W124 (300 Diesel)

[callingdx]

Help !
Came back from 100 mile drive yesterday, still got at least 3 gallons of diesel in tank - today the engine refuses point blank to start.
Seems very much like no fuel is getting to the filter / fuel pump.
If I have read the threads properly it seems that there isn't a fuel solenoid shut off on the 606 engine, and that the shut off is via a vacuum actuated operation that closes the fuel off on the fuel pump rack.
Where should I be investigating to check the most likely cause(s) of the fuel starvation.
Car has never been run on Veg Oil and has a new fuel filter.
Why is there no where to prime the fuel ? (or maybe there is and I can't suss it)

 

[bolide]

I would think you have an air leak into the fuel lines. This is a common 606/605 engine problem and if you do a search you'll find hundreds of posts regarding it

Replacing the O-rings on the fuel pipes cures the problem most of the time

Nick Froome

 

[Number_Cruncher]

Did the glow cycle work properly?
Is the engine showing any sign of firing?
Is the starter turning the egine over fast enough?

If your answers are Yes, No, Yes; look at the upper diagram in this link;

Êàòàëîã

Remove the pipe closest to the passenger side of the car from the fuel filter housing, number 86. This pipe is the output of the fuel lift pump. Point the end of the pipe into a jam jar, and ask an assistant to crank the car over. You should see regular pulses of clean fuel. Look into the jam jar, and make sure that a) it's diesel, and b) that is isn't contaminated by water, sand, or anything else nasty.

If no fuel, you need to trace your way via the lift pump, primary filter, fuel heater, and pipework back to the tank. The fault lies in one of those items.

If you do get good spurts of nice clean fuel, then, you are looking at problems after the liftpump, namely, the secondary filter and the injector pump itself. At this point, I would reconnect pipe 86, and see if there's any output from the high pressure pipes.

If your answers are not Yes, No, Yes to the questions at the top, another approach is necessary.

 

[callingdx]

Thanks, Glow cycle is fine, no sign of firing, starter spinning the engine like a good 'un.
Getting a few spurts of diesel from 86, but suspect there should be more fuel than what is being delivered
I'm suspecting the fuel pump relay ( among other things)...where is it ?
Is it behind the battery ?

 

[callingdx]

Found it, and what an annoyingly simple yet well hidden fault.
The plastic pipe that exits a double tee piece near the fuel filter had disconnected from its' outer rubber pipe - inside the protective sleeve that goes under the inlet manifold.
Anyhow it's now been secured (along with others) with some pull tie cable.
Job sorted, engine starts first time every time, went for a serious blast and all is well - BUT for some reason I now get a "clunk" when she changes gear !
Never had this before -ATF was replaced 6 weeks ago and I've done a few thousand miles since then, and ATF level is fine............Any thoughts ?

 

[Number_Cruncher]

>>Getting a few spurts of diesel from 86, but suspect there should be more fuel than what is being delivered
I'm suspecting the fuel pump relay ( among other things)...where is it ?
Is it behind the battery ?

There is no fuel pump relay, because there's no electrical fuel pump.

The lift pump, on the side of the injector pump pulls the fuel from the tank *, and pushes it through the secondary filter and injector pump. A ball & spring pressure relief valve in the banjo union fitting on the outlet of the pump sets the low pressure inside the fuel gallery of the injector pump.

* Here, a pedant would say atmospheric pressure pushes the fuel.

With pipe 86 off, as the engine cranks over, you'll get only one spurt of fuel for every 2 revs, as the injector pump runs at half engine speed, and the lift pump is driven by a simple cam on the injector pump's camshaft. So, it will look *nothing* like the output from a fuel injected petrol engine's feed pipe when the electrical fuel pump is running - your description of the fuel supply sounds right to me, and you don't need to do any more there.

 

[johnsco]

>>

* Here, a pedant would say atmospheric pressure pushes the fuel.

"pedant" ... No pedants here !!

In my work (Inspection Engineer), I am internationally known as the ultimate NPB
(Nit-picking *******)

Cheers
Johnsco

 

[callingdx]

>>Getting a few spurts of diesel from 86, but suspect there should be more fuel than what is being delivered
I'm suspecting the fuel pump relay ( among other things)...where is it ?
Is it behind the battery ?

There is no fuel pump relay, because there's no electrical fuel pump.

The lift pump, on the side of the injector pump pulls the fuel from the tank *, and pushes it through the secondary filter and injector pump. A ball & spring pressure relief valve in the banjo union fitting on the outlet of the pump sets the low pressure inside the fuel gallery of the injector pump.

* Here, a pedant would say atmospheric pressure pushes the fuel.

With pipe 86 off, as the engine cranks over, you'll get only one spurt of fuel for every 2 revs, as the injector pump runs at half engine speed, and the lift pump is driven by a simple cam on the injector pump's camshaft. So, it will look *nothing* like the output from a fuel injected petrol engine's feed pipe when the electrical fuel pump is running - your description of the fuel supply sounds right to me, and you don't need to do any more there.

Thanks, I was a seriously peed off when the spurts were next to nothing, an ex mechanic had a look and said "your fuel pump is duff mate - serious money for a new one - blah blah blah.
Long live this forum !

As per my previous post I've found the problem...lucky me.
Thanks agian Hugh

 

[bolide]

BUT for some reason I now get a "clunk" when she changes gear !

You've got a disconnected vacuum hose. The most common one is the hose to the butterfly valve in the middle of the inlet manifold on the offside. The pipe connects under the crosspipe to a fitting on a circular boss. When that vac line comes adrift you get hard shifts as the vacuum to flare shifts is lost

Nick Froome

 

[callingdx]

Sure enough it was a disconnected pipe.
While I was at it I cleaned both of the butterfly valves, mid engine manifold section and bottom one near water bottle.
Not a pretty sight on the bottom one, serious amount of gunk, the mid section was just a bit sooty.
When I get time I'll have the whole lot dipped in an ultrasonic bath...not the car just the manifold !
If the mid section one was for the auto change what is the job of the other one ?
W124 - 300 Diesel 24v

Thanks for the info, I was struggling.
Regards Hugh

 

[Number_Cruncher]

>>If the mid section one was for the auto change what is the job of the other one ?

Neither are for the automatic gearbox as such - rather both control the effective length of the inlet manifold.

However, if that pipe comes off, the vacuum in the whole of that part of the vacuum system is lost, and the valves and pipes for the automatic gearbox modulator valve are fed from nearby.

 

[callingdx]

Thanks, but I don't understand "controls the effective length of the manifold"
Would appreciate a bit more of your knowledge on this.

Mega pleased it's fixed though!

Hugh

 

[Number_Cruncher]

The idea that the gas movements which allow the 4 stroke cycle (or indeed any high speed engine operation) happen instantaneously provides a reasonable explanation of engine cycles for lay people, but doesn't really capture the fact that the gas in the manifold has its own inertia and its own dynamics.

For example, when the inlet valve opens, the column of gas in the inlet manifold cannot begin to move at speed instantaneously, it must accelerate up to speed. Similarly as the valve closes, the gas in the manifold can't just stop instantaneously, and so a pressure wave is formed.

The combination of these gas dynamics with wave effects superimposed upon them mean that if you have a fixed manifold length, the manifold only fills the cylinder really effectively at one engine speed. By (very approximate) analogy, an organ pipe of fixed length can only produce one note.

By incorporating these valves, the inlet manifolds on our OM606s have three effective lengths, the longest for low engine speeds, one for mid, and the shortest (just like the short organ pipes for high frequencies) for high engine speeds.

The effect of this is to flatten the torque curve, or equivalently, to maintain high torque at higher revs without sacrificing low speed response, and, along with the 4 valve per cylinder layout is responsibe for the better performance of the naturally aspirated OM606 when compared to the OM603 equivalent engine.

 

[callingdx]

Wow, great explanation.
I assume it follows that any deposits on the inner bores of the inlet manifold will affect the combustion air velocity and cause some weird air patterns around the inlet, maybe if left too long without a damned good clean could have a noticeable adverse effect with weird and wacky symptoms.
Pity Mr Benz didn't incorporate a velocity / vacuum gauge on the dash.
As stated - great explanation.

 

[Number_Cruncher]

The combination of EGR and the crankcase ventilation system can lead to some horrid build-up of deposits in the inlet manifolds of these engines.

The crankcase ventilation system has a dual role of allowing the crankcase fumes to be burnt, while also providing some lubrication for the otherwise dry inlet valves and seats. It's therefore well worth while making sure that the crankcase ventilation system is working well, and all the rubber elbows in the inlet manifold are clear. Inlet valve seat recession is not unknown on the rearmost cylinders.

 

[callingdx]

Thanks, I have the EGR blanked off - does the cleaning of the rubber elbows require the full removal of the inlet manifold ?

 

[Number_Cruncher]

No, you don't need to remove the manifold, but, alas, the rubber becomes britle with age, and tends to crack and break as you remove them from the manifold - they're hidden away under the edge of the black plastic engine cover. However, the rubber elbows aren't particularly expensive to buy.

It's a good opportunity to renew the injector leak off pipes if they also have aged and embrittled.

 

[callingdx]

Thanks, I had a try today, but the 5mm Allen screws were a bit too tight for my Allen key - off to Mr Halfords for a decent square drive / allen key socket, plus a torx (I'm sure that is spelt differently) for the inlet manifold.
Really appreciate all the help you've given.

 

[callingdx]

Typical - all the bolts came out except the one nearest the bulkhead N/S.........
aaarrrgghhh !
Damned thing is now far from hexagonal on the inside , need an extractor of some sort to grip the head - Mole Grips were useless - tap tap tap with a fine chisel - still no joy - I eventually chickened out.

 

[Miguelxj]

Wow, great explanation.

x2!!

Thanks for taking the time to write that!