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?

It is not unheard of that the high pressure pump will give issue. Not certain if DAS can check out that pump since it is mechanical other than checking fuel rail pressure.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

Probably not but from what I gather the HPFP does not usually have problems, or at least I think I have heard that.

HPFP I can't say I've seen issues with the HPFP but I have seen issues with the fuel rail pressure sensor. It is found at one end of the fuel rail. Check it out too. IIRC you also have a controller on the rail that could potentially cause the issue you are experiencing.

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Jim

If you have DAS see what the rail pressure is during cranking. It should tell you the acceptable limits and see if you're in spec.

Next thing is to see whether the sensor is lying or the HP pump has gone bad.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Semi-related...my HPFP started leaking around 175k miles. A new (rebuilt) one can be had for about $500.

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

I did not think about it yesterday but shortly I would go back out and mess with it a little bit and check what it says the rail pressure is. I have heard something about disconnecting the rail pressure sensor to see if it will start. Refresh my memory please is this the plug at the front of the rail or the back?

The fuel rail pressure sensor is located in front. The pressure valve or quantity control valve is closest to the firewall.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

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?

DAS should be able to test the valve. I have used the Foxwell reader diagnose fuel rail issues before.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

I only recall seeing some electrical tests you can do with a MM, but might need to check again.

Look closely at the fuel pressure control valve located at the rear of the rail.

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Jim