NEEDED: FPR for testing '84 280SE

1979-1991 280SE, 300SE, 300SEL, 380SE, 380SEL, 380SEC, 420SE, 420SEL, 420SEC, 500SE, 500SEL, 500SEC, 560SEL, 560SEC
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Astro-Benz777
C Class
Posts: 28
Joined: Tue 03 May, 2016 7:40 am
Model you own: w126
Region: Victoria
Location: Melbourne

NEEDED: FPR for testing '84 280SE

Post by Astro-Benz777 » Tue 01 May, 2018 7:39 pm

Hi everyone,

One day my lovely 1984 280se was working fine, perhaps a slightly rough/high idle but started every time without a hitch but after not running her for a few days, went to start her and was greeted with the usual turnover sounds but then when I released the key (at the point the starter would disengage and the engine would start chugging along normally) it died and has not started properly since. The most I get out of it is that sound like she is turning over right but whether I release the key from the starting position or hold the key in the starter position, I am met with the same result: She sounds like she's about to turn over perfectly but then dies.
I think I've narrowed it down to either:
  • Fuel Pump
    Ignition Control Module
    Fuel Pump Relay
I had a spare fuel pump knocking around so have switched it over with no joy, next on my list is the Fuel Pump Relay (hoping it's not the ignition control module) unfortunately I don't have a spare to test it with so was wondering if there is anyone in Melbourne's Eastern Suburbs who has one they are sure works that I could pop into my 280SE to see if that is the issue to save me throwing new parts at the car unnecessarily that wouldn't mind helping me out?

I have another spare fuel pump I'm going to try tomorrow just to be sure the one I had wasn't crook already and will keep you all updated as to how that goes.
Any other suggestions gratefully received.
W126's truly were the last real Benz in my opinion! :occasion5:
FORMER FAMILY:
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)

User avatar
Lance
Adenauer
Posts: 374
Joined: Thu 06 Mar, 2014 9:33 pm
Model you own: w114
Location: Altona Meadows, Melbourne

Re: NEEDED: FPR for testing '84 280SE

Post by Lance » Tue 01 May, 2018 8:00 pm

I reckon you have hit on the 3 likely causes, but an indication that the ignition module is playing up is if the tacho needle has been jumping about, or erratic, though I believe that sudden failure is also possible.
Regards,
Lance Smart

W114 280E 5 speed manual
W123 280E

User avatar
Astro-Benz777
C Class
Posts: 28
Joined: Tue 03 May, 2016 7:40 am
Model you own: w126
Region: Victoria
Location: Melbourne

Re: NEEDED: FPR for testing '84 280SE

Post by Astro-Benz777 » Tue 01 May, 2018 9:00 pm

Lance wrote:
Tue 01 May, 2018 8:00 pm
I reckon you have hit on the 3 likely causes, but an indication that the ignition module is playing up is if the tacho needle has been jumping about, or erratic, though I believe that sudden failure is also possible.
Thankfully no sign of the ignition control module failing prior to this "Sudden Death" incident, my money is on the Fuel Pump Relay....any idea roughly what they go for off the top of your head?
W126's truly were the last real Benz in my opinion! :occasion5:
FORMER FAMILY:
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)

User avatar
Lance
Adenauer
Posts: 374
Joined: Thu 06 Mar, 2014 9:33 pm
Model you own: w114
Location: Altona Meadows, Melbourne

Re: NEEDED: FPR for testing '84 280SE

Post by Lance » Wed 02 May, 2018 12:53 pm

I bought a genuine one from MB classic USA for quite reasonable money. Including shipping it was less than half the local price. Steer away from KAE.
Regards,
Lance Smart

W114 280E 5 speed manual
W123 280E

User avatar
Astro-Benz777
C Class
Posts: 28
Joined: Tue 03 May, 2016 7:40 am
Model you own: w126
Region: Victoria
Location: Melbourne

Re: NEEDED: FPR for testing '84 280SE

Post by Astro-Benz777 » Wed 02 May, 2018 7:10 pm

Lance wrote:
Wed 02 May, 2018 12:53 pm
I bought a genuine one from MB classic USA for quite reasonable money. Including shipping it was less than half the local price. Steer away from KAE.
Wise advice that I will endeavour to take. :notworthy:
I'm guessing the W123 or W116 equivalent of the W126 280SE/L FPR would suffice seeing as how the 280SE/L W126 was never officially released to the US market and remains a "Grey-market" oddity for the most part?
W126's truly were the last real Benz in my opinion! :occasion5:
FORMER FAMILY:
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)

User avatar
Lance
Adenauer
Posts: 374
Joined: Thu 06 Mar, 2014 9:33 pm
Model you own: w114
Location: Altona Meadows, Melbourne

Re: NEEDED: FPR for testing '84 280SE

Post by Lance » Wed 02 May, 2018 9:55 pm

Check the part number on the current one to make sure you get the right one.
Regards,
Lance Smart

W114 280E 5 speed manual
W123 280E

Henry Schuman
C Class
Posts: 47
Joined: Sun 29 Apr, 2018 11:25 pm
Model you own: I own multiple different models
Region: Other (please specify below)
Location: Laguna Park Texas
Contact:

Re: NEEDED: FPR for testing '84 280SE

Post by Henry Schuman » Wed 02 May, 2018 11:47 pm

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.
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Don't Squat With Your Spurs On !!!!

User avatar
Astro-Benz777
C Class
Posts: 28
Joined: Tue 03 May, 2016 7:40 am
Model you own: w126
Region: Victoria
Location: Melbourne

Re: NEEDED: FPR for testing '84 280SE

Post by Astro-Benz777 » Thu 03 May, 2018 6:43 pm

Henry Schuman wrote:
Wed 02 May, 2018 11:47 pm
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.
:pray:
W126's truly were the last real Benz in my opinion! :occasion5:
FORMER FAMILY:
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)

Henry Schuman
C Class
Posts: 47
Joined: Sun 29 Apr, 2018 11:25 pm
Model you own: I own multiple different models
Region: Other (please specify below)
Location: Laguna Park Texas
Contact:

Re: NEEDED: FPR for testing '84 280SE

Post by Henry Schuman » Thu 03 May, 2018 11:30 pm

Astro-Benz777 wrote:
Thu 03 May, 2018 6:43 pm
Henry Schuman wrote:
Wed 02 May, 2018 11:47 pm
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.
:pray:
Glad you figured it out with your techniques.
Don't Squat With Your Spurs On !!!!

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