Hoping to purchase the spring mod from Greazzer in a few weeks. Meanwhile, I’m planning to stretch my IP delivery valve spring back to 27mm because why not?

Of the 240D owners of you who’ve done this, how did it work out for you?
See any difference? Any issues later?

Just FWIW a delivery valve and fuel pressure regulator (what you mean to say) are two completely different things

I stretched mine to about 50mm...

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1978 300D, 373,000km 617.912, 711.113 5 speed, 7.5mm superpump, HX30W turbo...many, many years in the making....
1977 280> 300D - 500,000km+ (to be sold...)
1984 240TD>300TD 121,000 miles, *gone*
1977 250 parts car
1988 Toyota Corona 2.0D *gone*
1975 FJ45>HJ45
1981 200>240D (to be sold...)
1999 Hyundai Lantra 1.6 *gone*
1980s Lansing Bagnall FOER 5.2 Forklift (the Mk2 engine hoist)
2001 Holden Rodeo 4JB1T 2WD

I’m referring to the side fitting banjo bolt on the IP -the one facing the engine.
If we’re talking about the same thing, the FSM suggests stretching it to 27mm. 50mm is a lot!

NZScott is right, you're talking about fuel pressure regulator spring. Delivery valves are a whole different doohickey.

I can heartily recommend Greazzer's spring mod.

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617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap

Ah, roger that. I’ve already preordered one, looking forward to installing it.
Have you done the stretch?

I had it out at about 60mm but it wouldn't fit. 50 it did, It was actually one of Greazzers too (sorry). Nearly impossible to get it to open when hand priming so not really ideal

__________________
1978 300D, 373,000km 617.912, 711.113 5 speed, 7.5mm superpump, HX30W turbo...many, many years in the making....
1977 280> 300D - 500,000km+ (to be sold...)
1984 240TD>300TD 121,000 miles, *gone*
1977 250 parts car
1988 Toyota Corona 2.0D *gone*
1975 FJ45>HJ45
1981 200>240D (to be sold...)
1999 Hyundai Lantra 1.6 *gone*
1980s Lansing Bagnall FOER 5.2 Forklift (the Mk2 engine hoist)
2001 Holden Rodeo 4JB1T 2WD

My 240D has good compression, properly adjusted valves, and rebuilt injectors. then a year or two ago mileage dropped to 21 or 22. After reading the fuel pressure threads, I made a gauge and tested the pressure per the FSM. Way low. I was lucky enough to buy the overflow valve and a rebuilt lift pump from Greazzer. The overflow valve put the actual operating fuel pressure well above factory minimums. Mileage moved up to 26 to 28. And much more power. Even at 70mph.

You want to make sure that you still have overflow from the relief valve after any modification of the spring. Wise to verify it even before. For example the lift pump might be weaker with age and need refreshing as well. Also filter obstruction can lower base fuel pressure in the injection pump.

For example if the lift pump has weakened in age to the point it is unable to open the current relief valve. Changing the spring will do nothing. Neither will restoring the original to the intended length before sagging.

At the same time I feel that having proper fuel pressure in that supply system is important on the 616 engines especially. Fortunately things that can impact this are easy and cheap to rectify if found lacking.

So for those that restore a sagged spring or replace it. If they feel no difference In the seat of their pants especially. Further investigation is warranted.

A weak fuel pump or lift pump if you wish. Is pretty easy and cheap to rebuild. If in a weak condition the chances of failure on the road increases as well. Now that can be expensive. If for example it tests weak you have to eliminate things like a fairly obstructed tank filter is not the issue.

In other words the relief valve regulates the pressure of the fuel in the injection pump. It cannot regulate really low pressure.

There also is considerable localized heat created by the compression of the fuel in the injection pump elements. The overflow from the relief valve removes some of that heat. Yet another reason to keep the system in good shape.

Proper pressure out of the lift pump means a better and more constant flow out of the relief valve. Removing more heat in the process. Over and over again I read posts of difficulty in starting in cold weather. A good lift pumps check valves if sealing well stop back draining. So when they are tired. You start cranking but fuel is not present in enough quantity from the elements to light off intitially.

It instead gets blamed on many things like the engine is old. Where this is true in a lot of cases. The situation if it exists still makes the situation harder than needed. There is a simple test to check this. Say it is thirty degrees out in the morning. Have someone pump the primer pump before you try to start. If there is a massive improvement in start up time. You have a back draining problem to examine that occurred during the night.

To me it is not a case of the valves in the lift pump have failed. As much as crud over the years has accumulated on the valve seats allowing leakage. The kit is cheap to renew them so it is also not a big issue.

In fact after rebuilding the pump if needed it may be good as a test to check it for back leakage. When off the car. When it is not working both valves in it act like two closed check valves in series. .

Why do you check things out before plunging in? In my case I never usually got enough service records to determine what was repaired before I got the car. Maybe that lift pump was rebuilt or replaced five years before and is still like new. I see some people randomly changing things without thinking about this factor. It instead is better to spend the money where the proven need is.

If you want reliability close to a new car. Or as close as you can get in practical reality with cars this age. Over time there are a lot of things to check. I have two 240ds, a 300d NA and a 300d turbo. These are all very old cars. The best thing of all is the needs are cheap in general to address if and when found. If you do them yourself usually fairly inexpensive compared to paid for service as well.


Many are for your own safety as well. In the 240ds you want all the power that is available out of those engines. It may even save your posterior getting into a traffic stream someday. This means checking valve clearances, Chain stretch and some other things that can kill your engine with time as well if ignored.

Good post of what is possible. A system that checks out marginally at idle. Will further decline under engine load. Starving the engine for the fuel it could deliver if in decent shape further. Another issue is the 616 lift pump by design has a weaker pressure output regulating spring than the turbo lift pumps.

Not the relief valve spring but the spring in the lift pump. My feeling for what it is worth is that over time a pressure differential increases across the secondary fuel filter. This has an effect of lowering supply pressure further in a system. The weaker the lift pump the worse the possible effect. Also as that differential increases dirt that would be stopped by the filter may get forced through.

Since the 616 lift pumps output pressure is weaker than the turbo engine 300d.It may be prudent to change out the secondary fuel filter from time to time. If you fuel at high volume outlets as much as possible the fuel is pretty clean. Small volume places will give you trouble eventually unless you are very lucky.

I live by a simple rule with cars. With any reasonable preventable road breakdown. It is better found and rectified before it creates one. Always far cheaper and you do not also lose a day or more in the process. There will be those breakdowns that you cannot expect or avoid of course.

This poster purchased hopefully a 0-30 or 0-60 pound liquid dampened pressure gauge and used it. This is the right way to do it but you can still get around using that gauge.

This periodic check incidentally is in the Mercedes engine tune up check list of that period. They want a gauge used. The gauge was about 10.00 at harbor freight but might be a little more now.

I have suspected for years that low fuel pressure may be the cause of a very serious problem with the 616 engine. I am not sure I can prove it as the effect I suspect takes place over a long time period very gradually..

So I just decided instead why risk it? Just keep my 240d engines at or above the minimum acceptable fuel pressure. There are also many other benefits in doing so.

Scott, Mark, Barry, I appreciate the thoughtful advice. Mark we're in roughly the same boat sans severe mileage drop. I have noticed it dip a touch however.

This is the first diesel and the only w123 I've ever driven. Therefore, any improvements I experience are entirely relative. To be honest, I don't actually have any real issues (that I'm aware of). The car starts on the first crank, has a fine idle, mileage is in the 25-26 range. Hills are an issue though. I live on a very steep street and pulling out of my drive way in the morning to climb it is a bit of a joke. I'd estimate 7-8 mph and obviously in first gear the entire way. I also struggle mightily to keep over 50 on a highway grade, say 4%.

More than anything, I find incremental improvements to be very satisfying. I imagine we all do. Because I have no clue what this car was like off the assembly line, the idle can always be a little smoother, engine quieter, and hills more surmountable than they presently are.

I stretched the factory spring back out to the 27mm spec. Next time I opened the overflow valve, the spring was broken.

I put Greazzer's spring in, completely happy since. I don't notice any extra power in normal driving, but after Greazzer's spring I was able to pull hills in 5th gear that I'd previously had to drop to 4th gear for.

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617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap

That wasn’t making a rattling noise by any chance was it?

Maybe, but nothing that could be heard over the rest of the racket the engine makes. The new spring did make an improvement in engine noise when running, though. Pure supposition, but my guess is that without sufficient pressure in the fuel gallery, the fuel elements don't fill completely, causing nailing.

If you're tracking down a rattling noise, there's about a million things it can be, including stuff that isn't rattling at all. Head to YT and listen to videos about injector nailing, important to be able to distinguish the difference. SOME rattle is normal, nailing is not.

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617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap

I’ve been tracking down, trying to track down, some very intermittent arythmic rattling that occurs only on load around 20-40mph -infrequently enough to pin down to anything obvious. Not nailing but rattling. Almost like a bearing ball... maybe.

.

I've put 2 mm shim to compensate 4 mm stretch missing...no problems since

cheers

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w126 500SEC gen II euro, powered by OM617 turbo stolen from 84 300SD 2.88 diff,EGR blinded
next wish/project: w114 coupe OM603 powered