electronics problem. Also I wouldnt rule out your knackered exhaust, difficult to do a proper methodical fault diagnosis with a kenked exhaust.

[TheFrequentFryer]

The wastegate actuator membranes can go soft, or the boost pressure valve on top of the radiator can go wonky.

The other extreme is what I reckon mine is doing and you get overboost and the apc cuts fuel to stop the boost going over 1.3 bar. That is when the pressure control valve or the wastegate is sticking and when the fuel cut hits, you get the steering wheel slapping you in the chest.

The wastegate can stick if the car has been grannied about and the wastegate never needed to operate. The last owner only had it a few months and the one before was an old bloke.

[tigran]

Meatball - i've had overboost kick in on my lpt and it's nowhere near that violent, just like a really subtle on-off of power.

I will have a feel of the turbo see if there's any play in it. If not i'll wait to get a new exhaust on then figure it out.

[tigran]

May 25, 2008 9:41:32 GMT xbo11ox said:

Doesnt sound like a 'mechanical' probem in the turbo to me, almost certainly not the turbo bearings or actuator. Is the actual boost fluctuating? or is the actual power delivery on-off-on-off? If so it sounds like a fueling/electronics problem. Also I wouldnt rule out your knackered exhaust, difficult to do a proper methodical fault diagnosis with a kenked exhaust.

Oh on that front i can hear the turbo whine surging.

[10mpg]

Knackered exhaust could be messing with the back pressure and messing up the wastegate control??

I know nothing about turbos but my work truck (mitsi L200) did a similar thing after I clouted the rusty exhaust and it fell off, a new one put the truck and the on/off turbo back to normal..

Then the egr packed up and the turbo wouldn't boost at all till tight at the top of the rev range.... On the recommendation of a mate I took the egr off and replaced it with a metal blanking plate! worked superbly and the truck has been faultless ever since..