Mercedes-Benz Forum banner
1 - 16 of 16 Posts

· Registered
Joined
·
26 Posts
Discussion Starter · #1 ·
Ive searched high and low with no luck...I made a mistake and didnt label all my vacuum lines when i unplugged them. Ive seen diagrams of what seems to be close but not quite. I have 4 lines on the throttle body that i have no idea where they go. And theres a line in the very front of the tb that i cant find no mention of. Could those lines keep the car from starting?..By the way its a 91 420sel...
 

· Registered
1990 420 SEC
Joined
·
1,178 Posts
Also this thread might be helpful:
 

· Registered
1990 420 SEC
Joined
·
1,178 Posts
If there is no canister then the hose to canister or hose connection at throttle body must be plugged somehow.

How did you check there is no fuel coming to injectors? You have to have fuel pumps running and air flow measuring plate deflected in order to get fuel flowing to injectors. You can simulate that by jumping fuel pump relay and pushing air flow measuring plate down. If everything is ok you can hear injectors squeal as you push the plate. Search forum for fuel pump relay jumper. As car is cranked air flow deflects the plate and injection takes place.
Also if you undo the lines to injectors you should see fuel flowing from the ports as car is cranked.
 

· Registered
1990 420 SEC
Joined
·
1,178 Posts
Does taco needle move as you crank? Taco shows RPM signal from ignition control unit (EZL). If there is no RPM signal called TD fuel pump relay does not stay on. As you turn key on fuel pumps run for one second. You should hear that. As you crank EZL sends TD signal and relay turns pumps on. If you kneel next to right rear wheel you should hear the pumps while someone cranks the car for you. TD signal is used by idle control and injection control too. If taco needle moves but pumps do not run suspect pump relay. There is a fuel accumulator to maintain a low fuel pressure while car is not running. That pressure is lower than what is needed for injection system to work.

Normally air flow caused by engine being cranked deflects measuring plate enough to get fuel to injectors. One can test if injectors can be heard by deflecting the plate when engine is not running and pumps are but that easily floods the engine.

Undoing the fuel lines to injectors and deflecting the plate while pumps are running gives an idea how evenly fuel is distributed between cylinders and at what position of plate injection starts. Do not burn the car.
 
1 - 16 of 16 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top