450sl usa djet

hello d jet fans,

i have a 73 450sl usa. it does not run as it should. when i put the ignition timing on 3 deg BTDC the engine starts to stumble an HC values go up. I have to set ignition to 20 degr advance to get a good idling engine. At that point idling is ok an Co can be adjusted an hc values are a fair 290 ppm... but the engine stumbles when you hit the gas, and has trouble starting cold. starting cold is rather rich at 10%vol , but lowers as it should when the engine warms up. co is set to 2.8vol.
The timing marks on the camshafts and cranckshaft line up , there is some stretch on the chain.., checked the valve clearance, did an oil change.  checked the fuel pressure, had the injectors cleaned and tested. , cleaned the injector points , changed the ignition points,checked the advance wieghts and springs...vacuum advance is leaking and out of order. changed the ignition wires and sparkplugs. have tried a different ecu ( same nr) and tried a bosch reconditioned map sensor. other injection parts have been tested, temp sender water is ok  air temp sensor to, idle contact is ok and acceleration contacts are tested and are good. all components where mesured at the ecu plug so wiring should be ok...  maybe im missing out on something, but at the moment i cant see the issue and keep moving in around and getting nowhere... could it be compression related? i did preform a vacuum test , it has between 16 and 18 inches vacuum, vacuum that goes to practicly zero when hitting the throtlle ...or do i have te search the fault in the ignition system? probable you guys will ask for a compression test.. and i know, i had to measure that way sooner , but will perform one in the next couple of days....;
maybe some of you will have an idea?
best regards
pasj

Hi Unknown,

would be great if you could sign with your firstname so that we can directly address you here.

I would propose following actions at first:

• Check engine compresion
• Check valve timing
• Do a fog test to verify that manifold is air tight. I have seen another leaking engine where that has caused similiar problems as you describe
• Check that ignition distributor sets ignition timing correctly at idle, 1500rpm and 3000 rpm according to table in workshop manual
• Verify that you have correct products installed according to Appendix A of D-Jetronic compendium - notice that ECU and MPS must match on 450 SL US engines

Good evening Djet fanatics,

its been a while since i posted this question...
so here we go...
compression 10.8 to 11.5 on all cilinders, smoke test = no leaks... all the injectionparts have the right numbers...
so i checked and doulble checked all djet components... they are all ok...
I did check ignition timing, but could not get the car running on idle on the right degrees... although i had wired the car to the ignition osciloscope and checked it, i still had to try something...So i switched the ignition coil to an breaker point type , ditched the electronic ignition and placed a condensor. and disconnected the rev counter....
result... tada... engine runs good, can get to 700rpm on the right ignition setting... co is adjustable on a stable 2% vol and rev up like new....

the electronic module has been changed before...
searched the net for a replacement... but seems i have to buy at gold prices...
any alternative ignition modules on the market that i can use and on witch i can get the rev counter working again?

best regards
Pascal.

Hi Pascal,

in 74 we have both wheeltype and standard ignition module. Which one do you have?