Need some collective wisdom here. I am at my wits' end on the problem of my 87 300D, OM603 engine. It will shake or mis-fire intermittently as if it is firing on 5 cylinders or less. Then it will run perfectly smooth the next day. I am at a lost as to what could be the problem. I check opening pressure of all injectors and they are within spec. My questions are:

1) Can an injector fail to open sometimes and is normal again?
2) Can the IP fail to deliver fuel to 1 or more injectors sometimes and is OK again?
3) Any other things I should check?

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Check fuel pressure and check for leaks in the fuel lines and fuel heater. Sometimes hoses swell internally and restrict fuel flow.

I had a problem like this on my 190 which turned out to be a rusted fuel hard line. It wasn't quite leaking yet, but was porous enough to sweat fuel and I assume allow air in.

Is this at speed or while idling? If while idling, check the connection to the ELR actuator (red round plastic thing) on the tail end of the IP. Check also the OVP relay and fuse/s.

Sixto
83 300SD

The problem is at idle. Will check the connector and OVP relay. Thanks.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

If its the OVP, your RPM will dip. There are no effective tests for an OVP other than substitution.

The disc valves in the Fuel Supply/Lift Pump seem to wear out much sooner then the older types.

Idle Shake gone after Fuel Supply/Lift Pump cleaned
Fuel Pump Suction/Delivery Valve - PeachParts Mercedes ShopForum

There is 2 threads in the DIY section on installing new Valves and O-rings in the Fuel Supply/Lift Pump

Then there is the Fuel Pressure Relief/Overflow Valve. If yours have it some have found the plastic piece distorted or falling apart.
This is the only pic I have and I have no idea if yours looks the same as the one in the pic (copied from one of the members).

Air leaks on the suction side can be intermittant.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel