Hi My car (octavia Vrs 2003) used to Boost at roughly 19psi and drop off to roughly 15psi. It now only boost to 11-12psi but holds it all the way and does not drop off. I was wondering would this still be a leak/split even though it does not drop or am I looking more like turbo or something equally as bad. Could it be N75 hence why its holding boost. NO codes at all

Edited 17 August, 201510 yr by stewyp1983

Are you getting any whooshy noises, running issues or smoke?

It could be the wastegate actuator. You could try a short run with N75 unplugged so it only runs off actuator pressure, it should then peak at 5psi iirc and hold a steady line, if it's below that or drops off from that it looks as though the wastegate is bleeding off boost prematurely or even constantly due to a weakened spring or perished internals.

Could be a few things but that is a cheap trial for starters. If it was an N75 issue boost would normally be more erratic.

How many miles has the turbo done?

Car has done 110,000 miles. There is no whining/siren noise from turbo. There is no smoke either. Car runs fine and idles fine. Turbo spools nice but soon as it hits 11-12 psi just holds there. It does drop to about 10psi at higher revs.

Is your boost measured at throttle body? Could it be a leak in the charge line? A weak actuator would also amount to the same kind of symptom.

My boost gauge is plumbed into the fpr. What is the charge line??

Id the actuator easy to change?

Just mean somewhere along the route from turbo through to intercooler and on to inlet manifold. The pipework down the drivers side.

Actuator change hhmmm, not really. It's straightforward but bloody awkward because of access. You can undo pipework from the top to drop the turbo, get the exhaust manifold off because a couple of bolts on the actuator are inaccessible with the manifold on. The bolts on the mani aren't too bad but there's one behind the turbo that's bloody awful to get out with a slight drop on turbo, let alone putting it back in.

Garage will be looking for around 4 hours labour I expect, although if they do it as above it shouldn't take someone with skills and ramps that long.

I'd do as much testing and checking as possible first before you dive into jobs like that to make sure it's not a big waste of time and effort.

So with the test O just done does that sound like wastegate is working or not? Was going to phone about smoke test tomorrow and got someone going to let me try there N75 valve later in week

Sorry what test?

Those are other good things to try by the way. If it turns out to be N75 I've got a worker if you need one.

Lol i posted the following but its not actually saved it. Here is what I done following your advise.....

Ok just unplugged the N75 and took the car down the dual carriageway boost went to 5psi and stayed there. I changed each gear at 37500 and every gear all way through the revs it held at 5psi and only dropped when I came off the accelerator.

Edited 17 August, 201510 yr by stewyp1983

Actuator is fine then I dare say. As the n75 was unplugged and there was no strangeness with boost it could hint at a problem with that, could be that it shows up at higher boost but definitely worth trying that spare working one. Other than that I'd be thinking about a charge line leak, could also be a MAP or some other sensor issue I suppose. If nothing shows up there it could be worth logging some numbers if you know anyone with vcds? See what intake temps and n75 and maf are up to. This would help you make sure all the sensors are doing what they're supposed to do.

Trouble is I dont know anybody with vcds. I have tried 2 other Mapped ECU's and where they run roughly 17-18psi on other cars they came from they only run 9-10psi on mine so know im deffinately losing 7-9psi somewhere

Could be a trial and error sensor thing then apart from checking for boost leaks. Like you say try the n75, try a smoke test and see how you go. Could also be worth cleaning the air intake temp sensor near throttle body, you can use carb cleaner or contact cleaner, just don't scrub or damage the copper element. I think I have an old MAP sensor which I think is fine, you can try that for postage if those attempts don't turn anything up (and I can find it!).

I have similar fight with my car, it can not reaching specified pressure. So, I tried logging car. Found 2 issue. First, car got CF, and after logging  maf, showed there is some kind of issue (results only 120, but it should be close to 160-170). Then I replaced maf, it was all better, but at high revs, there was no fuel. Then changed pump. Now, CF = 0, BUT, still unable to reach pressure. Then I put spring on actuator and it is working almost fine, but I need to find better spring, not so strong.

 

Anyway, my point is to start with blocks 031 - see fuel, block 020 - CF and 115. See where U are, before trying anything.

 

This is picture of my current state of blocks, without spring. Will log today with new one today and post results.

 

Yes fueling and maf would be another key area, but the OP isn't easily able to cary out logging.  I still think its worth trying the spare n75.  His actuator seems fine and the standard one should cope fine in these ranges, it could be weak at higher pressures but that would show up, his actuator pressure was bang on the money.  Logging would definitely help, is there anybody on here local who could help you stewy?

How much would you want for the N75 valve YellowCar? Going to try somewhere local breaking one but not having much luck

15 posted?  If I can find the MAP sensor I'll chuck that in as well.  Let me double check their whereabouts later today when I get in and I'll drop you a pm.

Ok mate cheers

Mainly want to say thanks to YellowCar popped to northampton and got N75 valve and new clamps and oh my god. My boys $#!t themselves. Just over 19psi of boost and feels like a new car. Panic at first as I thought the clutch was slipping in 3rd gear then realised it was wheels spinning. Have owner car since Feb and looks like it has been down on power all that time the poor girl.

No problem mate, glad it's sorted. Do you want a spare n75 lol?

Lol thanks but im good at the moment need window regulator though as my window has decided to just drop. There is always something with cars

What side? My drivers side has gone

My passenger side. Its quite annoying

Well cars are annoying. Boost has dropped down slowly again first to 15psi now about 12psi again. Bought new N75 valve £60 and no difference so luckily got my money back but I am thinking where I had 20psi for couple days its hopefully just made a split pipe bigger as I am sure I can hear hissing when at my max boost or popped a clamp loose where the pipes ect are old and not used to the extra pressure..... is anyone near milton keynes able to do boost leak test or smoke test. Not sure which is the best test to do

Smoke test. Ring around yellow pages and see who has got the equipment.

Cheers bud you are a star