Om621 still no vacuum after pump rebuild - Page 3 - PeachParts Mercedes-Benz Forum

Ryancoolwind · #31 04-04-2018, 05:37 PM

Quote:

Originally Posted by Diesel911

I am wishing someone would actually hook a up vacuum gauge; just curiosity.

I will when I get everything situated with the vacuum pump

BillGrissom · #32 04-04-2018, 07:35 PM

When you do test it, connect the vacuum gage directly to the pump source, with nothing else in the car connected. That is the only way to know if the vacuum pump alone is not doing its job.

NZScott · #33 04-04-2018, 10:36 PM

Quote:

Originally Posted by Ryancoolwind

I think you guys are mixing up compression ratios and air fuel mixtures. The compression ratio isn't a dynamic number (except the new Nissan variable compression engine). When you momentarily block off an intake, the engine will only run richer due to the remaining air being used up faster then it is replaced. The engine will then stall once the rotating inertia isn't enough to overcome the vacuum in the manifold, or when the mixture is too rich and is unable to burn. Modern diesels have throttle bodies on them for emissions reasons, in certain drive cycles the TB will partially close to better have egr gasses pushed into the intake

The dynamic compression ratio is dependent on volumetric efficiency, as normal static compression ratio is based on a full cylinder worth of air (I should have been clearer). As soon as your cylinder has less than that (which it almost always will to a certain degree as our engines aren't anywhere near 100% VE NA) the effective ratio decreases which is my whole point as restricting too much air into a diesel will stop it working. Nothing to do with A/F ratios as we know diesels will still work spewing huge amounts of smoke

....(sorry to digress)

KCM · #34 04-07-2018, 02:59 PM

Just came across this thread. I am very familiar with this engine so I can shed some light.

First, if the picture you posted early on showing the front of the engine where the vacuum pump is attached is of your engine, then you are definitely missing something. The front of the injection timing device needs to have the roller coaster track in order to run the pump. The track is integral to the visible part of the timing device, not bolted on. The ball bearing rides on the track, which in turn moves the diaphragm up and down pumping air. The two check valves in the pump keep air flowing the correct direction, from the brake booster to the intake manifold. Thus they must be inserted correctly so the air flows in that direction.

Second, early 190Dc cars (OM621.912 engines) did not have a vacuum pump. All 200D cars (OM621.918 engines) did. The change was done in the mid 1963 model year. This is because early cars did not have front disc brakes, but had drum on all four corners. No power booster was used on these cars so no pump. In place of the pump was a cover, and most likely there was no roller coaster track as well. Front disc brakes may have been an option up to 1963 but not sure. So either your car does not have front disc brakes or the engine is probably from a 190Dc (or other vehicle whether it be a truck, boat, or power unit). The engine model and serial number is stamped on the block and ID plate at the top left rear of the engine looking from the driver's seat.

As for the manifold vacuum, yes there is a butterfly in the intake manifold to create a small amount of vacuum to control the vacuum operated governor. When closed it pulls vacuum to reduce fuel injected into the engine by the injection pump. As the throttle opens, the vacuum is reduced and more fuel is injected. This is unique for diesels as the time as most did not use a butterfly or vacuum and fuel was controlled at the pump itself mechanically. The amount of vacuum created by the engine with the butterfly is closed is not enough to power the brake booster and provides very little braking assist. And as soon as the butterfly is opened up a little, then the boost is back to zero and you have no boost. You can trust me on this as I have had first hand experience.

So if you do have front disc brakes, you do need the vacuum pump and you need the parts to fix the injection timer to add the ramp. If you do take the timer out, make sure to install the small bronze washer between the timer and engine block/injection pump drive shaft to space the timer and sprocket correctly with the other sprockets in the timing chain system. Of course the camshaft and injection pump will need to retimed to the crankshaft.

Diesel911 · #35 04-07-2018, 08:15 PM

Quote:

Originally Posted by KCM

Just came across this thread. I am very familiar with this engine so I can shed some light.

First, if the picture you posted early on showing the front of the engine where the vacuum pump is attached is of your engine, then you are definitely missing something. The front of the injection timing device needs to have the roller coaster track in order to run the pump. The track is integral to the visible part of the timing device, not bolted on. The ball bearing rides on the track, which in turn moves the diaphragm up and down pumping air. The two check valves in the pump keep air flowing the correct direction, from the brake booster to the intake manifold. Thus they must be inserted correctly so the air flows in that direction.

Second, early 190Dc cars (OM621.912 engines) did not have a vacuum pump. All 200D cars (OM621.918 engines) did. The change was done in the mid 1963 model year. This is because early cars did not have front disc brakes, but had drum on all four corners. No power booster was used on these cars so no pump. In place of the pump was a cover, and most likely there was no roller coaster track as well. Front disc brakes may have been an option up to 1963 but not sure. So either your car does not have front disc brakes or the engine is probably from a 190Dc (or other vehicle whether it be a truck, boat, or power unit). The engine model and serial number is stamped on the block and ID plate at the top left rear of the engine looking from the driver's seat.

As for the manifold vacuum, yes there is a butterfly in the intake manifold to create a small amount of vacuum to control the vacuum operated governor. When closed it pulls vacuum to reduce fuel injected into the engine by the injection pump. As the throttle opens, the vacuum is reduced and more fuel is injected. This is unique for diesels as the time as most did not use a butterfly or vacuum and fuel was controlled at the pump itself mechanically. The amount of vacuum created by the engine with the butterfly is closed is not enough to power the brake booster and provides very little braking assist. And as soon as the butterfly is opened up a little, then the boost is back to zero and you have no boost. You can trust me on this as I have had first hand experience.

So if you do have front disc brakes, you do need the vacuum pump and you need the parts to fix the injection timer to add the ramp. If you do take the timer out, make sure to install the small bronze washer between the timer and engine block/injection pump drive shaft to space the timer and sprocket correctly with the other sprockets in the timing chain system. Of course the camshaft and injection pump will need to retimed to the crankshaft.

Thanks for your experience that provides clerification of the manifold vacuum issue.