87 560 SL hard starting after sitting - PeachParts Mercedes-Benz Forum

Johnhazen · #1 06-23-2010, 12:26 PM

I notice that my 560SL has to be cranked way too much after it sits for a period of 1 hour or more. (requires 8-12 seconds of cranking)
Once started I can smell a chemical order like gas, but it seems to be a slightly different smell. (goes away after a few seconds) After starting up it runs pretty good. If I shut it off and restart (within a few minutes) it starts immediatly. It is like it is losing fuel pressure. I have tried turning the key on and off several times (without letting the starter motor engage) and it seems to help a little. (As if it is pumping up the fuel pressure) I have read where some say its the fuel accumulator would be the culprit and others say no, that the fuel accumulator's function is not to hold pressure, but rather to relieve pressure slowly after shutdown. I welcome any suggestions on what to look for and how to test suggested part(s)?
One other item: It also has a strange idle, almost like a pulsation. (Idles at 500 rpm) Can't tell if this is caused by miss or the computer trying to compensate for something. Someone said put a timing light on each wire to find which one might have a miss, but I do not see how that would identify a bad spark plug.

SunGuy · #2 06-23-2010, 12:59 PM

When almost identical symptoms appeared on mine, it was the 02 sensor that was bad. I found that after the first warning light comes on at around 40K, the original sensor is replaced. After that, MB did not design a resetalbe warning light for the next time it goes bad and encouraged techs to remove the bulb when changing the sensor for the 1st time. Good Luck-

Bob

ctaylor738 · #3 06-23-2010, 04:52 PM

You are correct about the accumulator. But if it has a hole in it or otherwise lost its ability to hold pressure, it will allow fuel to drain out of the lines and it will take a while to restore the pressure so the car can start. You can check it by clamping the line back to the tank and see if that stops the pressure drop.

Another thing to check is the pressure regulator to the left of the FD. Unscrew the return line. Only a tiny amount of fuel should come out of the regulator.

If you have a rythmic change in idle, it may be a worn-out o2 sensor reacting slowly and the system overcompensating.

Finally, if you put a light on a spark plug wire and it doesn't flash, then it's certainly a clue that something is going on. It could be the plug or the wire, obviously, so the next step is to move the plug to another cylinder, or try a different wire to isolate the problem.

Johnhazen · #4 06-23-2010, 05:55 PM

Thank you for the quick responses. They help a lot.

Johnhazen · #5 06-23-2010, 06:04 PM

Re: "Another thing to check is the pressure regulator to the left of the FD. Unscrew the return line. Only a tiny amount of fuel should come out of the regulator."

"to the left" is passenger side or driver side? I haven't looked in that area yet, but I think I read somewhere that there is a line going into the valve cover on the passenger side from the regulator. Is that the line you mean or is there another line going back to the gas tank.

ctaylor738 · #6 06-23-2010, 08:33 PM

In Mercedes-speak, left and right refer to the side of the car as if you were standing behind it, also referred to as "direction of travel."

The pressure regulator is on the driver's side "left" on a US car.

If you want the CD chapter, which has pictures, send me an email.

Johnhazen · #7 06-24-2010, 03:59 PM

I just read another thread recently posted that talks about spark plugs and how you need non resistor. My rough idle did start after new plugs from autozone so I bet they are resistor type. Any one have a source for the hard to get non resistors? 560SL

KCM · #8 06-30-2010, 12:20 PM

Quote:

Originally Posted by Johnhazen

I notice that my 560SL has to be cranked way too much after it sits for a period of 1 hour or more. (requires 8-12 seconds of cranking)
Once started I can smell a chemical order like gas, but it seems to be a slightly different smell. (goes away after a few seconds) After starting up it runs pretty good. If I shut it off and restart (within a few minutes) it starts immediatly. It is like it is losing fuel pressure. I have tried turning the key on and off several times (without letting the starter motor engage) and it seems to help a little. (As if it is pumping up the fuel pressure) I have read where some say its the fuel accumulator would be the culprit and others say no, that the fuel accumulator's function is not to hold pressure, but rather to relieve pressure slowly after shutdown. I welcome any suggestions on what to look for and how to test suggested part(s)?

Could be a bad fuel pressure regulator as previously mentioned. If it is leaking, it will bleed the pressure out of the system. Could also be fuel injectors that are not holding pressure. This will also relieve pressure in the system. The smell might indicate that one or more injectors are leaking down and flooding the engine.

One other thing to check is the ignition system. When it does not start, check to make sure you have a hot spark out of the coil when cranking. The tachometer needle should also slightly move when cranking the engine. Electronic components can absorb heat when a car sits hot and malfunction. The ignition module is one component that can cause problems on these cars, but coils and pickup sensors can also malfunction.