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Old 09-04-2019, 09:35 PM   #1
Murploid1
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Default 240 Turbo Boost Guage

Hello,

I had my wiring harness replaced in my 1982 Volvo 240 Turbo, picked it up after hours and there is now an issue with the turbo boost gauge.

I will take it back but wondered if there are some easy checks?

When i build boost the gauge rises then stays at max boost (in this case 10psi) it doesn't move from there

The cars performance is not affected - its just not showing the correct pressure. When I turn the car off the gauge then reduces back to normal.

What should I be checking?
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Old 09-04-2019, 09:45 PM   #2
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Look for a check valve installed backwards
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Old 09-04-2019, 09:57 PM   #3
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How do I know which way is correct? The line was actually unplugged from the check valve and no reading was showing, I plugged it in and now its got issues. There are TWO check valves.

This is what I see standing in front of the car looking at the plumbing. The line coming from the gauge is on the right and it connects to a check valve (black side) the others side is white. That white side then has another vacuum line which has a diverter, one side goes to inlet manifold the other goes into another check valve (white side), the black side then going into something on the bulkhead.

Any ideas?!
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Old 09-04-2019, 09:59 PM   #4
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Blow through it, the side you can blow though is the engine side. Sometimes they have an arrow but if not ya gotta test it.
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Old 09-04-2019, 10:07 PM   #5
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The valves are correct - just checked.

I cannot imagine that its vacuum lines - they look ok and were working fine. I also checked the plumbing under the steering wheel - its all plumbed in.

Any other suggestions?
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Old 09-04-2019, 10:15 PM   #6
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I got nothing, hopefully someone does. The 240 boost gauge has a vacuum line and wires for the light bulb like any other boost gauge right? So it is not a wiring problem. Either there is a chunk of crap in the line, the gauge has an issue, idk. Do you have another boost gauge to plug in to see what happens? That is what I would try since it's easy.
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Old 09-04-2019, 10:29 PM   #7
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it plugs into some blue thing on the bulkhead which is electrical - or at least has an electrical socket.
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Old 09-04-2019, 10:33 PM   #8
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I believe that would be an overboost switch, but once again hoping some 240T guy chimes in here. Maybe that is sticking, I don't know. You say it has a socket, does it have wires plugged into it?
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Old 09-04-2019, 10:40 PM   #9
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It does have wires plugged in. Something is plumbed wrong, I believe the gauge should work just plugged directly into inlet manifold. However, there is a lot more plumbing and i do not know what it does.

I guess i need to find a vacuum line diagram.
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Old 09-04-2019, 10:43 PM   #10
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https://www.240turbo.com/vac-B21FT.jpg

The electrical thing - I think its the charge air over pressure switch...
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Old 09-04-2019, 10:54 PM   #11
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Ya, an overboost switch. Do you have the delay valve pictured in that diagram? For an automatic car? The gauge will work fine just plugged into the intake manifold. I would think you could just bypass all that crap and run a vacuum line directly to the gauge, you will know if you make too much boost and then back off.

Like I said, I don't know what the overboost solenoid does when you have too much boost, cuts boost? Fuel? Timing? IDK. The automatic delay valve is probably just to save a bit of shock on the transmission. My V50 T5 will only allow 8 PSI in first and second gear, then 17 psi in the other gears. Probably a primitive version of that.
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Old 09-04-2019, 11:19 PM   #12
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Yes, not sure. I think that one check valve should be used for the boost gauge, I will try that tomorrow.

Which means I have an "extra" check valve with vacuum lines on either end and I have no idea where that is mean to go...

So if anyone has any clue where these check valves should be installed let me know!
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Old 09-04-2019, 11:51 PM   #13
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Pictures?

The boost gauge hose should go directly to the intake manifold plenum with no check valves. There's a separate hose with a check valve that goes to an egg-carton-ish vacuum reservoir under the blower fan, and then on to the vacuum actuators used for the HVAC flaps.
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Old 09-05-2019, 08:48 AM   #14
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Here are some images

Unplugged boost gauge line:

https://imgur.com/rfBE6IW

This random line with check valve that I thought connected the above but doesnt..

https://imgur.com/cGjeTZQ

Where is this meant to be plugged into?

https://imgur.com/Rd78dzr

https://imgur.com/RLcsjTx
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Old 09-05-2019, 09:13 AM   #15
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If memory serves me correctly, that line should be connected to the intake manifold right below the throttle body on the intake runner side.
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Old 09-05-2019, 09:27 AM   #16
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What line? The random one near WUR?

Anyone got any ideas regarding the boost gauge and all that "extra" plumbing that goes into that switch?
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Old 09-05-2019, 09:45 AM   #17
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The one in the last picture you posted. It looks like it runs down to a tee and connects to the vac advance on the distributor, correct? Your other line that is in your first picture with the white vacuum coupler that is not connected should be connected to the tee that goes to the switch on the firewall that has nothing on the one side of the tee. Not sure what the extra check valve and hose are for.
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Old 09-05-2019, 09:50 AM   #18
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240turbo.com has vacuum diagrams that may be helpful.

https://www.240turbo.com/vac-B21FT.jpg
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Old 09-05-2019, 10:23 AM   #19
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Yes, I looked at that already but it didnt really help me.

I have the boost gauge working now, having connected the two lines in picture one - I just removed the white T and connected them.

Still have no idea about this:

https://imgur.com/Rd78dzr

https://imgur.com/RLcsjTx

Or the extra check valve.
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Old 09-05-2019, 12:29 PM   #20
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Old 09-05-2019, 12:57 PM   #21
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Excellent! What is and where can i find that canister?

Charcoal canister?

Last edited by Murploid1; 09-05-2019 at 01:02 PM..
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Old 09-05-2019, 01:01 PM   #22
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That's the charcoal canister. It's under the drivers side fender in front of the tire.
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Old 09-05-2019, 01:03 PM   #23
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Thanks!
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Old 09-05-2019, 01:28 PM   #24
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so, then this is weird....

that diagram shows one line going to inlet, one to distributor, and other to canister.

I have a third because there is a T. The diagram mentions additional lines for AC, I have AC. Do you have that diagram?
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Old 09-05-2019, 01:49 PM   #25
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The diagram doesn't show A/C idle compensation for the turbo engine. I believe it's done through the IAC computer and not a separate solenoid that the diagram shows for B21F.

The disconnected hose coming off the tee in your pic is supposed to connect to the distributor. Where is the hose connected to the distributor coming from?
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