617: Probability of fuel shutoff valve failure?

[phasmatisnox]

I bought my '84 300D Turbo with some problems. One is that it does not shut off with the key. I know it has a weak vacuum system, so my first suspect is the fuel shutoff valve actuator on the side of the IP, as seen on DieselGiant. I'd link, but the site isn't responding right now. I traced its vacuum line back through the firewall. What's the best way to isolate the problem? Can I just try to shut off the car by hooking up a hand vacuum pump to it? How can I find out if my vacuum is so leaky that it won't actuate this valve? Thanks!

[rhodes2010]

Sounds like you have the hand vacuum tool like mighty vac - good.

You need to determine if vacuum will kill the engine.
Hook the mighty vac style tool to the connector on the back of the IP and apply vacuum with the engine running.
This should shut off the engine.
If it does not - replace the rear of IP shut-off. (I bet it is fine).

The vacuum shut off is really simple, - two lines - the one going into
the interior that has vacuum constantly which goes to the keyswitch.
The other line comes from the keyswitch - that is the one you disconnected to test if engine shuts off. Locate the one into the keyswitch and attach the vacuum guage/tool and look at the vaccum while running.

If you get vacuum here, then attach the gauge to the line coming from the keyswitch that should go to shutoff.
Turn off the key while running and check the vacuum reading. It should jump up when switched to off.

If all those things worked out - you just need to snug the fittings. Shove them in tighter.

If you get a low vacuum on the vacuum source line going into the key then at worst you need vacuum pump rebuild (cheap and easy), or maybe just a leak somewhere.
If you have good vac on ythe source line, but low after the key, then it may be the key switch. I have never had to replace this - others here can assist.

[phasmatisnox]

Wow, great info! Thanks!

Originally Posted by rhodes2010

Sounds like you have the hand vacuum tool like mighty vac - good.

You need to determine if vacuum will kill the engine.
Hook the mighty vac style tool to the connector on the back of the IP and apply vacuum with the engine running.
This should shut off the engine.
If it does not - replace the rear of IP shut-off. (I bet it is fine).

The vacuum shut off is really simple, - two lines - the one going into
the interior that has vacuum constantly which goes to the keyswitch.
The other line comes from the keyswitch - that is the one you disconnected to test if engine shuts off. Locate the one into the keyswitch and attach the vacuum guage/tool and look at the vaccum while running.

If you get vacuum here, then attach the gauge to the line coming from the keyswitch that should go to shutoff.
Turn off the key while running and check the vacuum reading. It should jump up when switched to off.

If all those things worked out - you just need to snug the fittings. Shove them in tighter.

If you get a low vacuum on the vacuum source line going into the key then at worst you need vacuum pump rebuild (cheap and easy), or maybe just a leak somewhere.
If you have good vac on ythe source line, but low after the key, then it may be the key switch. I have never had to replace this - others here can assist.

[phasmatisnox]

Okay, now that I'm awake and my four-hour class is done for the day...
I don't know a Mityvac, but I can borrow one. Should I buy some vacuum hose to do these tests? For some, there's no break or junction where I can hook up the vac tool. How much is some cheapo stuff just for testing?

Also, if my valve ends up being bad, can it possibly be refurbished? It looks fairly straightforward for a $50 part, and I've got facilities and resources here that could come in handy. Is it likely just a leaky diaphragm? I'm startlingly cheap sometimes, and I might attempt to repair it with skilled application of RTV.

Your input is highly valued. Thank you!

Originally Posted by rhodes2010

Sounds like you have the hand vacuum tool like mighty vac - good.

You need to determine if vacuum will kill the engine.
Hook the mighty vac style tool to the connector on the back of the IP and apply vacuum with the engine running.
This should shut off the engine.
If it does not - replace the rear of IP shut-off. (I bet it is fine).

The vacuum shut off is really simple, - two lines - the one going into
the interior that has vacuum constantly which goes to the keyswitch.
The other line comes from the keyswitch - that is the one you disconnected to test if engine shuts off. Locate the one into the keyswitch and attach the vacuum guage/tool and look at the vaccum while running.

If you get vacuum here, then attach the gauge to the line coming from the keyswitch that should go to shutoff.
Turn off the key while running and check the vacuum reading. It should jump up when switched to off.

If all those things worked out - you just need to snug the fittings. Shove them in tighter.

If you get a low vacuum on the vacuum source line going into the key then at worst you need vacuum pump rebuild (cheap and easy), or maybe just a leak somewhere.
If you have good vac on ythe source line, but low after the key, then it may be the key switch. I have never had to replace this - others here can assist.

[rhodes2010]

I can say that I too have used RTV silicone to fix diaphragms and even speakers that tore.

You won't have any trouble connecting into the system.
A foot of cheap rubber line of small size would not hurt, but may not be needed, the vac tool should have some attached.

[phasmatisnox]

Originally Posted by rhodes2010

I can say that I too have used RTV silicone to fix diaphragms and even speakers that tore.

You won't have any trouble connecting into the system.
A foot of cheap rubber line of small size would not hurt, but may not be needed, the vac tool should have some attached.

Okay. Do you know what size the hose is, should I need to buy some?

[phasmatisnox]

I just took a look at all the fittings that I could see, and they look soft and fairly new- I suspect someone might have changed them out before, because it seems like there are some substitutions- two tees connected together to make a four, for example. I suspect that a previous owner tried to fix it, and reconnected something wrong. Maybe.

I still don't have a Mityvac- I might end up buying a cheapo $20 one from HF.

[whunter]

Run away diesel, why does it happen?
http://www.peachparts.com/shopforum/showthread.php?p=824840#post824840

Diesel Injection:
http://www.peachparts.com/shopforum/showthread.php?t=142405

[dieseldiehard]

As WHunter's link will show you, changing the shut off device can be a very risky proposition if not done properly. That is good advise if you do have to reoplace it (they sometimes allow engine oil to get sucked up into the vac lines too so be on the lookout for any oil in the lines, they should be dry!)
rhodes2010 covered this already and did a very thorough job of it too!
I was preparing this text when I saw that post so I hope I'm not confusing you or usurping anypne else's points.

If you don't want to spring for a Mity Vac, you will at least need a vac gauge, these should be available at the tool section of a decent car parts store. An inexpensive one is all you need.

Check the vacuum at the line going into the shut off element (rear of the IP) and turn the key to the off position with the car running and see if you don't get good vacuum (-15 or better) if its hardly metering anything then you have a vac leak in the system (called the Central Locking System in the FSM).
If your door locks are pulling down slowly or not at all, then that is a good indication that the vacuum is low or not and that means near the source, so the vac lock is on the same branch roughly.

Main Vacuum is sourced from a large plastic line coming from the vac pump. It has small nipples that get busted off easily, like when doing an oil change
Near the firewall it tees-off thru a one-way valve (yellow cylinder with three nipples on it) and there are plenty of places in that area where a vac leak can occur and cause several things not to work, including the shut off valve and door (and trunk and gas flap) locks.
By looking at these clues you might save yourself a lot of grief in changing the shut off device (It has been called a real PITA by more than a few people!)
If necessary plug some other lines that feed the door locks temporarily and see if that is where a leak is bringing down the entire vac system.
Just be sure to put any hoses you take off right back where they were or you'll be in worse shape then just having an engine that won't shut off!

[dannym]

You can borrow a mity-vac from autozone for free.

Danny

[phasmatisnox]

Sounds good. I poked around in that area today, and I found some great diagrams of the vac system in the parts section.
Locks do not work at all. I hope it's a connector or a check valve, those are cheap and easy.

I'll see if I can't get a gauge this week. BTW- the Mityvac can't double as a gauge, can it?

Edit: Oh gosh, I can't beleive I forgot this. I hear the sound of something leaking in the pedal area. I have a faint recollection of someone replacing 'pods' down there that were leaking. Could those be my culprit? Are they easy to change? Thanks!

Originally Posted by dieseldiehard

As WHunter's link will show you, changing the shut off device can be a very risky proposition if not done properly. That is good advise if you do have to reoplace it (they sometimes allow engine oil to get sucked up into the vac lines too so be on the lookout for any oil in the lines, they should be dry!)
rhodes2010 covered this already and did a very thorough job of it too!
I was preparing this text when I saw that post so I hope I'm not confusing you or usurping anypne else's points.

If you don't want to spring for a Mity Vac, you will at least need a vac gauge, these should be available at the tool section of a decent car parts store. An inexpensive one is all you need.

Check the vacuum at the line going into the shut off element (rear of the IP) and turn the key to the off position with the car running and see if you don't get good vacuum (-15 or better) if its hardly metering anything then you have a vac leak in the system (called the Central Locking System in the FSM).
If your door locks are pulling down slowly or not at all, then that is a good indication that the vacuum is low or not and that means near the source, so the vac lock is on the same branch roughly.

Main Vacuum is sourced from a large plastic line coming from the vac pump. It has small nipples that get busted off easily, like when doing an oil change
Near the firewall it tees-off thru a one-way valve (yellow cylinder with three nipples on it) and there are plenty of places in that area where a vac leak can occur and cause several things not to work, including the shut off valve and door (and trunk and gas flap) locks.
By looking at these clues you might save yourself a lot of grief in changing the shut off device (It has been called a real PITA by more than a few people!)
If necessary plug some other lines that feed the door locks temporarily and see if that is where a leak is bringing down the entire vac system.
Just be sure to put any hoses you take off right back where they were or you'll be in worse shape then just having an engine that won't shut off!

[whunter]

Originally Posted by phasmatisnox

I'll see if I can't get a gauge this week. BTW- the Mityvac can't double as a gauge, can it?

Edit: Oh gosh, I can't believe I forgot this. I hear the sound of something leaking in the pedal area.
I have a faint recollection of someone replacing 'pods' down there that were leaking.
Could those be my culprit? Are they easy to change? Thanks!

Mityvac will function as a vacuum gauge.

If you hear hissing/sucking by your feet = YES it could be the issue you are seeking.

[phasmatisnox]

Good to know, not good to hear. Do you know where I can find any more information on the under-dash vacuum systems? Thanks for your valuable replies.

Originally Posted by whunter

Mityvac will function as a vacuum gauge.

If you hear hissing/sucking by your feet = YES it could be the issue you are seeking.

[whunter]

Originally Posted by phasmatisnox

Good to know, not good to hear. Do you know where I can find any more information on the under-dash vacuum systems? Thanks for your valuable replies.

Vacuum Diagrams W123 and W126 models

[phasmatisnox]

I poked around the vacuum system last week- I took the hoses off of the check valve leading to the brake booster indivudually and used the 'finger test' to see how much vacuum there was. There was almost none. I think this might call for a vacuum pump rebuild.