350SL Starts and Dies - Starts and Dies ...

[Keppie]

My ‘72 350SL has been stored all winter - full tank w/stabilizer. After checking things out and refreshing the battery, I started the car with assistance of charger just to give the battery a break. (I always unplug the coil, crank the starter – 5 seconds max – as many times as it takes to get oil pressure) As usual, it started right up and ran very smoothly. After running until it reached normal operating temp for a few minutes, I decided to remove the charger cables. At this point the engine died like someone had shot it.
I then attempted to restart the car. Nothing doing. All systems were checked, fuses all OK. Even though the car cranked well, no sign of the ingition firing. NADA. Thinking that it may have flooded, I let it set for half a day (warm temps) before I attempted to start it again. Tried again. No joy. Pushed it back into garage.

Fast forward two weeks. Today I rechecked everything again (wiring, fuses, etc.). Put the key in, rotated to "on", heard the fuel pump start, build pressure, then stop, and twisted the key to start it.
The good news is that it tried to start. The bad news is that the engine stumbled and tried to stay running for maybe 10 seconds then died. I tried several restarts with these results: The engine fired, attempted to run, but after a second or so, it died. Kinda like it was getting barely enough gas to fire up but then starved, and died.
One clue to the problem (maybe) is that, in the past, during the restart sequence, as the key is advanced to the position for starting the car, the fuel pump starts up, runs for a few seconds, and when fuel line pressure is up, it shuts off. I would then turn the key to engage the starter. Taking a pause in writing this, I just went out to try to start the car again. This time the fuel pump did not run as the key was advanced to the start position. I know it came on when I first attempted to start it today. This time it didn’t…
Checked the fuse is still OK. Maybe I have a bad relay?? Fuel pump relay.
(Here's one more symptom left over from last year. Last year, the car ran fine for about two weeks after getting it out of hibernation. One warm day, I took it out for a run of about 20 miles to a car show, parked it, came back several hours later, started it but it had to crank *much* longer than normal before starting. (normal was a second or two of cranking). Once started, it ran ragged for about 30 seconds before settling down. And that started a new pattern for the balance of the summer. Anytime the car was attempted to be started, it took a lot more cranking to start which was followed by a short period of uneven running. Lacking time and money and having too many other projects, my SL was pretty much ignored for the until this year.)
I dug into the '72 350SL Service Manual to study the wiring diagram and researched the MB forums. The wiring diagram was a big help. It identified the fuel pump relay as being on the #1 tag for the wiring harness. I got the kick panel off and there they were, seven relays that look identical. The left are numbered with harness tags 1,3,5 and the rights are 2,4,6,8.

Questions:

1. Is there a trick to removing these relays? (picture an upside down 69 year "young" guy with a piece of titanium in his back) I assumed that with a firm grip and a strong pull I could pull the %#&!! relay right out. NOT!. So before I resort to major mechanical assistance and break something, is there a clip or some other retainer I am not seeing??

2. In my manual, on page 54.1 (wiring diagram), I find a relay shown on the diagram and list as item 21, "Changeover relay air-conditioning optional". It appears to be the same relay as item 38, fuel pump relay. I would like to pull that relay (I have factory air in my 350SL) and substitute it in the fuel pump relay slot. Problem is that I cannot find item 21 anywhere else in the wiring diagrams or physically in the car. Is this an optical illusion to trick me?

2. I could find no reference to an OVP (over voltage protection) device in a '72 W107. Am I missing something? The OVP was deemed the culprit on several forum threads as causing the same symptoms as mine.

3. Does anybody have suggestions as to where I should go next in troubleshooting this problem? The 350SL service manual , as many of you know, doesn’t have a trouble shooting diagram.

4. While upside down in the car, I took pictures of my fuse panel and the relays above it. I will pass these along if they would be of help to anyone in considering possible solutions....or for any other reason.

Please excuse the long post. Thanks for the read.

Keppie