Mercedes-Benz Forum banner
1 - 6 of 6 Posts

·
Registered
1973 450SLC
Joined
·
4 Posts
Discussion Starter · #1 ·
I have a '73 450SLC that misfires after warm up. So far new spark plugs, distributor cap, plug wires, fuel fill cap and fuel filter were replaced by an independent, MB trained, mechanic. I have flushed the fuel tank, installed new after market fuel pump, added injector cleaner and replaced tank strainer. Also the brakes went on it and the master cylinder was replaced. Any suggestions on where I should look next?

Since the car is new to me I'm not really sure how well the engine is running when cold. Idle is fast when cold and jumps from 500 - 1200 when warm.

Thanks,
 

·
Premium Member
1975 450SL
Joined
·
2,440 Posts
These things have a LOT of vacuum control systems on the engine. Any failure of a connector or hose can cause these type of problems.

Get a manual (the factory manual on CD is recommended), take a deep breath, and start reading. You may want to get some tools and meters, but it only gets 'worse' from there. You'll be addicted, hanging out here and looking for answers to all sorts of weird problems, possibly helping out someone new. It can be a rewarding experience. Welcome to the madhouse.:D
 

·
R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
Joined
·
32,777 Posts
Did the mechanic replace and set the points, set timing etc?
 

·
Premium Member
'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
Joined
·
12,361 Posts
Points should be set properly according to proper dwell stated in manual, but 0.014" is good for a start. But on an old car, better still to replace points with a Pertronix Ignitor 1, model 1885 - about $80 from Retro Rockets.

Next, you could have a problem with oil leaking onto the trigger points. That is a set of points located in the bottom of the distributor that control the firing of the injectors. They sometimes get oil on them and sometimes they are just worn out (no adjustment)

There is a lot of other stuff to check - sounds like you may have sticking aux air valve and some vacuum leaks. Normal for these cars! Do a search here and on Peachparts - tons of stuff on the these D-Jets - will keep you busy for the winter!
 

·
Registered
1973 450SLC
Joined
·
4 Posts
Discussion Starter · #5 ·
Thanks for the quick responses. Looks like it may be a long cold winter and no quick solution.

Now I know why the mechanic said the fastest and easiest fix was a small block Ford. Not yet though. Maybe in March if there is no progress.

This week I'll checkout the point, vacuum, aux air valve, and trigger points. Will post the results when completed.

Thanks again.
Jim
First time MB owner.
 

·
Always Remembered RIP
1979 280sl 4 sp w/ac 1957 MGA 1998 volvo xc/70 2004 F150
Joined
·
6,050 Posts
Spray around all connections with carb cleaner and listen for a change in idle speed. It's a quick check for a vacuum leak.
 
1 - 6 of 6 Posts
Top