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I have a new (to me) 2004 E55 that is blowing the 30amp Maxi fuse to the fuel pumps. The fuel system was replaced by MB dealer 11/2/2015
when the car had 97140mi. It currently has 102k.
I have had the car for about 1kmi and it has been running great. Has stage 1 EC. with belt wrap, ect... Had the notorious highway die on Sat.
searching through the posts has led me to believe that my fuel pumps are blowing the fuse.
New fuse car starts right up, idles for about 10-15 sec and dies (fuse blows) I don't see any obvious shorts and tried replacing the relay with a known good one from the wife's CLK500, same story.
So before I buy new pumps and sender is there any thing else to check before I purchase? It seem awful early for this to happen.
I plan on inspecting the pumps and filter tomorrow. Thanks in advance for any advice.
being related to the fuel pumps ... if it were me Id call local dealer complain of fuel smell and that the car just died and let them take care of it for free on their dime and be done with it.
Within 5 minutes of picking my car up after the fuel tank warranty, I blew my FP relay fuse. Turns out theres a wiring harness that wasn't properly insulated and shorted out after some spirited driving. I'll try to find the part number when I get home, luckily its the only item on the second service document lol
Remove the rear seat, remove the metal lid over the fuel pumps. The wiring harness rubs against the bottom of the metal lid right were the wires fold over into the connector. The harness insulation becomes brittle from heat and cracks and/or flakes off allowing the wires to short to ground. One of the new parts is a piece of foam that you stick to the bottom of the metal lid over the wiring harness.
Also, check for the adapter harness depending upon the fuel pump part number. See these posts:
Thanks Simmelma, the part number or picture would be great.
Originally Posted by Simmelma
Within 5 minutes of picking my car up after the fuel tank warranty, I blew my FP relay fuse. Turns out theres a wiring harness that wasn't properly insulated and shorted out after some spirited driving. I'll try to find the part number when I get home, luckily its the only item on the second service document lol
Thanks for responding Barry. Interesting enough that this occurred the first time I had a passenger sitting in the rear. I will inspect all the wires before going into the tank. If I'm lucky I can leave the pumps and sender alone.
Do you have a schematic for building your custom reader? I down loaded the PDF but I don't see mention of a parts list and what wire goes where?
Originally Posted by bbirdwell
Remove the rear seat, remove the metal lid over the fuel pumps. The wiring harness rubs against the bottom of the metal lid right were the wires fold over into the connector. The harness insulation becomes brittle from heat and cracks and/or flakes off allowing the wires to short to ground. One of the new parts is a piece of foam that you stick to the bottom of the metal lid over the wiring harness.
Also, check for the adapter harness depending upon the fuel pump part number. See these posts:
Both of the harness (FP and sender) adapters have continuity on all wires. I can't see any breaks except for the FP connector, as seen in the PICs. but they are not shorting, just have some stripped insulation. The intermittent pump energizing makes it difficult to trace continuity back to the relay.
Any words of advice before I have to dig into the tanks?
Here is my cheap 30amp glass tube converter. Those damm maxi fuses start adding up...LOL
Last edited by Pmarino; 09-27-2017 at 01:12 PM.
Reason: add pic
Try leaving the metal lid over the fuel pumps off the next time you crank it. Double check to ensure the fuel pump harness is clear of any interference. I would hypothesize that if the pumps' fuse blows again, it is an over-current condition likely caused by clogged fuel filter or the pre-filter "socks" on the fuel pump inlets.
Hang a fuel pressure gauge on the end of the fuel rail; at idle you should see 78-82 psi. If much less, it's the filter or the socks on the pumps.
Snips attached of the circuit I built. There's an alternative Hall-effect sensor that's new but(!) it is not a clamp on; I'd have to buy two, pull the pins of the power wires, thread the wires through the Hall-effect sensor, reinstall pins in connector, and then leave the sensor permanently on the harness under the seat. (Might also be a different way...buy one and place it over the single wire back in the trunk at the relay. That way you'd only have to pull one connector out of the socket. You'd be measuring total amperage instead of individual amperage.)
I used the adapter cable to build my test setup. Don't forget the adapter cable reverses power and ground on one pump so one must remove the daily use adapter cable from the pumps and car harness and insert the test device into the circuit. Alternatively, move the two pins on the connector of the test device so one does not have to completely remove the daily use adapter cable.
No luck with keeping everything loose. I was able to check the ground and hot wires from relay to the back seat, all have continuity
so no breaks behind the back rest. Off to AZ to borrow fuel pressure guage. Hopefully can get a read before the fuse blows. I got a feeling I'm going to have open the tank up
Originally Posted by bbirdwell
Try leaving the metal lid over the fuel pumps off the next time you crank it. Double check to ensure the fuel pump harness is clear of any interference. I would hypothesize that if the pumps' fuse blows again, it is an over-current condition likely caused by clogged fuel filter or the pre-filter "socks" on the fuel pump inlets.
Hang a fuel pressure gauge on the end of the fuel rail; at idle you should see 78-82 psi. If much less, it's the filter or the socks on the pumps.
Snips attached of the circuit I built. There's an alternative Hall-effect sensor that's new but(!) it is not a clamp on; I'd have to buy two, pull the pins of the power wires, thread the wires through the Hall-effect sensor, reinstall pins in connector, and then leave the sensor permanently on the harness under the seat. (Might also be a different way...buy one and place it over the single wire back in the trunk at the relay. That way you'd only have to pull one connector out of the socket. You'd be measuring total amperage instead of individual amperage.)
I used the adapter cable to build my test setup. Don't forget the adapter cable reverses power and ground on one pump so one must remove the daily use adapter cable from the pumps and car harness and insert the test device into the circuit. Alternatively, move the two pins on the connector of the test device so one does not have to completely remove the daily use adapter cable.
I believe I see one issue already. EDIT: Re-reading your posts you state you have the adapters in circuit. If so, you can disregard the following except for the part about insulating the breaks in the insulation on the wires of the OEM harness fuel pump connector.
Your fuel pumps are part number 211-470-00-00. Those require the striped wires to be on pins 2 and 3. The original OEM harness has the striped wires on pins 1 and 3.
The adapter harness 211-540-07-00 connects between the OEM harness and the new fuel pumps. The adapter brings the striped wires in on pins 1 and 3 and sends them out on pins 2 and 3. Failure to install the adapter cable means one of the fuel pumps is running backwards (suction, not pumping).
Be sure to insulate the breaks on the insulation or pull the pins, crimp on new pins, and re-insert into the connector in the same orientation. Mercedes Parts Departments generally sell the pins and sockets.
EDIT2: Don't just check for continuity end-to-end, check for shorts to chassis. If the relay is out of circuit or de-energized, you can check for continuity to ground from the fuel pump connector pins to chassis.
Fuel pressure gauge reads 74psi when cycling the pump with the key.
Start the car and the pressure falls off rapidly. So I guess I'll have to take a look at filter sock. Thanks Barry for all the guidence
OK I'm feeling a little better this not being a short. You can see the fuel that collected when I D/C'd the fuel line on the filter/sender (driver side tank) is pretty dark. Indicative of a dirty filter.
Thanks BBirdwell for your time and expertise!
OK new pumps in and paper insert fuel filter (not complete sender unit) replaced. It was the primary fuel pump (the one with the level float) that was shot and drawing excessive current. The secondary pump works fine. It may have been possible for me to switch the pump wire leads around and disconnect the primary and be able to drive the car a short distance. That fuel filter was filthy though.
Good to know you got it working and much appreciated that you provided the solution to your issue. These E55s can be persnickity beasts. FWIW, what is your fuel pressure at idle with the new pumps and filter?
09-26-2017, 01:21 PM
