Holding back under wot in 5th?

[merc85]

Bit of a weird one, my 850 t5 manual is Holding back under WOT, and only boosting 10psi, she will not accelerate through it.Only seems to do it in 5th? perhaps i little in 4th not sure but can boost and hold 17psi its only 5th were the problem seems aparent.

Ive tried running mbc and Normal bcs but no difference, i have a copy walbro atm which i think is suspect, i took the pump out tonight and inspected it, the little brown rubber cap on the return was split in half, (i know) they should be able to open at the end but this one is torn up so is constantly open, although i dont think this will cause any issue or the issue i have.

When disconnecting the fuel lines from the pump the fuel did not spray out like it has done on my previous t5 which makes me think this is a fueling issue, just cant understand why it only happens in 5th! and the boost wont go higher than 10 psi. confused.

Im going to try another Air flow meter tomoz just to see if any difference. What do you peeps think?

Just one more thing to mention would a collapsed vac line from the turbo compressor housing to bcs/mbc cause this as its suspect. strange only in 5th gear

[craigoodwood]

thanks merc, mine is doing exactly the same but i couldn't of wrote it that well so i'm glad you've asked :wiggle:

[merc85]

thanks merc, mine is doing exactly the same but i couldn't of wrote it that well so i'm glad you've asked :wiggle:

Thank bud hopefully someone has the answear, i personally think its the fuel pump getting weak just dont understand why it only happens in 5th

[craigoodwood]

i presumed mine was the injectors they are the only thing not new or cleaned yet, i never imagined the pump though so the more avenue's to try the better ;)

[claymore]

I would put it down to the weather personally, I'm not even trying to live map my car at the moment.

[merc85]

Boost problem all sorted i took the Maf out and it was heavily clogged up with Oil blow back from the turbo, I put a spare air flow on a Wow the power is back :)

[craigoodwood]

nice one i've got a spare in the boot too :D

[V70 Graham]

Glad to hear it was an easy fix.....Blacky dodged the breakers lol

[AndysR]

Glad to hear you sussed it :)

[stribo]

Glad to hear it was an easy fix.....Blacky dodged the breakers lol
This time. ;)