I've had a fuel pressure problem on my 1992 300D.

Basically, the fuel pressure is low at the IP - 4psi while cranking.

I've restricted the return line to the filter, and pressure increases over 10psi.

So I took off the pressure relief valve from the IP. It doesn't offer any resistance to flow - seems like the spring is completely wore out.

Should it be offering much resistance to flow? I know the 616/617 has about 14psi on the relief valve, but I don't know if it's the same on the 602. The FSM calls it a bypass valve and says nothing about opening pressure.

Any ideas other than ride around with a clamp on my return line?

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1983 240D Silver/Blue "Sadie", unknown miles. 100k miles on WVO single tank, converted to 2 tank about 10k miles ago, FPHE, Injector Heaters, Aux Fuel pump. Alcohol/Water injection. Frantz oil bypass filter
1992 300D 2.5 Turbo Green/Tan "Jade" 267K miles Stock.
1992 300D 2.5 tan/tan "Rocky" on 2 tank WVO. Pressure actuated Turbo "rat's nest" surgery completed. 197k miles

Replace the relief valve? IIRC it's the same valve as on the 617. Further IIRC the spec is pretty loose with the high end pressure being about twice the low end. Something like 6-12 psi.

Sixto
87 300D

Yep, looks like I need to replace the relief valve - from what I saw on a UK seller of the same relief valve, pressure is 0.5 to 1.0 bar, which is about 7-15 psi. Mine is doing about 0 psi, maybe less!

The FSM says lift pump should do >0.3bar (4psi) at idle, >0.5 bar (7psi) at full load, so my lift pump is doing fine, hitting about 10 and 20 psi respectively.

Looks like I'll have to 'borrow' the relief valve off my son's 92 300D until he gets back in a few weeks....

The relief valve on the 617 is different - I checked in the peach parts, and on my 83 240D outside.

Thanks for the help Sixto, good to see you're still around and helpful as ever!

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1983 240D Silver/Blue "Sadie", unknown miles. 100k miles on WVO single tank, converted to 2 tank about 10k miles ago, FPHE, Injector Heaters, Aux Fuel pump. Alcohol/Water injection. Frantz oil bypass filter
1992 300D 2.5 Turbo Green/Tan "Jade" 267K miles Stock.
1992 300D 2.5 tan/tan "Rocky" on 2 tank WVO. Pressure actuated Turbo "rat's nest" surgery completed. 197k miles

I don't remember where I read that a 617 relief valve can be used in a 603, and might be an enhancement since it's adjustable. I also remember reading that it's NLA form MB. I've never done it. Relief valve is 601 070 01 46 (list $70!) with crush washers N 007603 012112. The 617 relief valve lists for $40. Oddly, I don't see a relief valve call out for the 240D. EPC shows a hose and washers but no banjo bolt. Hmm...

Sixto
87 300D

Some of the 617 Pressure Relief/Overflow Valves have a screw to access the Spring and Ball Bearing that is inside.
On those it is possible to go in and stretch the Spring some (see the FSM for details or look in the DIY section).
Or, instead of a Screw some have a Seel Ball pressed into it to hold the Spring and Ball in. Can't do anything with this type.

On the newer Diesel Engines that have no Hand Primer or a spot for a Hand Primer on the Lift Pump the Pressure Relief Valve is not the same and it has an Air bleed hole inside of it.

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84 300D, 82 Volvo 244Gl Diesel

Sixto, we're both right - the relief valve on a 616/7 is different from a 602/3, but, they have the same dimensions and thread and are interchangeable (as you so rightly said).

I took the relief valve off my 616, stretched the spring so it opened around 12psi, and stuck it on the 602. Working fine. Car idles better. Fuel pressure hovers around 18psi. Might be a little high, but I'm not too worried about that (unless I should be)

Diesel911 - I was wondering (with a hammer) if that spring and ball could be R&R'd, good to hear I wasn't useless in figuring it out!

Looks like another thing to put on the spares list for next time I'm at the junkyard.

Nice one!

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1983 240D Silver/Blue "Sadie", unknown miles. 100k miles on WVO single tank, converted to 2 tank about 10k miles ago, FPHE, Injector Heaters, Aux Fuel pump. Alcohol/Water injection. Frantz oil bypass filter
1992 300D 2.5 Turbo Green/Tan "Jade" 267K miles Stock.
1992 300D 2.5 tan/tan "Rocky" on 2 tank WVO. Pressure actuated Turbo "rat's nest" surgery completed. 197k miles

I think it is easier just to get used Relief Valve from the Junk Yard that has the Screw.

Where I used to work the Cummins PT Pumps had a Ball Bearing pressed in so no one could easily alter part of the Fuel setting. Part of the method for removing the Ball was to heat it up and drill it.
I did not work on the PT Pumps and I cannot remember what they actually used to pull the Ball after it was drilled as that was 37 Years ago.

If you have ever seen an Inertial Bullet Puller (for Gun Cartridges) something could be made on the same principle.
It could be if you put the Relief Valve in a Socket and were able to smack the Socket with the Square side down there would be enough inertia to lossen the Ball (which also might roll some place when it comes out).

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84 300D, 82 Volvo 244Gl Diesel

Little is known about fuel pressure problems and issues with the 602 type fuel supply setups. Keep an open mind and post if you notice any other differences as time moves forward with your 18 pounds current pressure.

The information could eventually motivate others to examine their current fuel pressures on the 602s as well. The improved idle at 18 pounds indicates to me there might be other things changed and improved as well.

At the first part of your post I was going to suggest that perhaps the fsm was wrong on some of their quoted specifications in my opinion. On this setup I could not see the lift pump putting out only 7 to 10 pounds.

The fuel filter setup alone with average usage could defeat the issue. Since you are seeing 18 pounds now in the base of the injection pump. Excess fuel flow or some other variable must have made the first reading very low. The 606 lift pump obviously puts more than 18 pounds pressure out if you have overflow.

You had me going for a minute back there. I decided to wait until more posts appeared before questioning what you had read initially pressure wise.. At best the fsm must have been reffering to rock bottom pressures perhaps. If this is so it is reasonable to expect simular serious issues with the four cylinder replacement newer engines starting in 1984 that the 616 had. Thats if they are run at really sub standard fuel pressure long term.

I still do not really want to question the fsm or get too involved with the 606 setup. People that own these engines should dig a little more. Like finding the recommended calibration pressure for the injection pump from rebuilding places. If it is in the 14-19 pound range we can consider that no major design changes occured with this injection pump system compared to the 616 and 617 pumps. Regulated idle is not a big issue to me.