380sl with severe stumble when cold

[halsk]

Have a 1984 380sl that has absolutely no power when cold - stepping on the accelerator and the car tries to stall. When the temp reaches 80C it is drivable but still lacking in power.

I have replaced the W.U.R. with 2 other units - although used - and have not solved the problem.

I have looked at the OVP relay - and the fuse checks out - but have not replaced it yet.

I have checked the fuel pressure at the WUR inlet when the engine is cold and it does measure about 40-50 PSI so think it is getting enough fuel.
The voltage at pins 2-3 of the diagnostic socket reads 13.8 volts constant - which I assume is wrong - but don't know what would cause this wrong voltage.
The only temp sensor replaced so far is the one that controls the instrument panel
Any thoughts would sure be appreciated -

[Strife]

It's quite possible that ALL of the WUR's are bad! (dirty filters). Do you have a 3-way tester that goes between the WUR output and the fuel distributor?

[halsk]

I did put the fuel pressure gauge on the input of the WUR - which I assume was the bigger fitting of the two ports.
As mentioned it was reading about 2-3 bar when first starting.
I can easily hook the pressure gauge to the output and check the pressure there as well.
When first putting in the WUR I did look at the screen at the input - looked fine and did spray carb cleaner into the port as well.
Big question still remains the voltage at pins 2 & 3 of the diagnostic plug.
I was told that if it was working it should be around 6-7 V DC.
With a constant 13.8 volts DC on those pins I understand that the Lambda control is in not working properly.
That seems to be the big question - what controls that loop voltage???

[petesmga]

this was just on BW, he gives a pretty good explanation.

http://www.benzworld.org/forums/r-c107-sl-slc-class/1503714-450sl-hesitation-problem-finally-solved-long.html

[halsk]

PetesMGA -
Great write up - and have taken one of of the WRA's apart and will look for an O ring that fits.
And perhaps that's why the lambda voltage isn't right - measuring on the wrong pins on the diagnostic plug for the duty cycle - should be 3-6 according to this post.
Don't know where I got the wrong info to use 2-3

[cclake]

I had a problem just like this and it turned out to be a vacuum leak at an injector. When it warmed up it sealed its self. Replaced the seals about 4 years ago and have not had a repeat of the problem. I used a spray bottle with water when the engine was cold

[450slcguy]

Originally Posted by halsk

PetesMGA -
Great write up - and have taken one of of the WRA's apart and will look for an O ring that fits.
And perhaps that's why the lambda voltage isn't right - measuring on the wrong pins on the diagnostic plug for the duty cycle - should be 3-6 according to this post.
Don't know where I got the wrong info to use 2-3

Pretty sure lambda duty cycle is measured on sockets 2-3. On my 450 it is as per factory service manual. Perhaps it changed for the 380's?

[halsk]

I did put a meter on pins 2-3 and all i get is a constant 13.5 volts - so that either is battery voltage or lambda controller is shot.
Again my car is 1984 380SL and don't have the diagnostic manual.
Unfortunately the adjustment screw on my fuel distributor is sealed so not sure I am going to have the nerve to cut open the adjusting tower to get to the adjusting screw.
I am going to try a new O ring in the used WUR that I will rebuild.
Buying a new O2 sensor and also a new OVP relay - hopefully that may get some results.
Running out of other options other than a rebuilt lambda controller??

[ctaylor738]

You should see around 1.4 bar with a cold engine measured at the large line on the WUR, rising to 3.5-3.8 when the engine warms. If you have 2-3 bar there is no way you will have any power cold.

The most common cause of high control pressure like this is a clogged filter screen in the inlet of the WUR.

BTW, you measure this with the gauge connected between the line and the WUR. I couldn't tell from your post how you had it connected.