Engine Specs

[Darrell Woods]

I have added a '75 450SL to the barn. Original motor (per data card) was 117982-12-038336. Obviously been replaced, since current engine is stamped 117.981--if my research is right, this came from a '71/'72 300SEL. I have the 107 CD, and am wondering if all the specs for the 300SEL 4.5 and 450SL 4.5 would be the same. Or, do I need to invest in another CD specific to the 300? Car has an intermittent (although severe) miss, and I really need to get it fixed. Local MB dealer "claims" to not have the spec info to do the job, but I think it's just not worth their time (hard to believe considering they've always serviced my trustworthy '89 260E and have been paid handsomely over the years to do so). Any suggestions appreciated. Thanks.

[psfred]

The 117.981 probably has a hotter cam (232 hp vs 190), otherwise the same. If you have to pass emissions controls you may need the newer cams, or your NOx will be too high.

You will need to determine if your miss is fuel or ignition related. However, a quick fix is to pull the distributor and clean the trigger points, also check the wiring there to make sure it hasn't broken at the connector. Also, put in a new set of points, the old ones are probably ancient.

Unless the wires and plugs are fairly new, I'd replace them too, just to eliminate the possiblity they are croaked. Ditto for cap and rotor if they aren't fairly new.

If none of this fixes the problem, pull the plugs if you didn't change them and look for lean or rich running condition on each one -- if you find one burnt from running lean and the others are fine, chances are you have either a sticky injector or a vac leak on the runner for that cylinder. If one is black and the others fine, you have an injector sticking open.

Vacuum leaks will cause all sorts of trouble on this engine, so make sure all the lines are good and that the locks and AC controls (if they use vac) are not leaking.

Peter

[Darrell Woods]

psfred, appreciate the info. Plugs, wires and cap are new. Haven't changed points (or trigger points...just learning about those). I'll check the plugs for the indications you discussed, and I had started to get a feeling that this fuel injection system is very dependant on proper vacuum. The engine is so smooth and strong, and the miss comes and goes so quickly, I've been leaning towards thinking it's electrical; like something losing contact and cutting out 2-4 injectors. At least that's what it feels like, and why I didn't really think it was one injector going bad. Thanks again.