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  #16  
Old 04-30-2022, 12:18 PM
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Tried it again this morning, cold engine. No GO. Is there any kind of fuel pressure switch in the system or is the pump constant run?

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  #17  
Old 04-30-2022, 12:49 PM
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Location: Modesto CA
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Quote:
Originally Posted by 3DawgDoug View Post
Tried it again this morning, cold engine. No GO. Is there any kind of fuel pressure switch in the system or is the pump constant run?
If you can always get running by jumping the relay, the fault will be with the relay. All to often "rebuilt" relays will exhibit intermittent operation. The usual problem is cold solder joints on the relay circuit board; a careful hand with a soldering iron may solve the problem. When the relay closes the pump runs.
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  #18  
Old 04-30-2022, 03:10 PM
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no power to fuel pumps

Another possibility is ovp relay , and or td signal to fuel relay may not always be there , monitor the td signal , when a freinds sl560 had similiar problem i used
two volt meters , one to ezl ignition module to check voltage to fuel pump relay
and other volt meter to monitor fuel pumps voltage , also check amp draw of pumps , if one pump fails the other may be erratic
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  #19  
Old 04-30-2022, 04:53 PM
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Location: bellevue, wa.
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Quote:
Originally Posted by 3DawgDoug View Post
Tried it again this morning, cold engine. No GO. Is there any kind of fuel pressure switch in the system or is the pump constant run?
The fuel pump relay on the 103 is another part that we replaced left and right back in the day. The late 117s too. We use to stock them like air filters until they went to the mas relay in the late 103s. Just buy a relay. You can get a rebuild from programa or a K.A.E. or a MTC brand. Just don't buy a Euro brand unless you buy three of them and keep two in your glove box.
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  #20  
Old 05-02-2022, 12:44 PM
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Trevor Hadlington
 
Join Date: May 2014
Location: Worcestershire in England
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So your relay needs replacing if you have to hot wire the F.P relay at no 7 and 8 to get the pumps working...you need a new relay .
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  #21  
Old 05-02-2022, 11:17 PM
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Quote:
Originally Posted by Frank Reiner View Post
If you can always get running by jumping the relay, the fault will be with the relay. All to often "rebuilt" relays will exhibit intermittent operation. The usual problem is cold solder joints on the relay circuit board; a careful hand with a soldering iron may solve the problem. When the relay closes the pump runs.

Just wanted to be sure there was nothing upstream of the pump relay.


I have two new relays cominging that should be here Thursdy.


I am more than ready to get her back on the road. Love the way she rides and drives.


Thank you for sharing your knowledge.
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  #22  
Old 05-07-2022, 07:16 PM
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Still no joy. I have a new MB relay and an aftermarket one. Neither relay will operate the pump.

I found a pin out on this forum of the relay and the pin from the ignition goes hot when the key is on. Am I correct in my thinking that this is what trips the relay?

Now, even with the relay jumped out the engine is a no run. What would kill the ignition system?
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  #23  
Old 05-08-2022, 01:35 PM
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Location: los angeles
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if the relay pin number 30 and pin 87 are jumpered it has to run the pumps if not you have wiring or pump short or wire short , for the pump to run with relay in you need a couple of pins with power, crank signal, and key on signal and grounds
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  #24  
Old 05-08-2022, 01:45 PM
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When it wont run, do you have spark from the center distributor cap coming from the coil?, it should jump a 1/4 gap, care full dont shock yourself
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  #25  
Old 05-10-2022, 03:54 PM
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Poking around the engine today and found a vacuum line loose. One line goes to the ignition unit. The other runs under the body of the jetronic body. Where does that line hook up.
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  #26  
Old 05-10-2022, 04:23 PM
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Quote:
Originally Posted by 3DawgDoug View Post
Working on a 1988 300SE. I have lost power to the fuel pump. Pump and engine run with a by-pass power supply to the pump.



Anyone have a link to a schematic of the fuel pump circiut?
I've one fuel pump
smithj6779@gmail.com
contact me

Sent from my itel W5504 using Tapatalk
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  #27  
Old 05-10-2022, 07:00 PM
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Quote:
Originally Posted by smithj6779 View Post
I've one fuel pump
smithj6779@gmail.com
contact me

Sent from my itel W5504 using Tapatalk

Thank you for the offer, but I put a brand new Bosch OE fuel pump right from the start.
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  #28  
Old 05-10-2022, 09:45 PM
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Well, it got dark enough to check for ignition spark. It's got spark out the wazoo.

I tracked down the loose vacuum line and still can't find where it goes to. The unit it goes to is mounted on the side of the fuel distributor. Standing at the front of the car this unit is forward of the fuel distributor with one pipe fitting to the top of the distributor and another out the side toward the fender. I can see discoloration on the hose from a rubber vacuum fitting but can't find anything it would attach to.
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  #29  
Old 05-10-2022, 09:55 PM
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The unit in question is the fuel pressure regulator. Where does the vacuum hose in the end of the fuel pressure regulator go?
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  #30  
Old 05-10-2022, 10:15 PM
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Well I think I found the answer on the pressure regulator. It's a vent line, not intended to be hooked up anywhere.

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