Stuart

I have verified power output to the pump from the K40/K1 relay box output during cranking but I will get under the car and directly connect 12V to the pump terminal to rule out any wiring problems during that last run to the fuel pump. In the event that I need a new pump and/or filter I see that3 filter brands are offered - Bosch, Mann, Mahle. Is there a preference?

Thanks,

George

 

If power gets to the pump and it doesn't run then the pump is seized.

The pump is fully sealed and cannot be repaired if found to be faulty. Likely seizeddue to corrosion. Water.

Strangely although my pump carries an MB part number BUT their is no additionalsupplier part number. Bosch components usually have Bosh Pt No on them as well so I guess it is not Bosch.

Suggest you get from MB rather than an independent. This way you will be sure the spec is correct albeit more expensive than an aftermarket look alike.

If the pump runs but you have insuffivent pressure then its likely the filter (pressure relief valve).

If you do not buy MB genuine spare don't be surprised if you get pump noise and other similar issues.

Stuart

 

Stuart

I called MB and asked them what the brand was on the pumps (Pierburg) and filters (Knecht) in stock and bought the same online, saving over $200. Hopefully, this strategy will work without issue. I will report back after the R/R.

Thanks,

George

 

Only a picky point.

Pierburg (aftermarket) MAY not be identical to Pierburg (OE) bought thru MB but the difference may only be theoretical.

Some components like the MAF sensor need to be genuine spares rather than aftermarket look alikes EVEN when made by the same manufacturer as the genuine part has intellectual property embedded.

Its all to do with proprietary intellectual property rights.

Pieburg makes pumps for MB to MB SPEC and MAY not be permitted to sell that spec on the aftermarket. However with components like pumps and spark plugs the component manufacturer usually specs the part for the car manufacturer and supply "stock items" in which case the after market restriction doesn't apply.

The problem is knowing when parts are special to the car manufacturer. Sometimes the spec difference can be as simple as requiring an MB part number on the part which obviously doesn't effect performance BUT on other occasions it can be a special process like "platinum plate" in order to give desired service life which is not on the stock item.

Sorry for the rant. I'd most probably have done as you did BUT you take a risk.
Manufacturers like MB make a substantial part of their bottom line from Service and Parts.

Stuart.

 

Good info.

George

 

Well this repair job is complete and was a success. A summary of what I found:

The fuel pump only gets energized for 2 seconds when the ignition is first turned on. If you turn the ignition off and back on, it will not energize at all until you crank the starter. Then the cycle starts over again. The fuel pump always energizes when the starter is energized. Keep this in mind when you are trying to find out if you have power to the pump under the car or at the K40 box. One poster stated that he measured no voltage at the pump but when the pump was replaced, the problem was solved. I suspect that the "phantom" power was the issue. It sent me on a wild goose chase for several days. BTW, WIS makes no mention of this, I found it in a footnote in Mitchell (much better diagnostics tool). In this model, the fuel pump is driven directly from the output of the K1 relay in the K40 box, there is no relay in the trunk. You can get the relay board out of the box and connected to the harnesses so that you can measure the voltages at all of the coil energizing, relay input and relay output points.

The fuel pump may click and sound engaged when energized but not pressurize the fuel system. Check at the Schrader valve on the fuel rail under the hood. The Schrader valve size and thread are the same for Ford/GM/Chryslers using the "large" Schrader valve without the Ford adaptor. Actron CP7818 works and is around $40. Also get a cheap spark tester and have someone read the fault codes for you. Then you can actually work on what's broken and not just start changing parts.

You have to remove the plastic cover protecting the pump and filter before you can start your work. The first 2 screws come out easily. Then for those of us laying on our backs in the garage with limited clearance, the MB factory played a cruel joke on us with a third, impossible to reach screw. Just bend the shield out of the way after the first 2 screws to get to the pump/filter.

Get some hose clamps and plugs ready and put a pan under the work area because you may make a hell of a mess. It's really hard to do this job without dousing the floor. BTW, if a hose clamp is "almost" closed, it makes the gas shoot out of the hose with a very small stream which bounces off of everything but the drip pan. The fixed factory clamps can be cut off of the hoses with a pair of snips but you do have to squeeze hard on the bigger ones and don't start twisting the assemble without looking because the clamp will break and the new knife edge will start cutting the hose as it gets twisted off. Replace them with standard spiral stainless hose clamps. You need 2 different sizes.

The same parts as factory (pump and filter) are $200 cheaper than at the dealership.

My car went from dead to running great. Thanks for all of your help.

George

 

Apologises GeorgG for not mentioning the fuel pump safety circuit.

Electric pumpos are usually wired as you point out to ensure that fuel is not being pumped without the engine running except during cranking. The circuit is controlled thru the oil pressure switch which in turn operates the K40.

An accident inertia switch is also sometimes in the circuit designed in order to sense an accident situation and so cut the fuel pimp supply in case of a partially severed tubing in the engine compartment allowing the engine to continue running while spraying fuel around.

I've given this advice so many times I think i overlooked it when replying to your predicament BUT I did say apply power direct to the pump to make sure since may people are unaware of these hidden features.

With respect to the fuel everywhere bit when replacingthe pump the usual way around this is to ensure that the system is not presurrised. Press the schraeder valve underthe hood to relieve pressure and use brake hose clamps on the tubing especially if you have a floor paint like mine which "melts" with petrol.

Stuart

 

Can you tell me exactly where this is located and waht the partnumber is on a 2001 SLK320?
I have been posting all over with a major problem with my car but nobody seems to be able to help.
I was going to start with this part you mentioned.

 

Stuart, would you be so kind as to tell me just where I may find the "accident fuel cut off" inertia switch you reference - in my 1990 300SL? I can't find any reference to it the owner's manual.

Doug

 

so where is the inertiaswitchon the slk320