Question on D Jetronic

[230/8]

This may be more appropriate for the vintage or SL forums, but...

With the D Jetronic system on a 350 SL (US model, actually a 350SL 4.5), the underhood emissions tag shows the desired idle CO range to be 0.5% to 2.0% CO. It is a snap to set the idle at 1% CO and it runs great there.

Does anyone know what a well-tuned D Jetronic system should have for a CO reading in the cruise range, say at about 2,500 to 3,000 rpm? I have always heard that the cruise CO figure will improve from the idle figure because the engine is operating in a more efficient speed range. However, this car runs richer as the speed rises, with much higher numbers as the rpm climbs to cruise range. Measured CO at 2,500 is about 6.5%. Seems awfully darn high.

Other info: all new plugs, wires, filters, timing is right on, all injector hoses were preplaced, new exhaust, you name it, it was done at the last major ($$!!) service about 600 miles back. Sensors meter out fine, and no leaks from the start valve. Can't find any vacuum leaks either. Gas mileage is 12 - 16 mpg. Car runs like a top otherwise but there is soot in the tailpipe from the too rich mixture. Plugs show rich mixture around town, but quickly clean up on the road. Have used NGK BP6ES plugs for years which seem just fine. (Car did not come with a cat converter, it's a 72.) All other items are MB/OEM. Car has been relocated from California at sea level to 3,000 foot elevation. Again, car runs like a top.

So, is it broke, or just a thirsty devil?

Any advice will be greatly appreciated,

230/8

[autozen]

230/8,

I worked on those cars when almost new. Mileage of 13 miles per gal sounds about right. Mileage really improved when thy went to the lightweight alluminum block. Your new ingectors should be blue and not yellow. That car was designed to run on regular gas and not premium. You can't get a better plug than NGK. They've been my plug of choice for 30 years. You can't look at tailpipes anymore. The reformulated gas makes them all look sooty. In fact I believe it was the lead that used to make them look ashen grey. It's called D Jetronics, because D stands for Druck or pressure in German. The computer adjusts fuel by monitoring manifold pressure. The manifold pressure sensor mounted on your left fender well should compensate for the 3 inches less vacuum you are experiencing where you live. Someone else will have to answer your question about CO at higher speeds. Hope some of this info is helpful.

Peter

[230/8]

Peter:

Thanks for the info. Yes, the injectors are blue. I also have used NGK for years and plan to continue. I've heard these cars are a bit thirsty, but still would like to get an answer on the cruise range CO. Hopefully there is someone out there who can pull that bit of trivia out of their nickel bag of knowledge.

Thanks again,

230/8