You may want to try sending it to Dr. A first (864-623-9110). https://sprinter-source.com/forum/showthread.php?t=5956
OM612 hard to start when parked uphill. (No air in plastic lines)
- Thread starter jensemann23
- Start date
jensemann23
New member
I measured the fuel pressure when cranking now, and its only 5-6 bar for the first 5 seconds of cranking. Then it goes straight up to 340 bar and it starts right away. If I try to stop it and restart again, the pressure comes right away and it starts after 0,5 seconds cranking. So this must be air in the rail or HP pump somehow... but where! Its still no visible air in plastic lines
maxsawicky
Active member
any update on this?
similiar issue.
replaced a fuel line that had visible leaking at the LP pump connection. replaced lien, primed, van started right up. turned it off, after 30 min fuel had drained back down to the tank.
cant figure out where/why
similiar issue.
replaced a fuel line that had visible leaking at the LP pump connection. replaced lien, primed, van started right up. turned it off, after 30 min fuel had drained back down to the tank.
cant figure out where/why
Repeat, repeat repeat. It is sooooo frustrating. Make sure to use silicone grease on the fittings. Also a priming tool is very useful on the repeats.
maxsawicky
Active member
gonna reinstall tomorrow.
i didn't use silicone grease and initially the LP connection was difficult to fit in. (had to use a small mallet and extension to tap it in).
hoping repeating the install and using silicone grease does the trick.
maxsawicky
Active member
so the O rings I bought from SD parts are not green, but in fact black.
i ordered these.
https://europarts-sd.com/item.asp?PID=2390
are these the correct o rings?
Don't worry about the color. My green ones came from UK via eBay.
This is not right. I have never had to put that much force on any of my Voss connectors. Hand pressure has always been enough.
maxsawicky
Active member
it might have been the angle of the voss connector because the clear plastic hose was quite stiff and hard to bend at the correct angle to put in smoothly. gonna use a hair dryer to warm up it up this time, plus some silicone grease.
I don't understand - the Voss connectors to the fuel filter and the low pressure pump should not require heat unless there is something wrong with their installation that is messing up with the pre-formed alignment. The heat gun solution is usually the recommendation for the installation of the lines as they cross over each other under the high pressure pump and over the water pump. I do not remember (you have two active threads on this one topic) as to whether you recently installed new plastic lines. If you have, maybe there is some problem with that? Instructions on installation of the new lines are otainable from the Search feature is in the blue bar at the top of the forum. There is also a list of Common Maintenance sticky in the T1N DIY sub-forum, specifically https://sprinter-source.com/forum/showthread.php?t=58974
vanski
If it’s winter, I’m probably skiing..
Another spot to consider finding air intrusion is on the supply fuel line prior to the FF. There’s a metal edge (body) which can chafe the fuel line. I got really ‘lucky’ finding that spot for someone once. Almost threw in the towel. Also, check for pending codes every once in a while.. you may have an intermittent crank or cam code which isn’t setting since you get it to start here and there. Oh the joys of the 612 fuel system.
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Midwestdrifter
Engineer In Residence
I would consider clamping the fuel return line, then using a hand pump to put 5psi into the system. That should show leaks?
maxsawicky
Active member
i meant for the hard clear plastic lines, so they bend a tad easier. not heating up the VOSS connector. the only line i replaced was the one from the fuel filter to the LP pump as I could visibily see a leak previously.
the other thread is not my thread, but me replying to it.
maxsawicky
Active member
yup, we replaced those remember
jensemann23
New member
The summer has passed, and the problem has been completely gone since march. Now its back again, with dropping temperatures. I still havent changed the HP pump or pressure regulator,... Any news in this thread? Its so frustrating...
Nautamaran
2004 140” HRC 2500 (Crewed)
Puzzle-solving mode engaged! ;-)
Are you still running without the return tee that recirculates warm fuel? Presumably that valve would now be wide open in cold temperatures?
I *did* reread this thread over a coffee (it would appear I need to get out more?) and am still left wondering where the air could be getting drawn into the rail?
You reported a rail pressure of 5 bar for the first 10+ seconds of cranking, then a jump to 340 bar and engine start. This is certainly consistent with air in the HP pump and/or fuel rail.
You reported fuel being syphoned towards the LP inlet when you opened the filter, that stopped when you plugged the hole with your finger. That tells us the return path is clear, and sucking on the whole system. This is a condition that can suck air into the system.
The problem went into remission with warm weather, so it’s unlikely to be the return fuel draining back to the tank, with an air bubble working its way forward through the return lines.
So it sounds like the air is entering at one of the upper engine components, under vacuum created by the supply and return fuel sitting in the hoses.
The system is not weeping fuel when running, so the seals are all holding against their normal operating pressure. You’re not pulling air into the clear lines when running, so supply hoses are tight against vacuum.
Seals can be tight against pressure but pass air in under vacuum. For example, air can enter the ABS solenoids if you pull too hard using a vacuum pump to flush the brake lines.
Seals can also get stiff in cold weather and not do their job as effectively (as in the failure of Challenger’s o-rings).
The HP Pump has O-rings on the LP supply and return line, and a shaft seal behind the eccentric that seals the shaft against the LP fuel supply pressure (not Item #2 below... that seals crankcase oil). The shaft seal may be getting stiff in the cold, or one of the plastic fittings could be shrinking in the cold and reducing o-ring pressure at the joint.
Any air entering the HP pump’s LP gallery through that shaft seal or an o-ring could be drawn up into the fuel rail by the vacuum on the return line, passing the various ball valves in the normal direction of flow. The HP Pump also has a LP relief valve and return line connection, but the path up through the Rail has less resistance, and any air would want to rise up to the outlet port.
Unfortunately this is a hard theory to test... You could remove the HP fuel line between the pump and rail and apply a slight vacuum to the HP pump outlet port and see if you pull air through?
You could also block the rail inlet and see if it still fills with air, which would point to the issue being downstream of the HP pump.
If you can pull air from the HP pump, then smearing grease on the o-rings is a common method to improve their seal, and you might identify (cure?) the problem if you can no longer pull air from the outlet port.
Smearing some grease over the back of the shaft seal would help it seal out air and help with your diagnosis, but I suspect that the seal is not accessible, even with the HP pump off the engine? You could cap the inlet and return ports of the HP pump, then apply a stronger vacuum to the HP pump’s outlet port and see if you can pull air out if it, which would directly implicate the HP pump, and likely the shaft seal (though you wouldn’t have confirmed the seal as the fault with the pump)
I remain very curious about your problem, and the eventual diagnosis.
Good luck,
-dave
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B
billintomahawk
Guest
612 fuel system. I'll bite since I have one.
So the siphoning is from the fuel pumps to the fuel filter back to the tank, correct?
The system does not leak fuel when the machine is stationary or running. The fuel filter isn't leaking. Neither is the rail. The siphoning is worse when it points uphill or is cold.
Does it siphon if you plug the return line to the tank?
Does it siphon if you plug the supply line from the tank?
The problem must be in the pumps, the tank, or with an injector.
Since it starts hard, air in the lines, I'd start at the tank???
There has to be a check valve(function) that has failed?
Williams Diesel in Ocala, FL. are Sprinter fuel experts and give free advice.
They are clear thinkers.
bill
So the siphoning is from the fuel pumps to the fuel filter back to the tank, correct?
The system does not leak fuel when the machine is stationary or running. The fuel filter isn't leaking. Neither is the rail. The siphoning is worse when it points uphill or is cold.
Does it siphon if you plug the return line to the tank?
Does it siphon if you plug the supply line from the tank?
The problem must be in the pumps, the tank, or with an injector.
Since it starts hard, air in the lines, I'd start at the tank???
There has to be a check valve(function) that has failed?
Williams Diesel in Ocala, FL. are Sprinter fuel experts and give free advice.
They are clear thinkers.
bill
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trc.rhubarb
Well-known member
How about testing the fuel cap? If the cap isn't venting, you could have positive pressure during warm months, preventing flow back and a vacuum in the cold, drawing fuel back into the tank.
jensemann23
New member
Ordered a vacuum tester now, will try to clamp the return line from the rail, and apply vacuum on the LP feed line..