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Another 6.9 that wont raise (diagnostic tips)

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Hi All,

Same old story, new member.

Inherited a 6.9 that came from California which had been parked on blocks since 1999. I won't say there is no rust as the passenger floor had water in it, but it's refreshing working on a car who's fasteners are all easy to turn.

So far I

* Rebuilt the fuel system, new pump, accumulator, regulator, fuel distributor, injectors, and rubber lines.
* Rebuilt the ignition system, new coil, new ignition box, new resistors
* Rebuilt the engine wiring harness with new plugs for the WUR, CSI, and re-wrapped the loom
* Rebuilt the engine vacuum system with new lines, fittings, and kept the California spec air injection system
* Flushed the cooling system and got the thermostat to behave, still needs more flushing but it circulates
Thing starts up without any hesitation, and while I still need to fine tune the CIS, it will idle fine, and rev in the driveway. I'd like to get it on the road so I can do more diagnostics...and thats where I am in need of help.

I've replaced the five accumulators which had Mercedes tags and said made in west Germany... The rear leveling valve was replaced at some point as its got paint marker that says 500se on it.

Put the car back down, and of course its fully flat.

Disconnected the outlet of the pump and directed it into the reservoir and started the car up, fluid comes out albeit a little foamy.
Cracked the front bleeder valve with the car off as I have NO IDEA how to do it while running without losing a hand, a little fluid came out.
Next up I'll crack the rear bleeder, and suspect the same.

Now...the questions...

With the car running and the pump line re-connected, my pressure adjuster disk is floppy with no discernible detents.  Do I have fully bypassed leveling valves, do I have a bad pressure regulator, or do I have a bad pump?

Im going to jack the car up next and let the thing run, but im hoping for more diagnostic tips here before I go buy parts. I'm fine doing this right, but I also don't want to replace working parts.

The goal with this car is to get it running, and only drive it when it's dry. It's relatively rust free (yeah...none are clean), and thats the only way I know I can keep it that way. It's got new brake lines waiting to be put on, and I'll be rebuilding the brake system next...but I gotta get it off the ground!

Any and all advice would be appreciated!


TJ 450:
I’ve had this sort of challenge on a couple of occasions and it can certainly be frustrating.

I’m inclined to think that the pump might be marginal, but the way to be sure it’s not a valve bypassing is to look at the return into the tank... if a considerable volume of fluid is flowing back into the tank then I would then think that the valve(s) are worn and bypassing.

Also, the pump needs to be primed by running the engine and directing flow back into the tank, kill engine then refit high pressure hose and start engine again. Try revving the engine up to say 1,500-2000 rpm and see if that makes any difference.


To me, there is a significant amount of volume coming through the pump when I direct the line into the tank, to the point where there is foam being formed from the splashing, meaning the valves are probably bypassed?

If they're bypassed, would I still not feel detents or do I also have a pump that can't make enough pressure?

I take it there is no way to test the valves?

Sounds like a problem in your height control switch and/or pressure regulator. Have you checked the little filter in the pressure regulator?  There is a plug (throttle screw) which houses the little filter.  Remove and clean the channel and filter. Don't lose it as they are NLA.
You can also remove and clean the 3x channels in the height control switch.

Filter was clean when I pulled it, and I cleaned it more with brake parts cleaner.

Can I take the height control switch knob apart without things flying?


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