austinramsay

Just bought a 1990 300SL with 88k miles on it. It runs very smoothly and drives solid. I just have one problem with it, starting it can be an issue sometimes. Sometimes it starts easier than other times, but it usually does the same thing where it will start right up the first try and then almost instantly die. I can not get it to keep running if I try to, although a couple times it has stayed running for me if I played with the gas a little. Usually after it dies after first try, I crank the second time playing with the gas and it will usually fire up. Sometimes I even have to do a 3rd time and it will stumble and then run perfectly fine. Any ideas? Here's a video:
Thanks, Austin.

austinramsay

Replaced the 2 pin blue coolant temp sensor on the thermostat housing last night with no change. I don't think leaking injectors could be the problem because I have the same issue even right after trying to start immediately after taking it for a drive. I would think it would start right up after being driven (since there wasn't time for fuel to leak into the cylinders) if that was the problem.

austinramsay

I found this article: https://mercedessource.com/problems/...-or-slow-start

"Depending on your model you may have one or two fuel pumps. These are high pressure pumps designed to deliver the correct amount of fuel to your injection system. These pumps do wear out and fail - often at the most inopportune time. With total pump failure your engine will just not start. Pending failure can often be detected by high pump noise while they are running or poor engine performance and hard starting. To order a new fuel pump or pumps check the related products."

I wonder if this could be a fuel pump problem? My pump is pretty noisy so it could be starting to go out but that could be determined with a fuel pressure test. Maybe with a weak pump it takes longer cranking time to create enough pressure to get it started? Where should I test fuel pressure while cranking?

Auzivision

Not sure how to fix, but my 1990 300SL exhibits the exact same behavior to a tee. Obviously it's either fuel or ignition.

At first I thought low fuel pressure and still suspect it. I know I need to borrow my fuel pressure test gauges I loan to a friend years ago to test that theory. However, I find after servicing the ignition system it goes away; albeit temporarily. The fact it goes away and comes back leads me to believe it is ignition related.
Replaced plugs and wires, went away… came back. Replaced cap and rotor, went away and came back. Replaced dust shield under rotor… again went away and came back. In each case I’d get a few weeks to a few months of good operation. Next test, wiggle wires open and clean distributor, but not replace anything. If it goes away, I need to figure out how to keep it away.

Maybe this weekend I can get around to testing both.

edit... WOW, 5 posts in 9 years... LOL, I better slow down before I loose by Newbie status Ha Ha