vacuum hose replacement

[Darrell Woods]

My 75 SL has a 4.5L from a 71/72 300SEL (117.982). It has D-Jetronic FI, and from what I've read this system is entirely vacuum dependent for it to work right. I have a big intermittent miss (more like a near total shutdown @70-80% power loss). Going to replace fuel pump, but also want to install new vacuum lines. Here's the question, I've seen this stuff in bulk and need to know if there are multiple sizes I need to have, or if there's one standard size when I start untangling this maze. There appear to be more than one size, but I have no idea which lines have already been replaced at one time or another. Also, do I need to be looking at replacing ALL vacuum lines. These things run from one end of the car to the other! Or, do I just need to concentrate on the FI related ones? Any suggestions/comments from anyone who has tackled this are appreciated.

[psfred]

Three set of lines :

Engine related (emission, vac to distrib, hose to MAP on the fender)

Climate control -- green plastic lines to interior

Door locks -- yellow plastic line to driver's door.

What I would do is check all the rubber connectors. You can replace the straight ones with plain 1/8 or 3/32" vac line from the autoparts store. T and Y connections are best obtained as MB OEM parts, the aftermarket ones are usually junk. I've done them all, it's a pain, but worth is as most of them, if not replaced by now, are leaking for sure.

You will also need to check the integrity of the plastic hose at the same time. cracks and breaks can be fixed with more vac line, at least temporarily. Be careful, any exposed to heat will be brittle.

Next, I'd get a MitiVac hand pump and check the door lock and climate controls by attaching at the engine compartment end at the check valve and pumping down -- if they hod vac, you are fine, if not, you need to fix the leaks. Temporary fix is to plug the line on the engine side.

If the engine runs fine with the vac leaks fixed, you are fine.

If not, first thing I would check is the points or the rest of the ignition system -- D-jet will run VERY rich if there is a big vac leak, to the point that black smoke will be visible when you floor it. Bad points for hte transistorized ignition or bad cap, rotor, and wires, or plugs will also cause a "rich" condition, too, so check them all out.

Peter

[Darrell Woods]

Psfred, thanks for the reply. In your opinion, would a vacuum leak be a likely candidate given the fact that the loss of power is so intermittent. It seems logical to me that if the vac was the problem, it would always leak and therefore the problem would always be there. But I do get a little black smoke when I kick it. When it runs good, it runs really good. But when it runs bad...you get the picture. Also concerned it could a trigger point problem. Distributor looks a little ragged and worn, and thinking I might put an aftermarket system in (been reviewing the threads on the Crane and Pertronix units). Thanks.

[tosbt]

bless you psfred for being here, always have a load of information for the mech handycaped. Say Darrell, for sure get rid of your points. I went to the Crain but whatever your choice get rid of the points.