G320 / M104 Fuel Pressure & Fuel Lines

[FreddyJ]

MODERATOR'S NOTE: This thread was cleaved off of the "HOW-TO" thread for checking fuel pressure on the M119 & M104 engines, which is found here: HOW-TO: Checking M119 & M104 fuel pressure


Thank you for this great how-to Gerry! I just checked my fuel pressure and it's just inside the specs (in the lower range). But when I shut off the engine, the fuel pressure goes down immediately and reaches zero in just 5-10 seconds, so it clearly does not hold the fuel pressure. What can cause this? Vacuum leak, bad FPR, bad check valve, bad fuel pump or what?

 

[gsxr]

But when I shut off the engine, the fuel pressure goes down immediately and reaches zero in just 5-10 seconds, so it clearly does not hold the fuel pressure. What can cause this? Vacuum leak, bad FPR, bad check valve, bad fuel pump or what?

Most likely bad check valves at the fuel pumps. If the pumps are original, replace with new Bosch... after 25 years they're about done.

Possible, but less likely, is a bad FPR - cheap insurance to replace if original.

 

[gerryvz]

As Dave notes, it is either the FPR, or the check valves. If you buy new pumps, they come with the check valves. To purchase them separately, last time I checked they were around $13 apiece (you will need two of them).

FPR is also not a bad thing to replace as a preventative maintenance item, per the HOW-TO on the site. ONLY buy the MB factory or Bosch aftermarket part.

 

[FreddyJ]

Thank you Dave and Gerry! I have now swapped the FPR from my E36 AMG to my G320 with no luck, the fuel pressure still drops to zero faster than the car can hit 60 mph...

I was going to swap the check valve from my E36 AMG too, I unscrewed what I thought was the end cap on the check valve located on the fuel pump, but it turned out to just be a banjo bolt. The other end of the fuel pump goes directly to the tank via a short rubber hose so as far as I can see the on how the check valve looks it can not be located here. EPC/Parts Information says this is the only fuel pump on the G320 without the Webasto Auxiliary heater which have it's own pump. So then comes the question, where is the check valve on a 1995 G320? Maybe you know Gerry, since you have a G320 too.

By the way, is the fuel supposed to just flow through the fuel pump when the engine/ignition is off? When I unscrewed the banjo bolt I mentioned earlier I collected a lot more fuel than it's possible to be stored in the fuel pump and the short hose up to the tank.

 

[nocfn]

the system is pressurized if working properly, so there will be fuel upon demand, if you opened the outlet, you will get a shower...as you know.

 

[JC220]

I was going to swap the check valve from my E36 AMG too, I unscrewed what I thought was the end cap on the check valve located on the fuel pump, but it turned out to just be a banjo bolt. The other end of the fuel pump goes directly to the tank via a short rubber hose so as far as I can see the on how the check valve looks it can not be located here. EPC/Parts Information says this is the only fuel pump on the G320 without the Webasto Auxiliary heater which have it's own pump. So then comes the question, where is the check valve on a 1995 G320? Maybe you know Gerry, since you have a G320 too.

By the way, is the fuel supposed to just flow through the fuel pump when the engine/ignition is off? When I unscrewed the banjo bolt I mentioned earlier I collected a lot more fuel than it's possible to be stored in the fuel pump and the short hose up to the tank.

The twin fuel pump setup is for earlier production models. There was an upgrade to a single fuel pump which produces the same output on later model years. (Around 1994 or so roughly IIRC)

The check valves are replaceable on the early twin fuel pumps. However, it is common that once the fuel pump is disturbed and if it's old/ original they can leak fuel from the pump body and cannot be repaired. So you end up doing the job twice. For me now, if there is a check valve issue on a early type pump I replace both pump assemblies with new and be done with it.

Now, what you are describing appears to be a later style single pump. Those do not have a replaceable check valve. The check valve is integral to the pump hence when it goes bad you have to fit a new replacement fuel pump. They do fail and if swapping the FPR made no difference the next logical step is to fit a new fuel pump and re-test the pressure after shutoff. Once the pump issue is fixed do also check the FPR after shutdown to see it meets the specs.

And yes you will have fuel draining from the tank when you undo the banjo fittings. Best to drive as much fuel out as you can and then drain the tank through the larger hose before renewing the pump and filter.

 

[gsxr]

FreddyJ, what year/model vehicle are you working on? Very late production 124's use different pump design, as JC220 explained above.

 

[gerryvz]

I think he's operating on an M104.996-based 1995 G320, like myself.

If your G320 has a VIN ending in a number UP TO 098907 (mine is 098065), then your G will only have a single pump. For G320s with VIN number of 098908 or later, then you will have two pumps (a regular and an auxiliary fuel pump).

The single-pump models like mine use part number 003 091 53 01. This pump comes with a screw-in (removable) check valve when purchased new. However, the check valve can be purchased separately, and it is here: https://www.autohausaz.com/pn/1587010536. From what I know, this early G320 fuel pump part number cross-references with the same Bosch/MB pump that the E500E uses, as well as the 560SEC, and earlier E320 models. This E500E pump is also known as the Bosch 69601 pump.

As far as I know, MB only offers this 003 091 53 01 80 pump as a "remanufactured" pump (hence the "80" on the end of the current MB part number), and it can be obtained for around $145. URO parts makes a replacement that references to the same part number, but it is around $55 and not advisable to purchase due to low quality. I believe MTC (Mission Trading Corp) also makes an equivalent part, but this also is going to have the same quality problems as the URO pump and is not advisable to purcahse. The Bosch part number for this pump is 69608.

Amazon.com sells this Bosch 69608 pump for $87.00 via Amazon Prime: https://www.amazon.com/Bosch-69608-Original-Equipment-Replacement/dp/B000BZIDP8

For G320s with the dual-pump setup, the second pump is part number 000 470 78 94. It can be purchased for around $170-200 on the aftermarket, and is also known as Bosch 67968. One example of it is here: https://www.autohausaz.com/pn/0004707894

The Webasto system is a separate, and completely self-contained system that uses its own equipment. It is separate from the main fuel system that supplies the engine. My G320 has a factory-installed Webasto system.

Bottom line is that whether your truck has one or two main fuel pumps that supply the engine, is completely dependent on the VIN number of your truck.

 

[FreddyJ]

As Gerry says I have a 1995 G320.
Mine is 099413, so according to Parts Information my car should have the same pump that later '94/'95 W124 with single pump have (000 470 78 94 / 000 470 59 94). I believe that Parts Information/EPC is not correct, as it's called "additional pump" and "auxiliary pump" while it also specifies 1pcs. If you study the drawings you can see that there is no fuel lines going in to a second fuel pump. I have also followed the fuel lines in my car and there is only one pump, which also makes sense since the pump is the same as single pump W124 cars. I am more surprised that G320 up to 098907 as your car only uses one pump, the same as dual pump W124 cars uses. A G320 does use about 50 % more fuel than a E320.

But regarding my fuel pressure issue, I have now ordered a new fuel pump - the Bosch 67968. The fuel pump in the car looks like the 69608 (I will verify when I replace it), so it have probably been replaced earlier (374 000 km now so that makes sense). But there is no check valve on the pump, so I believe this is a original MB part which probably does not come with the check valve as Bosch does. It looks like the car has been driven without check valve for a while.. I have attached a (bad) picture of my fuel pump, to me it does look more like the 69608 than the 67968 in the form factor.

 

[gerryvz]

As Gerry says I have a 1995 G320.
Mine is 099413, so according to Parts Information my car should have the same pump that later '94/'95 W124 with single pump have (000 470 78 94 / 000 470 59 94). I believe that Parts Information/EPC is not correct, as it's called "additional pump" and "auxiliary pump" while it also specifies 1pcs. If you study the drawings you can see that there is no fuel lines going in to a second fuel pump. I have also followed the fuel lines in my car and there is only one pump, which also makes sense since the pump is the same as single pump W124 cars. I am more surprised that G320 up to 098907 as your car only uses one pump, the same as dual pump W124 cars uses. A G320 does use about 50 % more fuel than a E320.

But regarding my fuel pressure issue, I have now ordered a new fuel pump - the Bosch 67968. The fuel pump in the car looks like the 69608 (I will verify when I replace it), so it have probably been replaced earlier (374 000 km now so that makes sense). But there is no check valve on the pump, so I believe this is a original MB part which probably does not come with the check valve as Bosch does. It looks like the car has been driven without check valve for a while.. I have attached a (bad) picture of my fuel pump, to me it does look more like the 69608 than the 67968 in the form factor.

You need to double-check on this. As far as I know, the "auxlilary" (second) fuel pump for those G-wagens so equipped, resides in the left (driver's side) rear wheel well, behind the wheel, co-located with the fuel filter in the metal bracket. My fuel pump is located where your pump is (adjacent to the fuel tank), but there is a line that goes to the fuel filter in the left rear fender well area. Then after the fuel filter, it distributes the fuel up to the engine.

You can see from my illustration, that the fuel filter bracket has plenty of room to accommodate a second pump, but it does not have one ... only the fuel filter installed.

You will need to remove the inner fender liner and check this carefully.

Please check this thread:

G320 (M104 motor) Fuel Hose Replacement | G-Wagen Models

Recently, one of the fuel lines on my 1995 G320 sprung a leak, necessitating its replacement. For that matter, necessitating the replacement of ALL of the fuel hoses. As far as I can tell, all lines are original. (all photos and illustrations in this thread are from Mike C. of the...

www.500eboard.co

The check valve looks like the following photos, and as mentioned is available separately from MB.



Cheers,
Gerry

 

[FreddyJ]

I just replaced the fuel filter and I have the same bracket as you, with place on both sides but it's empty. The fuel lines and hoses are all original rusty/bad MB parts, so this must be as it left the factory. Also if you study the drawings in Parts Information you will we that there is no lines or hoses for a second fuel pump.

I am going to replace all fuel lines and hoses now, so your thread about this is useful. Thank you very much! The only thing I could not understand is why you ordered nr 52 (A 463 470 07 75), not 48 (A 463 470 09 75) when you have the fuel cooler, was it NLA? Also, for Nr 54 - A 463 470 08 75 is the hose for left hand drive with auto gearbox, not A 463 470 10 75 as you ordered. But you have probably replaced everything now and it did fit?

 

[gerryvz]

I have not completed the job, but both of those lines were grayed out in the ISPPI (EPC) for my VIN number. I can see that if you enter other VIN numbers that they show up not grayed out, but my parts orders have generally followed the ISPPI/EPC for my specific VIN number.

 

[FreddyJ]

As you say the lines (hoses) to/from the fuel cooler is grayed out when you search for parts with your VIN (same with mine), that is why I was wondering why you ordered the A 463 470 10 75 - which is the grayed out nr 54 return hose from fuel rail into the fuel cooler. You did talk about the fuel cooler in your thread about the fuel lines, so have you checked if you actually have the fuel cooler or not?