Engine: T5/R - Boost spike on T5 Auto

dannyboy_turbo · Oct 19th, 2010, 19:41

A big hello to everybody!
i'm a bit of a lurker round here and despite searching this site and many others i found no solutions to my problem.

basically i've got a mbc on my v70 t5 auto (pre me7) and as the car changes gears and ONLY just as the box shifts i'm getting bad boost spike then it goes back to normal once in the next gear. apart from that the boost levels are all fine the rest of the time. i've turned the mbc down to 10.5 - 11.5psi to keep the spike as close to 14psi as possible for obvious reasons.

so far i suspect....

standard dump valve being worn.
mbc being faulty
or vac lines to mbc being too long (i'm trying this tomorrow)

any other suggestions would be fab!
cheers
DAN

Merc85 · Oct 19th, 2010, 23:23

Hi, I'm get bad over boost if i stay in the same gear ie top or 4th, and press the throttle. she will boost 16psi then cut out.

If i floor it, she will boost 14 psi, and then the boost lowers to 11psi and doesn't cut out.

I cant under stand why in a higher gear the car over boosts.... But as soon as i Floor it WOT she runs fine.

850 T5 estate mbc, de-cat lowered 40mm R front Bumper Auto.

New vac lines, new pcv system, stage 1 tune

Oct 19th, 2010, 19:41	#1
dannyboy_turbo Member Last Online: Jun 4th, 2020 14:21 Join Date: Nov 2007 Location: Newcastle Upon Tyne View Photos By: dannyboy_turbo	Boost spike on T5 Auto A big hello to everybody! i'm a bit of a lurker round here and despite searching this site and many others i found no solutions to my problem. basically i've got a mbc on my v70 t5 auto (pre me7) and as the car changes gears and ONLY just as the box shifts i'm getting bad boost spike then it goes back to normal once in the next gear. apart from that the boost levels are all fine the rest of the time. i've turned the mbc down to 10.5 - 11.5psi to keep the spike as close to 14psi as possible for obvious reasons. so far i suspect.... standard dump valve being worn. mbc being faulty or vac lines to mbc being too long (i'm trying this tomorrow) any other suggestions would be fab! cheers DAN __________________ 2006 Volvo V70 T5 ex-plod monstertruck! now with MTE stage 1 :-) Last edited by dannyboy_turbo; Oct 19th, 2010 at 20:28.

Oct 19th, 2010, 23:23	#2
Merc85 Premier Member Last Online: Apr 19th, 2024 12:58 Join Date: Dec 2009 Location: Harwich	Over boost Hi, I'm get bad over boost if i stay in the same gear ie top or 4th, and press the throttle. she will boost 16psi then cut out. If i floor it, she will boost 14 psi, and then the boost lowers to 11psi and doesn't cut out. I cant under stand why in a higher gear the car over boosts.... But as soon as i Floor it WOT she runs fine. 850 T5 estate mbc, de-cat lowered 40mm R front Bumper Auto. New vac lines, new pcv system, stage 1 tune __________________ HLM304, Forge unos 17.5psi at 3.8 bar, 18t, Me7 Manifold, Blues, Walbro, De-cat, Ported n Polished Head, 3" Dp stainlesss exhaust, Carbon Air intake, Polly Bushed thoughout.

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