What is this (turbo control valve)?
 

So, after having done the stage 0 tune (with exception of the fuel filter), I finally got around to doing the obligatory stage 1 tune (MBC and boost gauge).
After fitting the boost gauge (a cheapish VDO lookalike), it seemed like the car (late 1996 2.3 LPT) was only boosting around 0.2 bar stock, which should be a tad higher at around 0.4. The car did seem a bit slow, but again it´s a semi heavy car with only 135 bhp, so didn´t really notice it.
I then tried fiddling with the MBC (a cheap Aliexpress Turbosmart knockoff), but it seemed like I had to turn the knob a lot of clicks before the turbo would increase the boost pressure significantly. I started by resetting the MBC to the lowest settings, and then tried upping it 1 click, but as this didn´t really make a notable difference I soon starting doing 4 and 5 click at a time. After doing 7-8 4th gear full throttle pulls with one eye on the boost gauge, I ended up getting around 0.8 bar which seemed appropriate for the time, but it seemed like something was counteracting the MBC, as sometimes 4 clicks wouldn´t visible increase the boost pressure at all . The car did seem to pull nice, the boost pressure seemed steady, and no hiccups of any sort.
I then remembered that the routing of the vacuum lines for the wastegate did seem a bit off compared to the pictures I had found on the internet.
The wastegate was not directly connected to the compressor housing, but instead was connected to a unit with a connector and 3 lines (see the attached picture) sitting just in front the the air filter box. I haven´t been able to find anything regarding this item on Google, the closest I got was a device called a turbo control valve for the Volvo 850, and maybe some resemblance to one of the individual parts of the OEM Turbo Plus kit.
Can anybody shed some light on the function of this device, and could it be that there is causing the low boost issue/counteracting of the MBC?
Should I just disconnect it alltogether and just route the MBC directly between the wastegate and compressor housing to get full control of the boost pressure?

0.2bar is 2.9psi and 0.4 bar is 5.8psi, so being a Chinese gauge it is probably correct as it should be 3.5psi, you get what you pay for with this stuff, cheap nasty manual boost controllers aren't reliable and can introduce boost spikes.

0.8bar is probably in reality more like 0.9bar considering the inaccuracy of the gauge at even low pressure so it may even be more which means you are most likely running in to fuel cut from the ECU as a safety precaution, this can be mapped out with an ECU chip.

It looks like you have the turbo plus kit which means yours should be running 7psi as standard and should increase the pressure to 12psi at a certain rev range for a certain time. They don't seem to be very reliable at this age so I would gut it all and stick a decent boost controller and gauge on there.

Cool, thanks. I am aware that price and quality do go hand in hand to some extend, but this was only meant to be a stopgap solution. I do have an Innovate SGC-1 lying around, but that involves a lot more work to install, so that will be at a later time :regular_smile:
I also have a Ostrich 2 emulator somewhere, so the sky is the limit :tounge_smile:
I'll start by connecting the MBC directly between the actuator and the compressor, and then might try and fiddle a little with the Turbo Plus too see if it works.

Some info on Turbo+ attached.

Hi bud,

I too have a LPT 1996 940 and recently fitted a VDO gauge (bought from skandix). I'm reading 0.2 bar of boost after cleaning the wastegate membrane (which had some oil) and removing the foam from the air intake.

looks like 0.2 bar is the standard boost and not 0.3-0.4 as advertised, or am I missing anything?

Happy holidays

It's a bit low but the lpt was supposed to boost about 3.5 psi.
If your car is mechanically sound then you have the option to add a mechanical boost controller (ball & spring type pressure relief valve) and up the boost to a max 1 bar (14.5psi) without causing damage. I have boosted my lpt to 12psi and 15 years later no problems. The lpt is mechanically identical to the hpt (7psi) apart from the wastegate actuator.
I found that with the lpt in standard trim, you don't notice the turbo kicking in. Up the boost and you know it.

https://live.staticflickr.com/4298/3...e6e545fa_b.jpg

My 940 came fitted with a load of options.
Turbo+ included. It still works.
Car definitely gets a kick up the bum when it comes in😊