Hello Everyone, I'm new here, and VERY gratefull, This is a great resource and help to me. THANKS! I just got, (about 2 months) an 87 560SEL 75Kmiles. Runs great, but..... When cold, it starts easily. If restarted within 5 minutes, it re-starts easily. If left for 20-30 minutes it takes an extended cranking time to start, about 5-7 full (long) seconds. During the long cranking, there is no coughing, catching, no nothing for about 5 seconds, then it comes to life,... rough for about 10-15 seconds. The symptons are very consistent. From reading other threads, it seemed likely that the fuel line pressure was leaking off and fuel vaporizing? I've changed the fuel pump check valves, (both) and then the fuel accumulator. No improvement what-so-ever. So now what? Help.... I'm kinda clueless as to next logical step. Pressure checking? If so where? Thanks for you help in advance. JP

Fuel bleed off is a common problem that will cause this type of symptom. The only thing in the fuel pressure system that you haven't replaced is the fuel pressure regulator. However I would suggest that you have the fuel pressure tested to see whether the fuel pressure does bleed off when the car is shut off.
Many times a weak coil OR bad cap & rotor can cause the exact problem.

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Follow-up info. (It runs well so it’s kinda on a back burner among a million other things to do but,…as time allows…) Borrowed a fuel pressure gauge. It runs at 80 psi, shutting it off brings it pretty quickly to 50 psi. 30 minutes later it’s still at 40 psi. Bought the shop manual. (Talk about a hard reading, poorly index CD book). Ouch. Specs seem to be in line with what I’ve got. 6.2 bar, (which if 1 bar =14.7 psi) then it should be 91 psi. I’m at 80. At shut down book says it should be below 3.4 bar. (49psi) I’m at 50 falling to 40 after 30 minutes.

Brought the car to an independent MB shop who agreed to diagnosis for $50. He claimed electrical is fine, & no codes showing up, & checked fuel pressure confirming my findings and said it was good, but diagnosed with 90% confidence level the fuel injectors as the problem. Claimed he had pulled 3 injectors and all were bad. $600-$800 for him to do the work. I did it for $250 with great hesitation never having done it before. (It’s almost as easy as changing spark plugs.) During removal, I found gas in only 3 of the injectors. Things seemed like they were looking good. Well they must have been bad because it’s running sooooo much smoother, so I won’t complain, BUT absolutely no effect on the hard starting. When hot, and 30 minutes, it’s still 5-7 seconds till started.

Any one got some further thoughts?

I have a 78 450 slc and have the same long cranking time problem. I thought it was a cap and rotor problem as another person responding to your post did. I replaced them and the problem continues. I am now looking at the balast resistors
( mounted beside the coil) as the problem, if I have any luck I will let you know. If you find your problem, drop me a line- I would appreciate it. Good luck!

Here is a couple of long shots, but, they happen.

1) ign. switch.

2) fuel head leaking from the mertering pintle. Drops right into the a/f housing.

Joe

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