[Nutz 4 Benz]

The green control lead that leads from the ICU to the distributor base is what I was referring to. One side of ICU has 4 pins and the other side has a round insert that connect to the distributor.

 

[colarc01]

Ok, I will have to check that out. That lead was not connected. There was only a wire direct from the distributor to the coil. Someone had removed all the wiring from the ballast resistors and the ICU. I have not been able to find an electrical schematic for the ICU to be able to tell if it works out of the car yet. I have the equipment to test the componnents but not knowing what each one is exactly has stopped me. With all of my searching at this point I think I am going to try to re attach everything the way it belongs and replace the temp sensors on the head, try to figure out if there are other sensors I need to replace and where they are located. set and tune everything after that then see if I need an MPS. It has been an uphill battle for me considering finding the information on this Euro version car has been a fight every time. It has been a huge learning curve with the D-jet. My search now includes the temp sensor with the two round prongs. It is a VDO sensor and I cannot figure out the proper part number so I can order one. Both of the sensors that are not the level sensor have flakey readings with an ohm meter. I have tracked down the Bosch one but not the VDO one.

 

[colarc01]

Nutz, forgive me I had missed some of your post. This ICU may still be good and I will rewire everything and test the way you have suggested. I will look into fixing the board in it if these tests do not pass. I have the in car schemtic so I can rplace the missing wires and reattach the ones that are flying to their correct position.

 

[Nutz 4 Benz]

Sometimes you can disconnect temp sensor that is in the snorkel of the air cleaner to make it run better. Old trick for D Jet.

 

[colarc01]

Yeah I have tried that it does seem to run a little leaner. The problem is my idle is still way to high. I need to troubleshoot my MPS and throttle position sensor to figure out the idle issue. I was in that process today but I also have 15 mature hardwoods in my yard and the first dry day I have been home this fall so it was 12 hours of that today instead of playing car today.

 

[Nutz 4 Benz]

Is the vacuum line from engine to MPS in good condition and clamped at both ends? You haven't tweaked with the ECU CO adjustment have you?

 

[colarc01]

I have not tweaked with anything. I will add clamps to the hose. I have made sure it is a good condition hose. I have not checked the CO adjustment. I have actually just learned today that there may be a CO adjustment. I am looking into purchasing a CO meter if I ever get to the point of having to check that.

 

[Nutz 4 Benz]

I'm just wondering i you have a vacuum leak somewhere in regards to the high idle if you never adjusted the throttle linkage/stop

 

[colarc01]

When I received the car it had teh set screw for the linkage set all the way down. I have not tried adjusting anything. I did find that the flap in the intake was not resting straight up and down and was actually turning past where it should be resting and was sticking. This has not affected the idle speed. I really need to get a vaccum tester but I have replaced all but two vacuum lines that appear to be in good shape. I am honestly thinking that I am experiencing a vacuum leak but only through the MPS. I did have very high idle before my vacuum line replacements and it has gotten better. Just not correct. Now discussing with you more on this I beleive for my idle I really need to replace the MPS. I know if you pinch off the hose going to the intake from the mps I can almost stall it at idle. I had forgooten this piece of troubleshooting with all the other things I have been working on.

 

[Nutz 4 Benz]

Is your ignition timing correct? You'll need to do dynamic rather than static due to your high idle. Vacuum lines attached, rev to 4500rpm and ballpark is 40 degrees BTDC.

 

[colarc01]

I really need to get a timing light with the dial on it to be able to tell where I am at. I have timed it best I can with a light with no dial. I am going to order one once I have the money for it and start there.

I still need to figure out if I am going to replace my ICU or repair it if needed so I am thinking next weekend is going to be a busy one with this stuff.

 

[colarc01]

Nutz I have been in the middle of a few things with this car for a while but have not been able to get back with a report. I have done testing and have found out I have a bunch of bad sensors. The MPS is definitly bad. Both of the sensors that are in the head that are not for the temp light are bad. I have gone through the resistive values they should be at cold and at warm and they are not reading even close. The problem I have now is I can find oall of the part numbers for them to order them except one. There is a VDO sensor with two round prongs mounted in the head and I cannot figure out the correct number. I have been having trouble getting in touch with the classic center for the Mercedes number.

 

[bradsscooters]

This is an excellent post! Lots of information.

 

[colarc01]

More information on my car

Nutz I am not sure if you are still following this thread but I have new information on all of the work I have done researching this cars issues. I finally got to the bottom of my major issue after verifying everything was good in my car. My problem was from the begining and still is until I can find one the MPS. The MPS is not broken in my car but the previous owner had installed the wrong damned one. I have been crazy trying to figure this out until I was completely frustrated and started just blindly buying parts. Luckily it was only a few inexpensive parts into it and I decided to try to buy a MPS just because. When I contacted germanstar they asked for my VIN to verify the part I was ordering was correct. This is when I found my problem. My car has a 0280100100 MPS and requires a 0280100111. After speaking with germanstart just for the heck of it I decided to verify with Mercedes direct and found out that germanstar was correct. I am not on the hunt for an affordable replacement of the MPS so I can hopefully fix this thing properly.

 

[kcjhawks4]

Does anyone know where I could locate a diagram for all vacuum hoses under the hood of a '79 450 SL?

I bought this car a few years back. Runs well and is in largely good shape. Have changed out the plugs and wires, replaced some of the vacuum hoses, minor tune up stuff, etc. The issue I can't seem to solve is the idle RPM. When warm, it idles at around 500 in gear, should be 750, and in park around 1200. I've tried adjusting the idle screw, but it doesn't seem to do anything either way. The previous owner had it maxed out tight (clockwise).

Can anyone offer up some tips to triage this issue and get the idle back in line? Seems like vacuum lines are the first place to start at this point, but if anyone has other suggestions, it would be appreciated. Thanks.

 

[colarc01]

I would try the vacuum lines and also check with a vacuum tester for proper pressure. Also due to just going through this recently. If there is a manifold pressure sensor on the drivers side fender that needs to be checked also. You will find these symptoms can be caused by this. At idle check your vacuum pressure with this part bypassed. Then check the vacuum with it connected. If your vacuum drops at idle with this part connected replace it.

 

[ejboyd5]

1972 4.5 with D-Jetronic. Engine runs with Temperature Sensor 2 disconnected but dies as soon as sensor is hooked up. Swapped sensor for new one and problem persists. Where should I look next?


Update as of 12/13/13: Problem solved by replacement of manifold pressure sensor (MPS). This is a frightfully expensive part from M-B, but I was able to source a rebuilt unit for less than 1/4 of the OEM price.

 

[gring]

What voltage should I read at the cold start injector ? 1975 450 SLC

 

[Nutz 4 Benz]

12+ volts for like 6 seconds before thermotime switch grounds out.

 

[gring]

D Jetronic : cold start problem. Need more tests

12+ volts for like 6 seconds before thermotime switch grounds out.

Thank you for your quick response. That thread is really nice and useful.
Last time I checked I had only 3 volts. You wrote that the other injectors use 3 volts.
I will check again with another voltmeter and I will unbolt the injector to see if it spays.