Engine starts great from cold, then if hot, would take a good 30 second crank to get it started again. When hot the engine runs rough and rich. MPG is terrible.
I replaced a fuel pump check valve, a fuel accumulator and fuel filter in the hope it would cure a long cranking issue when hot due to suspected loss off pressure. I now need help to get the engine to idle smoothly / set the mixture, no turning of the hex screw makes any difference. Have checked for vacuum leaks, I am wondering now if the warm up regulator is faulty. Any suggestions would be greatly appreciated.

you can't tell what's wrong with it until you get line and control pressure tests. if the control pressure is too low, then, yes, you need the control pressure regulator. big money nowdays. hate to spend it when an ignition problem or other variables might be the cause. get the tools or find someone who can test it. here's a link for the tests-

http://handbook.w116.org/Engine/107/M117_45/073-120.pdf

same motor, different body. good luck, chuck.

That car's fuel system is all about fuel pressure,
knowing the system pressure VS the control pressure would be my starting point.

Also the US version of the 450's have a Lambda control & O2 sensor,
possibly the over-voltage relay is bad.

__________________
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Bought some fuel pressure test gauges today, I look forward to doing the tests

Greetings Members,

after doing much reading about Bosch CIS and tampering with the WUR on my 1980 450SL, I have learned a great deal and was able to get my car to run, albeit not smoothly.. I have decided to buy a reconditioned WUR that will at least be calibarated to the manufacturers specs.. After calling BOSCH America, and giving the part # 438 140 068, Bosch confirmed that it is discontinued and that a 0438 140 148 is a later replacement which is also discontinued. It looks like I might be able to secure a 0438 140 148. I have a question for any of you who can confirm if it will work before spending the money, it is non refundable. All the warm up pressures are within .02 bar of the 438 140 068.
The new Bosch part number is F 026 TX2092092
I learned that pressure is everything on BOSCH CIS.
Much obliged. Marty.
martykelly2@gmail.com

Good feedback.

Many of the early CIS fuel components are being discontinued by Bosch.
Have seen some good results with new electronic version.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator