Contemplating adding electric fuel pump to E300TD - Mercedes-Benz Forum
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post #1 of 14 (permalink) Old 04-18-2019, 01:21 PM Thread Starter
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Contemplating adding electric fuel pump to E300TD

I've been mulling adding an electric inline pump in a position similar to where the gas cars often have a fuel pump assembly, just below the fuel tank and near the left wheel. The pump would push the fuel column from the secondary tank mounted in the boot (normally filled with WVO, currently filled with B100 to clean the tank and lines, something I do quarterly before changing out all of the fuel filters). The purpose of this supplemental pump is to help keep the fuel lines air-free after tweaking component positions in the dual tank WVO/regular diesel system. The heating components strung along the fuel loop add coolant and electrically heated components into the fuel system, which includes its own large two-stage fuel filter situated between the switchover valve from tank #2 and the injection pump's pre-filter.

Ordinarily, when I fiddle with the fuel lines and heating elements, I deal with air-lock by using a hand pump to draw fuel from the tank through each fitting, filter, each length of hose, usually requiring about 30 minutes to open the hose clamps and attach the pump to eight different points along the loop. It occurred to me I could save myself some time by fitting an electric pump below the boot to burp the system, ameliorating the need to break out vacuum hand-pump and fittings whenever the fuel system needs to be taken apart. Other than choosing an unused switched circuit for the low pressure pump (something like the Facet pumps operating in the 5-7 PSI range, 8 mm fittings, with 4-6 amps draw protected by a 10 amp fuse), locating a good grounding point and fabricating a bracket for the pump and its small pre-filter (situated at the inlet of the electric pump), what else might I need to consider in adding an electric pump to the plumbing?

-bh
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post #2 of 14 (permalink) Old 06-14-2019, 06:08 PM
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wvo

I would steer clear of running straight wvo(even heated) in 606 motor. It will eat up the injection pump. I have done it, replaced Injection pumps. The old 80's 5 cylinder diesels handled it fine, but not the newer cars.
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post #3 of 14 (permalink) Old 06-14-2019, 06:26 PM
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The old 617 will handle it for a while but long term will destroy the IP and the engine.
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post #4 of 14 (permalink) Old 06-14-2019, 10:42 PM Thread Starter
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This thread wasn't about whether you should run WVO in an OM606 motor, but whether a Facet pump or a similar low pressure electric pump with 3/8" fittings was a meaningful upgrade to help keep the fuel lines air-free.

As for WVO, if and when I run it in this car again, the issue that crops up is the same as it its always been: The quality of the oil stock used for the fuel, the process used to clean it up before using it, and finally, reaching and maintaining sufficient fuel pre-heating temperatures that then have to pass the heated oil into the mechanical lift pump which in turn feeds the injection pump.

I realize some hobbyists are doing the absolute minimum with their oil and that's the problem. Oil needs to be treated through a number of processes before I would consider it safe to use. Folks who just let it settle and skim their settling tanks with a pickup tube attached to a 12V gear driven pump for transferring oil either into a storage tank or the car's fuel tank are missing steps that really shouldn't be skipped. I'll also say that where you get your waste vegetable oil is also important and one of the reasons I'm not feeding the car WVO right now - it's strictly B99. The tempura place I used to collect from has made arrangements (while I was off on contract in another state) for someone else to collect their oil. I've been cut out of the free fuel that I used to get from them and a lot of the other places with second-best quality oil have changed owners, changed the frequency of their oil refills and the quality of their oil has slid further down the preference scale in addition to needing to sweet talk the owner, who might not even live in this state, into allowing me to collect their waste oil and explain the legalities to them in 5 minutes or less, which is about as long as you'll get many owners to talk to you about this subject. Emphasis has to go reducing their expenses and that it is legal for me as the collector and for him/her as the authorizing party to allow me to take it off their hands and haul it away. "I'll take it off your hands for free sir/mam so that you don't have to pay for collection, and it's all legal, I even have my permit right here!". That tempura place had the cleanest, sweetest smelling and easiest oil to quickly let it go through initial settling before passing it through the filters. It was also only 2 blocks away. Too bad.

After settling, I run the oil through a modified 55 gallon steel drum with heating elements (30 amp circuit) that heats it to 185 F (it has an overvoltage and thermal cuto-off switch to avoid starting a fire) with the tank heating the oil for over an hour before I flip the switch (manually, I haven't rigged up a solenoid valve to automate this yet) and then pass it through three filtering stages. The filters are huge elements, they look like the ones used in big rigs. The lid of the drum has a steam valve welded into it to allow the fuel to flash off the water. After the oil is processed, it is allowed to coil. Without filtering and dewatering, it's just used vegetable oil with loads of water and inclusions of particles that don't belong in an injection pump.

-bh
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post #5 of 14 (permalink) Old 06-15-2019, 12:09 AM
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Instead of messing around with the fuel line and adding an inline pump at the fuel line at the tank.....why not do it at the fuel inlet right by the firewall?

There's even a convenient 12v and ground right there.

I've been mulling the thought for a while. Maybe a very weak pump, 1-2 psi max, keyed to a spare fuse connector that turns on with ignition in pos 2, and it always feed the pump. Just didn't have the time -- or the temperament to start hunting for such pumps. Most cheap pumps are for coolant and other whatnot, and not exactly designed to handle diesel or gasoline, and those that are, usually supply pressure beyond what I want.
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post #6 of 14 (permalink) Old 06-15-2019, 03:30 PM Thread Starter
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The type of electric pump I'm describing don't do a very good job of pulling the fuel column, they are best at pushing it along. This is why you generally see them below a fuel tank where the inlet is practically gravity fed due to the low suction they produce. By comparison, the mechanical lift pump is exceptionally good at pulling fuel, but only so so at pushing it along. It is for this reason that if I mount a auxiliary fuel pump, it's going to have to be under the tank. I haven't picked a fuse position for a switched 12V supply, but there are several unused circuits to choose from. Running a wire conduit won't be difficult and the getting a ground is a matter of scuffing off some paint with a die grinder and applying a thin film of dielectric grease to the new ground point (no need to run another wire back to the engine bay).

The only downside I can think of for the installation of the pump is that most manufacturers want a pre-filter inline in front of the pump to protect its impellers from crud. That adds to the length of the installation to avoid creating a C curve or an S curve in the fuel hose between the tank and the pump which really should be done with hardline instead of resilient hose to prevent hose kinks and folds.

-bh
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post #7 of 14 (permalink) Old 06-15-2019, 04:30 PM
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You already have priming pump about a foot from firewall.
That on the system, where tank center line is above injection pump, what makes the system mostly -self priming.
Bottom line- when need for such a pump is very questionable - it will bring additional headaches.
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post #8 of 14 (permalink) Old 06-17-2019, 05:55 PM
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I've got one of these on the return line just under the inlet manifold.
Good for priming, with ignition on of course.

https://www.amazon.com/Hand-Fuel-Pum.../dp/B01LXOJR4Z
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post #9 of 14 (permalink) Old 06-17-2019, 11:06 PM
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I added electric pumps to both my 87 and 97 diesels just below the fuel tank. It makes changing fuel filter very easy. Just swap in the filter completely dry and run the electric pump for a few sec. Engine starts right up first crank. On the 87 turbo diesel the pump is on a 3 position switch. ON, OFF or AUTO. In auto the pump activates any time boost pressure exceeds 3 psi. It makes a noticeable difference in power. On the 97 non turbo it's just ON or OFF. Mostly use it for cold starts or starting on a steep hill with low fuel where the column of fuel has to be pulled up hill.

These cars should've had an electric pump under the fuel tank from the factory.

Pump on my 87 mounter under the rear seat. It's a Delphi something or other diesel pump.

Last edited by tjts1; 06-18-2019 at 06:17 AM.
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post #10 of 14 (permalink) Old 06-18-2019, 01:24 AM
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Any info on the pump? How much pressure/power draw? Cost?

Curious....
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