My 1997 w202 C250DT story

[svengali0]

Thought i'd post up a brief summary of my w202 C250 OM605.960 adventures.
I purchased (see images) this car in August 2015 for next to nothing. Upon getting out to the vehicle some seven hours drive from here in Batemans Bay, I find that the engine was indeed unwell.
Upon removal of the head, I find that pre-combustion chambers number two and three had completely disintegrated- scoring those pistons. The motor did run however- only just. Bare in mind the car has over 517km on the clock. It is otherwise very well preserved pre-update elegance with good wiring and nice paint. It had been cared for.
I can post some images of the head if this is of interest.
Anyway, i decided to trawl fleabay in the UK for suitable donor engines- electing to try the import experience because- well, some of us need to learn the hard way.
I subsequently found a good motor, complete with accessories for less than $400 and reputed to have less than 160k on the clock.
I used an import agent (unmentionable) whom promised ' all in- Door to Door' for one lump sum.
So after prevailing on the seller to clean the item and place it on a suitable pallet, it arrived here in AU some four months later for just under 2k all up inc the engine....then I learn of all of those charming extras that my 'all in door to door quote' just didn't quite get around to mentioning (ok, so it's my learning experience not theirs).
Next time, I'll do the paperwork myself. It is NOT rocket science and I believe that I can halve the cost if I do this 'next time'. I digress.

So the engine is fitted up. It was cranky to start with. Fuel had to be attended to, the damned wrecker in West Midlands cut the IP electrics (I was very pleased to discover this), the starter was missing on the sent motor. But- it is as good as promised thank heavens. I have further sorting to do (aircon compressor, lower control arm bushes, refinish the bonnet and sort out the sunroof internal cover). What a lovely car to drive. very impressed at the mid range torque and that little VNT garret turbo is sweet. I live near a rather windy mountain that separates Batemans Bay from Canberra (130km away)- there are lots of long fairly steep hills and lovely corners. This little w202 has proven itself in short order. Considering it's miles (apart from the engine), it drives very well indeed.

Now, I need to decide how to go about rebuilding the old motor. I'll go down the route of new pistons and liners- the head is another story. Not sure what to do about those pre combustion chambers. the head itself looks fine apart from the scrapes and knocks on port two and three, all 20 valves are seated of despite the hammering- cam lobes and bearing surfaces are fine. This motor had been cared for, not much sludge residue evident at all- and service history (up to early 300k) indicates this. I'm at a loss as to why the pre-combustion chambers destructed (sheared at the holes, so the upper seat is still there, but the dome is missing at pot two and three).
I'd like to have an answer to this.

[Tony From West Oz]

Welcome to the joys of w202 C250D ownership.
Have you used the tank until the fuel low light comes on? Yes? that is good Your fuel venturi are working well. Just do not get any crap in the tank or you will only have up to 3/4 tank usage when the drivers side venturi blocks up. Why MB did not put the drivers side venturi on the gauge sender mount, like it did on the passenger side, I cannot fathom. They put it in an inaccessible position at the back of the tank, where you cannot clean it!
Have you replaced all of the fuel O rings yet? If not, you had better get a set for when the car sucks air from one or more of these O rings. They are a PITA. I replaced them on my wife's car in Jan 2015 and there is evidence of air in the fuel lines already (at hot start up).

All good learning experiences, but a bit more thought at design stage would have eliminated these issues.

Yours is the same colour as mine. I replaced the whole roof lining and sunroof trim as the foam in it was all disintegrating. Save money, do it all at the same time.

Regards,
Tony

[svengali0]

Thanks Tony.
Curiously, I have air bubbles at cold, none while warm. The O rings on the filter housing and clear lines were done but not the lift pump. Cold start- one to two revolutions before firing. Warm start- tow to three or so revolutions on firing.
I haven't performed a fuel purge yet, but have added napthaline product to the fuel. This helps.
The head lining does have to be done at some point- but my partner's w202 wagon needs it first. What a horrid job. I'm going to have to pull the complete board out. Tossing up giving it to someone but that is coin that could be spent elswhere- like B6 Bilsteins...

[tsharkey]

Anyway, i decided to trawl fleabay in the UK for suitable donor engines- electing to try the import experience because- well, some of us need to learn the hard way.

I doubt you would have found an OM605.690 locally. $2K is probably not a bad outcome. Whilst excellent engines, they are notorious for

1: O Ring deterioration (as mentioned by Tony)
2: Fuel shut off solenoid upsetting the ECU (and leaking into the loom)
3: Idle Arm failing to rest in right position, causing IP rebuild
4: Glow plugs seizing into position - having to be drilled out
5: Crank ventilation plumbing ageing and cracking
6: Injectors fuel return lines going hard and leaking fuel into the injector pots, effectively filling them up whilst you are unaware as there si a cover over the top
7: Fuel tank 75% effective capacity (as described by Tony)

I have had all 7 out of 7 of these and performed the repairs for all the above bar #3 myself. I like the perky nature of them, particularly as I run it on B100. I have imported an IP off an OM602 Turbo and the mounting arms from the US, and will import another OM605 from the UK and fit this alternate IP as it has none of the electronics on it and then fit using the arms into a W123 (I prefer these to the W202). Another project for another day...

Will be interested to follow your rebuild of the engine - Please keep us posted

The 722.6xx trans hanging off it is fantastic but these are also notorious for

1: Leaking wiring plug, wicking the fuel up the loom
2: Bad change solenoids
3: "Mother board" failure, impacting the gear change sequences

I have had the 1st and 3rd of the above.

Welcome and keep telling us what you are doing (and why those chambers deteriorated if ever you learn that one).

Tim/

[Tony From West Oz]

Yes,
I think that there are only 3 of us here with this model, so please continue to share your issues and solutions.
You may also wish to check out http://www.vegetableoildiesel.co.uk/mybbforum/index.php as there are many more of these cars over there, than here.
Regards,
Tony

[Tony From West Oz]

I wish to share what posted in a PM discussion over the past month:
My PM

• Have you had any issues with the return lines (black rubber braided hoses) popping off at irregular intervals?
  I have had this issue since well before I added the fuel pump to move fuel to the passenger side of the tank, so I cannot see it being the cause.
  
  I had one injector return line pop off, this soaked all of the other hoses. I replaced them all, then another popped off (soaking them all again). I plugged the end of the hose coming from the Tee on the filter return line port and added a hose to a temporary return line jug (cable tied to the ABS pump pipes). A few weeks later, the plugged hose blew the plug out, sending a lot of fuel onto the road and the engine eventually cut out. Once I had plugged the hose again, I had to add fuel to my tank so I could get the car would start (and so the venturi would suck fuel to the anti splash container)
  
  I suspect that I have a high return line pressure at some point in the start / run / shutdown cycle, causing this to occur.
  I have used hose clamps to secure the hose to the plug and to the Tee at the Fuel filter. I will see what happens next.
  I plan to get a pressure gauge and fit it to the hose from the filter return line tee, so I can see the actual pressures while driving.

Response:

• Yes, yes and YES and it drove me nuts !
  
  The return line leeks and the pots with injectors fill up - My wife notices straight away as she has a keener sense of smell than me. I only notice when they overflow and there is a puddle under the car.
  
  Will be very interested in where the pressure cycle pops them off ...
  
  I bought new lines and a super long pair of pliers to press the lines on, that seems to have stabilised it for the moment. It took several goes and I left the cover off constantly checking and it seems to have stabilised.

My reply

• I put the pressure gauge onto an extended piece of 3mm return line hose so the gauge sat on the wiper hub.
  I ran the engine and turned it off. While running, the pressure was 0.3 bar, but then the engine was turned off, the pressure rose to over 1 Bar. The pressure remained in the system after 10 minutes. I ran it several times each day for the past 6 days and found that pressures up to 1.5 - 2.0 Bar were sometimes registered.
  This should not happen, the return line should be open to the tank, so I now need to investigate the fuel line routing to confirm correct routing of the hoses.
  
  Could it be that someone has swapped the fuel delivery and return lines?
  If the there is a non-return valve in the fuel delivery system, then this could be the reason for the high return line pressures, but would not explain the 0.3 bar pressure when running.
  
  What to do about it until a correct diagnosis of it's cause is made?
  I tried turning the Ign. on again after switching off, and this allowed the pressure to fall to zero. This is a no-cost solution.
  I will do the switch off / on / off routine at every shutdown, until I have a foolproof solution.
  I have a short video of the fuel gauge and connection point, but will delay putting it on U tube until I have the answers I need

That ended the discussion.

I have investigated further and found that in their wisdom, MB included a fuel solenoid in the return line from the engine to the fuel tank, which is closed when the engine is turned off. This may have been their attempt to solve the issues with fuel draining back to the tank when the O rings no longer sealed properly. Well, that didn't work - did it?
Can anyone else explain why they included this solenoid valve in the return line?

I have bypassed this solenoid and I find that the return line pressure is lower when running (0.2 Bar) and is zero with the engine off.
Now, it could be that the non-return valve in the fuel supply line is the real cause of the high pressure (because the engine shutoff valve reverses fuel flow back to the fuel delivery line at shut down and this flow causes the return line pressure to spike). Why? The fuel filter has an air bleed to the return line and this allows high pressure in the fuel supply line to be transmitted to the return line. My non-return valve in the fuel supply line is part of a priming pump (so I am not removing that permanently - I did remove it for a test though).
Here is a photo of the solenoid valve and the bypass I installed:

DSCF5245.JPG

Regards,
Tony

[svengali0]

Tony that is a complicated issue. I cannot understand why the return line is pressuring to that extent- only two considerations come to mind- you have identified one, being incorrect hose fitment (swapping supply and return) but really, the hoses are different diameter and swapping these would require intent and effort. the second is an occlusion or blockage on the the return line circuit- the obvious candidate is the return pressure solenoid/pump situated on the firewall.
Apart from that, I have nothing to add, sorry. It sounds like you have been having all manner of fuel issues.

[Tony From West Oz]

Tony that is a complicated issue. I cannot understand why the return line is pressuring to that extent- only two considerations come to mind- you have identified one, being incorrect hose fitment (swapping supply and return) but really, the hoses are different diameter and swapping these would require intent and effort. the second is an occlusion or blockage on the the return line circuit- the obvious candidate is the return pressure solenoid/pump situated on the firewall.
Apart from that, I have nothing to add, sorry. It sounds like you have been having all manner of fuel issues.

The pressurising is due to the 2 conditions I have listed:

• Non Return Valve (NRV) in fuel supply line (non-standard fitment) and
• Solenoid valve blocking return line when ignition off (standard fitment on my C250D).

By removing one or the other of these, the pressure does not build up, the reverse fuel flow displaces fuel back into the fuel tank.

As a result of the Shutdown switch on the IP reversing fuel flow on shutdown to stop fuel injection, some fuel is sent back into the fuel supply line, pressurising the delivery line (against the NRV). The air bleed from the incoming fuel line causes this pressure to pressurise the injector return line hoses which do not have any clamps on them, and one pops off. Even with the rubber return line hose which normally connects to injector 1 plugged by a suitably sized nail head, the nail was forced out by this pressure.

I plan to get a couple of metres of MB return line hose, as the stuff supplied by Diesel Injector workshops is as soft as can be and it fails in normal usage, to replace the injector return line hoses on both of out C250Ds.

Regards,
Tony

[tsharkey]

I have investigated further and found that in their wisdom, MB included a fuel solenoid in the return line from the engine to the fuel tank, which is closed when the engine is turned off. This may have been their attempt to solve the issues with fuel draining back to the tank when the O rings no longer sealed properly. Well, that didn't work - did it?
Can anyone else explain why they included this solenoid valve in the return line?

I have bypassed this solenoid and I find that the return line pressure is lower when running (0.2 Bar) and is zero with the engine off.
Now, it could be that the non-return valve in the fuel supply line is the real cause of the high pressure (because the engine shutoff valve reverses fuel flow back to the fuel delivery line at shut down and this flow causes the return line pressure to spike). Why? The fuel filter has an air bleed to the return line and this allows high pressure in the fuel supply line to be transmitted to the return line. My non-return valve in the fuel supply line is part of a priming pump (so I am not removing that permanently - I did remove it for a test though).

As always, thanks for sharing Tony as I have learnt a lot form your investigations. I am of a view that we should collect all your Diesel Fuel investigations and create a sticky (for the 3 OM605 owners on this forum and any googlers that drop in ...)

My 250D doesn't have that valve but I added a one-way valve myself. Worked brilliantly in enabling almost instantaneous start but what I found was the shutoff solenoid struggled to shut the engine down and the leaky return lines. So I removed it and things stabilised, that said, air does bleed in.

Is your priming pump for the flow between tanks or do you have another in situ to deliver more fuel upfront ?

Tim/

[Tony From West Oz]

The priming pump is a squeezable bulb which has 2, non Return Valves (NRVs) in it. I installed in the fuel line between the steel fuel pipe and the stock fuel heat exchanger. Due to the high flow of the fuel pump, the bulb is sucked in while the engine is running. This has caused the bulb to take on a permanent 'deflated balloon' shape (a bit like half of a tennis ball) but I can still use it to prime the system by squeezing it so that the inverted half comes out, I can then release pressure on the other side, so it draws fuel in from the tank. Once squeezed out, I repeat the process. It is a bit slower than when new but it still gets the job done.
I still pre-fill fuel filters before installing them (rag over drive belt, 2 bolts holding the filter housing removed and juggle the filter in under the housing. Do up the filter bolt, reinstall the housing bolts remove the rag and all is well)
The electric pump is only for transferring fuel from the Drivers side of the tank to the passenger side of the tank.

Are you saying that you do not have a NRV in your fuel delivery line now?

I just purchased some fuel line from my Diesel Injector place (not return line hose) and I am trialing it in my C250D to see how it stands up to biodiesel. MB wanted $64 a metre for their return line hose, I got this for $16 a metre.
Regards,
Tony

[tsharkey]

The priming pump is a squeezable bulb which has 2, non Return Valves (NRVs) in it. I installed in the fuel line between the steel fuel pipe and the stock fuel heat exchanger.
Tony

Nice idea. I have been using the Mityvac to prime the line where it plugs into the prefilter and then a hose clamp to stop it returning back to the tank. I also clamp the return line when prefilling the filters etc as I tend to get runoff in that direction. Tis a bit clunky but has meant much easier starting after filter changes.

Are you saying that you do not have a NRV in your fuel delivery line now?Tony

Yes, there is no NRV - I get air leak in overnight so it takes a few cranks in the morning but no popped off fuel return lines.

[Harvey]

Dear Tony and other past and present c250TD owners.

A question regards the fuel return solenoid. Whilst rummaging through the main fuse / relay panel I accidentally knocked the positive wire that goes to this solenoid out of its terminal.
I can’t find where it should go to, but from this thread wonder if the solenoid is really needed.

Does anyone know where the wire is meant to connect within the fuse relay box, OR, can I just bypass the solenoids and forget the hassle of where the wire goes?

Kind regards Harvey

[tsharkey]

Hi Harvey,
I don't have that solenoid in my 96 W202 C250DT so am not sure if it is required ...