92 300SL - Occasional engine stutter/cutout

[stevecora46]

My 1992 300SL has 87K miles on it. Every once in a while it doesn't seem to want to run smoothly. It starts fine, but then when you give it some thottle, it cuts out and acts like it's not going to run. You can nurse it along and it will finally get going and run OK, but when you give it too much throttle, it cuts out. Once it gets up to speed, it seems fine, unless you apply too much throttle. After a while, the problem goes away and car runs like it's supposed to. Today, I took it out on some errands and it started cutting out in city traffic. I haven't had it out in about 2 weeks. This is a very sporadic problem. It probably happens about once every 20 times I take the car out.

It seems like it's fuel related. I've had the car since August, 2003. I had a new E.H.A. valve put in it about a year ago. It actually had the same symtoms as it does now. I was taking it to the local Mercedes dealership to have the oil changed and a new battery installed (I've since learned to avoid the dealership), and on my way it started cutting out and I didn't think I was going to make it to the shop. They diagnosed the E.H.A valve. I've put new plugs in the car, but I've not changed the fuel filter nor have I replaced the plug wires or anything else ignition-related. Any suggestions would be helpful.

Thanks, Steve

[tecqboy]

This could very easily be a clogged fuel filter. It acts like the fuel pressure is too low. There's enough gas for lite throttle, but not enough for load. Also, it could be the fuel pump itself. But why not start with the cheaper filters. Check the fuse for the fuel pump too. It's obviously not blown, but these older fuses get corroded in their sockets. That can cause an intermittent failure or a lowered supply voltage to the pump. The fuel pump uses quite a few amps, and any resistance could cause lowered fuel pressure. A good shop can measure the fuel pressure. And then of course, it could be something entirely different. Injectors, throttle position sensor, high tension wires, and on and on. Good luck.

[bwheitman]

Is the car going into limp mode? Mine does this when ever I wash my engine, the reason is due to a fault, or an arc in the ignition. When it happens it is like the engine is running on 3 cylinders, no power. I have to shut it off and re-start it, it is fine and then it will do it again until it dries out. I don't wash my engine anymore, but if you have faulty plug wires that are arcing or causing attenuation that faults the computer and the things goes into limp mode. Just an idea, can't really diagnose without more info. Good luck!
Brian

[sldan]

I had the same problem with my 1991 300SL 50K miles. I found a defective distributor cap. The center electrode was cracked. I replaced the cap, rotor, and spark plugs. The problem is gone.

I first suspected a fuel injection problem during warm up. The problem was intermittent and a pain in the rear.

Dan

[ASJ101]

SLdan is right, these cars eat caps. Check the cover to the rear of the rotor arm as well. If it has any damage to it it will give you the same symtoms as injectors, wiring loom, throttle body, leeds or water in the petrol issues

[LeaUK]

Interesting. I was just about to make a post on this too..... My '93 500 has EXACTLY the same symptoms.

When I first bought her, around two years ago, I had to replace both rotors and caps as I suffered this exact problem but with much greater virosity, however I now find intermittent problems with similar symptoms but to a much lessor degree.

Although this is very intermittent I find it's generally after rain and after the car has run for a while (15 minutes or so) and is then restarted - maybe the caps are condensing inside?

I'll check the fuel filters as suggested but suspect the caps or maybe the cap seals?

[LeaUK]

Inspected both caps this morning to find one in perfect condition but the other had clear tracking across the cap surface. This would suggest moisture.

However both seals are perfect. Interesting that one's perfect?!

Check your caps regularly as SLDan is right - these cars EAT caps