Boost Spiking??

[0151rhys]

Hi All, I have recently purchased a c70 t5 which supposedly had been remapped. Anyway this weekend I changed the PCV unit and pipework, replaced the turbo vacuum lines and it has had a full service oil,plugs,rotor arm and cap etc. Prior to this it would occasionally pull aggressively and other times not. Now it boost all the time and feels good, however I noticed the boost gauge is now hitting almost 1.5 bar and dropping to about 0.9 bar. Does any one have any ideas what could be causing this. In addition to the above work I removed the nasty badly modified inlet pipe and fitted an original between the air box and turbo. Could some on assist me and tell me which connection go where so I can ensure I am correct.

[0151rhys]

Quick video I recorded of the issue:

https://youtu.be/VPGq2Skr5LM

[martin_r_smith]

Try doing another video but in say 4th gear so the boosts is held far a while. That looks to me like a fairly normal spike then the boost drops off because there isn't enough load to sustain it.

[0151rhys]

Hi Martin, thank you for the reply, it is an automatic if that makes any differences?

[PNuT]

Can you select a high gear manually on your box? like the W mode?

You ideally need to see what the boost is doing right through the rev range at wide open throttle.....

[0151rhys]

I will do this on my way to work tomorrow. What does the w do exactly?, I guessed it changes gear earlier to prevent wheel spin in the ice.

[PNuT]

Users higher gears from the start.... 3 and 4 ithink

[0151rhys]

Went on a short run tonight but didn't really hit a stretch of road to get any speed.with w on I put my foot down and it was struggling, and the boost pressure stayed at 0.5 bar. How ever when I did the same but pressed the throttle harder it kicked down and went straight up to 1.5 bar and stayed their longer than the usual second so I let off the throttle.

[PNuT]

Originally Posted by 0151rhys

Went on a short run tonight but didn't really hit a stretch of road to get any speed.with w on I put my foot down and it was struggling, and the boost pressure stayed at 0.5 bar. How ever when I did the same but pressed the throttle harder it kicked down and went straight up to 1.5 bar and stayed their longer than the usual second so I let off the throttle.

It's quite difficult on normal roads to see how these things are boosting!

without knowing what revs you are doing as well as boost its difficult to tell

a mapped car should boost to around 7-10 psi up until around 4000rpm & then up to around 16-19psi & hold it for as long as the turbo can manage

obviously it will vary from map to map & car to car!

1.5bar is likely a little high! & maybe someone has adjusted the wastegate actuator to solve another problem a little too much

[0151rhys]

Today I drove to work and placed it in W mode on the motorway, boost stayed at 0.5bar untill around 3500-4000 rpm when it creeped up to about 0.7bar, I could not go much further due to the stretch of road and the fact I was already doing 120. What pressure should I not be seeing to avoid bent rods or any other problems.