Having a problem with run-on with a '85 300CDT. What are the vacuum specs for the fuel shutoff solenoid to operate and how much vacuum does the vac pump produce?? Is there any electrical switch that controls the vacuum lines associated with the fuel shutoff solenoid? I have a vacuum guage but have not connected it into the vac lines for any readings yet. I only have a Haynes manual and there is little useful infomation in there. Any help appreciated!!

Hey there and welcome, if you are talking about what I think you are I think I should mention to use the search feature before anyone else sees this post. It would most likely be in your best interests.

Oh, and you didnt hear that from me.

Your vaccuum pump should produce at least 12" vacuum after a few minutes of running.

If you have vacuum, either the vacuum switch on the key switch is bad or the cutoff solenoid is bad. You can check with a vacuum pump.

The supply for the cutoff is a brown hard plastic hose going into the passenger compartment from the main vacuum line (that goes to the booster). The operating line is brown with a blue stripe.

You can do a quickie test of the solenoid by disconnecting the vacuum line, pushing the stop lever down, putting your finger over the fitting, and let up the lever. If the lever moves at all, other than very slightly, or creeps up slowly, it is shot. Otherwise, you either have no vacuum supply (plugged or leaking brown line, bad vacuum pump) or the switch is bad. If you have vacuum, the cutoff is good, and no shutoff, the switch is bad.

The usual problem is that the rubber connectors for the hard plastic lines go bad and leak, easy to fix.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I now have a hand vac pump/tester and plan on troubleshooting today. It is plain to see that just the vac gauge is not going to be sufficient for troubleshooting this. Thanks for you two providing more infomation. I did a search and now have lots of info to go on. I have already poked around and made a crude diagram of most of the lines and should be able to get to the bottom of this quickly. I have the sinking feeling that the vac pump is the culprit but I am hoping not. The locks are not working as you mentioned. This ought to be fun. Thanks again. This is the best MB information site that I have seen.

Ron G,

An easy test for the shutoff valve on the injection pump (IP) is to disconnect the brown vacuum line at the nearest connection to the shut off valve (not AT the shut off valve) and suck on the brown line when engine is running. This will shut off the engine if the IP shutoff valve is OK and the problem is a leak or low vacuum somewhere else. Its an easy test to do and no special tools are needed.

P E H

I was able to get the problem sorted out. Pin hole in the lock(Yel/red) vac line at the RH side where the vac lines transit from the door pillar area to the floor board area. The hole was right at the area of where the clamp holds the bundle of lines to the panel at the turn-up point. I went ahead and got good use out of the vac pump I bought and tested door, fuel, trunk lock system components, seat back latch, vacuum resivoir, and fuel shutoff solenoid. Also found the fuel door (unlock side) actuator leaking as well.

Vac Pump read 22in. merc. (pump to brake booster only) and approx. 6.5 in. merc. with all branches of vac system connected and vac gauge teed in. Is 6.5 a good number? Car seems to be happy with that amount of vacuum.

Thanks again for the help!

I've got an 84 300 CD with some similar gremlins. Where'd ya get the vaccum pump, what did it cost, etc? Sounds like I may need one of those to get to the bottom of the vaccum mystery.

Thanks

-Gil:p

Mighty-Vac is a lightweight aluminum/plastic model available at almost any auto tool place or E-Bay $30 - $50 depending on the accessories and the box, or Sears has a pretty nice one with steel handles and a brass vacuum cylinder for $40

The hand held vac pump is available from Disount auto parts $35.00 or NAPA $39.00. Same exact parts only different brand label. It is a must for vacuum problem troublshooting. You may find that like my case it was the lock system. read back through the posts here (really good help). When you are checking the lock system you can use the vac pump to operate the door locks without having to tear into the door panel, providing the lock actuators are good. Access to the fuel door and trunk actuators is OK as well as the vacuum reservoir. The reservoir will take some pumping, don't give up, it is a large area to evacuate.

Always keep in mind that some vac branches under the hood are proportional bleed-off and will look like a leak but are not. Get some vac line before you start. You will find yourself tossing lots of pieces away.

I do not remember the exact numbers but I found the main line off the pump to the brake booster to be at 22"Hg (no other lines connected) , the first Tee point (with vac guage"T'd" into the vac plumbing/all lines connected) approx 11"Hg, and the aftmost Tee point (T'd in ) 17"Hg.