Henry Schuman wrote: ↑
Thu 03 May, 2018 12:47 am
A few things you can try before getting a box of parts to guess repair your car .
Fuel Pump: 1. listen to pump while someone bumps the starter (it should cycle on and off but not necessarily depending on type of fuel distributor you have )
2. hook 12 volts to the pump and see if it runs both on car and your spares to determine if any of them actually work.
3. If no pump noise and no pump working with 12 volts hooked up then we start trouble shooting some more options.
Ignition Control Module ,could be but unlikely however to check this
1. Remove coil wire from Distributor cap and and have someone to crank engine while you hold the end of wire close to valve cover or similar ground just a few millimeters away and see if you get a nice blue spark taking care not to be holding your hand or any other body part to the engine or too close to the end of the wire .
Fuel Pump Relay if bad you can actually repair them some times by removing it and taking a pocket knife or small flat blade screwdriver and sliding it around the bottom to crack the silicone seal then gently pry the edges out to remove the board. Then look very close at the solder joints prefarbly with maginifers if your my age and look for small cracks in one or more of the bubbles of solder .I f you find some simply re-solder them and you probablly will have it working .
Maybe some of this will help you get a better picture of the problem.
Despite the lack of detail in my initial post, I'm not one to randomly throw parts at a car until I either a) fix the problem or (more likely) B) Run out of money. On the contrary, I think I posted earlier on in the troubleshooting process than I ought have.
Allow me to update with new/more information:
In daylight it became apparent that the fuel pump had sprung a leak around the end seal (the end with the contacts & banjo fitting) with a definite constant moisture seeping out between the end-plate & the housing. In hindsight/looking at the big picture I'm assuming that either the relay failed due to the leaking pump requiring it to stay on for an excessive period/work excessively hard causing it to get hot & so melt/excessively stress the already weak (?) solder OR (more likely) the pump failed as a result of the Relay failing; The relay was telling the pump to keep pumping despite excessive pressure having been accumulated but having nowhere to go (injected not carby)....but I am getting ahead of myself.
Realizing the danger & fortunately already having a spare working fuel pump on hand (along with a pack of copper crush gaskets from when I replaced the thermo fan switch a few months ago) I tested the replacement pump by running 12V directly (success) swapped over the fuel pump but before removing the old pump, I turned the key to acc 2 & tested the contacts at the pump with a circuit tester (alligator clip > insulated copper wire > light globe in-line > probe) to ensure the pump was getting power all appeared well, light lit up but (for reasons explained & others that would become apparent) the pump didn't respond with it's usual "Whirr of gusto", more like a soft hum. At the time I put this down to the leaking pump also being otherwise damaged so without having a Multi-meter on hand, I continued with the necessary task of replacing the fuel pump with my spare (VERY lightly used & not leaking) replacement.
The following morning with a few hours research & countless hours pondering the issue under my belt I tested for spark to eliminate the Ignition Control Module using the method you outlined (though discovered on YouTube) > ICM Eliminated
, all plugs firing as they ought.
PROCESS OF ELIMINATION COMPLETE: Culprit > Poorly/Failed Fuel Pump Relay
Having opened up the relay (as you described) it became immediately obvious with countless joins displaying both minor cracks as pictured in your post & others with clearly dried out/Cracked/Perished solder joins. In fact it seems like more joins have failed than are viable. This coupled with my lack of both confidence working on circuitry/soldering electronics & not actually owning a soldering iron have lead me to source a brand new Fuel Pump Relay from a local supplier for an extortionate, albeit cheapest available (for over the counter purchase within a few day timeframe) price.
At the end of the day, a 34yo relay is going to fail eventually and judging by the amount of damage visible inside the relay, this one has seen better days so for both peace of mind as well as longevity of the repair, I'm going to swallow the huge lump in my throat that developed upon seeing the price, shew the moths away from my wallet and tell myself "this one should
last another 30 years, buy the relay, install and (if the Mercedes gods are happy) listen to my sweet little 280SE purr quietly back to life when I turn the key.
I'll keep y'all posted.
W126's truly were the last real
Benz in my opinion!
1989 300SE (W126) Midnight Blue, Blue/Grey Interior (Gearhardt)
1982 380SE (W126) Thistle Green, Tan Interior (Sherman)
CURRENT DAILY DRIVE & BELOVED FAMILY MEMBER
1984 280SE (W126) Thistle Green, Tan Interior (Hilda)