IP pressure relief valve, performance mod - inline pumps

[spock500]

Need a bit of help here chaps (see link below for performance mod)

On the OM605 the pressure relief valve is shown as No 125 in the diagram which I suspected to be faulty but this may not be the case.

The old relief valve is shown below

The thing is there doesn't seem to be any difference between the old one and the new although I have only tested

them both by blowing through the bolt end and not actually fitting it.

Is there anything I can check for before fitting just in case its not faulty, the new valve was £42 so not cheap.

I noticed this difference looking down at the top - the new valve is on the left with a smaller inlet hole - do they wear through flow of fuel?

Are there any checks that can be done to determine if its working ok?


Original thread with details of the mod with spring operated valves;

http://www.mercedesshop.com/shopforum/showthread.php?t=234609&page=17

 

[Number_Cruncher]

Why did you suspect it to be faulty?

The best way to check would be to temporarily plumb in a pressure gauge between the secondary filter and the injector pump. On an older system, I would hope to see something like 10 psi there, but, I'm not sure what to expect on an OM60x engine.

Although the older engines use a ball and spring relief valve, I *think* that the system would also work well if there just a calibrated orifice in that bolt - as long as the amount of fuel discharged by the orifice during one revolution of the injector pump is small compared with the lift pump maximum delivery volume, the pressure variation during the lift pump cycle will still be small.

 

[spock500]

Cheers for that NC,

Basically the engine after a head recon refuses to start - everything has been tested inc recond injectors.

When I contacted them they suggested this valve as being the likely cause which does sound probably.

Going to bolt it in gently and give it a go see if she fires up

 

[spock500]

Well thats didnt work so back to the drawing board

 

[Number_Cruncher]

>>everything has been tested

That can't be true - or it would be running!

I would double check all the basics;

cam timing (both inlet & exhaust)
injector pump timing
compression values
fuel supply to the injecor pump (if needs be, rig up a temporary small header tank to test)
fuel supply at the injector while cranking

before spending any more money

 

[spock500]

>>everything has been tested

That can't be true - or it would be running!

I would double check all the basics;

cam timing (both inlet & exhaust)
injector pump timing
compression values
fuel supply to the injecor pump (if needs be, rig up a temporary small header tank to test)
fuel supply at the injector while cranking

before spending any more money

That Mr Cruncher is a very astute observation

Ok, cam timing both inlet and exhaust checked -

IP timing checked

Fuel supply to pump ok, plenty coming back through the return.

When I first cranked it with a full battery it fired a few times but then I stopped to give the motor a breather after which it didnt have the same whizz on cranking.

There is pressure hiss from the inlet valves which I am told by the head refurb company is normal and will disappear after being run in.

The head was sent back and pressure tested which came up 100% and this was with the cams/lifters in place as is now.

I think once she goes it will be ok, its just getting the first run which is a problem. I might disconnect the glow plugs and try a drop of easy start after heating the head with heat gun.

 

[Dieselman]

Forget that banjo bolt mod for the non starting, what that does is raise the fuel pump low pressure by restricting the return flow.

You probably have air in the fuel pipes and lines. Crack the HP lines free and wind the engine over then tighten up and see how it goes.

Have you carefully checked the cam and IP timing.? If so what IP timing have you got, it should be 14 deg ATDC as measured.

Have you tried running it straight from a can to reduce the air in the pipes.

To answer Number Cruncher the lift pump should supply fuel at 25psi.

 

[spock500]

Checked several times, took the IP sprocket cover off to see if chain had slipped but it cant due to a dowel fitted.

Removed timing plug anyway and its centred with timing mark at 14degrees after top dead.

Injectors have been refurbed a pop tested twice

New glow plugs all tested and working well

Its a real puzzle

 

[Dieselman]

I note you said it fired a few times, in which case pretty well everything is ok and it sounds like there is air being drawn into the pipes.

I know it goes against all wisdom for batteries and motors but once cranking don't stop for a while as this allows the fuel to fall back from the pump.

If it won't go on the starter give it a tow start it will probably fire straight up even if compressions are a bit low.

Don't disconnect the glowplugs, it'll never go in these temperatures.

 

[230K]

Hi

Have you filled the filter with fuel and put a second battery to her, slacken an injector pipe while she is turning over too??

230K

 

[spock500]

She has been spun over enough to fill half litre bottle on the return pipe -

Filter has not been off and I have fitted a small priming bulb to help, theres fuel at the top of all injectors has cracked them all of half a turn and fuel spurts upwards when cranking.

 

[Dieselman]

If it gives clearly defined squirts with no air visible then you can forget the IP apart from possible timing.

 

[Number_Cruncher]

When I rebuilt mine, I left the glowplugs out. Then, with all the high pressure injector pipes off, I cranked it over - obviously, it spun very quickly with no compression, and didn't take much out of the battery. Once fuel was spurting out of the injector pipe ends, I tightened them all up, fitted the glow plugs and manifold, and started it straight up.

Dieselman - I take it that 25 psi is into a clamped off pipe, and is the maximum that the lift pump can deliver

 

[spock500]

This is what i used to check although only visually not using the MB tool.

If you hold a mirror to one side with a torch you can see the peg that the tool latches onto

 

[Number_Cruncher]

>>then you can forget the IP apart from possible timing.

Yes, you're back to timing, compressions, and odd things like blockages in the exhaust system.

A blockage in the exhaust would allow the odd firing, and then as the pressure of the burnt gas increases, the 4 stroke cycle gets abruptly stopped!

From your descriptions, it sounds like it's probable that you don't have enough compression to start. What are the compression pressures?

 

[Dieselman]

This is what i used to check although only visually not using the MB tool.

If you hold a mirror to one side with a torch you can see the peg that the tool latches onto

Not a method I'd chose to use as you could be a number of degrees out which is then multiplied by a factor of 2 due to the pump going at half engine speed.

Buy a blocking pin or beg/borrow a tool.

Another method is to remove No1 HP pipe, dry hte delivery valve out then slowly turn the engine over and watch for the valve to fill, or make a spill pipe and watch for overflow. The timing should be set to ~15 deg BTDC using this method.

Where are you.?

 

[spock500]

>>then you can forget the IP apart from possible timing.

Yes, you're back to timing, compressions, and odd things like blockages in the exhaust system.

A blockage in the exhaust would allow the odd firing, and then as the pressure of the burnt gas increases, the 4 stroke cycle gets abruptly stopped!

From your descriptions, it sounds like it's probable that you don't have enough compression to start. What are the compression pressures?

There is compression but I wouldnt call it high, it dissipates quite quickly at TDC with each piston as you can hear it hissing past the valve seats -

The head was sent back because of this and checked with the cams in place, tested up ok - the chaps there said the machines used to cut the seats are so accurate that lapping in is not necessary but they do need to bed in and the leakage I am experiencing is normal.

There is no oil in the hydrallic lifters so they are probably not opeing too far until she starts so may need the extra oomph to get going.

You mention the exhaust, thats a possibilty as nothing is coming out of the back in terms of unburnt fuel/smoke?? I could drop the bottom part of the downpipe and see if she goes -

 

[spock500]

Not a method I'd chose to use as you could be a number of degrees out which is then multiplied by a factor of 2 due to the pump going at half engine speed.

Buy a blocking pin or beg/borrow a tool.

Another method is to remove No1 HP pipe, dry hte delivery valve out then slowly turn the engine over and watch for the valve to fill, or make a spill pipe and watch for overflow. The timing should be set to ~15 deg BTDC using this method.

Where are you.?

I am in Milton Keynes.

The pump has not been off and I checked the chain for splipping a tooth, this is not possible due to the dowel close to the sprocket which i removed. In tried one tooth in either direction and it was miles out, could just about see the peg so it really has only one place.

 

[Dieselman]

I seriously doubt it will be a blocked exhaust as that would allow it to start and after running for a while would build pressure and cut out, but it could be the exhaust valves not opening due to the hydraulic tappets not having taken up slack yet.
That would tally with the inlet valves leaking as the compression builds to very high levels.

Slip the exhaust off at the manifold and listen for the valves operating.

I still think it just needs a good winding over, with a good battery and maybe the timing checking.

 

[Number_Cruncher]

>>You mention the exhaust

Yes, I mention it because an odd case once caught me out, and had me chasing my tail for an hour or two before the penny dropped!

However, it sounds like you aren't getting the compression you need - what are your compression pressures?