Problem with starting C250 (1996) Diesel

[John Gallen]

Car is very slow to start requires prolonged turning over, eventually starts if battery does not go flat first. Seems worse since it has become cold.

Changed glow plugs ? not much different.
Battery ok and holding charge.
No warning lights.
Runs ok when started.
Starts ok when warm.
No obvious fuel leaks or smell of diesel.

I believe there is a glow plug timing relay, cannot locate it at present, and it is also possible to test circuit.

Questions.
Anything I have missed?
Where is glow plug timer relay?
What should voltage be at glow plugs, suspect 12 volts
Can relay be tested, cleaned, or adjusted?

Any assistance advice much appreciated.

Regards


John

 

[sixpack]

Hi John,

The Glow plug relay is under the washer bottle. You can find it by tracing the wires from the plugs, they run inside a plastic duct.
Youre right there should be 12v during pre heat, but it will probably measure lower (maybe 11v), as the load is high. Relay has a fuse built in. I too had starting probs recently, cured by replacing the clear plastic pipes around the pump. My problem was eventually traced to an air leak on one of the 3 pipes on top of the filter housing, strangely it didnt leak fuel normally but did when we tried pressurizing the fuel tank slightly, (using an air line carefully !) Sounds dead easy but all this took about 2 wks of head scratching etc. Keep us posted as i know how frustrating this fault can be !

 

[Andy]

Hi

I would agree with sixpack. You more than likely have a air leak. Finding it is the problem. If you park on a hill. With the front pointing upwards. Try reversing it to rectify the hard starting.

This of course is sorting the symptons but not the cause.


Regards

Andy@ www.mercedesservicing.com

 

[John Gallen]

Thanks for advice, relay found and tested checks out ok, 11 volts as you said, will examine pipes as suggested, no signs of fuel leaks when I looked this morning. Will check again tomorrow, especially around fuel filter.

Regards

John

 

[John Gallen]

Examined pipe work no signsof any leakage, replaced fuel filter and similar starting problem occured. Removed filter and bowl was only full of a small quanity of fuel. Primed filter bowl and refitted. Old filter flushed out and seem somewhat dirty.

Started very soon afterwards. Can anyone tell me how fuel filter is primed is it by gravity or is there a pump?

Have read somewhere about a lift pump - could this cause the problem?

I would be grateful for any assistance, clues etc.

John

 

[sixpack]

Hi John,
Yes there is a lift pump, but there is no means of operating it manually, you just have to keep cranking on the starter. I think the pump is the small aluminium device with 2 pipes, below the black shut off module. the shut off module is the one with a black electrical plug going into the side. I say think because I cant see how the thing is driven, but its hard bit to see clearly. If you change the filter again, fill the new one with diesel, it saves a lot of cranking. Anyway,sound as though you may have cured it !.

Good luck
Peter

 

[pcman_jh]

Re C250 Diesel (1996) slow to start

My 1994 C250 had this problem as well. It was down to air ingress through the black rubber seals that are fitted on the ends of the fuel pipes around the pump/filter assembly. Rather than trying to find which of the 5 (or so) pipes it is, I changed the lot. They're all reasonably priced from a Merc garage - I think the dearest was about £6. I had great difficulty getting one of the pipes refitted into its orifice and had to give up and use the old pipe but with the new O ring transferred over.

The only clue that it was air ingress was the some of pipes which are transperent showed no fuel in them. The filter was notibly empty of fuel when it was removed. I highly recommend you fill the filter with diesel before refitting it as simply cranking the engine takes a loooong time which could wear out the starter motor. I also fill diesel through the retaining bolt to make sure as much diesel as possible is in the system - this all reduces cranking time.

I've experimenting with Veg oil mixture and this exacerbated the problem due to the increased viscocity of the Veg oil.

Hope this help with your problem.

 

[maybach]

Hi John
If you are still having problems starting after an overnight stand, there is a modification issued by M.B to prevent fuel drain back this involves fitting a couple of one way valves and a simple wiring loom. Your local dealer should be able to help, but if not then drop me a line and I will dig them out for you.
Regards
Maybach

 

[John Gallen]

C250D Starting Problem

Progress to date, replaced all plastic fuel hoses except one with banjo connection to Injector pump (seal at fuel filter end renewed).

Replacement appeared to cure fault for three days until today.

Observations
1. Air bubbles were visible in two of the new fuel lines at top of fuel filter, centre one of three and one on near-side, ie right hand side when facing engine. Engine started ok.
2. Outside air temperature at zero degrees.
3. Alarm turned back on yesterday.

Defect
1. Glow plug light goes out (12 volts at relay, 11 volts at glow plug).
2. Engine appears to crank and momentarily fires, then stops, will not start afterwards.
3. Battery appears ok, takes charge.

Conclusions
1. Other fuel system fault.
2. Faulty battery (battery 2 years old).
3. Fault in alarm system.
4. Something else!

Any suggestions welcomed, I have noted commets re NRV more info would be helpful.

 

[sixpack]

C250 fuel system

Hi John

At the moment my C250D is starting reliably, the final cure seems to have been replacement of all 6 of the pipe/union assemblies. One of the new ones (the centre one on the filter housing) had a small crack on the clear pipe part & this caused no end of grieff! (this was genuine Merc part & was exchanged by dealer) We also found that some of the O rings seemed to be of the wrong size, making it very hard to press the joint together. We used some of the old rings. There is now no air bubbles present in any of the lines. Maybach talks about a modification using a check valve in the feed & electric shut off in the return pipe, a helpful Merc service adviser got me a print out of details & part Nos for this. He said it cost about £80 for parts. IMHO I dont think this should be necessary if all the O rings are properly sealed. As Maybach said, a dealer ought to know about this mod but I have 4* A4 sheets of details. I dont have a scanner but I could mail them if you want to see them.

Regards Peter

 

[John Gallen]

Peter

Thanks for information, I will recheck all the pipe connections again, I didn't have any problems with fitting the pipes so I am assuming that the seals were correct. I have also tried a soapy water solution around the joints and they all seem sound. How did you access the banjo connection on the injector pump, that is the only one I have not changed. Just replaced the seal at the fuel filter end.

I will let you know about the A4 drawings, thanks very much for your kind offer. Somebody mentioned a couple of filters in the fuel senders - are you aware of these or perhaps its only on the petrol models.

I also noticed that new fuel filter comes with two seals, but I can only see a location for one on the top retaining bolt?

Regards


John

 

[sixpack]

Hi John,

I did not personally remove & refit the banjo joint, but the chap who did used one of those ratchetting flat ring spanners. He seemed to do it without any problems, but he was a real mechanic unlike me!. He didnt like the kind of washers fitted & I think replaced them with soft copper ones. The fuel filter definitely uses 2 O rings, both fitted on the bolt thing that that holds the filter on. I will email you the drawing that shows the filter housing, it shows the 2 o rings. Looking at the filter it was not obvious to me what the route of the fuel is, but this drawing helps. note that the inlet on the top of the filter housing passes through some sort of valve then leaves the housing (marked 56 on drwng) It doesnt connect to any of the 3 pipes to the rear of the housing. Cant see why there are 3 pipes here either. If your anything like me you will be totally p****d off of looking at this pump/filter thing by now but persevere. This 2.5 5cyl is really the best diesel in the world !. Happy Xmas

Peter

 

[John Gallen]

Starting Problem C250D

Car was not started for six days, when amazingly it started first time and has continued to do so since even at temperatures of minus 4. However, I have not turned the alarm back on and there are still bubbles visible in some of the plastic pipelines.

Does anyone know if the alarm somehow inhibits the fuel system?

Can this cause the problem I am having?

Regards

John

 

[sixpack]

Hi John

How is your car starting now?
I have had a recurrence of the no starting/air in lines again.
To cut a long story short, it was due to bad O ring between the shut off module (the black plastic box) & the side of the inj. pump. The last time I looked at this part I was very reluctant to remove this part as I didnt know what was inside. I thought that this module was also the throttle control, & I didnt want to risk the runaway situation that can happen if you get it wrong. This is not the case, the black box is just the shut off module & removing it reveals another O ring on a spigot going into the body of the pump. Fitting a new ring seems to have cured the last of the leaks & this area is now dry. Dead easy to do.

Regards

Peter

 

[Keith]

same prob on my E300D - where you get the o rings?

Six pack

have followed this thread and have identical starting syptoms on my E300D (124).
I also know I had a minor fuel leak in December related to one of the o rings on the clear pipes into the pump but which I did not solve. The problem was I could not buy the right o ring anywhere and the local Merc dealer is particularly dense so could not locate the pipe assy for me either (M606 engine).

do you know a source of o rings as I know I could fix this properly with the right one.

help appreciated as I am starting on borrowed time i think!

Keith