In a message dated 1/30/2006 11:48:28 A.M. US Mountain Standard Time, [EMAIL PROTECTED] writes:

My SD has it's moments of fuel pressure loss. You can be crusing down the interstate and suddenly feel a power loss that lasts less than 1/2 second...something exactly like taking your foot off and back on the throttle. Also, at cold start it's very rough and needs to have enough throttle to keep at least 800-900 RPM to run somewhat smooth and not die. Glow plugs are barely 2 years old and the injector pump and injectors were replaced by the P/O (maybe 50kmi ago). I've replaced all the rubber fuel line from tank to primer in the last 8 months. I'm thinking from my experience in the semi-diesel world that I have a lift pump that's weak. I read 07.1-145 "Checking fuel pump and bypass valve" and it seems that the bypass valve can get clogged and needs to be cleaned and the spring lengthened to increase tension. Is there anyone else that has had an issue similar to this where cleaning the bypass valve fixed the issue or did they have to replace the fuel pump?

Don't overlook the possibility that it is the boost protection switch, mounted on the intake manifold. These will go bad and cut fuel just as you describe but at only 6 or 7 psi instead of 14-15 psi. When the switch closes it interrupts the pressure signal to the ALDA and the engine gets fuel, the equivalent of an unblown car, which feels fairly anemic You can pull the wire from the switch to see if your problem goes away. Or you can remove it and rig a test connection with your mitevac or air compressor. Or a remote possibility is the turbo unloader valve is failing and the pressure is excessive.

Unlike when the wastegate opens to limit further boost and power, when the overboost switch activates, power instantly drops about 30% (but the engine should NOT stall - there should be sufficient fuel to allow the engine to run at about 70% of full power). Check this by disconnecting the electric line to the switchover valve of bypass the pressure line thru the switchover valve (directly from the intake manifold to the ALDA). Vacuum in the tank can choke off fuel/power and may even cause the engine to stall, but simply opening (and then reclosing) the gas cap and letting air rush in, restores fuel flow (at least for many miles). This tends to happen unpredictably but usually only after you've been driving for a while.

          Marshall Booth (who doesn't respond to unsigned questions)
      "der Dieseling Doktor" [EMAIL PROTECTED]
'87 300TD 182Kmi, '84 190D 2.2 229Kmi, '85 190D 2.0 161Kmi, '87 190D 2.5 turbo 237kmi

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