'84 300TD: air in hard return line of fuel injector

Are you absolutely certain you have this valve plumbed properly? I recommend you remove the valve and connect the return hose directly to the white T looping back to the heater and see what happens.

Are you certain the solid bolt was installed properly in the factory filter and you have good washers on both sides of the banjo fitting?

Thanks, Kent--good advice. Turns out I only had one washer on the banjo, not two. And by taking the 3-way valve out, I discovered I'd misinterpreted the wording of your installation directions. The lever on top--I'd thought the handle side pointed the direction of fuel flow, but it doesn't--that little beak on the other side is the pointer.

I put a second washer in, and tried the direct plumbing. That hard return line, which had been half full of air, is now only 1/10 full of air (a few frothy bubbles on top). So a definite improvement. I tried reinstalling the 3-way valve, and it's no worse than the direct plumb. I was even able to bleed all the air out of that hard line by putting the 3-way valve on return mode for 10 min.s.

She still lacks power, though. My 3 test drives couldn't get above 25mph, and all ended with her dying. I bled all air out every time, and found air in that hard line again after every time it died. After the last test drive, I couldn't bleed all the air out like before.

I'm still convinced the trouble is somewhere in between the 5-micron filter and the fuel injector. I checked the tightness of the final filter again, undid & re-tightened all the hose clamps, and tugged at the old-style hand pump to verify it's on tight. I noticed that, in my heater, all outlets were marine epoxied except the one with the glow plug; but it's on tight and I see no leaks.

Any ideas where the air's getting in?

Without seeing it - at this point - I would suspect air is being pulled in through the hand pump or somewhere at the lift pump

I removed all the hosing and both the hand bulb pump and the old-style factory pump. A careful visual inspection showed me nothing suspicious. After reinstalling it all, I still could never quite bleed all the air out--even on return mode.

Any advice as to how to go from here? The only Mercedes specialist in the area recommends against the WVO conversion, so I don't know who I could get to look at it.

I took it to a mechanic, who repaired the fuel boost pump. Now she runs on WVO, but won't go above 45 up hills. If I push her in such situations, she lags & dies. She'll reliably start up again & run, but it definitely feels like now I have restricted fuel flow.

I've been through the troubleshooting checklist for "PROBLEM: engine will start and run but not produce adequate power," but nothing has improved.
And she still does better on diesel (almost full performance), which tells me it's not a mechanical problem.

Is there anything else I can do or check, Kent?

The fact that it runs better on diesel does not necessarily rule out a mechanical problem. For example, if there is a problem with your injection pump, your delivery valves, your injection pump timing, or the conditions of your fuel injectors- then adding the heavier fuel could create a problem with a mechanical part that is excessively worn.

If it were my diesel I would want to make sure I rule out all potential mechanical problems first. These would include

• Valve adjustment
• Condition of camshaft
• Camshaft timing
• Compression test
• Injection pump timing
• Condition of delivery valves (located on top of injection pump
• Internal condition of fuel injection pump  (loss of pressure). This can only be tested at a Bosch facility....
• Condition of ALDA and overboost protection circuit
• Test pressure release and spray pattern of fuel injectors
• Check for any intake or exhaust restriction (is the turbo producing the right amount of boost- condition of mufflers, etc_

Once you are assured that all those items are performing to spec then move back to the fuel system. At least you can eliminate those specific mechanical issues.

I bought an 82 123 with a pre installed Grease car kit. It came with your older manual with the tear out page for setting up the filter, fuel selector switch, and loop system. It had the loop disconnected and I believe the Diesel line going directly to the lift pump and the cigar hose replaced at the main filter. I removed the old Raycor filter and installed your FM100, reconnected hoses according to the tear out page. I purged air and got it running fine on diesel. Every time I switched to WVO it would eventually die. The clear filter after the fuel selector switch (installed near lift pump instead of near switch as in photo) would be full of air. I connected a 7 psi electric fuel pump after the electric fuel selector switch to see if it would keep it filled. No luck, ok on diesel but not WVO. After a lot of time pumping air, getting it running on diesel again, etc. I removed the hose from the IP which came from the out put of the lift pump to the IP and connected the electric fuel pump to it and then the output hose from the fuel pump into a milk jug. This would draw fuel (whether diesel or veg) from the selector switch through the clear pre filter, lift pump and into the jug. While watching the clear filter on the input side of the lift pump, it stayed full on diesel as I pumped into the jug. I flipped the switch to go to veg and it started pumping veg (the veg was pretty warm at this point from the heat exchanger in the poly boat tank and an electric wrap around the FM100). I had enough play in the hose that I could twist a loop and get the clear filter upside down so the out put of the filter was on top (so that any air would be near the out put side and more easily drawn out by the electric fuel pump). As I watched veg flow through the filter and eventually into the jug (flowing pretty good) it was staying full. Then suddenly (about every 5-10 seconds I would see a string of good size bubbles (about pencil eraser size). I kept it up for a while thinking that even though the flow was pretty good these may just be purging from pockets of air trapped in the FM100. I repeated several times and still like clock work the bubble pattern. Since I was sucking from the output side of the lift pump and the fact it pumped with no air when on diesel, I believe the air would be having to come from before the selector switch because when it comes out of the switch to a single line it's all the same set up whether on diesel or veg and no air on diesel. So if the leak is on the input side of the selector, this would include fuel line from veg tank to input of FM100, FM100 itself, then hose from out put of FM100 to input of fuel selector switch. I put Teflon tape on FM100 fittings, all clamps are tight. Where the fuel hose connects to the poly boat tank it is a plastic swivel fitting. I thought about just disconnecting and sticking directly into the tank filler opening to rule out a leak at this swivel. I did mount the FM100 on the wheel well at an angle like the Raycor had been, but you would think any air would be purged by now or does the FM100 need to be completely upright? I guess I could temporarily connect the veg fuel line to the clear filter and see if I still see air. That would be bypassing the FM100, and selector switch. If I had air that would only leave the fuel line, especially if the tank end was submerged in veg and not on the swivel connector. Any thoughts would be appreciated.

Also, I have been reading in several forums that wvo should not be over 160 at the injectors. Do you have any information on the best temp?

MAG600