S40 t4 twin piston dump valve open at idle. Boost drop.

[Volvulate]

Hello, I bought djx11b volvo s40, he has some threads on here. Ive slowly but surely worked through the volvo, fixing bit n bobs, such as yesterday I checked the vacuum check valves and one was ****ed. But it hasnt made any change. Boost drops at 4500rpm, not sudden or our, just decreases smoothly, but enough to think "wtf!!". Also ive noticed my dump valve is wide open on idle and shuts a lil bit on low load, and shuts completley when ya open throttle. But after my research (altho sone people say it should be open) that it shouldnt be open on idle, and that the single piston ones should be open on idle. But twin piston should only open to vent? Is that right? Why is mine open? Could I maybe put a check valve to stop vacuum on dump valve?

[m1tch1987]

What blow off valve is it?

[Volvulate]

Bailey twin piston dv26 I believe

[Volvulate]

Also I when I hoof it, I get 1.3-1.4 bar of boost from really low revs but at 4500 they fade off to about 0.7-0.8. Which sucks, as its quick as it is, but it wud be a beast if it held the boost.

[m1tch1987]

I guess you have upgraded the wastagate actuator to hold the higher boost already yeah?

[Volvulate]

Pass. I think djx11b said something along the lines of you need a manual boost controller, which I do have, but he said it was boosting to the line before I got it...

[djx11b]

no manual boost controller needed as the remap i got the ecu controls the extra boost

the car was running the standard volvo actuator when i sold it as the uprated one i got made it overboost but this may need replaced now or upgraded. You canget a 0.3 bar one from japan that would work to do this

when i had the boost issue before the air filter was choking the car have you removed this and ran the car ?

ALso most remaps will start to tail off when you hitting the end of the rev range to protect the car a little. Might be worth tighten the actuator arm a turn or two ...

[960kg]

Originally Posted by Volvulate

Pass. I think djx11b said something along the lines of you need a manual boost controller, which I do have, but he said it was boosting to the line before I got it...

Originally Posted by djx11b

no manual boost controller needed as the remap i got the ecu controls the extra boost

the car was running the standard volvo actuator when i sold it as the uprated one i got made it overboost but this may need replaced now or upgraded. You canget a 0.3 bar one from japan that would work to do this

when i had the boost issue before the air filter was choking the car have you removed this and ran the car ?

ALso most remaps will start to tail off when you hitting the end of the rev range to protect the car a little. Might be worth tighten the actuator arm a turn or two ...

A remap does not control the boost it just allows a higher boost as the protection has been removed.

You can set the boost with the actuator or MBC if the ECU has removed the limit.

Most remaps do not tail off, it is where the actuator or MBC is set and mainly the type of vacuum hose you use which may be crap (silicon) as they pulsate or expand and compress which alters the boost pressure. Just use again the proper Volvo hose £9 for a metre which is sufficient.

To be honest, all this boy racer filters and noisy extras to the intake only lose power but make a noise as if you are really travelling ,the sad thing is that your not.

Best to remove all that is not standard and replace as per Volvo and it will fly....full stop.

All the standard intake gismos are good for up to 250 bhp before you need to upgrade.

[deathrider311271]

a dv26 is a single piston dump valve, the dv36 is twin piston.

[mitchyboy01]

Hi,

On a 14T turbo boost will drop at high revs. At low revs the engine isn't flowing as much air so the small turbo will produce a lot of boost pressure as it is trying to 'cram' the air in faster than the engine can consume it. At higher revs the engine is consuming all the air the small 14T can throw at it, hence the boost pressure drops.

My car hits 1.5bar at 3.5K but by the redline it is under a bar which is normal. If you had a huge turbo which could produce a lot more airflow with lower IAT's boost wouldn't drop.

DJX is right, a remap does control boost if you are using the standard Volvo BCS. A remap doesn't remove a boost limit, it resets it but still controls boost to a preset limit otherwise your engine would pop! Hence if using a MBC caution is key, as essentially you are overriding one of the ECU's safety parameters. Also as DJX said, at prolonged high boost the IAT's will steadily rise (due to small turbo, high boost heating the air) and the ECU will lower boost to protect the car from det. Hence why many fit larger intercoolers.

My advice is remove the dumpvalve and chuck it in the bin. They are a load of cr@p.