When you disconnected the VR, did you plug both ends? If you left open the supply side where it splits from the BFS vacuum supply line, you were running without benefit of the modulator. I don't know what linkage you can adjust to compensate. In fact, I don't know what linkage at all you can adjust besides the shift linkage which aligns the shift lever with the shift gate, and the pressure control cable which adjusts shift points. Removing the VR shouldn't affect all the shifts all the time.

When the car performs to your expectations, there's little reason to touch it. When it doesn't and the indication is there's a fault in the pre-OBD EDS, there's simply no good documentation on diagnosing the problem. Someone with time and resources should smog check a 2.5 before and after the conversion to determine the environmental impact. Then delete the report because I believe it's more environmentally sound to keep a 2.5 on the road than replace it with another car... while the next owner of the 2.5 does the conversion to keep it on the road

Sixto
MB-less

On my 91, there's a Y-connector vacuum line where one side goes to top of BFS and other side goes to VR. I've disconnected the line that goes to VR and plugged that side of the Y-connector. As to the other "side" of the VR, that's removed by virtue of the entire passenger side rat's nest being removed.

As I've indicated, that line going to the VR wouldn't hold vacuum....that was my primary reason for deleting it.

__________________
14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 159k miles
06 E320 CDI "Rutherford", Black on Tan, 178k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 145k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 75k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

That's exactly what I did, but I don't understand the vac system, so if it's pushing pressure from the top of the BFS to the vacuum reservoir, I don't know if I should plumb it back up and block it on the rats nest side of the VR. Maybe this would help maintain pressure better in the system, I don't know.

Here's A video of what I did with you guys help:

http://youtu.be/qWm3OIWHEVU

There is one thing that I have not seen mentioned anywhere and something that I feel is very important for the life of the motor and that is the flap in the airbox is spring loaded shut and requires an inrush of air to open it ( which creates a situation that could result in at least a partial air starve if lines and connections are not all pristine )... since you have done the mod the air mass circuit is no longer required. Here is what I did and what I would recommend doing. pry the plastic box / cover off the top of the airbox/airmass and move the spring keeper inside it to a position that holds the flap open instead of shut and then replace the cover and you are done. As I recall it is just a screw holding the spring detent keeper in place.

Just an FYI to those tapping the turbo for the wastegate actuator line, there is a port on the other side of the intake manifold that takes a NPT nipple/barb perfectly fine. That's what I used, I was too lazy (and ill equipped) to tap the turbo.

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82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

that one will be for the eventual boost gauge

have got the turbo off the car & a drill press, so I may as well keep the plumbing runs short as possible.

__________________
1991 300D

To your original question - the vane is closed by a very light spring. Airflow pushes it open.

Tweaks... flips... it's all good

Sixto
MB-less

Steady state pressure should be the same. Instantaneous pressure is another matter. With a stock and at this stage tired turbo, it's unlikely the distance from the manifold back to the wastegate actuator will delay wastegate response appreciably. I'm not keen on sharing the ALDA line because it's so easy to use a capped port on the manifold. I'm not sure if all 2.5s have a MAP sensor. 92-93 2.5s do and IIRC it tees into the ALDA line. The MAP sensor does nothing without the vacuum actuator so that pressure signal point is available.

I'm no physicist either.

Sixto
MB-less

Hi Sixto. Thanks for the reply. Interesting point on the response time vs. constant pressure.

On air compressor hoses, I read that there is a drop in pressure over distance due to friction. I suppose the same would be true in this application, but we're talking a few feet distance. It makes me wonder if that is why the hard vacuum lines are used (smaller volume but/and/or less friction)? So, Im thinking of trying a hard line if I try tapping into the ALDA line. I can always drill and tap a hole on the other side later if it doesn't work well.

I opened the hood and looked at the configuration on my '93 300D. There is a single additional hard vacuum line on the ALDA-to-manifold circuit that disappears into the firewall. The vacuum schematic for my iteration shows that this line runs to the EDS, presumably to monitor boost pressure (which would make sense). Makes me wonder where the EDS resides anyway.

I have a couple of more questions ...

1) Any thoughts on setting the replacement actuator on 15 psi vs. 12 psi? The stock spec is between 13 and 14, so I'm thinking 12 psi to be on the safe side, especially if there is a potential pressure drop from coming around from the injector side of the engine.

2) Any guidance on bobodaclown's observation that the replacement actuator works in the reverse from stock (starts in the "fully on" position vs. in the "fully off" position)?

I assume this means that the starting position for the replacement actuator is all the way in (and it is pushed out by pressure) and the stock plunger would start out fully extended (and is pulled in by vacuum). Does this affect how the actuator should be installed? I assume the replacement actuator still needs to be modified to shorten it and add more threads ...

Thanks again.

0a) I don't think there'd be much difference between plastic line and silicone hose. The nice thing about fresh hard line is you can see it get dirty to do something about it.

0b) The EDS module is in the cubby behind the battery. There's a MAP sensor somewhere in there at the end of the line that tees into the ALDA signal line.

1) 90-91 2.5s have an overboost switch that triggers at 1.1 bar or 16 psi. 15 psi should be fine in bursts but don't hold the pedal to the floor up Pike's Peak without a pyrometer. The overboost switch attaches to the manifold within an inch or so of where the ALDA gets its signal so that's where MB felt it relevant to measure pressure. That's not to say that's an appropriate place for the wastegate actuator to source its signal.

2) That's more the intention than an observation. Back in the day, turbo wastegates were fully mechanical in that compressor outlet pressure pushed the wastegate flap open to reduce manifold pressure. These days trees are things we hug rather than live in. For more precise wastegate control, the pressure actuator gave way to a vacuum actuator. The vacuum actuator works with a wastegate lever that's twice as long as in a pressure system and operates on modulated vacuum signals rather than a simpler on-off signal. The added parts and pre-standard OBD controls means it's a PITA to figure out why EDS limits boost. Rather than spend time and money figuring it out, many convert to simpler mechanical boost control.

3) Yes - a pressure actuator pushes, a vacuum actuator pulls. But think in terms of opening and closing the wastegate. I've never worked with a MB T25 so I can't comment on geometry. Whether you adjust rod length or reposition the actuator seems more a matter of convenience. When I converted the T3 in a '93 SD, I swapped over the actuator *and* lever from an '87 SDL because I wasn't sure the actuator would work properly with the longer lever from the vacuum setup. It would seem from the number of successful T25 conversions that lever length isn't an issue.

Sixto
MB-less

Thanks, Sixto. That is good information. Interesting about the lever length.

One last question. Location of the boost line.

Can you help me understand why it would be better to tap into the turbo or the soot flapper pipe or even the cross over pipe and if you have a preference?

I see the point about dirt getting into the line from the ALDA line.

I'm wondering if it would be better to have the boost pressure coming from closer to where it enters the cylinders, rather than from closer to the turbo where it is presumably stronger.

Thanks again for your help.

It has to do with reaction time. When you accelerate hard, pressure increases rapidly. There could be a lag between the time 15 psi builds in the manifold and 15 psi registers at the wastegate actuator - which is another meter away if the signal line taps into the far end of the maniold - at which time the manifold could be at 17 psi. So you set the wastegate to open at 13 psi. Well, when you accelerate less aggressively, the actuator will see 13 psi about the same time as the manifold so you'll never get to 15 psi you want under those conditions.

This thinking comes to me by way of engines that rev more quickly and to higher rpms than MB 60x engines. Said engines were very sensitive to manual boost controller location and setting. I had one engine that peaked at 16 psi in 'normal' driving that then spiked to 22 psi with the pedal to the floor in lower gears until I sorted signal line routing, boost controller spring tension, etc.

Try it the 'easy' way first. If you don't see boost spikes driving the way you normally drive, pat yourself on the back and go on to the next project.

Sixto
MB-less

That is persuasive and helpful. Thanks, Sixto. I get it now. I found a picture of a turbo from an 87 300TD. Sure enough the actuator is plumbed to just below the output flange on the turbocharger. You are correct.

The question I have is why an actuator at all. In the GM 6.5 turbodiesel world, the hot setup is to replace the vacuum actuator with a spring! Pressure in the turbine inlet pushes the wastegate open at the setpoint. Does that work because these engines rev to all of 3500 rpm and get there oh so slowly?

http://heathdiesel.com/performance/turbo-master-gm96-boost-control.html



Sixto
MB-less