'75 450SEL emissions control problem

[Guru]

It seems that I'm not far away from having a very nicely running car. It's a (July?) 1975 450SEL D-Jetronic which was spec'd for Australia (option code 625) and privately imported.

I am keen to know which emissions control systems this model has. No emissions stickers anywhere on the car. The Haynes 350/450 manual lists mostly US versions but I think the simple 1971-73 system (Fig 6.2) looks like what I have - although mine is a '75. It appears that proper emissions control was introduced in Australia from late 75, so probably just missed it.

And while I'm at it: warmed up, the motor runs very nicely. When cold, the revs are high and gradually decrease with rising temperature. This may be normal but revs seem pretty high (will have to measure). What is a worry is that aside from running generally smoothly there is a stumble every 10 seconds or so. A complete drop in rpm, but the motor recovers immediately and all is well until it happens again. I blew though all plastic vacuum lines and replaced all rubber hose vacuum connectors. The distributor plate rotates smoothly when moved by the vacuum actuator outside the distributor (assuming the valve works). I know this because I spent a good amount of time servicing the distributor. Before I embark on much testing, any suggestions are most welcome (TJ450 maybe?).

Chris

[rumb]

With the AAV operating correctly it does start cold at a higher engine speed and after about 4 minutes the idle should drop to the specified value.  you can turn the small knob on it to set the idle speed once it is fully warmed up.


Is the stumble when the engine is cold, hot, or all the time at idle?

[Guru]

Thanks, rumb. I have adjusted idle speed and revs are good when warm. Will have to measure actual rpms when cold.

The stumble is only at idle, when cold and A/C off. If I increase revs and keep them there it goes away. And when the motor is warm the stumble disappears.

[Guru]

I've uploaded a video to YouTube
https://youtu.be/5pjccnzv-j4

Engine running from cold start to warm:

0:00 Start engine, cold
2:00 First stumble
3:18 last of 13 stumbles
4:40 warm

[rumb]

that is very pronounced drop in speed.  Almost like it runs out of air./gas.

what do you know about the condition of your WUR?  that controls the fuel pressures during warmups.

can you measure the fuel pressure when it does that?

maybe you  can call CIS Flowtech and ask them about your symptom?