sudden loss of boost?

[Anth1223331]

I've been looking around and can't really find anything similar to my problem. I've got a mk4 gti with a ecs tip and forge dv and I used to peak about 12 on a good day and hold about 10psi. Then one day all of a sudden I just couldnt get over 7psi. It's been like this for about 2 weeks and still can't get over 7psi. I've checked my dv and a couple vacuum lines for and leaks but can't find anything. Could this be a symptom of a faulty n75? Or just a boost leak somewhere I haven't checked?
Thanks

[elcono]

Same here. Be interesting to see what it turns out to be

Changed my DV out for a 710n and a new intake and it now feels like I'm on half boost

Going to try and replace any hoses that look split this weekend

[Anth1223331]

Yeah I've had to replace the vacuum line to the fuel pressure regulator and the one onto the dv. I've done the pcv delete and have a catch can so I cant be loosing anything through there. Maybe your dv isn't holding pressure and Is leaking? I've got the 007p with the weakest spring, green I think, and one shim. If anyone had any suggestions about that that would be great too.

[Anth1223331]

Just a quick little update, made a boost leak tester from parts I got from bunnings and I only found that the n75 wasn't very tight in the tip and air was leaking past, but that shouldn't affect boost at all should it? I pressurised it to about 12 psi and couldn't find any leaks in the actual system but tightened everything anyway. I doubt this has to do with anything but I think the fuel might be abit old cause I was running on empty and had to fill up at a dodgy servo and got 98 for like 30 cents cheaper than everywhere else.

[h100vw]

When the N75 isn't working, either the valve itself or the wiring. It fails open and you will be running actuator pressure only.

This pretty much sounds like it is the case. If you clamp the pipe to the actuator, it should boost madly.

Gavin

[Anth1223331]

Okay thanks heaps I'll try it tomorrow. I've already had to buy a new plug for the n75 and solder it in because when I bought the car, some how the wires had been cut at the plug. If I do end up having to replace the whole unit, would you recommend an oem replacement or a n75j or any kind of race type valve? Thanks again for the info

[h100vw]

Just get the original. I have a couple of spares if you want one. What did you do with the one that was on there before the J?

The tune's written for the stock Valve.

Gavin

[Anth1223331]

I still have the stock valve in the car but just had to get a new plug, maybe that's acting up a bit. Yeah I'll test it tomorrow and if worst comes to worst I'll try and figure out how to pm you for a spare haha thanks heaps.

[Anth1223331]

I was just searching the net again, and someone was talking about a barometric sensor that had come loose in its casing and had effected his boost. Could this be what I am experiencing aswell? I'll check everything again today at some point.

[Anth1223331]

Wow... Okay that was kinda amazing. Just clamped off the line to the actuator and went for a drive... What an improvement like holy ****. I think I got to about 17 psi but I wasn't gunning it fully just incase something blows up.. Hehe. So why don't people just clamp it and rejoice in all that untapped boost? I'm guessing it's dangerous and unhealthy for the turbo? Thanks Gavin for the help, probably be looking for a new n75 now then haha

[h100vw]

Wow... Okay that was kinda amazing. Just clamped off the line to the actuator and went for a drive... What an improvement like holy ****. I think I got to about 17 psi but I wasn't gunning it fully just incase something blows up.. Hehe. So why don't people just clamp it and rejoice in all that untapped boost? I'm guessing it's dangerous and unhealthy for the turbo? Thanks Gavin for the help, probably be looking for a new n75 now then haha

That's just a test, I can promise a sad face if you leave it like that. Before buying another N75 you need to work out if its the valve or the wiring.

Gavin

[Anth1223331]

Yeah i took the clamp off straight after i finished my little test run. I had a look at the wiring and it seems okay, my soldering isn't the best but it all appears connected and i wrapped them in electrical tape so it shouldn't short. So just for my knowledge, what did clamping that line do? Pretty much just stop the ecu from controlling the actuator and letting the turbo run as hard as it can? Will buying a new n75 just bring it back up to approx 10-12psi? Sorry if im being a nub, still new to this

Edit: I stated the engine and let it idle and tested the n75 plug with a multi meter and got like 7.6 volts. Is this okay or is it off?

[h100vw]

google how an actuator works. Always better if you see it yourself first hand. Don't buy the N75 first. You need to check the wiring. Possibly with the ignition on, you will see voltage across the N75 plug. Never had to check this with a meter as I can use VCDS to do an output test of the N75 which makes it click once a second. Proving it works.

Gavin

[Anth1223331]

Well yeah I measured about 7.6 volts across the plug with the engine running. Is this about right? I read some where that it's ment to be 12v?

[elcono]

Spooky......

I also went to bunnings and made a boost leak tester. Used a pvc cap and a tyre valve insert sealed with epoxy

I am in the opposite situation. Pumping air through I get about 3-4 psi. I've checked everything on the TIP, pancake pipe, used soap suds but it just wont hold any pressure. Oil cap off and the pvc cap is on the inlet just before the maf

Any ideas?