92' 190E 2.3 fine idle, stutters and lack of power when accelerating

[edz755]

I am working on a friend's 1992 190E 2.3.

The car had been running very rough and missing when accelerating.
I immediately checked distributor cap and rotor - both pretty burned, so I replaced them. The car ran better at idle then, but still missed, ran rough, and balked when accelerating.

So I checked to see if fuel was being delivered to injectors - unscrewed each line at fuel distributor first until fuel was observed and engine speed dropped, then tightened. Did same to injector lines at injectors. Injector line #4 appeared to be plugged or low pressure. Opened line up more until good fuel flow was observed, then checked at injector as before. Car ran a little better then, but still acts as if timing is off when accelerating.

Then tried to check timing. Can't find timing index marker on block (anyone know where it is on this engine?). As throttle is opened slowly and engine accelerates, timing at first appears to be advancing as expected, engine running smoothly. Then at around 1500 to 2000 rpm, ignition timing retards at least 20 degrees and engine starts running roughly (as would be expected with timing retarded under load).

I don't have tools to check fuel pressure at injector delivery line, or I would check this. I would have to build a special fitting this small to fit my pressure gauge.

What would cause timing to jump back under load as engine accelerates? What do I test and what can I replace if failed to correct the (apparent) timing problem?
Thanks in advance.
Signed, a frustrated diesel MB mechanic trying to help a friend with a gaspot.