940 Lpt not making or barely making any boost

[SalvadorP]

Hello everyone.

So, I just installed a boost gauge to check what's up and the car is barely making 2 psi, as seen in the video.
I installed the gauge into the cruise control vacuum line.

How should I proceed to troubleshoot this?

 

[dl242gt]

Start by checking the wastegate preload. If it has an adjustable rod on the wastegate you can tighten that up a bit. However, the LPT is only supposed to make about 3psi or so. You could change the wastegate actuator to an FT version or other pressure ratings if you shop around like at ATP Turbo or ebay.

 

[SalvadorP]

Start by checking the wastegate preload. If it has an adjustable rod on the wastegate you can tighten that up a bit. However, the LPT is only supposed to make about 3psi or so. You could change the wastegate actuator to an FT version or other pressure ratings if you shop around like at ATP Turbo or ebay.

Thanks for the reply. No, the lpt wastegate is fixed rod lenght. I think the default pressure of the lpt is between 4 and 5. I'm not even making 2

 

[dl242gt]

One of the things that can happen is the puck inside the turbo can break or crack letting exhaust past and not making boost. Also a clogged catalytic converter will prevent boost. You can test the exhaust back pressure before the converter. There is usually a test port in the front pipe. It should only have about 1.5psi back pressure.

 

[SalvadorP]

One of the things that can happen is the puck inside the turbo can break or crack letting exhaust past and not making boost. Also a clogged catalytic converter will prevent boost. You can test the exhaust back pressure before the converter. There is usually a test port in the front pipe. It should only have about 1.5psi back pressure.

I know what you mean. A faulty puck could be the culprit. I have already disassembled the bypass valve and the membrane looks brand new. The wastegate is not stuck, since I could move it by hand. And the membrane of the wastegate is certainly not torn, otherwise I would have the opposite issue.
Now, the catalytic backpressure. My catalyst is due for replacement and I do have some exhaust issues like leaks on all silencers and catalyst lol
I did not know about the possibility of testing backpressure. I will look into it right away. Thanks

 

[MasterBlaster]

I installed the gauge into the cruise control vacuum line.

Measuring manifold boost pressure by tapping into an unrelated vacuum line?
Wouldn't it be more logical to measure at an intake manifold fitting, or somewhere else along the turbo-hose-intercooler-hose-intake path? Or am I missing something?

 

[SalvadorP]

I have switched to the manifold to bypass line. Same reading. Switched guage, same reading.
Have since tried a mbc on a significantly higher boost, same reading.
Disconnected wastegate and although I have not pushed the car significantly, I got the same reading.

 

[SalvadorP]

Thread update.

I have a 940 wagon b230fk, manual. 510.000km, all maintenance/repairs done at volvo dealership until I got it from the original owner 2 years ago. Need help diagnosing low boost pressure.

I will describe the situation in topics:
- Installed boost gauge and it barely read 2psi. Don't remember vacuum value.
- Installed another boost gauge. Same boost reading. Vacuum at idle = 11psi
- Checked condition of the bypass valve. Bypass Membrane looks completely fine.
- Checked condition of wastegate actuator arm. Wastegate arm is assembled and moving.
- Looked for vaccum or boost leaks with smoke test and brake cleaner. No leaks found. Brake boost check valve has some play. Fastened all clamps.
- Checked Turbo from the intake side. No play on turbo shaft. Blades spin freely and noiselessly.
- Installed MBC and increased pressure gradually but significantly 2 times. Same boost reading after pressure increase.
-Disconnected wategate hose. Ran the car for a short time and cautious manner. Same boost reading

Observations:
- All engine gaskets were changed not almost 4 years ago and 38k km ago. Visually they look fine. Brake cleaner on intake did not change rpm.
- Compression test 13 months ago had Cyl #1 - 161, Cyl #2 - 160, Cyl #3 - 162, Cyl #4 - 164
- Catalytic converter needs to be changed and might be clogged. It was changed 190k km ago in 2007 (oem)
- Car has a slight misfire at idle that I couldn't yet diagnose.
- Almost all vaccum hoses have been changed recently.

To do list:
- Compression test.
- Vacuum test.
- Exhaust backpressure test.
- Check intercooler for leaks. Drain it???

Any ideas are welcomed. Thank you.

 

[hessam69]

This might be your problem

B230Fk swap, no power.

Hi yall! I swaped an b230fk engine into my 740 (b200e) I am using an completely new wiring loom for 2.4, new lambda sensor, new TDC sensor, new sparks and Cables, fresh oil etc. But i lack power! (I think) It feels like the turbo does nothing, Already modified the turbo actuator to get...

www.turbobricks.com

 

[SalvadorP]

You mean that the puck isn't ever fully closing and that i'm exhausting nearly all boost? Or is there a physical defect that I missed.
If the former, yes, that's one possibility. But that involves taking the turbo off, so I wanna do a few tests first.

 

[Janspeed]

2 physical defects are typical on high mileage B230FK:

- big cracks in the hot side of the Mitsubishi td04-13C turbo. Waste gate side. It means the WG valve is never fully closed which is needed to start making boost. This never sets a check engine light because at no point exhaust gas is leaking from the exhaust.
No idea if it is fixable. You need to closely inspect the hotside which requires the turbo to be removed.
- cracks on the underside of the exhaust manifold. Those cracks leak exhaust gasses away that are needed to spool up the turbo. This might set a check engine light.
Those cracks can be fixed by hard-soldering.

- the tdo4-13C is also known for the CBV membrane (under the chrome 3bolt cover) to fail/leak. (it is basically a short circuit on the boost side.)

 

[Janspeed]

hard-soldering = brazing?? not sure.

BTW stock boost should be about 0,3-0,35bar (= 5psi?) and the turbo should start spooling from as low as 1700-1800rpm , all boost in at 2250rpm

 

[SalvadorP]

2 physical defects are typical on high mileage B230FK:

- big cracks in the hot side of the Mitsubishi td04-13C turbo. Waste gate side. It means the WG valve is never fully closed which is needed to start making boost. This never sets a check engine light because at no point exhaust gas is leaking from the exhaust.
No idea if it is fixable. You need to closely inspect the hotside which requires the turbo to be removed.
- cracks on the underside of the exhaust manifold. Those cracks leak exhaust gasses away that are needed to spool up the turbo. This might set a check engine light.
Those cracks can be fixed by hard-soldering.

- the tdo4-13C is also known for the CBV membrane (under the chrome 3bolt cover) to fail/leak. (it is basically a short circuit on the boost side.)

I have checked for cracks from the outside and I haven't find any. Offcourse doesn't mean they aren't there. Although I don't have common signs like black smoke marks.
Before thinking of taking the turbo off I wanna check a few more things. Namely exhaust bacjpressure and check exhaust and turbo with a borescope. That is, if I can remove the o2 sensor on the downpipe. Today I failed to do so. Gonna try again tomorrow with different tools.
I'm also gonna use the borescope to check bellow turbo/manifold and other harder places to reach and get a better visual inspection.
I have removed the byspass valve and honestly the membrane looks in great shape. Granted I don't really know how it is supposed to look, but there are no obvious tears, holes, cracks, etc. Looks healthy.

At this point I guess this has to come down to either manifold crack, turbo crack, wastegape flapper or flapper port defect, intercooler leak or clogged exhaust. Hopefully tomorrow I'll cross some of those off the lits.

Thanks for the tips.

 

[MasterBlaster]

Checked the calendar... almost 3 years ago, I got to swap out both turbos on a 2007 BMW 335i. The "flapper" shaft holes had worn so much in the casting that the valve/puck was no longer centered or flat on the port. Leaked, rattled, uneven boost (if at all), etc.

 

[SalvadorP]

Checked the calendar... almost 3 years ago, I got to swap out both turbos on a 2007 BMW 335i. The "flapper" shaft holes had worn so much in the casting that the valve/puck was no longer centered or flat on the port. Leaked, rattled, uneven boost (if at all), etc.

It may be possibly what's happening to mine. But I don't here any rattle even when I play with the WG arm back and forth. You know, I hear it move, but nothing I would think is out of the ordinary. Also when I release it and the flapper hits the port it doesn't sound weird, it sounds like it makes good connection and sounds the same everytime. But this is very subjective. I need to check inside with the borescope.

Nice ride you got there. Same color as mine, but mine is a wagon. Similar mileage.

 

[SalvadorP]

I didn't need anyone's help cracking this case...
Cause the case was already cracked!

Borescope video: