Hard (or no) startin when hot.

[aharley1]

My 1988 560SL starts right up when cold. When hot it starts hard & sometimes won't start at all. I've changed the fuel filter & the fuel accumulator. It has good spark, but with the air cleaner off, I can't smell any gas, so it appeares to be a fuel problem. I drive 5 miles & it won't start. Let it set overnight & fires right up. Anyone have ant ideas?? Thanks.

[ctaylor738]

Does the length of time that it sits make a difference in how hard it is to start? If so, you are losing pressure somewhere in the fuel system. I think there is a check valve in the filter or the pump that may be failing. Your injectors could be leaking down as well.

[aharley1]

Actually the LONGER it sits, the easier it is to start. When hot, I can shut it off & immediately try to restart & it'll fire, run on two or three cylinders for a second or two, stall, then not re-start no matter what. Sits an hour or two or over night & it fires right up.

[Tony1628]

Check the cold start valve. Take it out and see if there are fuel comes out..

[RickM]

I'll put my money on a very common warm/hot hard start culprit.....the Fuel Accumulator. My car was very hard to start after I parked and got back in and tried to restart. Very inexpensive and quick fix. Just be careful as the potential for a bit of fuel spilling on you exists.

[aharley1]

Been there, done that..the fuel accumulator. Local independent shop charged me $243 & it didn't make any difference. It's been there all week. Finally picked it up last night because they haven't touched it since Monday. Same thing...I let it run about 15 minutes. Shut it off & it won't start.

[81SLWASTATE]

New memeber, owner of a 81 380sl with same problem, and chance it can be in the fuel dist. Maybe a worn "o" ring. I have replaced all of the parts I see in your messages, but not the fuel pump relay. I will be checking that out REAL soon. Mine will not start when hot either. Fires right off when cold. If I sit for 5 minutes to one hour, it stumbles, acts like it is firing on 4 to 6 holes and then after you keep the RPM's up for 2 or 3 minutes at 1500 or so, it settles down. Thank you for your help and let me know if you need any more info. 81SLWASTATE

[aharley1]

Sounds exactly like my problem. If you can hear the pumps (or have someone else start it & listen), you should be able to hear them when it's cold & not when it heats up & won't start.
Im a little skeptical that the relay will fix it, but we'll see.

[aharley1]

The saga continues...
I picked my car up Friday. They replaced the fuel pump relay this time. I drove about 15 miles, shut it off, looked at a car, got back in & it wouldn't start!!! AGAIN! After much coaxing, I got it started. Drove it this weekend with no problems starting.
The worlds finest engineered car..... my others don't have this many problems!

99 Harley Davidson Heritage Softail
98 Dodge truck
88 Mercedes SL560
04 Chrysler convertible

[Tony1628]

Did you ever check the cold start valve. It happened to my 380sl. I replaced it and now it start fine...just do a search.. it is very easy to check..

[aharley1]

Well, the relay was installed, I drove 12 miles, stopped & it wouldn't start!! Drove the rest of the weekend with no problem???

[ctaylor738]

What kind of coaxing did you do to get it to start?

When it started, how did it run? OK from the get-go? Started firing on one or two cylinders, then all, then ran smoothly? Sputtered for a minute after starting? Could you hear the fuel pump when you cranked the engine?

[aharley1]

It started 3 times this morning while hot. Then I went home for lunch & 30 minutes later, no start. It tries then sputters, then cranks but won't fire. If I pump the pdal hard, sometimes it will start. I talked to a different shop mech. he said possibly the ck valves in the pumps. I couldn't find anything on a cold start relay in the shop manual. Hopefully this guy will diagnose instead of changing parts.