95 855T5 won't hold boost.

z31jaime · Post by **z31jaime** » 01 Dec 2013, 08:39

this is going to be long, sorry, but I want to try and cover everything that has already been tested and checked....

ok, so for over a year now my car has been running on lower boost than what my Green tune is meant for.

Car was running fine at 14psi ish with OEM ecu and MBC. Then suddenly 1 day it was stuck at 10psi.

Ordered ARD green tune.

While doing the tune I decided to strip down the car and do a total build on it (external)
new PCV system.
3" Dp 3" exhaust
NA cams
NA throttle body
16T upgrade (fresh rebuild)
Snabb spacer
samco and snabb silicones all around.
white injectors
new fuel pump
new EGR
Bosch plugs
kingsborn wires.

still wouldn't boost past 10 psi..even on the green tune.

well after a few months I found a leak in the snabb spacer so I assumed that was my boost leak. I removed it and still had low PSI.

so I swapped my 16T for another 15G... still no more than 10 psi. (thats 3 turbos)

swapped out the waste gate actuator... still nothing. Brand new CBV.... nothing.

Multiple MBC, BCS, and now I'm running an AEM true boost EBC and still can't get it over 10psi

Then FCP did the "recall" on the leaking PCV system and sent me a BNIB Volvo PCV kit... still no more than 10psi.

Vac in park is -17
Vac when in Drive but not moving is -13ish

I removed all the silicone and went back to OEM rubber intercooler lines and still got nothing. placed everything back and made a DIY pressure tester.

Turbo to intercooler holds 20psi no problems....

intercooler to TB holds 20 PSI no problems.

Capped intercooler weep hole....tested full system to 22psi.... no leaks.

Tech suggested I do a short run with the WG line disconnected to see if I build boost.... slight improvement to 12psi but thats it. the car won't build up any more than 12psi even with the WG disconnected.

now, whats strange is that the car will build more/better boost at half or 1/4 throttle than at WOT. If im on the highway and use the cruise control to accelerate it will his 16.5 psi and hold. but the moment I touch the gas I drop PSI.

Tech put the green tune in his car and it hit 18psi on the highway no problem. so its not the tune

Adjusted my timing to specs suggested on ARD site still nothing....

After 5 pages of talking to people On VS, yesterday I completely stripped the car down to the turbo.
CBV removed, wastegage actuator removed, all intercooler lines removed, and vac lines removed, I spent the afternoon going 1 by one and re doing ever single one and testing everything as I went..... Still not boosting like it should. its actually all over the place now.... WOT 13psi, let off, WOT again 8psi, WOT 13 psi then bleeding off, WOT 11 psi...wot 16psi and bleeding off...... so whatever I did yesterday changed something, but now the car is just all over the map.

At this point the only thing I see as an option is that the Waste gate itself... inside the turbo isn't sealing correctly in the hotside.....or something in the PCV under the intake manifold....only 2 things I haven't recently checked.......................

what do you guys think?

Post by **jblackburn** » 02 Dec 2013, 09:09

Is there any oil all over anything at the bottom of the engine from the PCV area? Any positive pressure?

If you've changed the turbo multiple times, I doubt it's the wastegate.

If you have a car that you could readily swap a few known good parts with, try:
-MAF sensor.
-MAP [actually barometric pressure] sensor (not sure if a 95 has one or not!)
-Throttle position sensor (may sound weird, but could do it).

z31jaime · Post by **z31jaime** » 02 Dec 2013, 20:22

Thanks for the Reply. I'll look into a different MAF, i do have a 96 854 t5 than I can mix and match parts from.

z31jaime · Post by **z31jaime** » 03 Dec 2013, 13:59

BTW I didn't have any oil leaks until about 2 weeks ago. I have started to leak from what looks like the front crank seal (rear main seal was replaced before I got the car). And has new cam seals. New oil cooler lines, only old seal is that one so it figures it would fail next.

Car has a BNIB TPS.

I was thinking..... front 02? I know this tune runs a little lean compared to the speed tuning which would = higher EGTs, if the front O2 is burning up it could not be reading correctly......

Post by **jblackburn** » 03 Dec 2013, 14:07

For some reason I'd thought you'd tackled that.

That may be a new first on the list of things to try.

Post by **matthew1** » 03 Dec 2013, 14:20

The car would tend to go rich if it's detecting (or thinks it's detecting) a failing front O2 sensor. This is why poor MPG is hallmark of a failing front sensor.

Wish I could help more on this one, it's a stumper. That's my $.02.

z31jaime · Post by **z31jaime** » 08 Dec 2013, 19:27

WELL I do have Crappy MPG according to the other Volvo guys I hand out with. For me 14MPG is a GOOD day. recently I started to get 20MPG.... don't know why...

chax · Post by **chax** » 08 Dec 2013, 19:57

FWIW, I don't suppose the CE light is on. I've read that, if it's on, the ECU WON'T allow boost over 7psi.

My '94 850 has been like this for a while. A couple months ago, though, that changed: it was suddenly OVERboosting, with no mechanical changes whatsoever. Then, after I brought it in for some work, it's not boosting past 7psi again.

Post by **bmdubya1198** » 17 Apr 2019, 12:50

Sorry for reviving an old thread, but was this issue ever solved? I'm also having a strange low boost problem in my M56 swapped 2000 V70R. 1st gear won't go over 5-6 PSI and 2nd-5th only peak at about 8.5 PSI. Other times, especially if I start out slowly, toward the higher RPM range in first gear my boost gauge shoots into vacuum and the car barely moves. It doesn't make any sense. I've swapped the TCV multiple times, MAF with a known good unit, I pressure tested the intercooler piping, checked all vacuum lines, replaced the CBV, checked the wastegate pressure, etc. and it still won't boost past 8 PSI. I just don't get it. According to Rob at Hilton Tuning, in the logs I viewed on VIDA, the ECU is requesting boost from the TCV, but clearly that boost isn't holding.

I have a stage 1 tune from Hilton on this car, but I still have the issue when I flashed back the stock tune. I have codes on VIDA for the brake pedal position sensor, clutch pedal position sensor (not currently attached, however I was told that this part was unnecessary and does not affect boost on Motronic 7), and two strange codes for MIL signal too low (ECM-6B00) and ETS light signal too low (ECM-6300).

Post by **matthew1** » 22 Apr 2019, 12:06

Any word from Hilton Tuning? That's where I'd start.