Vacuum?? In the INTAKE??

[350SL4spd]

Hi all,
Finally got my 602 nightmare running, idle smooths and fires right off!!
But she seems to only be pushing about 20hp (might be the tranny, acts like it's starting in 3rd...looking into it... )
Anyway, When I run a boost gauge right on the intake manifold, you get into the throttle and right off it spools out about 1psi and then immediately pulls back to about 5-6 in/hg on my gauge and hold there??!? Now, I may not be the most pious guy at church, but this seems odd. The whole reason a diesel has a vacuumpump is because there is (unlike a gasser) pressure in the intake manifold!
Now, I've played w/ my fair share of MB diesels (second car was a 617 when I was just getting serious about wrenching) and no matter how bad the boost control fails I've never gotten less than zero pressure, never a vacuum ....
I guess what I am asking is: Does this point to anything in particular??
The car is very very doggy and I need to figure out why and I am sure that this has something to do w/ it...
Thanks guys,
-Matt-

[boneheaddoctor]

wow???????????? and I didn't think that was even possible. Hope someone has an idea.

Are there any throttle-like flaps in the intake? I know there is atleast one in the NA version of the OM602 to help lowend/emissions. Should also check to see if there is anything like a plastic bag/leaves in the air ducting to block flow.

Good luck.

(Vacuum in a DIESEL )

I'm assuming your boost gauge measures gauge pressure and not absolute pressure.

Just to be clear: the 5-6 in Hg is negative gauge pressure - correct?

What happens in neutral?

[psfred]

You are connected to the pressure line off the center of the intake, right?

Does the turbo turn (assuming there is one!). If not, you will get vac.

Also, is the ducting to the air filter, air filter, and ducting to the intake clear and connected?

On a turbo, you will get some vac from the air filter until the turbo spools up, and it's not likely to do much unless you are under load, but you indicate the car has very poor performance, too.

I'd guess either a bad turbo or a fuel problem (new filters?). Need more information to help much (ie model, engine, condition).

Peter

[whunter]

Turbo toast.
You need to bring the RPMs up and listen for the turbo spooling up.
A bad waste gate will never let the turbo build pressure.

[350SL4spd]

Gauge I am using shows pressure on one side and vacuum on the other.
Everything is free and clear, I have at least double checked all of it. Intake flap is open and stays open. Turbo turns freely and it sounds like it is spooling. I have yet to pull the hose btw the filter and the turbo and actually watch the turbo turn while it's running.
I know I have a computer issue of some kind. It won't clear 2k rpms under load unless I pull all the electrical connectors off the injection pump. Then it will pull up and shift but it is still increadibly slow.
I know the computer needs to be at least reset if not replaced, but I am not totally convinced that it will solve the vacuum in the intake dilema.

[whunter]

If you know it needs to be reset, do it!!!
The ECM is in engine protection mode = LIMP mode.
Take it to the dealer and have it reset, as I recall, you need the star tool on the E class.