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Car Forum / Mercedes-Benz Cars / April 2005Injector bleed line replacement
Last year I replaced the bleed lines that were leaking with regular bleed lines from an injection service shop. One year and very few miles later and they are leaking again. I?m now trying "weed whipper gas line", 1/8" clear plastic tube - .25 a foot. So far so good. With the new clear lines I see a lot of bubbles of air going thru the lines. Should this be? I?m thinking maybe I?m pulling in air somehow and that may be why it?s a hard start even on warm days. Any thoughts on this? Thanks in advance for any help. ken Good observation about the air bubbles and hard hot starting. However, an air leak in the fuel system, I believe, would make cold starting even harder for a greater time would have passed for the air to enter the fuel lines. Check fuel line connections, including both fuel filters and especially the hand primer pump, a common source of air leaks. Engine may need its valves adjusted, especially if last done more than 15K miles ago. > Good observation about the air bubbles and hard hot starting. > However, [quoted text clipped - 11 lines] > more than > 15K miles ago. Soooo, then I should not see any air bubbles in the bleed lines between injectors? Right, the bleed off fuel comes from the injectors so it should contain no air. The fuel injectors opening pressure is about 2,000 psi so they can't open if there's air inside the high pressure line (the air compresses). That's probably the reason for the delayed start - the engine has to first purge the air from the injectors and then probably has some misfiring until all the air has been purged. The hand primer pump is a known site for air leaks; replacements sell for about $20. First check the fuel system's connections and tightness of the fuel filters. mine sucked a little air once while i was on the road. just trimmed a little off the ends of the rubber hoses pushed the works back together, by by air. the case, minus a few cans! I doubt the problem is in the bleed return hoses themselves. However, I did replace all mine once and for all with plastic fuel hose that I bought at the local parts shop. It's been on my 80 300SD for about 3 years now, with no more leaking. The std MB rubber/fabric hose only lasts a couple years, then starts weeping. The plastic one is sort of a clear/yellow and fuel rated. Here's something interesting. When I did the replacement, I overlooked the stub on the last injector. This is basicly a short piece of the tubing that has the end closed off, as there is no next injector to go to. Eventually I figured out that this thing was weeping a little too, but I neve payed a lot of attention to it, figuring I'd fix it eventually and it didn't appear to be leaking much at all. Then one day I noticed my MPG was down to near 20. I checked it several times and sure enough that's what it was, consistently. I still didn't think it could be the stub, cause there was no diesel on the garage floor, etc. Finally, one day when it was raining, I happened to leave the car running while I was standing next to it and saw the classic oil sheen on the water. Replaced that stub with the plastic hose, plus some silicone sealer in the end to cap it off. Voilla! Mileage now at 24, which isn't quite the original 26, but then the car does have 110K, so I'm not complaining. > I doubt the problem is in the bleed return hoses themselves. However, > I did replace all mine once and for all with plastic fuel hose that I > bought at the local parts shop. It's been on my 80 300SD for about 3 > years now, with no more leaking. The std MB rubber/fabric hose only > lasts a couple years, then starts weeping. The plastic one is sort of > a clear/yellow and fuel rated. Bubbles - Good for Don Ho (anyone here old enough for than one?) Not good for high-pressure diesel injection. Enough of that squishy air gets into the high-pressure side of your injection pump and you will definitely have issues. I have to agree with trader - the return lines are more likely to seep, weep, or leak (the three grades of european motorcycle oil leakage ;-)) than they are to suck in air - but the only other place I can see for the air to get in is earlier in the system. Which would seem to mean air is getting shoved through your injectors. Any votes for a loose/cracked connection in the line from the small fuel-filter? Or for that matter, the supply line to the large filter? BTW - Anyone played with the Dupont/Dow Viton tubing? http://www.greaseworks.org/viton http://www.dupont-dow.com/Applications/Automotive/emissions.asp This stuff looks interesting - we used Viton bottles in the lab to store a number of nasty volatiles. Conrad > the return lines are more likely to seep, weep, or leak > (the three grades of european motorcycle oil leakage ;-)) I guess Harley gush then, huh? I got your tiny bubbles joke too... Guess I am old :~) Marty >> the return lines are more likely to seep, weep, or leak >> (the three grades of european motorcycle oil leakage ;-)) > > I guess Harley gush then, huh? I dunno, but apparently Harley chicks do. > I got your tiny bubbles joke too... Guess I am old :~) Well, I considered going for a Lawrence Welk reference but I though that would be too easy. Yep, you're nailed. Definitely old - but then old age is just the reward for not driving around with a wobbly front end and your steering wheel cocked at 40 degrees :-o Conrad > Right, the bleed off fuel comes from the injectors so it > should contain [quoted text clipped - 16 lines] > tightness > of the fuel filters. TG: You mention prime pump replacement. Is this a dealer item or is there an aftermarket source? Ken Both dealer and after market supply the "hand primer pump". |
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