Air filter housing - vacuum related? - PeachParts Mercedes-Benz Forum

mbzr4ever · #1 07-30-2018, 04:53 PM

Trying to isolate the source of these problems for my 1979 240D W123:

1) Started with the engine not shutting off when turning the key at ignition.
Went to the STOP lever under the hood, still would not quit. Have to remove the air filter cover and place a canning lid over the air intake hole to shut off engine.

2) The air housing unit shakes... A LOT. It is loose and sits precariously in place with one wing nut on top - isn't this supposed to be fastened or tight somehow?

3) At first I thought it was a failing vacuum pump because I just replace the diaphragm only a year ago. But before I take all that apart (again), I wanted a second opinion on this perhaps easy fix.

tyl604 · #2 07-30-2018, 05:49 PM

What about the stop valve located inside the rear of the injection pump? It has a nipple out the back and a vac hose. Try a mityvac on that nipple; if it will not hold vac, it is bad. Easy replacement.

Assume, like my SD, that the air cleaner rests on rubber bumpers which holds it fast to a bracket on the engine. These bumpers fail a lot. Take a look. The air cleaner should hold tight.

Diseasel300 · #3 07-30-2018, 06:30 PM

Let's back up.

If the engine isn't stopping with the stop lever, FIX IT. Something in your throttle linkage is out of whack or broken. Before doing ANYTHING else, find out why the stop lever isn't stopping the engine.

The air filter flopping around like a dead fish is probably due to broken rubber isolators or a broken bracket. It's an annoyance, but not the reason the engine won't stop. The only reason it's stopping when you block the intake hole is because you're starving the engine for air.

If you have a Mityvac, you can test for vacuum presence anywhere on the vacuum system that's convenient. If you have vacuum, it isn't the pump. If you don't, you may need another diaphragm.

mbzr4ever · #4 07-30-2018, 09:16 PM

Quote:

Originally Posted by tyl604

What about the stop valve located inside the rear of the injection pump? It has a nipple out the back and a vac hose. Try a mityvac on that nipple; if it will not hold vac, it is bad. Easy replacement.

Is this valve in addition to the RED STOP lever that is on top of the engine?
Going to look tomorrow to try and find this. Have mityvac.

mbzr4ever · #5 07-30-2018, 09:19 PM

Quote:

Originally Posted by Diseasel300

Let's back up.

If the engine isn't stopping with the stop lever, FIX IT. Something in your throttle linkage is out of whack or broken. Before doing ANYTHING else, find out why the stop lever isn't stopping the engine.

The air filter flopping around like a dead fish is probably due to broken rubber isolators or a broken bracket.

Flopping around like a caught fish, LOL!
Will check out photos of brackets, cause if I had em, they are gone!

But you are correct - something basic is wrong with the stop lever.
Going to look tomorrow when I have more time.

Diseasel300 · #6 07-30-2018, 10:05 PM

Quote:

Originally Posted by mbzr4ever

Is this valve in addition to the RED STOP lever that is on top of the engine?
Going to look tomorrow to try and find this. Have mityvac.

I think he's talking about the vacuum pod that the key switch operates. If you pump it down with a mityvac, it should stop the engine. So should the red STOP lever, which is clearly out of adjustment!

The later M pumps have the stop lever on the side of the IP. It was mechanically coupled to the vacuum pod for a simpler system, but you did have to reach down and flip a tiny lever instead of the big "STOP" paddle on top of the engine.

Diesel911 · #7 07-30-2018, 10:08 PM

As Diseasel300 said concerning the linkages.

Each of the linkages has a specific length and the Bell Crank on the Fire Wall has to be in good shape or people start fooling with the linkages to compensate.

If it is an MW Fuel Injection Pump when you activate the manual lever it pushes up on a spring loaded plunger on the idle screw. If the Plunger cannot move up far enough due to internal rust you won't be able to shutoff when the manual shutoff lever.

The arrow in the pic points to the plunger.

There is a vacuum shutoff on the Fuel Injection Pump and a Vacuum Shutoff Valve on the Steering Colum Lock and of course tubing in between that can leak.

What vaccum is your vacuum pump putting out?

tyl604 · #8 07-31-2018, 08:35 AM

Do not know the 240d but assume it has a stop valve inside the injection pump like the 300sd.

tyl604 · #9 07-31-2018, 08:45 AM

Also called shutdown valve. Has L shaped lever inside which hooks and pulls a gear? Inside when hit with vacuum and stops engine.

Diesel911 · #10 07-31-2018, 01:57 PM

The Vacuum Shutoff Valve on the Fuel Injection Pump is also sometimes called a Servo is at the rear of the Fuel Injection Pump (actually attached to the Governor Housing).

While the Vacuum Shutoff Valve/Servo is supposed to hold vacuum they can still function OK if there is some porosity in the interior diaphragm (mine is like that).
However, when that happens Oil sometimes gets pulled unto the Vacuum Lines and can end up inside of the Vacuum Shutoff Valve on the Steering Colum Lock where said Oil sometimes comes out and drips on a Leg.

mbzr4ever · #11 07-31-2018, 08:36 PM

Linkage around the STOP lever appear intact.

When I tested the valve at the back (the Servo?) it did not hold.
The post above mentions a diaphragm inside that may be the cause.

tyl604 · #12 07-31-2018, 09:14 PM

If it did not hold a vac, this is the cause. It needs to be replaced. Before you remove it, notice the orientation of the nipple and put the new one in exactly that way. If you do not get the L shaped piece hooked inside the injection pump properly, you risk having a runaway engine.

Check the threads on shutoff valve and there are multiple comments about it. Check my thread:
1981 300SD No shutoff - how do I find vac leak? Look at posts #11 and #13 to see where it is located in the injection pump and exactly what it looks like.

Should immediately solve your problem.

PS - I have no info about the diaphragm and suggest you replace the entire shutoff valve. On the SD I do not believe it is repairable from looking at my old one.

Diesel911 · #13 07-31-2018, 10:03 PM

If you replace the vacuum shutoff on the fuel injection pump be sure to look up some threads on how to do that.
A lot of people in the past have installed it wrong and when you start the engine accelerates/ runs away.
As a safety precaution people remove enough of the Air Inlet that they can place a piece of Plywood over the opening to cut off the Air and stop the Engine.

Concerning the Manual Shutoff. The linkage that goes to the manual lever and down to the Fuel Injection Pump Throttle Lever; spray WD-40 on the ball joint and carefully pry it off of the Manual Shutoff Lever. It ought to pop off.

Start the Engine and pull up on that linkage rod (that is no longer connected to the Manual Shut off Lever). Pullin up on that rod should stop the Engine. If it does not stop the Engine you have an issue with that Plunger I spoke of in the other post.

If the Engine does shut off normally then your linkeages need to be ajusted to the factory specs or it is also possible the linkage is missing some of the Plastic Pieces on it.

mbzr4ever · #14 08-01-2018, 05:36 AM

Looks like the vacuum shutoff valve needs to be replaced.
The air filter housing mounts had no bolts at all - will have to order those, too.

mbzr4ever · #15 08-16-2018, 05:41 PM

First nice day to work on car, volcano has gone to sleep for..who knows?

Afraid it is the vacuum pump...

Installed the replacement shut off valve - works and shuts off when vacuum is applied (hand pump). Otherwise no change.

Replaced the mounts, air filter - mounting now stable.