05 cdi fuel rail low pressure

[dieselbenz1]

Well lately on ocassion I've had longer cranking times then went into limp. Reading the codes I had a low fuel rail pressure. I cleared the code and its back to itself with the occasional long starting cranks. Not sure if it's the in tank lift pump or the high pressure pump. Filters were changed 15,000 km ago.

[GregMN]

Look for an injector stuck open. I used a iCarsoft for MB to find the exact injector that was bleeding off pressure. https://www.icarsoft.com/Product/s-300-iCarsoft_MB_V2.html

[dieselbenz1]

Ok well I traveled 200 km home today and it ran great 5.7 l per 100km just like normal. No codes today but did use my foxwell communicator the individual injectors looked good with the provided running info. It had a fuel pump test I could turn it on and off. There was also a high pressure pump test that I tried but it killed my engine both times. High pressure fuel rail looks normal 358 bar and increases with engine speed. I switched to canola oil when I ran out of 2 stroke as an additive and filled up at a small town diesel pump which could be suspect. This morning it did start with a long crank time but that was the only time all day. Im suspecting the in tank pump as no visual leaks on the high pressure pump.

[dieselbenz1]

I pulled the fuel pump relay after a drive and noted it was hot to the touch.will look at replacing it. I did replace the fuse just because.

[dieselbenz1]

Ok well today I ran errands all day and the car preformed as nothing ever had happened. I did put in a new relay and a can of strong injector cleaner the kind used to clean the turbo impeller as well. So I'll run that polished fuel and wait for more symptoms I guess.

[dieselbenz1]

So this morning after a 100km highway run coming home from the girl friends I get a check engine and im in limp. Low rail pressure again so now im a bit stumped but I'll try and see if I can hook up a pressure guage to see if the lift pump is putting out 120 psi. I just read that the fuel filter should be changed every 20k miles? I'd be overdue im on a 60k mile replacement schedule but only 30k miles into it now. I'll also try live data monitoring.

[engatwork]

I had one in shop with issue a while ago and IIRC it was the sensor at the end of the fuel rail (towards firewall) that needed to be replaced.

[GregMN]

From my experience: Get a scanner that can read the system. Look for an injector that is bleeding off pressure via the return line. Or. remove all the return lines from all the injectors. Attach a clear hose as the return line for each of the injectors. Route each return line into it's own container. Have someone start the engine while you monitor the returned fuel level in the bottles so you can tell them when to turn off the engine so you don't make a mess. If a bottle has more fuel in it than the others, that is your problem injector. This can also work with a non-starting engine by running the starting motor for a short while. If you do find a problem, some miracle oil in the fuel tank may clean it and free it. That is the easiest/cheapest route. If that doesn't work, replace the injector.

The high pressure injection pump is very robust and would not randomly fail. Same with a clogged filter. it would not randomly fail but would gradually degrade the performance and would not suddenly work fine and then not.

[dieselbenz1]

Thank you for the comment on the sensor at the end of the rail Jim. I had thought that was the rail pressure valve? With my foxwell scanner I was able to move the valve and observed the rail pressure change.

Thanks Greg for the procedure to identify a faulty injector I'll have another look through my scanner but I just saw the injection timing corrections for each injector.

Today went 160 kms on the highway to chase my gal and the car ran great except for another code I'll look into tonite.

[engatwork]

I think you are right, fuel rail pressure controller. The one at other end is sensor.

[GregMN]

In the video linked below you can start watching at about 7:30 and then go back and watch the whole thing if you want. I did the same thing with clear hose and small clear plastic bottles that I had on hand. I had one returning enough fuel to reduce the rail pressure below the start/run threshold.
This may or may not be your problem, but I thought I would post it for anyone who may find it valuable information in the future.

https://youtu.be/u5LO11Cm-zE?feature=shared

[dieselbenz1]

Interesting video I had built a injection tester for gas engines using a raspberry pi so I may have some hardware as the return test is way easier but may take a bit of time.

[dieselbenz1]

Today I had a 200 km road trip other than a bit longer crank time the car ran great
Just to recap the low fuel rail pressure dtc was triggered twice only in the past 2 weeks with having on average of 8 starts a day
Long crank time occurs more frequently maybe 1 in 15 starts. Also the low fuel rail pressure is triggered when traveling at speed.

[dieselbenz1]

Out of the past 10 starts one was a longer cranking 3 seconds vs 1.5. But today I wanted to check full throttle so I hit it from the green light and about half way to 100km/ hrs i getaway dtc and limp. Thinking that maybe my low rail pressure problem oh no just to throw a twist into my thought process the dtc was high fuel rail pressure??? WTF so any ideas now?

[engatwork]

Focus on the sensor at the back end of the fuel rail.