450SLC after years in the garage runs roughly

[Djenka]

Recently got my self one fine example of 1980 450SLC Euro specs with 49500km (~33Kmiles), full house, original "virgo intacta" condition.
Engine has very bad start (takes more than 10seconds of cranking to start) and once started it will run very rich for a while with bad missing. Shortly, engine will run more or less fine with occasional missing. Once started engine, tekes a split second to restart. A 10 minutes pause will cause another long kranking to start.
As the simplest remedy, i've changed fuel and air filter, spark plugs and did minor engine service (oil, filters). Furthermore, i had replaced very bad (stiffened) rubber seal on injectors and O-rings on their plastic sleeves. That seemed to improved idling but after adjusting CO2 to specified levels (without air filter installed) the overall performance of engine improved significantly. Unfortunatley, all the original problems stayed there but with much shorter period before normal-like operation of engine.

Now, with everything being 23yrs old i just don't know where to start.
Coil? Electronic ignition? Spark plug cables? Temperature sensors? Cold start valve? Suplemetary air valve? Intake manifold gaskets...
The list is big and if i start to replace all one by one it'll cost an arm and a leg.
Where to start, what to do first?

(Note: engine is 117985 with no emission control devices)

[G-Benz]

My first guess would be a vacuum leak of some kind.

Vacuum hoses follow the same physical laws of entropy and as they age they get brittle and lose their sealing capabilities. But you probably have an intake manifold leak of some sort as well.

The long cranking times indicate that you are losing fuel pressure. I don't know much about your engine configuration or the associated components, but there is probably a fuel component (accumulator or regulator, I can't remember) that maintains fuel and pressure when the engine is not running. This allows for quick starts when cold. If the component is not doing its job, you have to crank the car several times on a cold start to build up the fuel pressure again.

These are not the wise words of an experienced tech, but some suggestions on where to start looking...good luck!

[David Speed]

I suggest an 'Italian tune'……(injector cleaner & long hard run) before doing anything else..........a good clean of the fuel system might solve a lot of problems...........did you check the injector spray pattern when you replaced their O-rings & sleeves?

I recently got a 1978 280CE going after being unused for 5yrs Original post ......... the key to get it running was flushing the fuel injector system with injector cleaner (see post 25Aug2003).............I would certainly advise this before pulling anything apart or or taking the replacement route..........I used injector cleaner at ~ 100 times normal concentration first......full bottle in near empty tank.........expect short filter life

I have just pulled my fuel tank and couldn't believe the crud...........amazing it ran at all...........if your car has been garaged for a while you should consider cleaning the tank - the strainer screeen in the tank in particular.....as it is best to start here and work downstream......filter etc.

My cold start injector checked ok, but my injectors needed flushing

I also found a vacuum leak that caused loss of vacuum advance and lean running.....perished rubber connection the EGR valve

You probably have a fuel acumulator near the pump & filter.........mine needed replacing after 25yrs.......maintains fuel pressure for restart...........fuel pressure gauge should help to diagnose

Link to my 'Italian Tune......should have pulled & cleaned tank first"

[Djenka]

Well, the Panzerwagen seem to run better with more petrol being burnt but still not good enough.

Checked at local MB dealer, intake manifold gasket (to head) cost me R40 (~5EUR) each and had to buy'em. Dunno when will I fit them, I am short of time now. Also, just a thought of work required to remove fuel regulator and bits and pieces to reach intake manifold gives me goosebumps.
Haven't checked the spray pattern of injectors when had them removed because didn't know they can cause problems (at that time). All but one looked very clean.
Decided to perform "Italian tuneup" this weekend after it being praised so much here.
Vacuum leaks will be next, I think I read somewhere here that cold-start spraying will reveal a breach of vacuum line by changing the idling speed for the moment after being sprayed.

Engine have light knocking of at least one valve or rocker arm and resolving that is a top priority now.
I will keep informed here what work had made what kind of changes in the engine operation.

Thanks

My 73' 450 was also garaged for some time (5 yrs) before I bought it. I contacted a flyer buddy of mine and got some 100 no-lead from him, running a full tank of that through cleaned the inside up real well.
Next thing you will have to look out for if your luck is like mine. The fuel hoses on top of the engine, along with the injector boots may have cracks in them.
Check these over well, you would not want your SL to burst into flames while driving down the road. Mine struck a leak on the main injector line and spewed gasoline all over the top of the engine under pressure. Good thing I was not far from the garage.

Good Luck

Housesurgeon@earthlink.net