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  #1  
Old 11-27-2007, 11:22 AM
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Previous owner Removed Crossover Setup

The guy that owned my 300SD (83) decided his ALDA wasn't right so he removed the crossover canister on the firewall and routed the pressure line from the manifold directly to the ALDA. The car is sluggish and I can't feel turbo boost at all, but I do see smoke at full throttle. Any ideas what having manifold pressure going directly to the ALDA will do?

I suspect the vacuum is a bit wierd too as the transmission shifts very hard (especially into 4th gear at any throttle position). Any chance they are related?

Any thoughts would be appreciated.

Joe
83 300SD
82 Bluebird Wanderlodge FC33 (3208NA Cat)

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Old 11-27-2007, 11:48 AM
ForcedInduction
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Bypassing the overboost valve will not hurt performance. The valve was probably leaking so he bypassed it rather than replacing it. No harm there, it will even slightly help performance.

Vacuum is not related in any way to engine power.

On the back of the intake manifold is a banjo bolt that is for that tube going to the ALDA. Remove it and clean it out, chances are it is clogged. Also, if it is not done already, plug the vacuum line going to the EGR valve and/or the two vacuum lines going to the box on the valve cover.
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Old 11-27-2007, 01:36 PM
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Quote:
Originally Posted by ForcedInduction View Post
Vacuum is not related in any way to engine power.
Is this entirely true? I know you know way more about this than I ever will but... I don't know what it's real function or name is, but there is a line that runs over the top of the valve cover near the rear of the engine, that terminates on one end between the trans fluid dipstick tube and the valve cover. I once had that line pop off on my old 300TD and I could hear a constant hissing and I had poor acceleration. When I put it back on everything was back to normal...
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Sold but fondly remembered: 1981 300TD Turbo Tan 235K miles, 1983 300SD Astral Silver 224K miles

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Old 11-27-2007, 01:40 PM
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Quote:
Originally Posted by chetwesley View Post
Is this entirely true? I know you know way more about this than I ever will but... I don't know what it's real function or name is, but there is a line that runs over the top of the valve cover near the rear of the engine, that terminates on one end between the trans fluid dipstick tube and the valve cover. I once had that line pop off on my old 300TD and I could hear a constant hissing and I had poor acceleration. When I put it back on everything was back to normal...
It is entirely true.

The line that you are referring to is the pressure line from the manifold. That's the line that has the banjo bolt at the manifold end and it's what FI recommended for removal and thorough cleaning.
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Old 11-27-2007, 01:45 PM
ForcedInduction
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BC is correct, the line you are referring to is the ALDA tube, which is not vacuum related.

The vacuum system is a completely separate system from the engine. The engine only drives the pump so as long as the pump is good and the engine turns it will make vacuum. The only three ways I can think of vacuum affecting the engine is the pump seizing, or vacuum not being sent to the EGR or ARV (on later engines only) at the correct times which will affect boost.
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Old 11-27-2007, 02:51 PM
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I see... the ignorant man thinks clear plastic line with air going through it = vacuum system. Thanks for the edumacation.
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  #7  
Old 11-27-2007, 03:32 PM
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Quote:
Originally Posted by jd4614 View Post
The guy that owned my 300SD (83) decided his ALDA wasn't right so he removed the crossover canister on the firewall and routed the pressure line from the manifold directly to the ALDA. The car is sluggish and I can't feel turbo boost at all, but I do see smoke at full throttle. Any ideas what having manifold pressure going directly to the ALDA will do?

I suspect the vacuum is a bit wierd too as the transmission shifts very hard (especially into 4th gear at any throttle position). Any chance they are related?

Any thoughts would be appreciated.

Joe
83 300SD
82 Bluebird Wanderlodge FC33 (3208NA Cat)
I've run directly from the manifold to the ALDA for years with no problem, but I finally nabbed a switchover valve from a wrecked car and installed it back like the factory intended it, to protect the engine if the Boost gets too high. If the switch gets activated it reduces fuel to the injectors to prevent possible damage to the headgasket, etc from excessive boost (over about 14.5 psi).

Proper Vacuum is necessary for proper transmision shifting. Harsh shifts are an indication that vacuum levels is too low (meaning not there).
On the rear of the Inj Pump is a vacuum modulator valve, its plastic and has some vac lines running to and from it. These valves can get leaky internally, the best thing is to replace it if your vacuum is proper at the vac pump but shifts are getting harsh. Check to see the vac lines are all in place and verify that you don't have a vac leak somewhere. Are the door locks operating OK? If not then you may want to temporarily plug the line that supplies vac to the locking system (at the firewall) to see if that is involved. Welcome to the world of vacuum stuff as it relates to the Mercedes. Troubleshooting this can be a challenge if you don't have a vac gauge and a Mity Vac (hand pump) on hand.
Also, has your ALDA been un-capped? A picture of it would help us see if soemone has cracked the seal thereby allowing the adjustment nut to be adjusted, that can, if overdone, make the engine belch some pretty black smoke.

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Last edited by dieseldiehard; 11-27-2007 at 03:39 PM.
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