This is more of an annoyance than a problem, however I would like to solve it. I cannot figure out what would cause a diesel to be more difficult to start when it is hot than when it is cold.

My 84 300D starts fine when it is dead cold (a little bit of stumbling & misfiring for just a few seconds, then it smoothes out perfectly). Once it is fully warmed up, if it is left sitting in a parking lot for more than a few minutes, it takes quite a bit of cranking to get started again. If I tip into the throttle to assist in starting, there will be quite a voluminous cloud of smoke from unburned fuel burning off. This really flies in the face of conventional wisdom regarding diesels in general -- it should be easier to start once it is hot. I have searched through the archives and cannot find a similar problem under the same circumstances.

The injectors are new, valve lash is set properly, compression is good, glow plugs are new & working properly,etc. etc. The only thing that I can think of is possibly that the fuel pressure in the injector lines is bleeding back down. I have seen references in a couple of posts to some type of check valve seals in the injection pump, yet I am not sure if this type of problem would be caused by that. If that IS the cause, could someone please outline the procedure for replacement of the check valves? (I cannot find the procedure on the service CD) Any feedback would be greatly appreciated!

Thanks again


RTH

Check the temp sensor for your glow plugs. My 220D (very old and raggedy) will not start well hot without a little bit of glow -- my 87 300DT usually runs the plugs a few seconds even hot, as does my brother's 300SDL.

You may have a plugged over flow line on the injection pump (causes very early injection) or air in the fuel -- check the suction lines on the fuel pump for leaks -- fuel will leak back down into the tank rather than out of the hoses. You can park nose down on a steep hill, or back up on oil change ramps and see if fuel leaks out. Worn and leaking fuel lines are pretty common since no one ever seems to replace them. Air in the IP can cause foam injection rather than solid fuel injection, and the fire goes out as the fuel foam sprays in, making it hard to start. Usually runs OK once started, but makes too much smoke.

The only other thing that comes to mind is a stuck injection timer, making the injection very early. Usually will crank hard and knock a lot under these circumstances.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Thank you for your reply Psfred. Sorry that it took so long for me to respond -- I have been up to my eyeballs lately

If air were leaking into the system I would most likely have the same problem when starting from cold in the morning. The suction lines are in good shape and not leaking as far as I can tell, however I think it would be prudent for me to replace them anyways considering the age of the car. The next time the engine is very hot, I will go under the hood and use the manual pump to see if any air bubbles present themselves in the return line.

I will hook up a test light directly to one of the glow plugs to check their functioning when the engine is hot. I'm not sure about the injection timer -- though mechanically proficient, I am relatively new to the diesel world, and I don't have a clue as to how to check and/or rectify that problem. I have already changed the overflow lines on the injectors. The overflow line on the injection pump seems to be okay; either way I don't have any of the other symptoms you described that are associated with early injection.

I'm not sure exactly how fast the starter should spin the engine over. I will try to take notice of whether it seems slower when the engine & starter windings are hot. I hope to be able to poke around at this later this week -- thank you for your assistance!

RTH

100 rpm miminum to start a diesel -- too fast for most people to count if you paint a dot on a fan blade. About four times as fast as most gasoline engines.

If the injection timer is stuck, injection timing will be too fast and the car, when it starts, will snort like a Mack truck. No way to tell but to check the injection timing with a drip tube or pull the timer (its behind the vacuum pump).

The overflow pressure regulator is behind the bolt holding the return line to the IP -- it is either an orifice in the hollow bolt or a check ball and spring. If plugged can cause serious hot hard start problems, also lots of black smoke and excessive fuel consumption.

You may also want to check the valve clearance hot -- the exhaust valves are sodium filled, so grow quite a bit, and if they were dirty when you adjusted them last, can end up with no clearance hot. Guaranteed hard start, what with no glow plugs and no compression! #1 on my 220D closed up to less than 0.005" cold between adjustments!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!