A Fuel Pump for the Trailer-Sailer’s Diesel Land Auxiliary

Enough about radio! This blog is also about sailing… so switching to sailing (well, kind of…): “Sassy Gaffer”, a SunCat 17 sailboat, could not possibly be the superb trailer-sailer that she is without her “Land Auxiliary”: the Jeep Liberty CRD (diesel) 2006.

This rare 10-year old SUV and mini-truck/tractor has kept very well throughout the years and is in excellent condition considering the ten springs (and Canadian winters…) that she accumulates under her fenders. However, a few parts have started to show signs of normal wear-and-tear, thus requiring prompt attention. In the last few weeks there was an erratic refusal to start due to air bubbles in the fuel line. Manual bleeding with the pump under the hood repeatedly solved the problem but finding the actual place where air might be entering the fuel line proved much more difficult. Without direct evidence, the most suspicious culprit was the seal under the cap at the tank itself. One alternative would have been to replace such cap with new parts.

However, Alex, the professional auto-mechanic (more like an “auto-physician”) who for the last seven years has been seeing and attending at the needs of the CRD Jeep, suggested the installation of a fuel pump where none existed before (see his own sketch on the attached figure):

pump3

Alex was quick to notice that – different from other Chrysler diesel models – the Liberty CRD did not come with a fuel pump inside its fuel tank, thus relying only on negative pressure for the fuel to flow from the tank in the rear to the engine in the front. This was intriguing because other Chrysler cars fitted with diesel engines did come with such pump, as also did her gas-engine sibling: the Jeep Liberty 3.7L. Such a pump would keep the inside of the fuel line pressurized enough to avoid air bubbles from entering the fuel via any small crack that might have developed at any of its joints. Furthermore, the cost of replacing the existing parts with similar ones would not have been much less than that of installing a brand new fuel pump inside the tank.

Hence, the decision was made to redress the initial flaw in the design and install an internal pump at the bottom of the tank with which to produce enough positive pressure to drive the fuel to the injectors and thus avoid any admission of air inside the fuel line. The pump chosen for the job was the Fuel Pump Module Assembly Spectra SP7181M (see the top left panel on the picture attached). This auto-part is sold to replace the fuel pump in Chrysler Diesel Turbocharged OHV vehicles: “05-09 Dodge Ram 2500/3500 5.9L-L6”. Of course, the Jeep Liberty CRD does not show up in any database as a candidate for such replacement (as it never had such pump in the first place…). However, although this was unknown territory, it was not totally unchartered: here is a very complete account of a similar job successfully completed seemingly by a non-professional mechanic: http://www.auerbach.ca/kj/lift_pump/.

New electrical connections were required. However, this was helped by the fact that the chassis of the Jeep already had all the wiring that would have been in use had it been fitted with a gas engine (thank you Chrysler!) – i.e., it included a hitherto non-connected terminal for powering the pump. Thus, no modification was required for the chassis harness and only two new wires had to be added to the tank harness: the power wire for the pump and its ground to the chassis.

Since then the Jeep’s engine has been purring like the feline that she is, and once again she is sailing the roads “in smooth waters and fair winds”, and “Sassy Gaffer” – though currently hibernating under heavy tarps – is once again the complete trailer-sailer that she has always been meant to be.

Thank you Alex !

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