Please HELP! - PeachParts Mercedes-Benz Forum

Tims450SL · #1 04-27-2008, 01:11 AM

Could some kind terrific mbz person tell me how do I adjust the fuel from rich to lean on the 1975 450SL? It reeks of fuel when driving, (From the exhaust-this is not in the car nor do i smell anything-it is from behind the car while it is being driven-a friend followed me the other day and mentioned this; I also started the car up outside, and the wife came and got me as it smelled from the driveway into the house with the windows open that afternoon) and when you remove the air filter unit it is sucking like a 500 hp vaccume. Never seen anything like it...I appreciate the help. And just in case, if anyone has any experience on a power sunroof that doesnt want to open, and mostly thank you for you time answering...

300SDog · #2 04-28-2008, 12:39 AM

Have ye thought about gettin injector tips tested? If blown out they'll piss fuel like a race horse.

t walgamuth · #3 04-28-2008, 07:15 AM

This does not look to be an adjustment problem. You need to have the system trouble shooted and find out what component(s) are failed and fix it. If you try to adjust this away you will get it so screwed up it will take longer to trouble shoot it later.

Good luck.

Tom W

GaryF · #4 04-28-2008, 11:54 AM

A common response to a lot of questions on these engines and likely in your case is a large vacuum leak. Check all the plumbing under the hood especially the hose running to the MPS which primarily controls the amount of fuel injected. If it senses a lower vacuum it thinks you have the throttle further open than it is and dumps more fuel than it needs to.
Check the state of your plugs as well which will indicate if tis running too rich, there is only an easy adjustment for the mixture at idle.
You may also have leaking injectors as already pointed out and/or a leaking cold start valve which is basically a 9th injector at the front of the fuel line.
Which of your cars has the sunroof problem, if its the SLC check the motor is turning in the right hand side of the trunk when the switch is pressed. If it is then try adjusting the clutch, if its not then an electrical problem and start with the fuses.

ctaylor738 · #5 04-29-2008, 08:41 PM

Running rich like this is usually not a problem with an adjustment being off. Like Dog and Gary said, it is almost certainly a vacuum leak, or the ECU receiving bad input that causes it to richen the mixture, or a problem with the injectors.

Here is a good post on the subject:

'72 350SL (4.5L) Rough Idle

Also, if you look in the Vintage Forum, you'll find thread I started "Waking up D-jet". In it, Arthur Dalton provides a link to a great D-jet guide.

Robert Squires · #6 04-30-2008, 10:54 AM

* One or both wires to the inlet air temp sensor frequently were broken on the D-Jetronic engines, given the movement at the end of the air inlet where the sensor lived. The control unit reads a disconnected air temp sensor (infinite resistance) as very cold inlet air temp. And, hence, richens up the fuel a lot.
* Take a correctly tuned D-Jetronic 4.5, idling at operating temp, and disconnect the air temp sensor. It has a dramatic effect. I used to keep a spare air temp sensor in my toolbox to connect to the harness when I was running a 4.5 with the air filter housing removed, since you couldn't just ignore the sensor.
* New 2-pole plugs, with 2 short sections of wire, complete with connectors, used to be readily available for wire end repairs (like the air temp sensor and coolant temp sensor connections). Resistance changes at the splice make a difference, so do it carefully.
* Air and coolant temp sensors for the D-Jetronic aren't very expensive and should be replaced automatically after this much time/mileage. Your richness could also be a coolant temp sensor broken at a "rich resistance".

Lexxani · #7 04-30-2008, 03:23 PM

as for the sunroof,

locate the motor, (right hand of trunk, behind the battery box) and run a hot wire and a ground wire from the battery directly to the motor, if the sunroof moves strong your fault is in the wiring (I had a smiliar problem, check your dash switch first before you tear things apart)

if the sunroof motor turns and the sunroof moves sporadically, tighten the clutch on the motor,

if the motor spins and the sunroof doesent move, the cable might be broken or stripped (its not a hard fix according to the FSM)...

If you have any other questions shoot me a PM, ill cross reference things against my SLC or the FSM if you dont have access to one. .

Tims450SL · #8 05-02-2008, 02:13 AM

WOW! Thanks you thank you! I appreciate the feedback so much. I just started up the old girl, and let her run for a quick wash. During this time I burned almost a quarter of a tank! I was like OMG! But I know that she sucks hard with the air cleaner housing off of the engine- I mean really hard...There has to be a open line of fuel swuirting-there is no way a car can waste that kind of fuel- My S500 is bad but not like this draining out deal. Does anyone know how to test the injector? how about the sensors-I will buy everything-she had sat for a few years before I reburbished the plugs, wires, cap/rotor cap, fuel filter, air filter, and the fuel pump. One thing when she is warm she runs very smoothly, but seems to lack the power my 78 450SL has. I am hoping to hear back from someone that has a good idea of what I should do first. She needs help! :0) thanks!

t walgamuth · #9 05-02-2008, 07:18 AM

My 280e did that. It was the warm up compensator, IIRC. Got about 9 or 10 mpg.

Tom W

ctaylor738 · #10 05-02-2008, 08:37 AM

WADR, if you are going to try to fix these cars, you need to get the basic tools. Buy yourself a gauge set and a multimeter, and figure out how to use them. Every question you have asked has been answered. Now you need to act on the excellent advice that you have been given. If you can't or don't want to, then you should look for a shop that knows how to work on these cars.

In addition, you can look at my two recent posts "Waking Up D-Jet" and "Adjusting D-Jet Fuel Pressure". They illustrate how to work through some of the issues you are facing.

For sure, print out the excellent D-Jet guide in the post by Arthur Dalton. This tells you step-by-step how to test each component in the system.

Finally, and I think I speak for others, stop cross-posting and calm down the histronics - no more "PLEASE HELP !!!!!" Pick a Forum, stick with it, and describe your issue or topic succinctly.

And I'll say it one more time, it all starts with the right fuel pressure.

BTW, ignore the previous post, D-Jet doesn't have a warm-up compensator.

Robert Squires · #11 05-03-2008, 08:41 PM

* I've been reading about this rich-running problem, in different threads, to this same '75 SL for several months now. NASA solved the loose tile problem on the shuttle faster than this.
* CTaylor has the right idea. The owner needs to do some homework and learn, at least functionally, how the D-Jetronic system works. And there are lots of references.
* Then test or replace things, systematically, and solve the problem. If the owner wants help, he's got to step up and do some of the work, or we just keep going over the same ground again and again.