Hello all,

I have a 1986 300E manual which has been giving me trouble lately.
The problems started one night when i got home, i pulled into the drive and it suddenly stalled on me. I couldnt get it to run and towed it to my garage the next day.
Started checking the basics, spark etc.
So spark was a bit weak. I checked timing etc and measured the coil.
After checking the dizzy cap i found the rotor to be a bit loose, turns out the holder for it which sits in the camshaft was broken.
So i went to the wreckers, picked up a second OVP relay, ignition coil, rotor+holder, Spark leads.
Got back to my car and installed the rotor holder, ignition coil and OVP to no avail...
My distributor cap is new and so was the rotor (not even 600 km)
My friend suggested id try the old rotor i took from the wreckers,so put that in and poof, car fired right away.

Issue seemed to be resolved, drove it all night without problems.
Next day i go to work and as i arrive and pull in the car just stalls and dies. Wouldnt run after that.
So i went to work and left the car for a couple hours. When i got back, after some cranking it fired up.
So i went for a short test drive and as soon as i gave a little throtlle and went past 3k rpms it started sputtering and died.

So next i started troubleshooting, measured all the sensors and dutycycles...
When i measure the duty cycle at KOEO it gives me 30% (which is up to spec as merc measures off time so corresponds with the merc spec of 70% on off ratio)
When i measure the duty cycle at cold idle it gives me 50% (which indicates no faults during open loop)
When i measure the duty cycle at idle with warm engine (closed loop) on diagnostic socket X11 pin 2 & 3 it gives me a 83.4% duty cycle constantly. This corresponds to mercs 20% fault, indicating the "full load contact with wrong pole connection or defective" However ive tested the contact on the throttle linkage and the switch at the throttle valve. and compared it to a unit i had laying around from a 260E (running car), no differences.
When i pull off the IAT it gives me a duty cycle of 20% which when inverting gives the 80% fault which is IAT. This makes me think the diagnostic system is working as it should
I am not measuring any amperage when measuring in series at the EHA (could be my method though).
The air flow potmeter is nicely calibrated at 0.7V
When measuring the 80% duty cycle and i give some throttle it goes down to 50 ish % (indicating the mixture i suppose) and as soon as i let it get back to idle it slowly rises back to 83.4%

The weird part is that i can ease up on the throtlle when its stationary without load and it builds up fine until the 6k rpms, however when i abruptly open the throttle valve it starts to stumble and stalls.
Same goes for test drives, ease up and it drives okay, until you reach around 3k rpms under load (not WOT but a decent amount of throttle) and it starts to stumble and stalls.
This made me think fuel shortage so i replaced the filter, checked the FPR, fuel pump is as good as new and functioning. Next i checked fuel pressure KOEO and it was 5.4 bars at both ports. (will check fuel pressure when driving later.)

At this point i have no clue what is causing this and i want to try to find out as much as i can because as we all know throwing parts at the jetronic system gets expensive quickly.

Thoughts i still have to check:

• Check the wiring harness from the throttle switch to the computer
• Check fuel pressures when (attempting to) drive
• Replace O2 with original part (has a universal one right now but i doubt that would cause the issues im seeing)
• Replace crankshaft pos sensor (again i doubt this is causing my issues)
• Replace currentregulator in the alternator (heard this can mess around with the system)

Any experiences and help are greatly appreciated!

Cheers,
Cas

 

Can i ask what engine you have ,,is it a m104 or m103 ?