Loss of power...briefly - Page 19 - PeachParts Mercedes-Benz Forum

funola · #**271** 09-24-2011, 10:00 PM

I have a vacuum fuel shut off valve on mine. On the IP's with the diaphram, I think if you pinch off the breather hose on the valve cover, the engine will stall in a minute or so. I tried that on mine, it did not stall with the hose pinched for around 9 minutes).

boneheaddoctor · #**272** 09-24-2011, 10:35 PM

Quote:

Originally Posted by funola

I have a vacuum fuel shut off valve on mine. On the IP's with the diaphram, I think if you pinch off the breather hose on the valve cover, the engine will stall in a minute or so. I tried that on mine, it did not stall with the hose pinched for around 9 minutes).

In my case you needed the load and accelerator position to at least maintain highway speed to have gotten enough blow-by to develop enough pressure against the aftermarket equipment induced restriction in my case to do that.

My engine had between 100 and 120K miles on it so the blow-by volume was not huge. It was simply one of those things you really would not have expected to do it. And a good reminder to everyone when you have been beating your head against the wall with a problem long enough its easy to assume a lot of things can't possibly be the problem. And that making any blanket assumptions can cost you a lot of time and money.

And I had made a mistake I learned in my real line of work many years earlier but didn't take heed of, when you can't find the problem where you are sure it has to be.....and you aren't making any progress and wasted a lot of time. Its time to step back, assume nothing is good and start all over again with a fresh set of eyes so to speak. Its easy to get tunnel vision and convince yourself it HAS to be in a certain area, and completely convince yourself that it isn't and can't be anything else. And too often, that's where if ends up being.

And worse....you might induce new problems that were never there before in the process and be chasing your tail.

Billybob · #**273** 09-24-2011, 11:19 PM

Quote:

Originally Posted by funola

Man I can't believe the ***** you went through! Up to what year IP's has the diaphram that can be affected by crankcase pressure? I am certain my 83 IP does not have it.

As far as I know any diesel with a vacuum operated shut-off solenoid can be affected by elevated crank case pressure. The IP's "block" is open to engine crank case pressure and the solenoid is open to the IP "block" the question is when and under what circumstances the crank case pressure increases enough to effect operation.

I had this happen on an 87 300D about 75 miles into a 1000 mile trip after I'd replaced a broken OE valve cover vent hose with a really nice reinforced braided hose that I had at hand. The combination of engine heat and blowby fumes passing down that hose started to melt it and constrict it. Started with loss of power and ability to accelerate, eventually smoking and overheating, and finally stalling out all while traveling south on I95 crossing the bridge out of Fall River MA.

I eventually made it off the bridge and got off the highway, started the engine and it would die a couple minutes later. Got the hood up and had my daughter start the car and while observing it running and starting to die I noticed very slight puffing and oil spray around the oil filler cap. Reached over and loosened the cap to a burst of blowby fumes! Yanked the vent hose and started the engine and it ran normally. Found the nearest parts store and bought a section of heater hose and a brass elbow so I could rig up an open exhaust crank case vent that allowed me to make the trip and the trip back home.

funola · #**274** 09-25-2011, 09:25 AM

Quote:

Originally Posted by Billybob

As far as I know any diesel with a vacuum operated shut-off solenoid can be affected by elevated crank case pressure. The IP's "block" is open to engine crank case pressure and the solenoid is open to the IP "block" the question is when and under what circumstances the crank case pressure increases enough to effect operation..................

What and where is this diaphram on the shut off valve then? I thought only pumps before a certain model year had it. Is this pinching off CC vent hose blow by test unreliable or do I have an engine with very little blow by?

boneheaddoctor · #**275** 09-26-2011, 11:13 AM

The Diaphram you ask about is actually internal to the Shutoff solenoid. the rear face is open to outside pressure, which in this case is crankcase pressure. Only the rear facing half thats outside is sealed to vacuum for it to function.

You would have to cut an old one open to see it. It literally pulls the rack to a position that completely shuts off fuel. (and why internal pressure can reduce or cut off fuel by PUSHING the diaphram) And why when replacing it, you can accidently push the rack into a near maximum fueling condition causing a runaway engine at startup if you aren't very careful putting it in.

I personally do not recomend intentionally pinching off or blocking the CC vent intentionally, it puts undue stress on all the seals and many of the gaskets and might damage them. Most of these still have the original seals and gaskets that are in the case of these OM617's, 24 years old or older. Why tempt fate.