No pot in the 380's, it's all mechanical.

Conrad, if your tach is not working right, you could have either a bad wire or a bad ignition control unit. The fuel pump relay will shut the pump off if it does not get a signal from the ignition unit, and this is the same signal that makes the tach register. Ask your mechanic about this.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Thank you Chuck.

I bought this MB in Aug-07 from the Manassas, VA area. Checked the
service records and the Ing Control Unit had been replaced twice in the
recent past. ( 2/6 years ).

The Fuel Pump relay has the numbers ' 85 ' on it. I assume, then it's original.
This device appears clean and w/o any visible corrosion. The sockets it
goes into appear clean. However, on the bottom edge of the relay, there
appears to be some cracked glue or bits of glue that are along the edge
of the case. Maybe this is the problem. It's not fully encased or air-tite ?
Is there a way to test this relay on the car or off the car ?
I will swiftly replace it, if I am convinced it is faulty.
Today the mech is replacing the Fuel Pressure Regulator.
I expect this replacement to 'fix' the stalling issue.

I'll ask him to check the wires for/on the tach.

I'll be baaccckkkk...........

__________________
THANK YOU. CONRAD

The problem is that you need to test the relay and the inputs to it.

Verify that the relay's inputs - tach, start, and engine brake (in 85) are correct, and that fuel pump works, wires are good, etc. If problem still occurs, replace the relay.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Chuck.

How to verify if the inputs to the relay are correct ?
As I look at the relay switch, there is only one way to
affix it to the sockets. No room for error on the switch
locattion. Are you suggesting the bottom side/underneath
the fuse box connections maybe corrupt ?
Is it possible to remove the fusebox w/o major disruption/sweat
to inspect it ?

I do appreciate your time & insights. They are welcome.

__________________
THANK YOU. CONRAD

Here's the official test procedure for the FP relay.

In your case, I would be concerned that you have a weak tach feed, and that the relay thinks the engine has died, and shuts the pump off.

Attached Thumbnails

     

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Update.

Changed the Fuel Pressue regulator, and the Fuel Pump Relay
plus had the air/fuel mix adjusted.

now, it fires up quickly, idles smooth and does not stall when coming
to a stop.

Not clear if the fix was only one of the three or all three.
Parts==$200.
Labor==$50.

On the road, again

__________________
THANK YOU. CONRAD