My 1988 300E will not start unless I jump the fuel pump with a straight 12 volts the engine runs until I remove the current. It does however run for a few seconds without jumping it. Maybe it runs on the intial burst when the fuel pump engages when the switch is turned to the number two position. I know sound dangerous, but a lot of forum reading got me here. Then I tried leaving it in the start number 3 position and holding it there and it runs until I let it rest in the nuber 2 position on the switch and then the engine stalls.

Now the laundry list of trouble shooting

OVP replaced
fuel pump relay replaced
all relays and modules behind the battery replaced

Maybe I should check all the main relays in the fuse box!

Help guys


What else is left, but maybe I have a bad switch and it will not let fire remain constant to the fuel pump. Wow what a leap!

All parts replaced from a freinds running 1988 300E!


Cardude,

Its getting dark and the car is not inside, no takers yet!


Cardude

Try the blower on key position 2....
if no blower , you have a bad ignition sw...

Will try that in the Morning. Had to give up for a while time for sleep. Keep it coming everyone. I wll search the forun for switch removal just in case.



Cardude

Nope the blower is working fine! Any other suggestions?


Cardude

Then the ign sw. is not suspect... try the fuse box. Benz fuses look good , but the ends sometimes do not make a good connection .. the proper way to test them is with a test light on BOTH sides of the connection [ or give them all a twist in their socket.]

All fuses check out ok. Could this be a wiring harness issue on a 1988?




Cardude

If you can get this to load , the fuel system schematic is on page 114 for your chassis..........

http://mb.braingears.com/124_DISC1/Program/ETM/ETM.pdf

...or, go to my site.
Note that the relay needs rpm sig ..also, change fuse #7 for starters

ftp://members.aol.com/ajdalton7/fuel.jpg

Hey that reminds me the tach does not function at all. Even when we send 12 volts straight to the fuel pump. It doesn't work when we use just the switch either. Dunno if that helps but I noticed in your last post you said it had to receive a rpm signal. I was curious if they are related. Fuse #7 is fine.




Cardude,

This is a tough one, We cannot trace this down. Anyone have anything similar to this case.


Cardude

You have the schematic .. at what test points do you have power and where do you not??

Haven't fiddled w/ a 124 in a bit but do the pumps take their power off the postive battery lead a-la a 126? If so I'd check and make sure everything is kosher up there.

Jonathan

__________________
Blue Ridge Mercedes
Jonathan Hodgman
http://www.blueridgemb.com/
Enthusiast Service, Restoration & Tuning.
Follow Us on Facebook!
Located in the Atlanta area
Specializing in all pre and post merger AMG's including Hammers and DOHC M117 engines.
Mercedes Repair Atlanta

All the testing is checking out normal. Jonathan everyhting is fine on the positive side of the battery. We will do more testing in the morning




Cardude

No luck guys thanks for all the help,



Cardude

Thanks for the Diagram worked perfectly.




Cardude