Common rail diesel pressures ?

[Smallfry]

After my recent breakdown with my previously dependable Renault Master, I have been (slowly) going through possible problems.

They have a rubber/plastic primer bulb, which is notoriously problematic. They get an air leak and the fuel supply is lost. I saw there was no fuel in the translucent feed pipe, so worked the primer bulb and the fuel came back up, enabling me to start the engine again. Was sucking in air though, and engine didn't run well. have now replaced this with a Facet electric pump, and now the feed is working well. However, the engine used to start almost instantly, summer and winter, but now takes about five or six seconds cranking to start.

On hooking up the diagnostics to look at the fuel pressure, when idling there is 28000 to 31000 Kpa (280 to 310 bar) as the revs rise it tops out around 480 to 520 bar but holding the revs steady, it fluctuates between these figures.

Looking on t'internet definitive and specific info seem impossible to find, like it is a closed shop cartel. Mostly I find general info which states these older Bosch systems work at between 250 to 1350 bar, which tells me the rail pressure is not high enough However, I did find a bit of Renault factory info that states that for an injector leak off test, the engine should be held at around 3000 rpm, and revs adjusted a little to get a pressure of 500 bar, held for one minute. So maybe the pressure IS high enough after all ?

What I have noticed though, is that when the engine is stopped, the rail pressure quickly returns to 20 bar, and then gradually drops from there. What I am wondering, and can find no info, is, should the rail be holding high pressure when the engine is off ?

I know there is a PRV in the rail itself, and would ASSUME there is a non return valve in the HP pump, leaving only the injectors themselves, or obvious leaks as a cause of the rapid pressure drop

Anyone got any ideas or info ?

I am going to do a leak off test on the injectors shortly, to see where I am with these.

 

[hotponyshoes]

Had similar issues with mine.
It had always taken a few seconds cranking to start.
Injection fault came up on the dash.
Non-original primer bulb fitted by previous owner had split and was dragging air in.

Replaced primer bulb which cleared the error but I could still see small air bubbles in the clear plastic pipes.
Removed and cleaned the fuel filter housing, fitted a new filter and new lubricated o-rings.
Bubbles disappeared and it now starts instantly.

Basically, if you have any bubbles in the fuel lines (either when priming or with the engine running) sort the leak before working about anything else.

Also, no, I don't think there is a nrv in the high pressure pump. I've not actually looked at the master but I could put a reader on it to check if required but I've seen the pressure drop quickly on other cars that are running fine.

 

[Smallfry]

Had similar issues with mine.
It had always taken a few seconds cranking to start.
Injection fault came up on the dash.
Non-original primer bulb fitted by previous owner had split and was dragging air in.

Replaced primer bulb which cleared the error but I could still see small air bubbles in the clear plastic pipes.
Removed and cleaned the fuel filter housing, fitted a new filter and new lubricated o-rings.
Bubbles disappeared and it now starts instantly.

Basically, if you have any bubbles in the fuel lines (either when priming or with the engine running) sort the leak before working about anything else.

Also, no, I don't think there is a nrv in the high pressure pump. I've not actually looked at the master but I could put a reader on it to check if required but I've seen the pressure drop quickly on other cars that are running fine.

Thanks for that.

Compared to before, those seconds that I have to crank it, seems like all eternity.

One thing I had forgotten and not mentioned, and have just though about, was when the engine cut out, I had let my foot off the pedal, and there was a sort of "pop". Not loud, but enough to draw my attention to it, and all the dash lights came on almost simultaneously.

So something had happened. Could have been the PRV venting ? Will check the injectors first though. Was just going to do the test, but now its raining

 

[m_c]

Pressures sound fine.
They'll only reach max pressure when under full load.

If the pressure was too far from what it should be, then a fault code would get triggered.