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fuel pumps replacement ? - 94 E320 coupe

9K views 19 replies 5 participants last post by  berniematic 
#1 ·
Hello -

Gas is dripping from the crimped end of the upper fuel pump. I replaced the filter and all copper washers - with generic copper which I can't be sure are crush washers. Fuel leak is the same. I think its the pump not the connections but I can't be certain. I think it would be a good idea to replace the 2 pump plumbing complexity with a single aftermarket pump. Forum search reveals other opinions on this, but the WALBRO GCL602 / 611 / 620 pumps are mentioned.

I would appreciate more input AND what is the fuel flow rate going to the engine out of the 2 stock pumps? Thank y'all !
 
#6 ·
When the pumps start to fail like that you should renew both at once.

Or what I did on my 500E was fit a new single high performance Walbro Fuel Pump. I have pictures of the install if you would like to see. It slots into the stock bracket. The Walbro pump I used is quieter than the twin stock pumps & pushes more fuel. It was specified with the Benzwerks NOS kits for the V8's so it is a good upgrade. I have tested fuel pressure and the stock rail FPR can handle it just fine.
 
#9 ·
you can calculate your fuel flow by taking the peak MPG (which is down in the mid single digits during peak acceleration) and dividing that into the MPH to get gallons/hour. divide that by 60 to get g/min if thats what the pumps are rated in.

example: 5 MPG at 130 MPH (full throttle acceleration at higher RPMs at near top speed), so (130 mile/hour) / (5 miles/gallon) == 26 gallons/hour. I believe HFM uses around 44PSI fuel pressure (double check this!), so your pump needs to be able to maintain that pressure at that flow rate.
 
#11 ·
Here's a couple of pics anyway -this single walbro replaced the original twin Bosch Pumps. (Which started to spring fuel leaks!) It's a quieter more powerfull pump. One thing to note is you should get the largest screw in Inlet pipe barb you can for the performance fuel pump. It should match the ID of the fuel supply hose from the fuel tank outlet.
 

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#12 ·
btw, I left out, I'd go with a pump with about double that peak flow rate, and capable of a static pressure of about half again the operating pressure of your fuel pressure regulator.

actually, if you get a pump intended for a car with similar performance characteristics and MPG, you won't be far off.

that all said, I'd replace Mercedes pumps with Mercedes OE pumps. they fit, they plug in, they work as intended. the original pump has lasted 20+ years by now...
 
#13 ·
JC - Thanks again. So there are various inlets available? Interesting that you have one to fit the original. I will try for that.

A guy on the other end of a Walbro site, says the GSL392 is 24.5 gph and 41 psi. I would probably need a smaller one but not aware of whats available at the moment.

Left Coast - Yeah I get the OEM idea and yes it has worked for a long time til now. But that 2 pump set up and its plumbing just makes me want to simplify. Further, if I got an actual MB part/pump(s), I suspect they would be Bosch. I've read in the archives here that they have been coming thru as being manufactured at various Asian locales now and some writers were unhappy with the quality.

I really appreciate all the input!
 
#15 ·
oh, I just looked it up, the fuel pressure of the HFM-SFI system, per http://mercedes-bulgaria.com/Downlo...jectionIgnition System-HFM-SFI/Engine 104.pdf is 3.7-4.2 bar when the vacuum line to the fuel pressure regulator is disconnected. that suggests you should have a fuel pump that can deliver at *LEAST* 60 PSI at full operating volume.

Mercedes expects that pump to deliver 1 liter in max 35 seconds, so thats roughly 30 gallons/hour at that 4 bar nominal pressure.
 
#17 ·
The Walbro pump is what you need. No need to reduce the spec of it or anything. Yes it might be slightly higher powered than the old twin pumps were but the stock m104 & m119 FPR valve can deal with this 100% fine. Indeed the factory fit pumps on m104 vehicles were changed on later production runs to a single Peirburg pump very similar to the Walbro. These pumps are more efficient / newer than the twin types. (Which cost more to replace, are noiser & have twice as many joints & parts to leak / fail)

The fitting you need to connect to the Walbro pump is a M10 x 1mm with 15mm Barb.

Finally – I did test my 500E’s Fuel pressure correctly after installing the single pump-
Running with Vacuum connected- 48psi.
Vacuum hose taken off gauge jumps to 56 psi.

Again – this Fuel Pump is also suitable for m104 equipped cars & is tried & tested. It is known upgrade if anyone wishes to add NOS to a 500E to safegaurd the engine against lean conditions. My 500E runs great with this pump.
 
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