no power at fuel pump

[catjim813]

All, I had my fuel pump, cold start valve, rebuilt and injection pump calibrated.  I now have no power at the fuel pump when I turn on the ignition switch.  I did remove all gauges to replace capillary tube as well.  I show power at the fuse box but nothing at the fuel pump wires with the test light?  center gauges, and speedo are back in but waiting on flasher relay switch before putting tach back in.  Would this cause my no power at fuel pump wires?  Pump will run using external power.   thanks for any help the team can give.    69 280 sl

[Tyler S]

Catjim, The fuel pump is fed from fuse 4. Make sure you have power on both sides of that fuse with the key on. Sometimes the fuse contacts can corrode and leave you with no power. If you have power on both sides start checking for a broken wire. Make sure you also check for a good ground at the pump. A test light will not light if there is no ground at the pump.

[wwheeler]

Twisting the fuses once a year seems to be a maintenance routine many people have and prevents fuse issues.

[catjim813]

Thanks Tyler, and Wallace got the fuse issue sorted out, pumps spins well and pumps a steady flow on the bench.  What would cause fuel not to get to the injection pump from the fuel pump.   Blocked line? or Once I placed injection pump back on is there something I may have done that will not allow the fuel to suck into the injection pump?   Car will start when I squirt gas into intake.  I will try tomorrow with the fuel pump on the car too see if it pumps like it did on the bench.  I do have power at the pump now when I turn the key and can hear it spinning but no gas is getting to the injection pump.  I am stumped.  Rebuilt injection pump, Cold start valve,  and fuel pump.   Car was running very rich before I disassembled all three parts.  thanks again for all the help 69 280sl

[wwheeler]

No fuel to the pump could something simple like a clogged screen in the tank. Possibly clogged fuel lines not allowing a continuous fuel flow in the system. Possibly dislodged something during the removal installation process. Did you replace the fuel filter?

How about crossed the wires at the pump. Ask me how I know about that one.....

[Tyler S]

Check the wire polarity at the pump as Wallace mentioned. If the fuel in the tank is very low the fuel pump will not prime itself. You may need to open the tiny bleed screw on the side of the pump while the pump is running to purge the air.

[catjim813]

Wallace, and Tyler the pump I have is the tall pump I have the multi color wire on prong 30 and the brown wire on 31.  I will check for blockage from the fuel pump to the injection pump to see where the issues lies, I wil thenl update the group with my findings.  I am looking but I don't see a bleeder screw on the tall pump.  Either way the two of you have been a tremendous help.  I am months away from retiring and taking on more projects my self.  I do not know what I would do with out the help of this group!!!!

[Tyler S]

No bleeder screw on the long pump. Loosen the fuel pump outlet fitting and run the pump to make sure fuel is actually available and the pump is attempting to push it. Good starting point.

[catjim813]

Tyler, you were spot on, pump is turning but not enough to get the fuel through the outline line to the injection pump.   Taking pump apart to see what is causing the issue.   Tapping on it got the fuel to flow but not strong and consistent  enough flow, as I tapped on the pump the flow and pitch also changed.   Impellar appears to be correct.    But it did appear that the injection pump and cold start are working correctly for the brief time the car was running so I am getting there.....

[66andBlue]

...  Impellar appears to be correct.   ..

Did you check its orientation? Could it be upside down?

[Tyler S]

Taping on it changes pitch, you could have an electrical issue inside the pump. If it was just rebuilt maybe the brushes need some time to seat correctly. I still think it may be air locked. How much fuel is in the tank? The flower pot in the tank could have an issue and with the whole system dry its not getting replenished from the return line. Check the filter screen on the bottom of the tank or fill the tank 3/4 full of fuel to rule it out.

[wwheeler]

Before you rebuilt the tall pump, was it making a loudish whine? I am not sure how successful people have been in rebuilding these older pumps. The short one seems to be no problem to rebuild. The tall one is hit or miss depending on what was wrong in the first place. Seems like if it was marginal before the rebuild, taking apart makes it worse. You may not be spinning at high enough RPMS to create suction to draw the fuel. The change in pitch indicates inconsistent motor/pump speed.

My old tall pump made an increasing louder whine over the years. I had it rebuilt and it never worked very well after that. I replaced with a short pump and lived happily ever after. That is one part I want 100% reliability because it will leave you on the side of the road with not much notice.   

[Tyler S]

As you mentioned it ran well on the bench. Think about what is different about running it on the car. Fuel and Electrical inputs.

[ja17]

These pumps must be mounted correctly (low). They are gravity feed. They cannot suck fuel up hill very far. Once fuel gets to them they will do much better. Try adding some fuel to the tank also. Also make sure that the fuel feed hose to the pump goes directly to it without wandering too high.

[catjim813]

Wallace, Tyler and Joe,  thank you so much for the replies I feel I have a team of experts helping me!!!!   From where I am now I feel the rebuild was a miss.  I have a older short pump from a 220 I had I will try, before I make the plunge for a new one. Being on the side of the road is not where I want to be, LOL  The good thing is I did get the car to run and from the information on putting the injection pump on and timed correctly I may have hit it out of the park due to the great posts from the forum.  Looking forward to the spring!!!!!   Thanks again for all the help!!!!!

[wwheeler]

My knowledge is based on hard knocks and the great information on this site. Primarily the latter. That is a good idea to try the old one first. Having just looked, I believe ALL of the new short pumps are through Mercedes now. The aftermarket availability has long since dried up and so the pump are $$$$$.

[mbzse]

.../...ALL of the new short pumps are through Mercedes now.../...

Not even that. The short pumps are NLA (Bosch dropped the production)
However, as I understood the matter, remanufactured short pumps should be available in coming years, from M-B and/or Bosch.
/Hans S

[catjim813]

On the road again after replacing the  O rings and deep cleaning the short pump I had from a 220 se,  I wanted to thank every-one for their replies in guiding me through the injection pump install, CSV and the fuel pump.  Still some fine tuning but the car is starting up great and purrs at 800 rpms at idle.  Snow in Tennessee is keeping me from road testing!!!   spring please hurry!!!!!