Help with starting problem 1991 300SL
 

Hi all

I hate this when it happens!

I replaced the alternator and the air pump with new units. Before I reinstalled the new ones, I degreased that side of the engine and hosed it down sparingly. I did not do the intake side at all.

I also pulled the valve cover off to check things out. No problems, chain fine.

Reasembled everything.

The car ran fine before I did my planned maintenance. Now the engine cranks fine, but no start.

I double checked the plug wires - all correctky installed. I find no wires disconnected anywhere. I do not see anything on the exhausr side of the engine that seems electronic in nature that I could have ruined or got wet when I cleaned that side of the engine.

I see a crank trigger - maybe I got it wet, but I suspect it gets wet anyway when driving in the rain.

What do y'all think I should check?

Thanks.

first is whats missing. fire, fuel or comp.

george

No fire. That's why I was suspecting the trigger getting wet with cleaner or water, or both. That's about the only electrical item in the area that I can see. Maybe there's something else?

How does one check the trigger?

spray the inside of your distributor cap with WD-40 might have gotten some water in there

Pulled the cap -dry.
Cleaned the bottom of the trigger.

Now I have spark, but no start.
What's a safe way to test if I have fuel at the injectors?

The car sat in the garage all winter. I started it once a month. It fired right up every time. All I did was change the alternator and the air pump! Sheesh!

I did notice a mouse had taken a little bit of firwall insulation covering. I looked all over and could find no wires the critter tried to strip. I pulled the cover off the fuel pumps/filter/accumulator and everything is ok in there. I check ed all the fuses.

What controls the fuel pumps? How do I check the circuit?

Thanks for your help.

It's too nice out to be working on it instead of driving topless!

Make sure your belt is not too tight. I had the same problem a day back, just felt like my belt was loose and I tightened it (on 87 260E). The next thing I knew was it had starting problems that I never ever had. I also had put some engine degreaser and some water to clean the engine's front area. So I thought it was water and I can wait a few hours and it will start fine. Infact, it did start couple of times fine the next day (today) but then failed to start again. I figured it had to be the tightened belt. So I loosened it a bit and guess what, the car started just fine, several times. I am not sure what the reason is but a belt which is tighter than needed causes starting problems.

The belt is on an automatic belt tensioner - seems like the same amount of pressure as any of the other later model cars with the tensioner.

O.K., I see, then it cant be the problem.

It started!

I've never checked for fuel on a fuelly before, so since nobody answered, I figured I'd loosen a line at the fuel distributor. I cranked a while and the fitting got wet. So, I must have had fuel all along. I never did hear the fuel pump run, but then again, I never do. I had nobody around to help me so I could not climb under the car and touch the fuel pumps to see if they were operating at initial turn of the key.

I sprayed the crank sensor down heavily with contact cleaner. I jiggled wires. I took the air cleaner asy off and followed the crank sensor wire - found it to go the ignition module. Disconnected and reconnected all of those wires. I soaked the sensor down with some more contact cleaner. I cranked the engine like crazy, and it started. And ran smooth as soon as it started. I figured it would at least shake rattle and roll. Nope, just kicked off and ran like it should.

I wish I knew what was going on.

I'll try to start it again tomorrow after work.

Anyway, the new alternator and air pump are real quiet. This engine runs quiet now - am happy.