[Okiebenz]

Any 648 experts here? I picked up a very nice 05 CDI at auction that had no keys. From the oil change sticker in the window it appears to have been recently serviced by a local MB only well known indy. It also has a set of brand new Michelins. Looked like it was a 1 owner car but was traded or sold to Carmax (had a Carmax stock tag in the in the window), then a small used car dealer bought it at auction. I suspected they lost the keys to it and just sent it back to auction and I half hoped it would start right up once I got a key for it. The key arrived yesterday and it cranks but no start. I threw the DAS on it and get code 2051 (001) low fuel rail pressure. I ran thru the tests for the low pressure side that is basically hook pressure gauge to supply side of filter, enter value into DAS, then hook it to output side of filter and enter the number, then hook line and run it into a container, system runs pump for few seconds and you measure the volume and enter that. Low side tests fine. The next step would be to test injector volume which involves the use of a special tool that you install on the return lines of the injectors and measure the volume. I do not have this tool so I can't do that. This is my first 648 so I thought I would ask to see if there are any common issues that could cause this error code and no start condition? I swapped out the quantity control valve on a 642 chasing phantom issues so I still have the valve off that car (I think they are the same part). I think tomorrow I may try swapping that out and see what happens. Any thoughts?

 

[mersum1es]

You are on right path. You won't need special tool for leak test, some people just use long hoses which fit to leak line, or they put a hoses to small bottles (search pictures 'cdi injector leak test'). You can roughly calculate volume of the hos if you want to know ml/min value but usually bad injector is found just by relating amout of leakage. Remember to block free return line.

Fuel quantity valve is very common culprit but I am not sure if OM642 part is compatible, check part numbers in EPC (you can see updated part numbers at same time). There is a test for fuel quatity valve too in SDS. Do acompression test too.

Then there is pressure regulator valve in and of the rail, which may be playing up, and sometimes pressure sensor itself (ECU won't give permission to injection unless pressure is around 200bar). This you can test by unplugging sensor, engine will start in fail mode if fuel pressure is enough.

 

[Okiebenz]

Interesting, thanks for the suggestion. From what I recall I think the quantity valve test requires the engine to be running, seems that is what I saw in DAS. I will consult the EPC as to part numbers and will try unplugging the sensor on the rail.

 

[mersum1es]

Oh yes, I forgot you cant get it running... quantity valve and regulator tests need running engine as well as check f the electrical correlation values of injectors.. Compression test is done by crank only, and leak test ca be done cranking engine one minute.

 

[Kajtek1]

What's the mileage and what rail pressure are you getting?
Most of the time it is pressure regulator that fails on the system.
Ask moderator to move the topic to diesel section for better exposure.

 

[Okiebenz]

I just did a little more digging. Car has 247k miles. I first tried disconnecting the pressure sensor on the front of the rail and seeing if it would start. It would not. Then went into DAS and looked at rail pressure. While cranking it is in the single digits until you crank it for about 15 seconds or so then pressure starts climbing and reaches as high as 62 bar. This is nowhere near spec of 340-380 aprox. Does that low of number tend to rule in favor of the HPFP or the pressure regulator on the rail?

I thought about posting this in the diesel section original but figured it would get more attention here. Maybe not. How do I get a moderator to move it?

 

[mersum1es]

You can't know for sure, but usually it is leaky injector. HP pump leak shows often out and happens because loosen bolt behind the pump, pressure regulator may have jammed open (you may try knockin it carefully) but why get eventually 60 bar... Regulator has also o-ring on valve body which rarely can be broken, I am not 100% sure but you should see how much regulator is passing fuel by if you open the hose coming from regulator end of the rail (I just can't remember out of memory is there something else connected to same line, be careful if you try it).

Do the injector leak test first. BTW do you have at least half tank fuel and fuel filter changed (yes you got ok measurement values of low presure side but just to be sure...)

 

[Okiebenz]

It has about a quarter of a tank and I have not changed the filter myself, but does not appear to be plugged up based on the pressure difference between input and output side.

 

[Kajtek1]

I remember those diesels idling at 5000 psi =330 bars, but should start at 4000 psi.
Anyway, your system is not building any real pressure and I don't think leaky injector can dump that much fuel. Obviously at this mileage pump could be wear, but that is unlikely as well.
Meaning I would steer into open pressure regulator as that IMHO is the only item who can dump the fuel at high rate.

 

[mersum1es]

I cannot remeber exact min. pressure either but it is somewhere 150-250 bars.

Remeber that cranking speed fuel flow is fraction of idle speed, so badly leaking injector may prevent pressure rising, thats why they usually work ok when engine managed to start and speed is at least idle speed...