General: v70 2.4t 51reg awd boost intemitent

[jameshaw]

hi all ive got a v70 2.4t and it pulls hard in first but some times the boost droppes off and in 3rd and 4th its worst its like the waiste gate leaks the boost sometimes but other times i get full boost i plugged it in and no faults anyone had same problems,it starts,runs and idles sweet,i thought the sensors in the boost pipe may be iffy?

[princepugh]

If you're suspecting a boost leak you should try and get a gauge or data logger hooked up so you can compare actual v expected.

Although yours is a low-blow turbo (about 0.4 bar from memory?) it probably uses all of the same control mechanisms as my T5, i.e. MAP sensor, Turbo Control Valve etc. so there's plenty of things which can play up and give you driveability symptoms but may not throw a permanent code.

[jameshaw]

i was thinkin the recirculating dump valve is leaking by because some times first gear gets full boost the when you grab second it comes in full boost breifly the you loose half the boost,i will plug a gauge on to see whats happening,also the waist gate dosent have a massive amount of spring,iam used to large deisels so not sure if its ok.

[princepugh]

Originally Posted by jameshaw

i was thinkin the recirculating dump valve is leaking by because some times first gear gets full boost the when you grab second it comes in full boost breifly the you loose half the boost,i will plug a gauge on to see whats happening,also the waist gate dosent have a massive amount of spring,iam used to large deisels so not sure if its ok.

Sounds like you've hit the boost cut, so you may have a 'pending' error logged relating to boost control, which might not show up on a standard code reader.

As you say, the fault could be any number of things including the recirc valve but it sounds more to me like you're getting into overboost territory, in which case I'd suspect the TCV, associated hoses and the wastegate/ actuator assembly as you'd be making too much boost initially, rather than losing it somewhere after the compressor.

However, as you probably know, if you lose pressure in the TCV hoses (fed by an outlet off the compressor), you are far more likely to overboost as the wastegate may not open sufficiently.

If you're investigating DIY and the 2.4T does actually run a TCV then you can easily check the condition of the TCV hoses and check the unions are tightened up properly. Only easy way to 'test' the TCV is to swap out for a known good component. Wastegate arm, recirc valve etc is a little more tricky.

[jameshaw]

i am an marine engineer and have been using my snap on ethos,no pending faults were shown i also looked under eobd ,nothing.thats why i assumed it wasnt an overboost because i would have thought it would show a fault,am waiting for a boost gauge then ile know a bit more i wll have a look at all the hoses when i get a chance its must be a simple fault iam sure!

[princepugh]

Yep, probably is something simple but these cars can be a real pain to troubleshoot! Boost gauge good starting point.

BTW the wastegate spring will probably be lightish on your your turbo as the base boost is fairly low but it should still offer some resistance and 'spring' although you'll find the actual travel is quite shortish. You can calibrate the base boost (search on here or VPCUK for procedure) but I've read the low-blow can be very sensitive to rod adjustment so you'd need to be real careful.

HTH