WOW...my 75 SL is a whole new car!!...
 

A little news on my 75 450SL...

I've been tinkering with it for nearly the last 3 years working out some issues familiar to anyone who owns one of these...have replaced every single rubber bushing underneath, steering box resealed, and all new shocks and it now rides and handles like a dream. The difficult issues have been related to the engine and performance...ie: rough idle, poor gas mileage, hot start problems and asthmatic, labored, lethargic performance. I had replaced a bunch of engine sensors, trigger points, fuel filters, etc all with limited success...that is...until today...

After slowly acquiring all the replacement parts needed, I have finally removed ALL the emissions controls...the combined exhaust manifolds/cats, the EGR system, the air injection pump and ALL the associated plumbing- 58 pounds worth of junk! Replacing it all with 18 pounds of exhaust manifolds from a '74 450SL, and I'm happy to report that the results are nothing short of spectacular! The rough, hunting idle is for all practical purposes gone...nice and smooth...wow. Acceleration now happens with an astonishing urgency and a free breathing rush that makes it feel like it just cannot possibly be the same car! Best of all, I just got back from a couple trips- one 135 miles, the other 170 miles- filled up the tank after each one (mostly highway driving 65-70 mph, a little stop and go, toll booths, and with several 60 to 100 mph blasts thrown in for the sheer fun!) the result was 16.5 miles per gallon!! Holy S..T!!! I'm pretty sure with a little more judicious throttle useage, I could break 18 mpg! This car hasn't EVER shown me more than 12 since I owned it, and the average has been closer to 9...

Had a local shop do the manifold change and adjust the fuel injection for proper mixture- the exhaust gas results were- CO: 0.43; CO2: 14.13; HC PPM: 46; O2: 1.2

Nice part is that in PA, (and other states too I'm told) that when your car is older than a certain model year, emissions controls are not required to be maintained, so this was a perfectly legal transformation! The ultimate win-win!

It is also amazing how much the underhood temps have dropped, and how much more room there is now between the frame rails and the manifolds without those lousy cats crammed in there...alot cleaner looking setup.

A little note on those trigger points too...the car had been running great, and then I did a little cleaning up under the hood. Afterward I started the car and it stumbled badly like the trigger points were gone again. Figured I must have moved something while I was cleaning. I moved and jiggled the big rubber plug connector from the trigger points with the car running and the engine instantly came back to life...turns out the female side of the socket has some loose connectors, and just a little movement made it lose electrical contact. I'm going to try to get a new replacement female side connector.

Hope this provides some hope and ideas for you other guys who have had similar issues with your D-jet equipped rides...this car is really a blast to drive now!

J.G.

Good News - Great that you haveher running well! Checking bthe trigger point connector is a good tip! Mileage is amazingly good. I don't bother checking mine!

The connector is a standard 6 point used in other electrical connections on the car. The back snaps on and off. You can remove the wires and crimp the connectors a little to tighten them back up. Just write down where each one goes before removing.

he may mean the big flat one on the front of the dizzy? Nort sure what points he has
If so that can be repaired as well have to remove each individual wire and heat shrink after repair

I was thinking about replacing mine with 77 or 78 so I could have a place to plug in the whatchamacallit. What is everything you removed and how much FI tuning was required?

A '75 has the square, in-line connector. You can get the pieces from either the dealership or by judicious hunting of salvage yards. Careful when trying to crim the connectors, they're delicate. Clean them with a stiff cloth to remove any corrosion. You might want to check out what would happen if you put a THIN film of contact grease on them before reassembly. This excludes air from the mating surfaces, preventing corrosion.

Scott

Replacing your what and what year SL is yours?

75 450Sl. I want to replace the exhaust manifolds to eliminate the "vapor lock" issue. It starts hard after heating up and after it chuks and spits it will run fine again until next restart when hot. I live in AZ and it is still 95 degrees this time of the year. I read about the changing of the manifolds to 77 or 78 to keep emissions but move the cat under the car to rid the engine compartment of some heat. Jay Gibbs went to the 74 so I was wondering all he removed and what kind of tuning was required.

There is a member on BW parting a '72. Don't know if he still has the manifolds.
1972 350SL parts gotta go. - Benzworld.org - Mercedes-Benz Discussion Forum

good to get the CATS out of there, I have heard of some that just moved them downstream. If the O2 sensors are pre CAT , take them out and forget about em.:)

Jay - when you took out the air pump what did you do with the block that went into the head?
Did you change distributors that had the vacuum line running from the EGR valve to a single vacuum line distributor?
Just block off the pipe that ran from the EGR to the throttle body?
remove the EGR switch valve?

All the questions as I am switching out manifolds and see all this stuff that may not be needed but want to know what to do with it.
I di have a distributor hooked up to a Crane system that only has 1 vacuum line but know the 75 has both vacuum advance and retard.

The shop that I had switch the manifolds cut the metal tube short from the air pump to the head, crimped the end shut and brazed it closed. I plan a more "aesthetically pleasing" cap in the future but this works fine for now. The original distributor was retained, and the vac line from the EGR has been plugged. FYI, I have an extra set of non-cat exhaust manifolds if you need them...I paid a couple hundred for them but will sell them both for $125 plus shipping costs.

Also just finished up some additional work, and the car now operates at what must be close to or better than when it rolled out of the dealership door in 1975 in terms of smoothness and economy...injectors were sent out to witchhunter for ultrasonic cleaning and flow testing. I recommend this service for ANYONE with a D-Jet car who wants a great bang for the buck in getting any of these old cars to run properly...I ignored them for a couple years and am sorry I waited so long to do them. Also installed all new underhood fuel hoses, new OEM D-Jet engine harness, new cap, rotor, Bosch W7DC copper core non-resistor plugs and plug wires...been a busy summer...What a great car this has become!

J.G.

thanks for the info.

I also have a extra solid set of 1974 manifolds, "I used the newer" ones with the springs and no cats.

I have been busy with other parts so exhaust still not installed but manifolds in. I rebuilt the power steering pump and waiting to add some seals to the removed trans.

The pump front seal was a nightmare, I received 5 wrong seals between 2 different suppliers. If any one has a Vickers Type 21, BUY THE MOST EXPENSIVE seal as that is the one that will fit!

try Ignitor 1885 to replace points
 

Hi, Also have 75 450SL. Did everything you did but also put in Ignitor points replacement. Care idles well no more roughness. You may think about it.

joe R.

Just an FYI on replacing your points on a '75 d-jet: The Crane/S&S kit doesn't require fiddly modicifation on the plate in the distributor.

The '75 was the only year they combined breaker points with a double-acting (vacuum advance and retard) spark control.

To use a Pertronix, some grinding and filing needs to be done, reportedly.

Hope this helps someone.
Scott