What else is needed? Its a ball and spring check valve, it can't get much more simple.

I suppose you could build a computer that controls a solenoid to regulate pressure.

How about a replacement spring, as opposed to stretching the old one????

As I recall, this is a sealed assembly???

Why? Unless its actually broken, elongating the spring is good enough for Mercedes to put it right in the Factory Service Manual.

Very few are sealed. I have yet to see one myself. The few dozen I've pulled from 1975-1985 240D/300D/CD/TD/SD models have all been serviceable.
Its the same as with which cars got a KKK turbo, there is no pattern.

Interesting!!!!!

My 617.950 IP relief valve is a sealed assembly. I suppose obtaining one from Pik-N-Pull that is serviceable would be easy enough.

Why not shim the spring????

Again, why bother? It takes all of 30 seconds to stretch the spring and measure it.

I've never been an advocate for stretching springs...Would you stretch a worn tensioner or valve spring????

Seems like adding a shim, based on pressure would be even easier. You could start by using a shim that would give you the correct OAL and then go from there...Robert

Because its what the German engineers that designed the engine and had an exponentially higher R&D budget than myself decided was the "proper" way to fix the low fuel pressure problem.

A- Remove spring, pull it to 27mm, reinstall. Done.
B- Remove spring, make a shim to fit in the hole, reinstall spring, check pressure, remove spring, replace/add/alter shim, repeat until done.

Nope. Doesn't seem easier to me.

A. remove spring, add shim to yield 27mm OAL
B. Enjoy ice cold Barq's root beer

Hmmmmm...keep in mind that when you are performing a front end alignment under warranty, there is a 'correct' setting and a 'warranty' setting that is very wide....Robert

P.S. keep in mind those same engineers with unlimited R&D budgets won't hesitate to save a dollar or a man hour, even if quality is slightly compromised...

>>Why? Unless its actually broken, elongating the spring is good enough for Mercedes to put it right in the Factory Service Manual.

Such a relaxed procedure is consistent with the IP relief setting not being particularly critical - if the setting were critical, the IP relief valve assembly would be much more likely to be a "replace as a complete unit" type of component.

True,

But I'm just not in the habit of stretching springs. I have such a vast assortment of shims at my disposal, that it just makes more sense to shim it...Robert

Well hell then, throw out the whole manual and do as you feel! Who cares if you waste a few hours doing it the hard way, its YOUR way.

Like the "bubble timing method", following third party created shortcuts and alternative methods are usually not a good choice when the FSM tells you how to do it easily and correctly.

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Forced,

I'm not trying to argue with you or the FSM. I made good money working in a flat rate shop, but I would always give my customers the best quality of workmanship possible. In my humble opinion, adding a shim to increase the free length of the spring to 27.0mm OAL is quick and easy.

My point is, if you have the ability/resources to shim the spring, then why not do that instead of stretching it out???

Forced,

You know, I was reading a post by you to another thread where you even tested the IP pressure by installing shims under the relief spring, instead of stretching it...

Am I correct in my recollection that the factory acceptable pressure specification is 11 psi to 19 psi on the IP pressure???

Now, I would think, without having my 617.950 FSM with me right now, that one would check the pressure on the nylon feed line between the filter housing and the IP itself???...Robert

Is it possible to mis-build one of these lift pumps so that it pumps via the plunger instead of by the spring?

This is the only way I can see to explain the anomalous observation made by FI that his pump delivers via the plunger rather than the spring, whereas the Bosch book, Yellit, and WHunter write that the spring is responsible for fuel delivery.

Until Forced posted the snippet from the FSM, I hadn't thought about the possibility of mis-fitting the suction and delivery valves to change the pumping mode of the pump. It will probably also swap the inlet and outlet of the pump around - are the fittings the same?

Before anyone tries it - don't! The fuel pressure spikes will be far more severe. Using the spring to pump gives an almost constant pressure delivery, which is exactly what the IP needs.