'87 Vac line Installed Now No Shut-Off - PeachParts Mercedes-Benz Forum

Duncwarw · #1 02-03-2008, 03:39 PM

Lots of stuff on this with earlier models but here's what's up with mine.

I recently found a hard vac line going nowhere. It ended in a short (split) sleeve of rubber hose and was laying loose under the air filter housing.

When I plugged it the fuel mileage increased dramatically to 30.4 MPG.

Today, I removed the housing and the only port I could find open was up against the back of the headlight housing on a round vac pot with one other line on it.

Since plugging the line in, the car no longer shuts down.
I'm sure this is the result of another vac leak, but as I haven't seen a vaccuum line diagram I could be chasing leaks for quite some time and time, I don't have as the car is going to be in use early tomorrow.

Until I have the diagram and the car for a day, is there any harm done if I just plug the line? The upper end goes to a thing that looks like an alda on the exhaust side.

TIA

Duncwarw · #2 02-03-2008, 04:20 PM

Sorted.

Maybe my post was premature as I've fixed it but I'd still like to understand how vac hoses on the back of the headlights (they'd fallen off) affect engine shut-down.

Thanks for your collective patience.

babymog · #3 02-04-2008, 07:04 PM

The two pods behind the passenger headlamp control the wastegate and the EGR. If the EGR line is plugged, it will not injest exhaust into the intake (IMO good), if the wastegate line is plugged the wastegate will not be able to protect from an overboost condition.

Duncwarw · #4 02-04-2008, 07:11 PM

Thanks

I plan to do some searching and reading about the egr as it seems pretty much useless to me. Maybe my opinion on that will change as I read.

I initially pulled and plugged the wastegate line (I suspect that's what it was), at the "pod" end in an effort to restore things to the way they were before the car refused to shut-down. doing the "proccess of elimination" bit. When that didn't work, I put it back on the pod and found the lines to both headlight backs off. Putting them back on cured the thing.

Are those vac lines for the light wipers or what? Strange stuff...

And another thing, why is the Alda adjustment under the intake where you can't adjust it. Some sense of humor those MB engineers had.

babymog · #5 02-04-2008, 07:15 PM

I doubt that the Engineers intended the ALDA to be adjusted.

If there are lines to the back of the headlamp housings, likely purple, they are European headlamps. The vacuum pods in them adjust the height of the headlamps. To meet TUV et al it was necessary to have a height adjustment to compensate for heavy/light loads. Some were automatic, some manual, the 124 adjustment was a thumbwheel to the right of the headlamp switch to set the lamps lower for heavy loads.

Duncwarw · #6 02-04-2008, 07:36 PM

My response disappeared.

Thanks Jeff.

The Boss just called from the road and she says there's no wheel next to the light switch. I have a spare pair of light housings in storage. They came along with the car among a bunch of spare stuff.

I wonder if one of the POs changed the housings as per the Bentley Owner's Bible to be able to use higher wattage bulbs?

POs, bastards. I foresee a lot of time spent sorting out what previous owners did to the car. Like the 190 wheels wasn't bad enough...

babymog · #7 02-04-2008, 09:28 PM

It is possible that the PO installed Euro lights. If the lights are one-piece glass instead of having a glass headlamp lense and plastic fog-lamp lense then they are Euro lights. Further, if the light says BOSCH on the lense, and has an E in a circle it is the good Euro lense (and I'll happily buy them from you if you would rather run US or have a spare set, the Euro are to most of us preferrable). DEPO is a cheaper Euro light, could be that also.

Anyway, if Euro lights, and no adjuster, not a big deal. I installed Euro Bosch lights in my '91 but never got around to installing the adjuster, just means that you can't lower the lights to compensate for a sagging rear due to load. Mine was a TE with load-leveling / SLS, so didn't seem necessary to me.

I have a spare leveling valve/wheel around here somewhere, but no 124 switch bezel, therefore kind of useless to the 124. You can find/buy them, if you want one.

BTW, in my opinion, higher wattage bulbs aren't really necessary if you have the Bosch Euro lights.

Duncwarw · #8 02-04-2008, 09:35 PM

They seem plenty bright to me but then my '73 VW Campmobile has 55W sealed beams so I don't have anything to compare them to.

In fact the MBs high beams are REALLY bright IMO.
They also seem to be all plastic. I'll compare the ones in the car to the ones in the boxes to see if there's any difference.

Another forum, another learning experience...

psfred · #9 02-04-2008, 11:55 PM

On the 87 300D you have "manual" turbo boost control, being a large pressure line from the turbo outlet housing to a servo that pushes open the wastegate when the maximum boost has been generated. It's not computer controlled.

However, there is a computer operated EGR transducer and an air recirculation valve on the turbo that are vacuum operated. The EGR reduces nitrogen oxide emissions at low power by bleeding exhaust into the intake and cooling combustion. What effect that has on milage I don't know, but I think it's minimal. The air recirc was primarily intended to reduce heat shock loading on the now removed trap oxidizer that was originally installed to reduce particulate emissions -- it should by now have been replaced by an insulated pipe from the rear of the exhaust manifold to the turbo and a trap catalyst under the floor.

The air recir valve does open on the highway, reducing boost under light (cruising) load while keeping the turbo spinning. When you tip into the pedal, it will close, greatly reducing turbo lag. This usually gives some milage improvement on the highway.

30.4 mpg is about right in fall and spring weather -- mileage drops in the winter due to the use of winterzied fuel (less btu per pound) and in the summer due to AC use.

Peter

Duncwarw · #10 02-05-2008, 08:53 AM

Good info.

In light of the post on low vs. ultra low sulphur fuel, I wonder if our increase in mileage came about because of the fuel?

We went to a station we hadn't used before after finding out they had a lower price. The car SEEMED to instantly run better and that's when we hit 30MPG for teh first time. Coincidence?

I'll check the sticker soon.

Thanks Peter, I'm learning all the time.

Paul