my car seam dead at low throttle . and really struggles for a fast get away,flat out its ok but needs to be reved.
i changed turbo a few years ago and got not much gain was a second hand unit
i cleaned egr , and then blanked it.
i swapped the vacuum/boost control unit for another and its mounted to the battery box and ive had cambelt done and some serviceing since but nothing made a difference

im thinking maf, inlet gummed up or boost controller or turbo actuator . but then that swapped when i changed turbo .

i put handheld vacuum tester on the vacuum unit thats off the turbo actuator and watched it leak quite fast . and if you tap it it dumps the pressure. im not sure what i am doing but seams odd. ;lol i took a video if that might help ?

You'll find this topic covered quite readily on the Alfa's which have a lot of these 1.9 JTD M-Jet motors across the 156, 147 and GT models.


As a rule of thumb - lack of power low down, say below approx. 2.5krpm = EGR leaking.


Lack of power above 2.5krpm = MAF failure


That's a very generalised rule of thumb to work to on these motors.


The turbos used are variable geometry turbos. There are a whole ring of small wing shaped flaps in a circle around the compressor 'fan' connected together by a big metal ring.


That big metal ring is linked to the turbo actuator which is the silver tuna fish can shaped thing with an arm going from it into the turbo and the vacuum pipe connected to the other side.


The vacuum is then controlled by the VGT solenoid which applies the vacuum to the actuator, pulling on the ring, moving the flaps in the turbo and changing the geometry of it.


You can run an actuator test in MultiECUScan on the VGT solenoid. You have to run the test with the engine off, so you'll have a limited amount of vacuum to play with but you should be able to run the test a couple of times before it runs out of puff although it will tail off at the end.


If any element fails you will end up stuck in high end boost mod, i.e. nothing before approx. 2.5krpm as the turbo spools and then it'll kick you like a donkey and take off with all the power it should ever have.


You can also run a trace on MultiECUScan of actual boost vs desired boost level so you can have an idea of whether you're getting anywhere close to the turbo response the engine is expecting.


Re the VGT solenoid you say you're replaced - I've had a number of debates on the matter and whether it's necessary or not - however I had one of these fail on my 156 JTD M-Jet and I kept getting random overboost events as it failed so had to replace. A very good friend of mine and ex-Fiat maindealer trained service tech who setup his own shop when the local Fiat dealer left town told me that these units have to be calibrated and can only be done by dealer level Fiat Examiner. True or not I don't know but he'd not lie to me and I trust him implicitly - plus when he fitted a spare part off a Doblo and said he'd calibrated it the thing never errored again ever.


I think for my money you'd have to start by suspecting EGR (although I know you say it's blanked) or the vacuum pipes. At least run the actuator test to see if you're holding a decent vacuum.

brilliant responce ,

so am i right in thinking when the engine is off , the actuator moves to the no turbo pressure possition ?

i am thinking if i use the vacuum plunger thing on it to see it move and hold vacuum that might show me something .
i cleaned the egr valve once in a parts cleaner but it again made no difference ,
but it did move
would the turbo vain ring be set in the high boost possition if the sctuator doesnt hold / leak . ? or if the vgt is leaking and allowing vacuum to bypass it cause the same issue.

my frined with the snap on scanner might be able to test it tommorrow for me
but i shall try and get multi scan ecu too

No such thing as a 'no boost' setting really so it's hard to define.

Variable geometry turbos are designed to give the response of a true twin turbo setup without having the physical headaches of having two of everything.

So they alter their characteristics to provide quick accessible low end boost and then open up to provide effective top end boost too.

This means you get very little in the way of turbo lag on a VGT setup.

Without variable geometry, i.e. a standard more traditional style turbo you would have a small turbo that would provide boost quickly, without a lot of lag, that would provide good lower at the low end but you'd soon exceed the efficient working range of the turbo as it wouldn't be able to flow enough air to supply the motor at high rpm, so you have to have a second bigger turbo to flow more air to provide continued power at higher rpms.

If memory serves and you're not holding vacuum on the turbo it should fail in the high rpm / higher boost setting, so you would experience noticable lag below around 2.5krpm before the thing would really kick in and take off.

You can if you want suck on the vacuum pipe to the turbo actuator and see it move - I would expect this to hold the vacuum fairly well although it will possibly drop off over quite a period of time.