Cold start mixture KE
 

Engine fires right up when cold, but needs to warm up for 2 minutes or else it stubbles and hesitates. Something is not kicking in to richen up the mixture. This wasn't too bad in the summer, but will become a problem on cold mornings. Otherwise runs fine.

I have a multimeter to check the water temp. sensor. I understand it can also be a fuel pressure problem. I don't have a pressure gauge but is it easy to do following the service manual? I'd like to isolate this before bringing it to the shop.

Got my shiny new gauge. Measured 5.5 bar system pressure, and 3.8 bar control pressure. I put direct vacuum to the front port of the warmup compensator and the pressure didn't change from 3.8 bar.

Do you have the service manual? All the pertinent test data and programmes should be in there.

I'm following the broken English online manual. A cold start test showed the control pressure a little bit high (2.3 bar at 60F), so the warmup compensator is sort or working. Do these things poop out all at once or do they die a slow death?

Your control pressure looks like a warmed up value. Is that value cold, with electrical disconnected? Two bar would be more appropriate cold.

The vacuum acceleration enrichment might not be testable the way you are doing it. It also only functions during early cold running. During running the two ports both receive vacuum only one comes through an oriface. On acceleration one side drops instantly while the other takes a brief moment. During that brief moment there is a 1.2 bar drop in control pressure. That moment is only a second or so. No constant throttle situation is benefited by this change of pressure.

The 3.8 bar is a warm value. After some searching on this site I found an item on tweaking the warmup regulator. I tapped the external pin down while the engine was cold to lower control pressure from 2.3 to a little below 2, wires off. So now everything I can measure is within specs, and I'll see if theres a difference tomorrow morning.

Cold start is improved, but not perfect. There is still some stumbling on acceleration which clears up fairly quickly. Thanks for the info on the port and orifice functions. The Benz is always a learning experience!