I tried searching using words such as 450SL misfire and only came up with a couple of posts. So hopeflly I can get some more adivce/info by posting a new thread. A friend has a '74 450SL with 105K on it. She just picked it up in Jan. The car had been sitting for a very long time prior to her buying it. When she starts the car for the first time of any given day, the engine runs real rough, sputtering and has very little aceleration. As the car warms up, the problem dimenishes. Though even at a warm idel you can hear a slight misfire. The dist. cap, rotor, wires and coil appear relatively new. I did not pull the plugs to see what shape they are in or even if they are the correct ones. She had a garage look at it and they told her that everything appears to be fine. They did see some corrosion on the wire connectors in the sparkplug boot, so put some dielectric grease on it to prevent further corrosion. They also said that because it sat for so long, they put in some fuel injector cleaner in the gas.

This is her first MB, it's not her daily driver. So I want this to be a good experience/owenrship.

What basic things can we check/replace? Definetly don't want to throw parts at it. What grade gas should she be running? The engine has a 8:1 compression and the owner's manual states a RON of 91 which I know converts to 87 here in the states. Also, what spark plugs should be in this engine. I have seen 2 different plugs listed for this engine. Fastlane lists WR8DC+, but Bosch's own site lists WR7DC+

I am no familar with the 450. My 190 is a straight six witha completely different ignition/fuel system. My E320 doesn't even have a distridutor. So I am sort of learning here as well.

thanks in advance for any direction/advice you guys can provide.

__________________
1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member

Thing is, if it's misfiring and as you say "some corrosion on the wire connectors in the sparkplug boot", you might as well replace the plugs, the wires, the cap and the rotor. I don't think that's "throwing parts at it"; misfires, ruff idle, what else could be the issue?

Maybe the warm up regular (if applicable). I have a 78 450, and I recently replaced the plugs, wires, cap and rotor and it I see it just as regular maintenance on an older vehicle. Small issue, but have you looked at the air filter? Or maybe even the fuel filter? Again, I look at it as maintenance and what else could be the cause of misfires.

p.s. I have the newer 4 electrode spark plugs in my vehicle.

This is very symptomatic of fouled EFI trigger points. Especially the "Gets better as it warms up" part.

350SE runs on 4 cylinders?
Testing Trigger Points
W109 3.5: distributor renovation

Also: I would never suggest using anything but a copper-tipped non-resistor plug in your vintage Benz(es) unless you've replaced your ignition system with a more capable spark-producing unit like Pertronix or Crane.

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

That is the exact symtoms my car had and cleaning the trigger points eliminated the problem.

__________________
Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT

Thanks for the replies.

As I mentioned, my 2 Benzes have completely different ignition/fuel injection systems. So to help my friend, I am having to research/learn this older system.

__________________
1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member

Your friend has a car with Electronic Fuel Injection -Bosch D-Jetronic.
http://www.scribd.com/doc/7303245/D-Jetronic

This system was used in SL's imported into USA from 1972 to 1975.

Regarding plugs and wires - There are two types of wires - OE type that have resistors in both ends and newer Bosch ones with no resistor in plug end. These newer wires work fine with Bosch and NGK resistor plugs. I have similar car and it runs fine with WR7DC+ plugs although I currently am using the NGK equivalent. If car has original type wires, then non-resistor plugs may be better although Bosch say it doesn't matter.

Points could be a problem. They should be set to about 0.014" for a start, I believe, then check dwell per specs. But I, like some others here replaced the points with a Pertronix 1885. This eliminates points problems and eliminates the effect of distributor shaft wear on points.

BTW, this car has no warm up regulator.

Trigger points are located in the bottom of the distributor, which must be removed to get at them. If you do this, be careful to mark just exactly where rotor was pointing because it is easy to get distributor back in slightly wrong position. The point contacts never wear out. They sometimes pick up some oil and benefit from cleaning. The fiber rubbing blocks do wear out and then a lot of misfiring and incorrect mixture conditions occur. Doesn't sound like that is the problem.

The injectors might benefit from a cleaning. There are places that do this. New ones are very expensive.

Look at the rotor and cap to be sure the contacts are clean and that there are no cracks or burn marks.

Check and clean injector ground connections back under air filter.

There is a lot more to check and very few mechanics around that still know these engines. So, you are doing the right thing by trying to get a good understanding of the system.

These links might help:

Troubleshooting:
350SL Starts and Dies - Starts and Dies ...

also here:
http://www.benzworld.org/forums/w116-s-se-sel-sd-class/1223523-bosch-d-jetronic-k-jetronic-troubleshooting.html

Engine manual:
http://www.startekinfo.com/StarTek/outside/11883/?requestedDocId=11883
(section 7.4 and 7.5 are good place to start)

Have Fun!

__________________
Graham
85 300D,72 350SL, 98 E320, Outback 2.5