M-Class Fuel Pump and Sender

Some tips

"Click, click, click" and no Start
When the engine doesn't crank but makes a 'click click click' noise it's a sign of a low battery or battery wiring problem. Don't leave the key in the ignition when jump starting or changing the battery since it might fry the key.

Cranks and no Start If the engine cranks but won't start try the other remote key or the spare key and try again. When the key is properly authorised the small LED below the LOW RANGE button and climate grille will flash briefly when the key is turned. However the brief 500 millisecond flash may be difficult to see in bright daylight. In model year 2000 to 2005 the instrument cluster may indicate "Start Error" when the key fails.

Cranks and no Start, RPMs briefly jump above 2000
The starter ring gear might require a thin coating of grease, see this bulletin.

Cranks and no Start
The fuel pump may be stuck. Kick the fuel tank from below a few times or hammer it with a wooden dowel while someone else cranks it. It may require quite some vigorous action and several tries if the pump is stuck solid. Change the station and brand of gas or diesel and have the dealer check the filters and pump assembly.

The engine stalls intermittently.
A heavy keychain dangling from the key may cause it.

Hard time starting when left off for more than a few hours The most probable cause is the check valve integrated into the fuel filter unable to maintain fuel pressure after the car is off for several hours. When turning the key to position 2 it activates the fuel pump and repressurizes the rails. 2 tankfuls of Techron DID not help. Fuel filter replacement fixed the problem. reported by roadsession

An intermittant or failed CPS causes a crank/no-start
A failing CPS usually makes it more difficult to start the engine when it's hot. After cooling off it might start again. How to replace the crankshaft position sensor (CPS) (Mercedesshop Wikki by dickiegoodman)

An intermittant or failed ignition relay (K12) wont light up all malfunction lights
If K12 fails only the SRS and AIRBAG malfunction lights come on in key position 2. To test it one can replace the relay in position K12 with an identical part number from one of the other positions, like K26, A/C fans.

Stuck Off-road: Reverse flush fuel pump repair
If one suspects the pump is stuck due to fuel impurities, one can try this reverse flush "repair". Connect the voltage in reverse, exchanging the positive and negative lead to the pump. And then run it backwards very briefly a few times so it spits out the accumulated gunk again. The wires can be accessed at the connector inboard of the left rear wheel. For best effect the pump should be taken out of the tank, though, and be flushed with diesel fuel.

X18/3 connector inboard of left rear wheel
pin A   orange fuel level sensor (empty tank: 200 ohm; full tank 0.5 ohm)
pin B   grey   fuel level sensor 
pin C   tan    ground
pin D   green  fuel pump (+12V) from fuse F38 and relay K3
pin E   blue   charcoal canister shutoff
pin F   pink   charcoal canister shutoff
pin G   -
pin H   -
pin J   tan    not used
pin K   white  not used

	Alfmeier static dissipating polyoxymethylene POMŽ fuel filler neck
	M-Class Fuel Tank The fuel tank houses the intank fuel pump and sender assembly. Two black hoses lead from the white pump assembly to the partially hidden fuel filter/pressure regulator. The filter is mounted on top of the frame rail, inboard of the left rear wheel.

Special tool to install the pump and sender assembly. The fuel pump can be checked by inserting an ammeter at the fuse F38 and measuring the current across it. It should draw 9 AMPS plus/minus 1.5 AMPS and more may indicate a problem. simple amps draw test

View into the fuel tank View inside the top of the fuel tank, showing the black splash guard. The charcoal canister to collect fuel fumes (and tank overflow) is mounted about one foot to the right of this picture, on the passenger side.

Fuel Filter upgrade The filter was modified starting March 26, 2001, so all 1998-2000 need the fuel filter up-date. Also SOME 2001 cars will also need that up-date. According to the technical service bulletin the service should be performed at the next service visit. filter upgrade instructions (Robert Hernandez) filter part number 163 477 02 01 discontinued 163 477 05 01 larger capacity 163 477 07 01 larger capacity A MB special tool for the Quick Connect lines is recommended, part 163 589 00 37 00. It's not so easy with standard needle nose pliers.

Part number KL-0121-38
Klann Fuel Line Pliers Mercedes M-Class.
"Klann has improved the design of these pliers by adding a special bend for easier access to the quick coupler. These are around 9 inches (230mm) long overall. With black plastic comfort handles. Chrome plated jaws. These are for the same job as Mercedes factory tool 163-589-00-37-00. Also good for VW-Audi, Fiat, and Opel, needing this type of pliers."
http://www.samstagsales.com

The fuel gauge never shows a full tank. Only 7/8 when full. The upper pump was misaligned during installation, rotated counter-clockwise by 10 degrees. We use our 6-inch pavers as reference grid. The yellow floating sender is too far forward, by about 2 inches and when the tank fills the floater hits the lowered tank top located in front of the pump. Even with a full tank it can not show more than 7/8. The part number of the fuel pump assembly can be found on the top of the pump next to the little arrow, which I blackened for better visibility. The pump n the lower picture is correctly aligned and the floater can lift all the way to the top of the tank and indicate 1/1 full.

The tank doesn't show full: sender corrosion
Sulfur in the fuel corrodes the contacts increasing the resistance and causes the tank to show less than full even when it is full. High sulfur gas appears especially prevalent in Texas, Florida, Louisiana, but also Erie, PA and Louisville, KY and may also cause other problems, like cylinder wall corrosion, catalyst pollution, premature bearing- and injector wear. Added: In November 2005 Chevron introduced Techron Concentrate Plus which can clean corroded fuel senders. Valvoline also produces fuel system cleaners: SynPower Complete Fuel System and MaxLife Fuel System Cleaner.

Recommended additives
Chevron TECHRONŽ Concentrate Plus Fuel System Cleaner
Mercedes-Benz part number 000-989-25-45-12: BASF Keropur

Maximum sulfur content in USA gas
=================================
Conventional gasoline    1000 ppm
Reformulated gasoline     500 ppm
California since 1996      80 ppm
California since 2004      60 ppm
California starting 2006   30 ppm

Alliance calls for improved fuel quality worldwide
PARIS, Sept 27 2002 (Reuters) An unprecedented alliance of 13 automakers called for international harmonization of vehicle regulations, worldwide acceptance of clean diesel technology, the promotion of advanced technology and for improved fuel quality worldwide.

M-Class Fuel Sender Calibration
Resistance values to measure if the sender is within specs: sender calibration specs

Off-road gauge averaging
Parking with one side down or the nose down results in low readings. Parking with the nose high increases the reading. When driving off these faulty readings will not be corrected at once due to the off-road averaging algorithm. It will take about 10 minutes of driving until the gauge suddenly becomes livelier and corrects itself. In '02 the algorithm is said to have improved, but I have not tested it yet.

Mercedes M-class fuel pumps A dual-stage side channel fuel pump was used in 1998 to 2001 M-Classes. It has two pickup locations, so fuel intake is ensured even when off-road at large tilt angles or when experiencing lateral acceleration in long curves. Hot fuel can be sucked and pumped reliably due to the pre-stage pump and vapor escape channels. For model year 2002+ it was replaced with a single stage single channel peripheral fuel pump. Fuel passes through a primary filter before entering the pump. The suction pump at the secondary fuel pickup assures reliable fuel supply even when off-road or in long curves. The pump works reliably up to 3 g.

Fuel pump and sender assembly OLD: Dual stage side channel pump: 163 470 01 94 installed from 7/97 to 9/99 163 470 11 94 second version, starting about January 2000 NEW: Single stage, single channel peripheral pump: 163 470 28 94 starting September 2001 163 470 35 94 starting October 2002; up to VIN A289559 163 470 37 94 from VIN A289560 Pierburg 7.00468.70.0 replacement pump info (pdf)

Single channel single stage peripheral pump explained The turbine's vortex flow around the impeller blades contributes to its high efficiency. The pump is so efficient that the required electrical current dropped, from the typical 9 A to around 6 A, when installed in a 1999 ML320, reducing the electrical load on the contacts inside the tank, and also reducing the electrical power lost to heat and radiated into the fuel/tank. simple amps draw test

Mercedes-Benz M-Class brake lines and fuel bundle supplier honored for excellence TI Automotive received the Shingo prize. Referred to as the "Nobel Prize of Manufacturing" by Business Week, the Shingo award is given annually to manufacturers who deliver world-class performance through lean principles and techniques in core manufacturing and business processes. It is named for Dr. Shigeo Shingo, credited with the development of the Toyota Production System. March 2004

Pierburg announces dual channel impeller pump TI Automotive introduced an all new dual channel single stage (DCSS) fuel pump which they claim sets the industry standard for efficiency. It operates at up to 30% efficiency, about 50% higher than conventional turbine pumps. The pump incorporates two rows of turbine blades feeding two parallel high-pressure pumping channels, compared to a conventional single-stage pump with a single row of blades at the impeller's outer edge. The DCSS 39/50 features a 50 mm diameter pump housing and retains the 39 mm diameter electric motor. Reduced rpm and lower brush wear enhance its durability. In tests, the DCSS 39/50 exceeded 10,000 hours of continuous operation, more than double the typical automaker requirement of 5,000 hours. Volume production is planned for model year 2006 new M-Class, R-Class and GL. pump pressure volume efficiency single channel 5 bar 180 liters/h 20% DCSS 39/50 4 bar 240 liters/h 30% DCSS 39/50 6 bar 200 liters/h 26%

Chevron, QuikTrip Meet New "TOP TIER Detergent Gasoline" Specification
ChevronTexaco press release: "ChevronTexaco Meets New "TOP TIER Detergent Gasoline" Specifications"
QuikTrip press release
www.toptier.com
June 14, 2004

shoptalk

written in 1998 and updated from time to time

2 + 2 = 4.1

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