Author Topic: I'm at my Witt's end.  (Read 721 times)


  • Enthusiast
  • *
  • Posts: 37
  • W116 Newbie, W123 Enthusiast
  • Location: Western New York
I'm at my Witt's end.
« on: 19 July 2021, 08:47 AM »
I don't know what to do anymore. Got this car about a year ago, and drove it 9 hours home, didn't skip a beat, then a couple days after being home, it had major loss of power and that continued until now it won't stay running unless the throttle is in the floor. 

1974 450SE 4.5

I've changed
The whole distributor "minus injector points"
All rubber fuel lines to motor

I've checked
Fuel pressure
Timring chain

I've timed it and re timed it

Any suggestions would be nice. I don't know what to do anymore.

Also what kind of plug is good for these motors.


  • W116 Addict
  • ****
  • Posts: 2,305
  • W116 Enthusiast
  • Location: Vancouver, BC, Canada
Re: I'm at my Witt's end.
« Reply #1 on: 19 July 2021, 01:14 PM »
To me it still reads like a fuel problem.   Did you check all the fuel screens at the fuel distributor and warm up regulator?  Can't remember if you have kjet or DJET?
1977 450 SEL 6.9 - Astralsilber


  • W116 Addict
  • ****
  • Posts: 1,735
  • MB Enthusiast
  • Location: Fort Collins, Colorado
Re: I'm at my Witt's end.
« Reply #2 on: 19 July 2021, 03:17 PM »
spark plug should be non resistor
BOSCH 0 242 240 592
MB A 003 159 57 03  - plugs are cheap from the dealer.

Wires should be good set like Karlyn

that would be a D-jet with trigger points (injector points)

Sounds like a fuel issue.

How about the fuel filters?

Could be that you sucked dirt into the system driving it home and now it has sat and plugged up.  Change tank filter, fuel pump filter and blow out in and out fuel lines.   Connect both ends in the engine bay together and run the pump for 1/2 hr.  - you can easily jump 12v to the pump terminals to do this or you can jump the relay sockets. - would have to look up that wiring though.

After all of that then either test/clean or replace the injectors to make sure they are all spraying.

'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550


  • Newbie
  • Posts: 4
  • 280se W116 D-Jet owner
  • Location: Hampshire UK
Re: I'm at my Witt's end.
« Reply #3 on: 02 October 2021, 06:52 AM »
Not sure if you have sorted this but the main issues I have had with D-Jet is vacuum leaks in the engine bay which leads to low pressure in the intake manifold pressure sensor (MAP) unit which send s a false reading to the ECU and the system runs very rich. If this is the case, check your plugs for black soot and give them a clean to see if it will start  and hold idle. If the throttle response is not gradual, you may want to inspect the Throttle switch - as this has all the variable electrical points to determine the amount of fuel required at any give rpm. These contacts are very delicate and if they are stuck in position, or dirty/rusty, this would create a erratic throttle response. These things are straight forward to assess before getting into timing chains ,etc. The truth is that back in the 70s, good 'housekeeping' was commonplace and now we are pickng up these over engineered cars for next to nothing but the service history is patchy and there are not many people left who remember these vehicles well. I had many problems with my 280se w116 D-Jet and nearly spent thousands on atop end rebuild because every one said the valve guides were shot. Actually, I spent £250 on a set of Mercedes engineer manuals and spent time learning about the injection system. I started at the fuel tank and made my way gradually to the engine. I found rusty a fuel tank, blocked fuel lines, a leaking fuel pump and replaced everything myself. New air hoses in the engine bay, removed the warm up valve, cleaned tested and put back. All new stainless hose clips and air,temp and fuel sensors (which were critical) . Took out the throttle switch,  tested it with a meter and replaced and swapped out the ECU for a couple of cheap (untested units on ebay). After all this, the car runs well and starts first time. I am getting really bad MPG but now I can work through fuel pressure tests and injector cleaning methodically. I  invested in a CO meter for the exhaust and the car was producing six times the normal CO levels which is controlled through the ECU. It ha been a labour of love but I don't think there is a quick fix to old cars. THe good news is that they can be fixed! Good luck and let us know how you get on.


  • Enthusiast
  • *
  • Posts: 31
  • W116 Enthusiast
  • Location: Lund, Sweden
Re: I'm at my Witt's end.
« Reply #4 on: 02 October 2021, 07:32 AM »
I second the fuel issue. Test pressuer, 2.0-2.1 bar, not more, not less. Test flow, 0.6-0.8 liter/ 30 sec. If pressure and flow is ok, then pump and filter is ok. If problem still remains, test spray pattern on injection valves.
350SL 1973
350SE 1975
SL500 1996


  • W116 Addict
  • ****
  • Posts: 1,397
  • Chrome Bundts & bundts with white walls are a sin!
  • Location: knoxville, tn
Re: I'm at my Witt's end.
« Reply #5 on: 02 October 2021, 11:08 AM »
Don't rule out a bad manifold pressure sensor or a torn hose going to the manifold pressure sensor. 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1971 280sel Black/black leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex