1975 450 SL runs too rich--need help

Have 1975 450 SL with 120K miles.
Engine is mechanically sound and well tuned.
Runs great with no visable emissions.
However it has been tagged as a GROSS POLLUTER here in California because it runs to rich at higher engine speeds. (it's fine at idle and just bearly legal at 1500 RPM. The faster it runs the richer it gets.)
This engine has the D-Jet injection system that was only used for a brief time.
I have a good mechanic but he is presently stumped.
He has checked fuel pressure and any other available adjustments with no luck.
He is about to begin replacing parts in a trial and error manner and they are all expensive.

Would appreciate hearing from anyone who has sufffered and solved this problem.

[Carlo(s)]

If your injection system has an adjustable primary fuel pressure adjusting circuit it may be the cauuse. It is a plunger like devise that sits at the borrom of the fuel distributor and regulates fuel pressure (maintains fuel pressure constant when hot to aid in hot starting). This plunger has tiny adjusting shims; the more shims the more fuel pressure and I theorize that if its set too high (too many adjusting shims; about 3-4 are normal but must be checked with fuel pressure gauge) it could just be passing too much fuel through the fuel distributor thus more pollution.

Make sure fuel pressure is adjusted to no more than 30 lbs.
Vacuum pressure sensor located on firewall is adjustable, even though the allen head adjustment in the end is epoxied over. A good MB mechanic will know how to lean your car out, and quite possibly pass the smog test. Re adjustment may be necessary for driveability reasons after you pass the test if you get my drift. The 1975 was the last year of the EFI on the 4.5 engines, and had lots of problems meeting emission requirements. Was also first year for catalytic converters, and they put them in one hell of a place, (under the hood so they could cook things.) I worked at dealerships on all the 4.5 engines when they came out in 1972 until the last ones of 1980, driveability of 1975 was the worst of the lot.

[Mark Herzig]

Rob;

What can you elighten us on with the fuel injection system in the '76 - '80 450SL's? I'm assuming they are easier to maintain but what are the common issues owners have with them...

Thanks!
Mark

Hello Mark,

In regards to your inquiry on 76-80 year model Mercedes 4.5 liter engines with C.I.S. fuel injection;
It has been my experience working on this system, that it is a very good fuel delivery system, and is relatively trouble free when kept out of the hands of tinkerers trying to fix problems that are no fault of the injection system. (Misdiagnosis).The injection system is susceptible to severe damage if exposed to a lot of water passing through it There are clearances within the fuel distributor that will not tolerate the least sign of rust or sludge from water.
The cars came from the factory a little on the lean side, Mercedes ,I believe was trying to impress the EPA instead of its customers, and they were all adjusted on the lean end of the spec sheet when it came to air fuel ratio. This makes for good air, and helps a little on the fuel economy I suppose, but effects power and driveability of car (early models had quite a surge going down the highway, and stumbled some trying to pull away from stop at normal acceleration. Also were poor runners when engine was cold. I made a special tool years ago to adjust the enrichment compensator and bring the engine in to the middle or high end of the specs. Made a world of difference in performance, and was still smog legal, just adjusted to high end of specs.

Just keep good fuel, fresh fuel filter every 30k miles and don't expect all your running problems to be in the injection system.

Happy to answer any specific questions you may have.

Rob

[Mark Herzig]

Rob;

Awesome information.... I'm glad to get some conversation going on these 450's as I am really enjoying mine.

My fuel mileage has been disappointing... averaging around 13 or so... maybe 14 freeway... These number actually represent an improvement when I had a major tuneup a couple of weeks ago.

I remember the tech telling me he set the timing at 5deg before TDC. I think the book calls for TDC.

Aside from the fuel mileage, the opposite end of the spectrum is performance. Do you think replacing the timing chain/rails will improve performance? What about replacing the Catalytic convertor? Any exhaust mods that will affect speed?

Finally, when the back end droops slightly, is that a call for springs, shocks, or both?

Mark: I believe 14 to 16 MPG is about average on your 1979 450SL. There isn't much I can tell you that will improve your mileage, except watch that right foot, and thats no fun. (LOL)
I doubt very much that you would notice any difference in performance if you changed the chain rails. They, the rails, may have a very small effect on the cam timing, but not enough to make a difference in performance. As for the catalytic converter, onlly if it were plugged up pretty bad would it make any difference in power, I have seen them come apart (the upper small cats closest to the engine) and plug up the rear cat. This is usually a really severe lack of power though, like 30 to 50 MPH top speed. I don't know about your emission laws or vehicle inspection programs in Texas, but in California we have a bi-annual smog equipment and emissions output check before a new licsence is issued, and could never get away with doing away with the catalytic or installing a performance exhaust system. If you can get by with removing cats and replace with free flowing exhaust system, it would definatly help performance and mileage also.

Rear springs do lose some of thier tension as the years and miles go by and cause some sagging. Two ways to fix if you are only concerned with appearance. Either replace rear springs, or you can purchase taller spring perch pads. Correct way would be to do it with springs. Shocks are not a load bearing part of the suspension system, however in my experience its a good idea to replace them if you do put on new springs. New springs have much more tension on rebound, and will make short work of wearing out old shocks.

Hope this helps some.

Rob

Hello Rob,

Seems to me like you know a lot about the 450 SL models.
I have a problem with my 1980 model 450SL, it just won't run anymore.
Wonder if you could do me a favor and look at my forum to see if you have any ideas?
The forum is under "Technical Help " and is under " Safety switch ".
Right now it at page 4.

Thanks in advance

Gunter

Gunter: I have read all the threads to your problem with your 450SL. I did reply to them, I said and still believe you are off on a tangent with your problem, sometimes with automotive problems you can let your mind wander too much, and come up some unrealistic solutions to your problems. I don't know how your original problem began, but I would issue one word of caution. As I understand your situation, the fuel pump runs anytime the ignition is on. This should not be, and can be extremely hazardous to to your engines health. Any time the fuel pump runs fuel is being sprayed thru the injectors into the engine. Since the engine is not running the fuel accumulates and can be drawn into a cylinder in sufficient quantities to bend a connecting rod, or damage a piston. Remember, liquids do not compress, this is how hydraulics work. This is the reason for the safety circiut on all CIS fuel injection systems, regardless of the year model.

With out more info on how problem started, I would not hazard a guess on your problem. I would however go back to basics, and find out the reason for the fuel pump running when the ignition is on.

Also you need to change the oil in the engine, the overfull condition you have in the crankcase is gasoline mixed with your engine oil, and can be very harmful to your engine, because this mixture does not lubricate very well. Hope this helps some.

Rob

Hello Rob,

First of all, thank you very much for your reply.
I changed the oil and filter last week and will do so again very soon, because I can smell fuel in the oil again.
My fuel pump is not running all the time, it starts running when I turn the ignition on, and only for about 2 seconds to build up fuel pressure.
I found out today that my lambda control relay has no power on socket # 3. So therefore my lambda control unit does not get any power. I tried to trace the wire to see where the wire gets its power from, but its very hard to trace.

Can you tell me where this wire goes to?

I hope I don't intrude into bchaney's forum, but I'm starting to get desperate for help. What started out to be a hobby to restore this car is getting to be pain in the rear.

Thanks for any help

Gunter

Gunter, if fuel pump is only running for 2 seconds, and then shuts off, how do you explain fuel in oil? Fuel has to be pumped from tank to engine somehow. Make sure fuel pump is not running with ignition on. It should not run even for two seconds with the ign on. 1975 and earlier cars with EFI type systems ran for 2 seconds to pressure systems, CIS systems should not run at all, because the injectors will open from the fuel pump pressure and inject fuel into the engine. Check this out by turning on ignition and crawling under car and feel of fuel pump. It should not be running. If it is running, start checking power supply to pump back to source of power, after you first disconnect wire to pump to prevent filling engine with fuel.

Rob

Rob,
That's what I did, I went under the car and had my hand on the fuel pump while my son turned the ignition on.
Every time I turn the ignition on the fuel pump runs for about 2 second and then shuts of.
I thought I get fuel in my oil do to starting the engine and since the car won't start the fuel accumulated in the cylinders drain eventually into the oil.

Gunter: Remove air cleaner from engine, disconnect fuel pump or remove fuel pump relay,remove and ground the coil wire at center of ign distributer. Next while you observe the air sensor plate (the big plate under the air cleaner housing) have your son hold the throttle about half way down while cranking the engine with the starter. Air sensor plate should be pulled down slightly, and should not flutter, while cranking. If you have fluttering of the sensor plate, this is an indication of a badly restricted exhaust system. I have seen this condition exist several times in the past, due to disintegrated catalytic converters. Its worth checking any way. On your year model the exhaust can be disconnected easily at the flange just forward of the center muffler-cat assemby. I do not presently have a complete wiring diagram of your cars electrical system, however the fuel pump does run during cranking of the engine, after 80 RPM the power for the fuel pump comes from a terminal on the ignition switching unit. I cannot see how a malfunction of the lamda sytem could cause your problem.

Rob

Hello Rob,

Thanks for the information, I'll try that this weekend, but my vehicle doesn't have a catalytic converter since the previous owner took it out.
I ordered a over voltage protection unit today, since I have no power on socket 3 at my lambda relay.

Thank you so much for your information.

Gunter

[RobertBiehn]

Originally Posted by Turbo240

Gunter: I have read all the threads to your problem with your 450SL. I did reply to them, I said and still believe you are off on a tangent with your problem, sometimes with automotive problems you can let your mind wander too much, and come up some unrealistic solutions to your problems. I don't know how your original problem began, but I would issue one word of caution. As I understand your situation, the fuel pump runs anytime the ignition is on. This should not be, and can be extremely hazardous to to your engines health. Any time the fuel pump runs fuel is being sprayed thru the injectors into the engine. Since the engine is not running the fuel accumulates and can be drawn into a cylinder in sufficient quantities to bend a connecting rod, or damage a piston. Remember, liquids do not compress, this is how hydraulics work. This is the reason for the safety circiut on all CIS fuel injection systems, regardless of the year model.

With out more info on how problem started, I would not hazard a guess on your problem. I would however go back to basics, and find out the reason for the fuel pump running when the ignition is on.

Also you need to change the oil in the engine, the overfull condition you have in the crankcase is gasoline mixed with your engine oil, and can be very harmful to your engine, because this mixture does not lubricate very well. Hope this helps some.

Rob

Hey Rob!

Wow, you seem to be so awesome! Any chance you'd be willing to answer a few questions for me? My email is: robertbiehn@hotmail.com

Here's more about my car/issues/what I'm trying to do: http://www.benzworld.org/forums/sale-wanted-trade-giveaway/1739193-fs-trade-1980-mint-mb-450sl.html

Sincerely and respectfully,

~Robert Biehn