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Proper fuel pump for d-jet cars

6K views 26 replies 5 participants last post by  Ortolani 
#1 · (Edited)
OF the 9 MB's I have 7 are CIS. Their fuel pumps are a bit different that the one I pulled from my recently purchased '73 450. I've read that the proper fuel pressure is 2-2.1 bar. That is quite a bit less than the pressure the CIS-E gets. So I'm wanting to source the correct part (I know Fonzi! I still need to get EPC! @maynard too) but the pelicanparts shows the same as the CIS-E.

Professional (quasi of course) opinion is welcome (as well as actual professional)!

And if anyone is rebuilding theirs I'm happy to hear about that too.

Learned that mine is this: BECK/ARNLEY 1520253 Electric Pump
 

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#2 ·
That Beck-Arnley is not original. I may be a rebuilt original Bosch or even a pump from Nissan which was similar.

We have been through this many times here.

https://www.benzworld.org/forums/r-c107-sl-slc-class/2663738-new-djet-pump-now-available-mb.html

Current sources are MB who now have a different pump kit (made by Bosch) for the djets. You can buy the same Bosch pump cheaper, but then you need some accessories like a rubber sleeve to increase diameter to fit holder plus some fittings for connections.

Pelican Parts do sell both (not same as K-jet pumps) https://www.pelicanparts.com/catalog/SuperCat/3446/MBZ_3446_FULFUL_pg3.htm#item7

You can also buy a Nissan pump off eBay or elsewhere. It is same as original Bosch Djet pump. Will fit exactly and unlike the new MB/Bosch pumps, does have the proper original spec.

https://www.tascaparts.com/oem-parts/nissan-fuel-pump-17011p7211
 
#4 ·
Unavita, the pump may have a higher pressure capability, but it is the fuel pressure regulator that is on the fuel return from the injectors that determines the pressure. Not the pump.

The pumps have an internal relief valve that limits the pressure. The one on the original pumps was set lower than the new MB/Bosch replacement. (Numbers in link I posted, I believe). Bosch assured me that the fuel system with rubber hoses and clamps can take the maximum relief pressure should the regulator malfunction or the return line become blocked. I still would go with the original type if I could, but the 042 would no doubt work if you already have one and can adapt it.
 
#5 ·
To use my favorite Russian phrase, "Yesbutt"...
That is as you said a diaphram also and meant to operate under certain perimeters. Eventually a 3+ bar pump will cause a premature end to the pressure regulator, nyet?
 
#11 · (Edited)
No, that is not right. The pump does not create any pressure unless there is something restricting the outflow. In the case of the V-8 Djets (I don't know about the 6-cyls) the fuel pressure regulator located on the fuel line leaving the fuel rails restricts the flow. It will only see 2 bar of upstream pressure regardless of pump used. No way it will get damaged by a pump with a higher rated pressure because the pump will not reach that pressure.

Only concern with using higher pressure pumps like the CIS pumps with a djet, is the possibility of the return line or the regulator somehow getting blocked and flow getting considerably reduced, maybe to zero. Then pump will try an reach it's maximum internal relief pressure which is likely higher than the pressure the djet hoses can safely stand.

The pumps have an internal relief valve that limits this pressure. In the case of the original Djet pumps, it may be something like 6.3bar (dropping when valve opens to 3.7bar - I tested mine and fuel pressure was 55 psig with return line clamped closed.). For the new Djet pumps they say 8.3 bar (dropping to 4.8bar). So long as the hoses and clamps can stand these pressures, no problem. Theoretically Bosch says they would. Otherwise fuel leaks could occur which is a concern.

For above reasons my first choice would be an original pump (or an identical copy like the Nissan or Beck-Arnley). Second choice would be the new Bosch/MB pump based on the Bosch 042 pump - Bosch say that these have been evaluated by MB and deemed suitable for our old Djets. (make sure all hoses and clamps are in new condition). I would not use a CIS pump.
 
#9 ·
OK. Now my curiosity is killing me. A few years ago, I bought a Beck-Arnly (I think) fuel pump for my DJet 107 off EBAY, not knowing if it was right or wrong. Honestly, I didn't know there is a specific fuel pump for DJet. The pump I bought has been working just fine. So what's the deal about a fuel pump that's specific to the DJet?
 
#10 ·
The djet was designed to function at 2-2.1 bar the way I'm understanding the documents I'm reading. All 7 of my CIS cars have a good deal more than that. Just throwing numbers around I believe 50-75 psi is common in CIS-E and the pumps are capable of 120psi in some cases. I haven't checked the pump pressure on my CIS-KE ('91 500SL) but it's high I know as is the LH version. The fuel pressure regulator is designed to discharge gas about that 2 bar (about 25psi). I've read too much pressure in a Djet will cause premature wear of that regulator as well as the fuel injectors themselves- I'm assuming should said regulator fail.
 
#17 ·
The diagram I posted was for the M110. It has flow arrows that show the damper on the fuel inlet to the fuel rail. And the regulator, like other djets is on the fuel return to the tank.

It has to be like this for the injectors to have the required pressure.
 
#20 ·
So after 13 years of believing the D-Jet worked one way, as Graham and the Bosch Yellow Book (which I have) have proven,
I find out it works the opposite. The fuel pump does indeed feed the injector ring through the diaphragm then back to the tank
through the pressure regulator. The opposite of everything I had been taught. My apologies for the confusion.
 

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#21 ·
confused-cius



Yes I was finding opposing literature from Dr. Djet on Oldtimer to the Bosch yellow book I'm reading. But it seems obvious to me that fuel is pushed through by the pump and the regulator, which is adjustable, sends back access through the return line but what isn't said is that is sent back at the same pressure as the fuel pump sends... which is one of the reasons having the proper fuel pump pressure is important- so that it doesn't blow the return line over time I am supposing. I'm sure the lines are made to handle far more than 2.1 bar (30psi). I've never seen a fuel line that isn't about 100 to 120 or more in capability. But I haven't seen everything and who knows what Jethro down the street put on his car.
 
#24 ·
Good morning, I ask permission to enter this subject. So the fuel comes from the tank, goes through the fuel pressure dumper (0280161002), follows the fuel pressure regulator (0280160007), which feeds the rail, and consequently the injectores and the bottom of the fuel pressure regulator, returns to the tank?
 
#25 ·
From tank through filter screen ( locatated inside the fuel tank- on the bottom and requires a very large socket/wrench to remove) down to the "DAMPNER" to fuel pump- to fuel filter- to fuel accumulator- to engine. Excess fuel is returned to tank via the return line entering the left/ US driver side of the tank.
 
#26 · (Edited)
That would depend on whether Ortolani has a Djet (71-75) or a Kjet (76-80). There is no fuel accumulator on a Djet.

Quiet day here today, so here goes :):

On Djet,
Fuel goes from tank (through screen in internal swirl pot)
-->damper cage (1074700216 - This NOT 0280161002 ) ***see below
-->pump
-->filter
-->front of fuel rail on engine
--> splits to two sides
--> injectors.
-->excess fuel from rails combines at fuel pressure regulator (0280160007) and flows out of third nozzle
-->enters fuel damper. (0280161002 )
-->flows back to tank.
--inside tank it enters mixing venturi before entering swirl pot (tank screen is inside swirl pot)

*** The damper cage is no longer available. I did see one for early Djets on eBay.ca - https://www.ebay.ca/itm/MBZ-FUEL-DA...ash=item23bffefedb:g:j3MAAOSw1S9Wdi-j&vxp=mtr (Luckily they seldom need replacing. Just an empty can)

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