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#1
08-05-2003, 08:21 AM
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Checking 380SL Fuel Pump Relay
On Sunday, the Wayward Woman ('81 380SL) turned over but refused to start. Very politely, in the garage. No noise from fuel pump. I jumped pins 1 & 2, and the pump ran, which would indicate a bad relay, but I decided to run through the tests in the manual to be sure. I thought I would write them up, since they are fairly straighforward, and there are conditions that could lead to replacing a relay when a wire or the TDI (ignition unit) is bad.
Note that this test is for cars with the older six-pin relay. The tests for the newer twelve-pin are different. Remove relay. 1. Ignition off. Pin 2 - ground: 12V 2. Ignition on. Pin 3 - ground: 12V 3. Ignition off. Pin 2 - Pin 5 (ground): 12V 4. Check for RPM signal at Pin 4 with starter operating. I ran this test with my twenty-year-old Sears analog dwell/RPM tester, connecting the lead that would normally go to "-" on the coil to Pin 4. Insert relay partially. 5. Check for voltage on the partially-inserted Pin 6 with the starter operating. Corrective action for steps 1-3 is fix open circuit. Step 4 is to check for a bad connection from the TDI, and if none, replace the TDI (gulp!). Step 5 is to replace the relay.
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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 
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#2
01-20-2008, 06:33 PM
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1985 380sl
Chuck, I have a 1985 380SL. I'm not getting a 12V from the fuel pump terminal and reading this forum it was recommended to check/replace the fuel pump relay. I did replaced the fuel pump relay last year and now I'm getting the same problem (won't start and no 12V on the pump terminals). Could it be the fuel pump relay again? Do you have any suggestion or how to test a 7 pin relay. Any help will be much appreciated.
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#3
01-21-2008, 11:13 AM
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How are you testing for voltage at the pump? You will only get voltage when you crank the engine. No voltage with just key ON.
Here are the basic tests if the engine is not firing at all when cranking: 0. Pull the relay out. 1. Test pin 11 for ground. 2. With key ON, test pin 8 for 12V 3. Jump pins 7 and 8 on the socket with a piece of #12 wire. Pump should run. If it doesn't then it's most likely a wiring problem between the relay and the pump. Be sure you have ground at the pump. 4. Put a meter or test lamp between 11 and 12, and see if you have current when you crank the starter. If no current, fix the wiring problem - I believe 12 gets current from the purple wire that runs from the big connector on the right fender well (where the batter is connected). If these four tests are OK, you need a new relay. Good luck. If the
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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
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#4
01-21-2008, 10:07 PM
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1985 380sl
Chuck, I would like to THANK YOU for all the help you are giving us in this forum. I will try the test procedures you have given and will update the results in this forum.
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#5
01-22-2008, 07:39 PM
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1985 380sl
Greetings Chuck. I tried to work on my car today, I did pull the fuel pump relay and the Pin Numbers you gave me are not on the relay. I got 7 pins total (3 on one side and 4 on the other side. The 3 pins are 31, 15 and 87. The other 4 pins are 50, TD, 30 and 87K. Can you please advise me what output I'm suppose to get and on what pin number. Regards and thanks for any help you can provide.
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#6
01-22-2008, 07:56 PM
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Take a look at the socket, it should have numbers next to the holes.
__________________
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
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#7
11-03-2016, 02:48 PM
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1981 mercedes 380 sl
I have a 1981 380 sl that will not start.The fuel pump is not working. It is about 2 years old. I removed the relay. It is a 6 pin. I jumpered pins 1 & 2. Now I have no power at all to anything. What did I do wrong?
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#9
11-03-2016, 04:55 PM
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Quote:
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#10
11-05-2016, 11:14 AM
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Unclear what relay you removed and what connections you jumped. You may have blown a fuse or even fried a wire. But if this happened, though, there would have been a spark or some smoke.
To make sure you have the right relay, look for a large red-white-black wire connecting to the socket where the pin marked 87 would go. To be sure you are jumping the correct pins, look at the relay and jump the sockets where the pins marked 30 and 87 go.
__________________
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
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#11
11-07-2016, 03:26 PM
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The relay is a 6 pin relay with 31, 15, 87 on one row and 50, TD and 30 on the other row of pins. I jump 1 and 2 on the socket and every thing is completely dead now.
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