Boost intermitent,

[Joel93]

Hi iv realised that after driving my impreza for 30 mins or so after a few hard accelerations the boost drops from 14psi to around 7psi. From what I've read this is limp mode but there is no CEL on, car has a cat back exhaust a panel filter and remap. Pulls really nice until boost drops off, after turning car on and off for 5 mins bost I'd back up to normal? Any ideas? Thanks 

[DaveRAC]

do you have an aftermarket boost controller fitted to vehicle if so my be worth dropping the max boost down a tad i had the same issue when it hit peak boost it shuts fuel off for a second and then runs normal.

[Joel93]

No, no boost controller, iv just got a boost gauge. It won't return to normal until I turn the car off and back on. 

[DaveRAC]

what impreza model have you got? how long ago did you get the map and what have you changed on the car most recently?

[Joel93]

It's a 2004 wrx and I only had the car on the road a week, map was carried out about 8 years ago, there must be somthing bost related tripping it into low boost setting because its only happening after a few hard accelerations 

[Linx]

Do you have super unleaded in it?

[Joel93]

Yes I put tesco moment in it although I'm not sure the previous owner did possibly still on some of his fuel. Can that make it lower the boost? 

[savage bulldogs]

Yes ,Lower octane fuel can cause it to lean off under boost,  which in turn might cause limp mode .

Have you got any proof it's been mapped ? 

As 14 psi (just under 1 bar) is a low boost target for a mapped car ,admittedly that could just be a inaccurate boost gauge .Most mapped cars will have the boost target upped to 1.2 to 1.5 bar pending on mods and engine condition .

If you dont have proof of a remap standard  boost target would be between 0.6 bar and 0.8 bar , you'd have to Google your model and year specific oe boost target. 

So if you're hitting 0.9 bar on a standard map boost target ,it could well be overboosting and that might cause it to go into limp mode .

Although you haven't got a cel light , I'd suggest to get the codes read while it's in possible limp mode . As it might log a minor fault on the ECU but not show a cel, due to it resetting when you restart the car .

[DaveRAC]

it could be due to the map that it needs to run only on high octane fuel too

[Joel93]

I have proof of a rolling road running 270bhp it feels fast enuf, I'll keep trialing the car and see exactly what coursing the limp mode. 

[Joel93]

My boost gauge is a cheap eBay one is it possible it is reading low by a couple of psi? It does seam a car of my remap should be running 16 psi ish. 

[DaveRAC]

at least does it have upgraded turbo at all ? i know the standard ones can handle up to 320bhp 

[Joel93]

No it just has a td04, drove 180 miles  today and still boosting fine, parked car up and when to the beach.

Next drive I put my food down 1st gear boosting nice, 2nd gear boost to 14-15 psi, 3rd gear boost to 15psi then dropped back down to 7psi it then stayed like this until I turn the car off and back on. It seams to droop off as I hit 5000rpm ish. Is this over boost? After trialing out it can pull boost all day in 1st and 2nd but a hard pull in 3rd upsets it.