Hard (or no) startin when hot.
 

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.

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.

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.

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

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.

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.

This sure sounds like an electrical problem.....the underhood temps typically are hotter right after shut-down then while running. It's not unusually for devices to become susceptible to heat as they age. Ignition come to mind first, including the OVR and fuel pump relay.

Good luck, and please let us know what you find....mine might be right around the corner. It is a little hard to start when warm......not bad, but you have sure caught my attention.

There are a couple of things to check.

When you try a hot start, put your hand on the fuel pump while someone cranks the engine (or vice versa) and verify that the pump is coming on. If you can't feel the pump running, then you have problem with the FP relay or one of its inputs.

If the pump is running, then crank it for a while. Pull a couple of spark plugs out and see if they are wet or dry. Wet would indicate either too much fuel (cold start valve firing when it shouldn't?) for a hot start, or no spark. Dry means no fuel.

Can you run these checks so we have some basic diagnostic info?

I'll try that...I have pulled a spark plug when hot & won't start and had a very strong spark, so it isn't that. I'll ck the fuel pump, tho. Thanks.

Harley, as Chuck asked, remove the spark plug when the hot no start condition happens and see if the spark plug electrode is wet. Since it starts o.k. cold it sounds like it's flooding when hot at start-up. Tony's suggestion is good. If the plug is indeed wet, remove the cold start valve and see if fuel comes out while cranking when the engine is hot

I had put it back in the shop. They now say it's a bad fuel relay & shuts down the fuel pumps when it gets hot.

Bingo.

You oughta try to get some money back for the perfectly good accumulator they replaced ...

They said they'd "make it good". We'll see. I told them I wasn't paying for them to change parts, I can do that. I was paying them to FIX IT. I ended up picking my car up last week, but then they told me to bring it back & they'd make it right. Should find out today.

Hard (or no) startin when hot
 

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

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.