IP delivery valve
 

Has anyone had any experiences w/ blockages in the delivery valves? Still trying to track down possible missing and hard starts, just wondering what symptoms would be?

1985 300sd

If the delivery valve will not seat may have been encountered by a poster reciently. You would see less coming out one of the injector hard lines was his initial observation. You canot jump to conclusions that it is a problem with out some real indication. You have to swap injectors etc first.

Most problems will be fuel supply related for your issues. Do you have a good flow of fuel with no air entrained flowing out your return line with the engine running? You also may have an air leak somewhere that lets the fuel return to the tank. This will result in harder starts and missing as well.

Just take a line from the return valve on the injection pump. Submerge the line in fuel or any liquid. Watch for the level to increase and no bubbles once the line has been purged with the fuel. That is a starting point. It has to pass this test first of all to move on..

It's quite possible. Easy enough to take them apart and clean.

I am not exactly sure what you mean by blockage. If the flow is blocked completely the hydraulic pressure is going to seriously ruin something.

As previously stated the Delivery Valve seating area can go bad. I have seen the Delivery Valve Springs break before (on many types of iline IPs).

I have also see rust stick them in the unseated position. Meaning that when the Fuel is Injected the valve goes up but does not return to its seat.

If there is enough water in the IP it can actually rust the Steel parts overnight.

I have seen a similar thing due to old dried out Fuel where the Pump has sat for a long time (even a rebuilt Pump that has sat on the Shelf for several years).

Not related to the Delivery Valves but down below the Plunger/Tappet Return Springs have also been known to break.
On some of the IPs like the M Pumps the part that attaches to the Rack where you adjust the Fuel for each individual Element; have also been know to come loose.
When it comes loose you lose control of the Fuel adjustment on that Element.

The MW Pumps do not have a Cover but the MW Pump and the IPs on the later Engines have a removable cover where you can view the Element Fuel Adjusters on the Rack and you can see the Plunger/Tappet Retun Springs.