Journeyman

My car has developed lumpy acceleration after a few long moterway drives (600+ miles). It's a Classic UK MY99 wagon

I'm pretty sure it not MAF related.
The MAF is less than a year old and the idle is fine. The Lambda is about a month old and as the car accelerates the boost pressure is normal.

I took it to my local Subaru garage today to get it investigated...

I've just picked it up and driven it home.
The hesitation is better but I've now lost 30% of my boost pressure
My boost used to be around +.98 - +1.1 now it only hits +.78

Upshot. The car feels alot slower and I'm not very happy.

The garage tested the MAF and that was fine. The Lambda is brand new.

Here's the garage synopsis:

"investigated judder/hestitation when accelerating. Carried out
breather modification to solenoid vaccum pipe to reduce air flow.
Road tested vehicle - all ok"

The proceedure consisted of putting a rubber bung in the solonoid breather pipe that narrowed the hole. One hours labour charge.

I asked if their modification was a standard procedure and the answer was yes. I cannot understand how a standard mod can reduce boost so severely.

John Roberts

Went for a drive in the scoob today.....It was Ok when I put it to bed last weekend....but today it pulses under heavy acceleration. When you put in the welly slower acceleration pulses last for some 5mph then it pulls strongly for about 10mph then goes back to a slower rate of acceleration for about 5mph and so on.
Is this what yours is doing?
I wouldn't say that mine is juddering it's more of a pulsing as if its loosing boost for a second or so and then regaining it.......perculiar indeed.

John

Neutral Cruiser

Coil packs. More likely though - boost solenoid. Are you coming up to an oil change? If it's been changed recently was it over filled (in other words above 3 quaters)

Journeyman

Yeah it's more of pulse like you said.
I've called the garage and told them I'm not happy with their resolution of the problem. I'll suggest they clean or replace the boost solenoid.
Anyone know how much a solenoid is?

Journeyman

Hmm ok. I seem to be going around in circles here.

Maybe I'm just being paranoid. The car to me feels as if its not pulling as hard since the boost pressure has been reduced with this presssure regulator modification. I've just spoken to the garage again (who have the car). They say that they have road tested it again and all seems ok.
Their senior mechanic has taken it out and the car to him feels ok.

Am I reading too much into this because I can see the boost output on the gauges is lower? Peak boost is now .7 whereas it used to be 1.0

The garage is insistant on not replacing the solenoid as they say this is a common mod that they do to classics and does not effect power...

I've still not heard from anyone on here as to whether they've come across this mod?

buzzard

various size restrictors can be fitted into the boost control system but these are usually installed in the actuator line. the restrictor simply damps the operation of the wastegate, in turn affecting boost characteristics.

as you now have lower boost the car cant pull as hard as it did and the 'pulsing sensation' is only being masked.

explain to your dealer that you are not happy with the poor performance and lowered boost and perhaps they could explain to you 'exactly' what mod has been carried out.

while replacement is 9/10 times unnecessary, the boost solenoid is the usual cause and a simple flushing with cleaner fluid will generally suffice, though there are other considerations.

Journeyman

Thanks for the info.