Not boosting properly

[Negative Creep]

I have a bit of an odd problem, wonder if anyone can help with it. Basically, car drives fine under 3000rpm but sometimes when going on boost, the engine revs wildly, drops back and then starts boosting properly. Other times however, it boosts as normal. The fact it only happens some of the time leads me to believe it isn't a boost leak, and I can't hear or feel anything amiss. It does seem more likely to do it up hills, or if you jam the pedal suddenly, which makes me think it may be the clutch. However, it just feels more like and electrical problem, as the car doesn't lurch or clunk at all when it happens. I can still hear the turbo spooling up at what appears to be the normal rate, and the wastegate noise and boost gauge don't act erratically. Any help or ideas appreciated.

Car is an Alfa 155 Q4, which is essentially the same engine and turbo as the 'Grale 16v

[ylee coyote]

Sorry mate ,sounds terminal
I will take it off you hands for a fiver ....

Seriously tho it sound as if you might have a sticky wastegate
either the actuator or on the turbo itself or maybe an erratic leak

I would have a good poke about the actuator /actuator rod /tubing going to it
your problem could be as simple as that ....

[Pigeon]

If the engine revs are rising without a corresponding increase in road speed it's got to be clutch slip.

[Negative Creep]

If the clutch was slipping wouldn't it happen all the time? Sometimes its fine for a journey, then does it all the way home. Also, it only appears to do it when the engine is boosting (i.e. above 3000rpm.) Is there an easy way to test it on a 4wd car?

[ACEparts_com]

Negative Creep said:

If the clutch was slipping wouldn't it happen all the time? Sometimes its fine for a journey, then does it all the way home. Also, it only appears to do it when the engine is boosting (i.e. above 3000rpm.) Is there an easy way to test it on a 4wd car?

Well it would do it when boosting as that's when you're getting maximum torque. Clutch.

[Pigeon]

Negative Creep said:

If the clutch was slipping wouldn't it happen all the time? Sometimes its fine for a journey, then does it all the way home.

The hotter it is the more likely it is to slip. My Morris Minor was exactly the same after I "did things" to it... driving hard (more heat from the engine), changing gear a lot (more heat from friction in the clutch), and hot weather would all make it more likely to slip. So it would do things like be fine on the way in to work on a summer morning, then at the end of a hot day start slipping the clutch half way back home.

Negative Creep said:

Also, it only appears to do it when the engine is boosting (i.e. above 3000rpm.) Is there an easy way to test it on a 4wd car?

There are only two points between the engine and the road where slip can occur without major banging, grinding and breakage - the tyres and the clutch. If the engine revs are rising without a corresponding increase in road speed, and the wheels aren't spinning, and nothing has gone bang, it's got to be the clutch...

A viscous coupling in a 4wd drivetrain won't suddenly lose its couple unless the fluid boils, which will blow seals and likely not work again.

[evokat]

I have had this problem before ( i think) I have an grale 16v Evo. On my third one now.
It could be
bent actuator rod causing it to stick ( weird I know but happened to mine)
base boost incorrectly set
bad chip
incorrect fuelling

or the most likely a bad electrical connection somewhere, maybe TPS?


or a combination of the above

Take it someone that knows....I have learnt the hard way that it is to always best to trust a specialist that is reliable and honest.
Where are you based?

[Mr2Mike]

Everything mentioned points to the clutch, happening as the turbo spools up, going up hills etc.. If the engine rev wildly without a corresponding increase in road speed it's either a traction problem or clutch slip, and the first should be obvious!

Does it happen more easily in higher gears?

[FWDRacer]

Put it in 4th and try and pull away. If the Engine spools up with no forward motion your clutch is toast.