DIY FPR vacuum line replacement

[jreed]

I was out looking around in the engine compartment (97 855 GLT with ~162k miles) for opportunities to fix something this morning. I've already replaced most of the vacuum lines in the car, but I found a short crumbly vacuum connector that I had overlooked the last few times I checked the car. This connector is located above the transmission, near the lower radiator hose. It is part of the Fuel Pressure Regulator line from the intake tube near the MAF Sensor and connects between a white hard plastic line and a metal line that runs over to the fuel pressure regulator on the passengers' side.

Rubber connector at end of white plastic hard line on the Fuel Pressure Regulator vacuum line

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Getting the line off required (for me -- if your hands are smaller you might not need to) loosening the black flexible plastic intake line that connects between the MAF and the PTC/Turbo intake region. I loosened the hose clamp and disconnected the line from the MAF. This allowed me to bend up the line enough to reach in and use pliers to loosen the metal spring clamp on the rubber connector.

Once I had the clamp loose, I found I needed to gently slit the rubber to allow it to be twisted and slid off of the metal line. Here is a picture of the little rubber hose after I pulled it off of the metal line:

Rubber vacuum connector -- cracked and crumbly rubber.

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I retrieved the metal clamp off of the metal line:

Metal clamp after removing with long needle nose pliers

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Then I snaked my camera down into the engine near the top of the transmission to get a picture of the metal line that runs over to the fuel pressure regulator:

Fuel Pressure Regulator metal line.

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To make a replacement hose, I decided to run silicone vacuum line instead of the rubber elbows and white plastic hard line. Here is a side by side comparison of the diameter of the original rubber connector and the silicone tubing I chose:

Original rubber connector (left) and Silicone tubing replacement (right)

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Here is an image of the new silicone line connected to the metal line. I ended up using two black zip ties to make a secure clamp to the metal line.

4mm ID silicone tubing connected to metal line. Black zip tie in place to hold tubing securely to line.

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This tubing is 4mm inner diameter platinum-cured silicone tube from Verocious Motorsports. I have no connection to them except as a satisfied customer.
http://www.verociousmotorsports.com/Sho ... d-Silicone
The 3.5mm ID tubing was actually a better fit to the metal line, but was too tight to fit over the black plastic nipple on the intake line. The 4mm was the best compromise I could find.

Then with the tubing in place down on the metal line, I reconnected the main intake line and tightened the hose clamp. Then I cut the silicone tubing to the proper length to fit on to the nipple on the side of the main intake, as shown:

Silicone line connected to main intake line.

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Not a bad job overall.

The tools/supplies I found useful included:
7mm socket and ratchet to loosen hose clamp on intake tube
flat blade screwdriver to pry off intake tube from MAF
nylon zip ties / tie wraps to secure and clamp tubing to line and nipple
4mm ID silicone tubing (~ 8" / 200mm long)
knife to slit old rubber connector
scissors to cut tubing to length
flashlight
snipping pliers to cut off end of zip ties after tightening
long needle nose pliers to loosen and retrieve the metal clamp on the old rubber connector

Have fun!

[TRuck]

I posted this in another thread but I think it is too old so am re-posting it here. Hope that is okay.

Recently I replaced the metal tube-part of this line with 1/8" copper tubing because the original had completely rusted in half. I couldn't find any other type of tube locally, and wasn't sure how to even order it as I was/am unsure of what to even call it. So picked this up from Pep-boys.

Questions:
a) Is it a bad idea to replace it with copper tubing as appose to other types of metal? The interior diameter is just slightly smaller than the original.

b) Is it necessary for the tube to be metal and run so close to the engine? Why not route it up higher against the firewall then down to the connection on passenger side and eliminate the metal part all together? Or does it need to be next to the exhaust heat for some reason?

Broken Line above new copper.

New line installed

Thanks.
T

[jreed]

That looks like a fine repair. Good work!


I have read that over a period of time copper tubing can work harden from vibration and shock, but I don't think you will have a problem with that in this application.
I don't think the line has to run next to the engine. My understanding is that the vacuum signal is used as a control or a reference pressure level by the fuel pressure regulator to adjust pressure to the fuel injectors. I don't see why distance from the engine would affect the signal.

[neworleans]

Thanks for the write up. Where did you get that slicon tubing from?

[TRuck]

thanks for the response. I have Since re-routed up along firewall.
I would like to know where to get that silicone tube as well.

T

[abscate]

Copper is soft so if it is rubbing on a steel edge or part it will wear through fairly quickly. It will wear better than plastic though, so if you routed carefully you will be fine

Your engine will warm the vacuum through the copper just fine......

[jreed]

I got the silicone tubing from Verocious Motorsports. I've bought tubing from them a couple of times over the past three years and it has been good quality.

http://www.verociousmotorsports.com/Sho ... d-Silicone

[beigg]

Am I correct to understand that the "reference" line from the FPR goes to the intake before the MAF but in that area? I question the purpose of that little annoying vacuum line. What if its connect to the intake manifold "tree"?

Terrible location for that FPR.

[jreed]

I didn't understand the purpose of the fuel pressure regulator very well until I read Probst's "Bosch Fuel Injection and Engine Management". Chapter 3 has a good section on the workings of the pressure regulator. I typed a bit of the text below:
"Pressure Regulator:
Relative fuel pressure in the fuel system is held constant by the pressure regulator, usually mounted on the fuel rail...Most systems operate on 2.5 bar (36 psi) gauge pressure but some higher-powered engines use 3 bar (44 psi) for greater fuel delivery per millisecond.

Relative Fuel Pressure and Fuel Delivery:
For each millisecond of injector pulse time, the amount of fuel delivered through the injector tip depends on the size of the injector opening: that's a fixed factor. But fuel delivery also depends on the relative pressure -- the difference between fuel pressure pushing the fuel out into the manifold and manifold absolute pressure pushing back.
As you know, manifold pressure changes with throttle opening. If fuel pressure were constant for all manifold pressures, then at low engine loads with the throttle partly closed reduced manifold absolute pressure would increase fuel delivery. To keep that relative pressure constant as the throttle is opened and closed, the fuel-pressure regulator is connected to the intake manifold by a vacuum hose. Manifold pressure acts on the diaphragm to hold the relative pressure constant."

Based on that description it should be OK to connect to the vacuum tree at the intake manifold.

[beigg]

I know how the typical fpr works. The volvo fpr is different. It has 2 vacuum ports it looks like.

Lets see if this helps what I see.