I think Jim Friesen's pressure cut-out switch was probably the correct diagnosis but ...
I bypassed the crossover valve, connected a pressure gage, and did a road test. Plenty of boost (maybe too much, looked like 1 bar or more, so now I wonder if the waste gate is functioning). Then I reconnected the crossover valve and disconnected the pressure switch. Everything still worked fine, plenty of boost. So I reconnected the pressure switch and everything still worked fine. Rats. So the problem is intermittent. I'll just have to get the problem to repeat and then troubleshoot some more. Thanks for all the help. Jim Cathey's comment about positive feedback is spot on. You cannot test boost without load. Think I'll leave my hose and gage in the back seat for the next time this happens. Scott Ritchey Kittrell NC 1982 300SD 220K 1979 300TD 350K -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of [EMAIL PROTECTED] Sent: Friday, May 12, 2006 2:12 AM To: [EMAIL PROTECTED] Subject: Re: [MBZ] Low Turbo Boost In a message dated 5/11/2006 9:55:52 P.M. US Mountain Standard Time, [EMAIL PROTECTED] writes: My 82 300SD (Garret turbo) suddenly lost turbo boost last weekend. The banjo fitting id not plugged and the circuit to the ALDA is not leaking. Measuring the manifold pressure, I get almost no boost until 3-4,000 rpm and then I get about 6 psi max. I don't see any obvious leaks in the intake or exhaust and I can hear the turbo turning. Any guesses on probable cause? I'm wondering if the waste gate is somehow suck open. I have noticed jerky boost at high power settings (boost cuts in and out near max power) in the past so I'm wondering if the waste gate may be sticking. And If it is a sticky waste gate ... what's the cure? Scott, #!. Look for loose nuts that hold the exhaust manifold to the head, much pressure can be lost here. #2 Disconnect the single wire going to the pressure sensor on the intake manifold. It sounds like it may be defective and is cutting off your boost signal way too soon. You can drive it like that for testing purposes. #3. Run the boost sense line direct from the banjo to the ALDA, teeing into it right at the ALDA to verify the boost signal is getting to the ALDA. #4. Remove the U shaped pipe from the filter to the turbo so you can reach in and give the nose of the turbo a spin with your fingers. It won't spin much but should feel free, with no roughness. Wiggle the shaft side to side to see if you can make the impeller touch the housing. Some play is acceptable. Look for FOD, foreign object damage, on the parts of the impeller you can see. #5. If all looks good, adjust the screw on the top of the ALDA about 1 1/2 turns CCW to add more fuel, which will add more boost, which will add more fuel, etc. #6. Get back to the list with your findings. Jim Friesen Phoenix AZ 79 300SD, 262 K miles 98 ML 320, 142 K miles _______________________________________ http://www.striplin.net For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://striplin.net/mailman/listinfo/mercedes_striplin.net
