Possible boost problem - Alfa Romeo Forum
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(Post Link) post #1 of 6 Old 12-03-12 Thread Starter
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Possible boost problem

I have a small problem with the 147 that i want to sort as i don't want it turning into a big one if you see what i mean.
The issue is this, when accelerating slowly on part thorottle (like you tend to in town) particularly in 1st and 2nd when the revs reach 2500-3000 i get a slight hesitancy almost like it's missing a bit accompanied by a sort of chuff chuff noise (thats a bad description i know) like boost/vacuum being vented almost like a dump valve. This can be made to continue if you leave the throttle position alone, but if you continue through or boot it, it stops after a few chuffs... also if you back off it stops aswell? At the moment it's completely driveable and doesn't lack power as far as i can tell either at low revs or high so this would suggest the VNT is working right?

Any suggestions:
My thoughts are EGR sticking (dont really think so as i cleaned it last year and i dont think the symptoms are right)

or split VNT hose/s, i think this rev range is where actuator is in the middle of it's travel right? I looked at the actuating rod and it does move on revving the engine but not far?
Anyone got a detailed how to with pics, on changing these on the 147 JTDm, i know the 156 is simple but apparently the 147 is a bit more of a pain, typically.

Internal turbo issue, don't really want to think about that.....
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The diesel makes a boost woosh noise anyway. Mine did with standard pipes and does still with hard pipes. As for the flat spot. Sounds like a standard alfa 1.9 map to me. They were known for having flat spots. Split vnt pipes will give poor boost at low revs. Split turbo hose will give black smoke out the back. Broken VNT will give an overboost on hard throttle and put the car in safe mode. Clogged actuator will give the same overboost fault.
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(Post Link) post #3 of 6 Old 12-03-12 Thread Starter
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Thanks for that, all seems to make sense to me, however i've had the car two years and the behaviour is definately new. I suppose it's the sound that is concerning, a bit of hesitancy i think i could live with short term. It may well be the map, but noise is... well strange really.
A better description would be the sort of sound a steam engine would make when pulling away from the station, not as loud of course but a sort of pressure release shhh-shhh-shhh sound.... If i idn't know better i'd say it was something rubbing in the wheelarch maybe a warped disk, but it's only at certain revs not road speed.
Maybe with the price of diesel going up i'm just driving more conservatively re acceleration these days.
Could another possible candidate be prolonged running on tescos fuel, they keep doing 5-10p off a litre and i can't resist. Would a couple of tanks of ultimate or v-power do the job?
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Had exact same noise and symptoms on my 156, egr is knackered which is why I descovered the previous owner had blanked it off!
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I have run my car off Tesco fue for the last year and my car loves the stuff, I have noticed a slight loss in power using other fuels before I changed my fuel filter, maybe tesco's is thinner or somthing......
I have a noise somtimes when i change gear that sounds like a dump valve but i dont think its anything to worry about, I always hear lots of noises that I havent heard before and mostly when driving past some houses with my window down!

Somtimes noises are like the guy with the perfect lawn, it was mowed with perfect lines and great grass and everyone loved it, but oneday he led down to take a look at his grass close up and saw moss and insects and weeds....... there was nothing wrong with his lawn he was just looking to close (well that just shows how boored I am today!)
If I get any strange noises I just turn the music up
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(Post Link) post #6 of 6 Old 12-03-12 Thread Starter
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My EGR was knackerd last year, warning light as well (not got that this time but could be a different mode of failure i suppose) 30min job to take off and clean, so i guess i'll start there. The noise could well be the valve opening and closing partially, or trying to and diverting gasses back and forth in and out of the inlet until it gets past the rev range in question. Anyone know the value at which it opens/closes, this depends on throttle opening/load etc i guess, is it a binary thing i.e. open or closed or is it gradual?
Top advice re. radio i think i'll do that if the EGR isn't to blame, diesel engine clatter's not much to write home about anyway is it...... compared to a V6
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