Sometimes when I first start my 78 300D the
idle will skip or stumble. If I hold down
the accelerator pedal I can make the skip go
away. There seems to be alot of exhause smoke on
the first start up.
Is this an injection pump issue? I have a new
rebuilt head, timing chain, both fuel filters
and use a fuel additive every other tank.

I would remove injectors and bench test. While out I would check compression. If all cylinders were above 300psi I would worry next about the pump. The first thing I would do to it is replace the pump element check valve to cylinder seals brass ring part# 000 074 17 59. Unfortunately I think you have the pump with external fuel correction. This can be determined by whether there are two 13mm wrench, 8mm nuts holding (and adjusting the pump cylinder) right blow the injection line. This adjustment is only for pump shops so they will have to replace the seals and probably the element check valves. To solve the problem. The early mechanical (as oposed to pnuematic) pumps had three updates to the check valve design. The problem is that a portion of the column of fuel in the line leaks back into the pump causing the first pump pulses to refill the line before proper injection can occur. As the leakage always varies cyl to cyl the engine starts running one the cylinders one or more at a time.



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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

The other thing here is to check and make sure that the glow plugs are working correctly. If one or two go south, it will skip a little on start up.

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Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM