I unplugged mine and left it all the way open. I have noticed since doing the pressure actuator modification that the car smokes a little, but I like that. The thing I like best is that it runs like a brand-new car!

So, do I understand correctly that, if no vacuum is applied (as my case where the vacuum is disconnected on that side), the vane stays essentially open?

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

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.

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


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.

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1991 300D

Are you talking about the flap that builds vacuum so EGR soot is drawn into the mixing pipe, or the flap in the MAF that opens as air is drawn from the air cleaner into the turbo? IIRC the mixing pipe flap stays wide open with no vacuum applied to the actuator, but the actuator is also the spring so who knows how the flap rests if you remove the actuator. I think Jeremy removed the flap so only the shaft is in the way. Others replace the mixing pipe with a section of hose. The spring in the MAF flap is very light. It would surprise me if wedging it open made a difference on a dyno. It doesn't hurt anything to wedge it open after defeating EGR and swapping in a pressure actuator. You can replace the MAF with an elbow but you'll have to fabricate brackets to hold the air cleaner in place.

Sixto
MB-less

I'm referring to the flap in the MAF. I already knew that I was good as far as no vacuum to the mixing pipe is concerned.

Car runs great....but I'm always open to new tweaks!

__________________
14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

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

wondering whether anybody else noticed a change in the exhaust.
For the clean air test my car has to undergo engine is left idling for 10 mintues and exhaust is checked for smoke during this time.

10 minutes ? running at idle?

I've only had one vehicle "Smogged" an '85 VW Golf I-4 N.A. 1.6 L Diesel
in Jacksonville (Duval County).in 1997
No Modifications to the Factory setup,so I know it was Dirty.

The technician simply measured the exhaust stream Photo-Optically.

Car Passed.

I'm sure the emissions tests now are much more stringent.

'Cause that wasn't a test,it was an amusement.

____________________________________________________________________________________________________ ______

D.F. ,

If there's ANY chance your Jurisdiction will look under the hood
(And be intelligent enough to understand the EGR/Wastgate mods)
It would help if most everything "looked" normal.
Do a Lubro Moly "Diesel Purge" fuel treatment + Then an Italian Tune UP before the Emissions test.

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'84 300SD sold
124.128

this is in Ontario, Canada

This work is done by younger technicians and mostlikely they would not have a clue what the standard equipment is in a W124.128.

How thoughtful of the Local Authorities.
Providing somewhat "I.T. only" capable technicians.

__________________
'84 300SD sold
124.128

Bobodaclown's write up on how he set up the pressure activated wastegate actuator is intriguing. It makes sense for the pressure reading to be the same as the ALDA gets. Plus there's no drilling and tapping the turbo or manifold.

It looks like he modified the set up to have the factory port on the driver's side of the intake manifold connect directly to the ALDA and spliced into that. I think there are other connections on that tubing circuit on my W124 300D. Is that correct? If so, what about the other connections?

The second question is whether the distance between the far side of the intake manifold and the wastegate actuator would affect the pressure reading? I imagine it shouldn't assuming an airtight connection, but I'm no physicist.

Thanks for any input folks might have.

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