E-pump inlet pressure
E-pump inlet pressure
50harleyrider
07-06-2018, 06:07 AM #1Could there be any issues with too much lift pump pressure into the Bosch E pump on an OM606.962? I've been running under the premise that with a return line, it wouldn't be an issue but doing that I haven't considered pressure drop in the return line which may affect the pump. The W210 had no lift pump so I'm a bit concerned about running one on a stock engine in my conversion.
The W210 has a mechanical lift pump on the side of the E pump. The spring driven piston provides a max of ~14psi, if I remember correctly. The overpressure valve on these pumps has internals that are made of plastic. They warp and fail, letting the pressure in the galley drop. I replaced the valve with a .5mm orifice, leaving the pressure regulation to the lift pump. That has worked nicely for the last 100K miles.
The lift pump on the e pump then only has to suck from the filter.
I've considered doing exactly this on my W463 G. The G's tank is fairly flat side to side. When the fuel is low you can run out of fuel when on a slope due to the fuel running to one side. I figure I could build in a small, but very tall tank under the hood (basically a vertical tube). Feed the tube-tank with a lift pump from the main tank. Have the engine take fuel from the bottom of the tube and return air/fuel back from the top of the tube. That way you can use all of the fuel in the main tank.
Better response etc is also a compliment to the pump.I'm running a carter 4600 atm. That should deliver 4-6 psi. But I'm thinking about upgrading to a pump that delivers 8-10.
Once you are on a slope with low fuel, the rear lift pump will simply pump air. The purpose of the tank in the engine bay is to keep the last liter or two for the engine and return the air to the tank. Basically treating the main tank like a dry sump. You can squeeze quite a bit of reliable distance out of the tank that way.
Used when fuel tank doesn't have baffles to prevent fuel starvation on hard cornering.
CutWeldDrive
07-13-2018, 05:19 PM #7i've always know what you talk of as a swirl pot. Off the shelf part.
Used when fuel tank doesn't have baffles to prevent fuel starvation on hard cornering.
50harleyrider
12-22-2020, 03:47 PM #8I wanted to revive this thread in light of my recent starting issues and did this. Replaced the oe gas fuel filter and the engine fuel filter today and thought I would check lift pump operation and get a bit of fuel in a beaker to fill the filter prior to starting. I removed the filter, placed the beaker in the filter cavity, turned the key on and nothing. Is there a valve in there that stops flow if the filter is removed and there is no back presure? I may have a lift pump issue. I am using the oe ford in tank gas lift pump and it has worked fine for a couple years. should I just remove it and rely on the IP scavenging pump or get another lift pump or fix mine? the donor W210 had no in-tank lift pump if I recall. From AlanMcR post 2 maybe that pump on the side of my IP is the culprit? right now I am going to disconnect the fuel line feeding it and see if my lift pump will work. I'm thinking it may have damaged those internal plastics in the benz pump over time. It does make about 3 bar pressure so we'll see.
My G and E both do just fine with the tiny lift pump on the side of the IP. Neither has hiccuped in all the time owned. The design self-limits system pressure. The IP cam pushes the piston back against a spring, then the return spring action is what pressurizes the fuel.
50harleyrider
12-22-2020, 04:47 PM #10I might just eliminate the tank pump. Should the fuel be spitting out of the housing with key on or should I crank it? maybe there is a safety feature for fuel delivery from the engine stopping for various reasons?
Is the shutoff valve still in place? It isn't designed to deal with pressure from anywhere but the IP mounted lift pump. Not sure what it does with pressure from the tank line. When I prime the system with a squeeze bulb, I use it on the return line. I'm getting tempted to just leave the squeeze bulb in the return line.
50harleyrider
12-23-2020, 01:39 AM #12I'm not sure about a shutoff valve. Don't know where it is or what it looks like. I have to investigate what's going on here. I didn't remove any plumbing when I pulled the engine out of the donor. I just connected the supply and return lines directly to the oe truck ones. I thought the oe tank pump just circulated to and from the Benz lines. I have to revisit my earlier threads where some of the folks on here explained it. I do recall they said it should be OK the way I plumbed it. Maybe over time it's not OK and has manifested in my current problem.
http://www.superturbodiesel.com/std/show...ir+bubbles and now I think it's my problem. The posts 19 and 20 may be the fix. The check valve in the banjo bolt barrote refers to in particular. Any updates or simple fix?
50harleyrider
12-23-2020, 03:55 PM #13I got the truck running just now and it took several tries but it started and runs fine. I did notice air bubbles in all the clear lines except the one on the left top of the filter housing. The tank is full and I don't see any wet spots anywhere on those lines including their connection points. In fact, all the fuel circuitry lines are dry around the IP including the fuel solenoid and the scavenging pump. Is that normal and if not, what's the trick to determine the air entry point? I saw this thread:
http://www.superturbodiesel.com/std/show...ir+bubbles and now I think it's my problem. The posts 19 and 20 may be the fix. The check valve in the banjo bolt barrote refers to in particular. Any updates or simple fix?
Note #2: Bubbles can also be gasses pulled out of solution by high suction. A plugged filter can cause high suction in the intake line, this pulled gasses out of solution. The gasses don't readily go back into solution, even under some pressure.
Both of these have happened to me. When the tank strainer got plugged the lines appeared to be full of air bubbles. They didn't come from outside the system, but rather from the fuel itself. Just make sure that the line to the tank is free flowing.
If the lines empty overnight, then you have a problem with air leaks.
Ah, something I hadn't thought of: The system you are working on was designed for a gas vehicle. The return line may not be into the bottom of the tank (as it is on my diesels). If so, this would allow the flow to reverse after the engine is turned off.
The check valve does fail. But it's purpose is really to maintain a minimum pressure in the IP. It is a plastic valve with a spring closer. The plastic element in mine failed and I replaced it with a bored orifice (1mm, IIRC), thus relying on the constant pressure function of the lift pump to keep the IP pressurized. No problems with that for the last 100K miles.
Note #1: Air is smaller then diesel fuel. It can get sucked into openings that the fuel won't easily leak out of. Also, o-rings can distort differently when under pressure from inside or under pressure from outside (suction inside the system).
Note #2: Bubbles can also be gasses pulled out of solution by high suction. A plugged filter can cause high suction in the intake line, this pulled gasses out of solution. The gasses don't readily go back into solution, even under some pressure.
Both of these have happened to me. When the tank strainer got plugged the lines appeared to be full of air bubbles. They didn't come from outside the system, but rather from the fuel itself. Just make sure that the line to the tank is free flowing.
If the lines empty overnight, then you have a problem with air leaks.
Ah, something I hadn't thought of: The system you are working on was designed for a gas vehicle. The return line may not be into the bottom of the tank (as it is on my diesels). If so, this would allow the flow to reverse after the engine is turned off.
The check valve does fail. But it's purpose is really to maintain a minimum pressure in the IP. It is a plastic valve with a spring closer. The plastic element in mine failed and I replaced it with a bored orifice (1mm, IIRC), thus relying on the constant pressure function of the lift pump to keep the IP pressurized. No problems with that for the last 100K miles.
50harleyrider
12-23-2020, 10:15 PM #15I'll check my lift pump operation in the morning to verify if it's functioning. Both filters were replaced. I would think it would overcome the overnight draining quickly. As for orings leaking enough to allow air ingress but no visible sign of leakage, ugh-don't know what to do. I wonder if jav1 got his air out? I'll send him an email and see although he doesn't regularly look at his email or this forum.
As a starting point for diagnosis. Next time, when shutting down the engine, clamp off the tank return line. See if you get the same amount of air in the lines. If the air is gone, then you know that air is getting into the return line. Probably because it doesn't go to the bottom of the tank.
The system does not recover well from any air in the IP. Any air in the IP at startup will get pushed into the high pressure lines immediately. Then you are in for a long crank-fest to push the air out through the injectors. It doesn't matter how quickly the lift pump pushes the air out of the IP, because the air embolism has already been shoved into the injection lines.
As a starting point for diagnosis. Next time, when shutting down the engine, clamp off the tank return line. See if you get the same amount of air in the lines. If the air is gone, then you know that air is getting into the return line. Probably because it doesn't go to the bottom of the tank.
AlanMcR The system does not recover well from any air in the IP. Any air in the IP at startup will get pushed into the high pressure lines immediately. Then you are in for a long crank-fest to push the air out through the injectors. It doesn't matter how quickly the lift pump pushes the air out of the IP, because the air embolism has already been shoved into the injection lines.
As a starting point for diagnosis. Next time, when shutting down the engine, clamp off the tank return line. See if you get the same amount of air in the lines. If the air is gone, then you know that air is getting into the return line. Probably because it doesn't go to the bottom of the tank.
I'll try that although air is trapped in there all the time but after successful starting, maybe clamping will keep more from being sucked in and it should start easier next time. I did fill the tank up till overflow and it still does it so I don't suspect a tank issue. The hard clear lines don't lend themselves well to purge air via mighty vac. Are those lines that hard when new? There shouldn't be much pressure or they wouldn't be plastic, right? Only scavenge and lift pump pressure. I've never had a clear line on my TDI's fail or let air in. I am ordering copper washers and orings for the delivery valves
50harleyrider
12-25-2020, 12:05 PM #17AlanMcR The system does not recover well from any air in the IP. Any air in the IP at startup will get pushed into the high pressure lines immediately. Then you are in for a long crank-fest to push the air out through the injectors. It doesn't matter how quickly the lift pump pushes the air out of the IP, because the air embolism has already been shoved into the injection lines.
As a starting point for diagnosis. Next time, when shutting down the engine, clamp off the tank return line. See if you get the same amount of air in the lines. If the air is gone, then you know that air is getting into the return line. Probably because it doesn't go to the bottom of the tank.
I'll try that although air is trapped in there all the time but after successful starting, maybe clamping will keep more from being sucked in and it should start easier next time. I did fill the tank up till overflow and it still does it so I don't suspect a tank issue. The hard clear lines don't lend themselves well to purge air via mighty vac. Are those lines that hard when new? There shouldn't be much pressure or they wouldn't be plastic, right? Only scavenge and lift pump pressure. I've never had a clear line on my TDI's fail or let air in. I am ordering copper washers and orings for the delivery valves
I found a set of new clear lines on ebay for $60. Does anyone know a source to buy a complete set of viton orings for those clear line connectors? If not, maybe sizes or part numbers and I'll find them separate from the lines?
50harleyrider
12-27-2020, 01:33 PM #19Well it's fixed now that I got the fuel pump relay on the oe ford wired straight through to the inertia switch and fuel pump with key on. I probably should put a regulator in the supply line so that tank lift pump won't run continuously. It will make 90 psi-way too much for a little diesel that already has a scavenge pump. No sense in letting it run continuously. Will just wear it out. The gas regulator went bye bye when the fuel rails on the 5.4 disappeared. I figure a 30 psi regulator with electronic control to the fuel pump relay should be plenty. Truck has never started so quickly. Lift pumps are the way to go. Definitely no air bubbles now. The 606 scavenge pump is a little close on margins especially on a low fuel tank location. If it was a Model A, it would be fine lol.
I found a set of new clear lines on ebay for $60. Does anyone know a source to buy a complete set of viton orings for those clear line connectors? If not, maybe sizes or part numbers and I'll find them separate from the lines?
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