MAF in 87SDL what's it do ????? - PeachParts Mercedes-Benz Forum

zbenz · #1 05-14-2003, 10:52 PM

Hi just wondering what does the vane style airflow meter do for the system in my 87 SDL ? I know what it does in my scoobie can't be the same can it?

sixto · #2 05-15-2003, 03:37 AM

It's part of the ADS system that controls the EGR and ARV systems. If you've disabled the EGR and ARV (who'd so such a thing?), it's just adding turbulence to your air flow.

Sixto
91 300SE
87 300SDL
83 300SD ... any takers at $1100?

airfoill · #3 05-15-2003, 10:21 AM

Sixto,

I have an SDL but I don't know what the ARV stands for? Air Recirculation Valve? And where is this ARV?

I do know for a fact that the EGR on my SDL and 2.5 Turbo have been "temporarily" nonfunctional.

Herb
'82 240D
'87 300SDL
'92 300D 2.5 Turbo

md21722 · #4 05-15-2003, 11:11 AM

ARV is on the front of the tube. There are two vacuum lines for emissions in that area of the car. One is for the EGR, the other, below it, is for the ARV. Its purpose dates to the trap oxidizer which has since been removed. The wastegate on the 1987 models is mechanically controlled on the turbo, not by any electrical or vacuum actuators.

How did you disable the EGR on the 2.5Turbo without losing your boost?

sixto · #5 05-15-2003, 12:35 PM

Quote:

Originally posted by md21722
ARV is on the front of the tube...

How did you disable the EGR on the 2.5Turbo without losing your boost?

The air recirculation valve itself is bolted to the compressor housing of the turbo. The vacuum amplifier is tucked under the turbo intake tube as Brian says. The ARV subverts boost charge to calm the onset of boost. There might be an ARV funciton related to cruise control as well.

I'm curious too as to how you disabled the EGR system in your 2.5. I know it can be done, I just don't know how.

Sixto
91 300SE
87 300SDL
83 300SD ... any takers at $1100?

airfoill · #6 05-15-2003, 02:17 PM

Well, on the 2.5, the vacuum line on the EGR "accidentally" fell off and somehow there is a golf tee attached to the end of it. I've heard this isn't the right way to do it because it is supposed to deactivate turbo boost but I dont' see how because I dont' see any wires going to the EGR valve. I will say that I have noticed a lack of boost since this the vacuum line has been off.

What I need to do next is cut an aluminum piece the same shape of the EGR valve and sandwich it in between the existing EGR and the housing the EGR sits on. After that I will reattach the vacuum line to the EGR valve.

I will say that on the SDL, it doesn't matter. The vacuum line on the EGR on this car also "accidentially" fell off and plugged with a golf tee; however, I haven't noticed any decrease in turbo boost.

Herb
'82 240D
'87 300SDL
'92 300D 2.5 Turbo

TX76513 · #7 05-15-2003, 02:46 PM

Sixto - it a Texas thing. Lots of golf tees on the highways, easy to pick up with front tires and they shoot right into those vacum lines. lol

gsxr · #8 05-15-2003, 02:56 PM

Airfoill, that's the problem... disabling the EGR on the 2.5 Turbo messes up the computer. There is a boost control flap/valve on the 2.5's that are computer controlled, and when the computer ain't happy, you lose power. That's why most people don't disable the 2.5 EGR. Installing a blank plate won't work either, AFAIK....

sixto · #9 05-15-2003, 03:07 PM

As I understand, there's a (temp?) sensor in the mixing pipe that expects to see an EGR charge. I don't fully understand it because the pressure in the mixing pipe would be greater than exhaust pressure under boost. EGR is typically a deceleration device anyway so why should it affect boost. Sounds like big brother more than engineering.

I think member oldsouth figured out how to disable EGR in computer controlled Diesels.

Sixto
91 300SE
87 300SDL
83 300SD ... any takers at $1100?

sixto · #10 05-15-2003, 03:07 PM

As I understand, there's a (temp?) sensor in the mixing pipe that expects to see an EGR charge. I don't fully understand it because the pressure in the mixing pipe would be greater than exhaust pressure under boost. EGR is typically a deceleration device anyway so why should it affect boost. Sounds like big brother more than engineering.

I think member oldsouth figured out how to disable EGR in computer controlled Diesels.

Sixto
91 300SE
87 300SDL
83 300SD ... any takers at $1100?

Rick Miley · #11 05-15-2003, 03:17 PM

This may or may not apply, but the way VW does it is to watch the mass airflow sensor as it opens the EGR valve. If the airflow across the MAF does not decrease appropriately, then the computer sets a code and lights the check engine light. This would be very difficult, although not impossible, to overcome.

The EGR itself is not a huge problem until you combine it with CCV. Vent the crankcase vapors to the atmosphere, or else use a really good oil separator, and you end up with dry soot flowing through the intake and very little of it sticks. That solves the problem of gunking up the intake manifold.

Big Brother, yes indeedy. It took me 2 cans of carb cleaner, a quart of mineral spirits, 2 rolls of paper towels, several pair of gloves, and a set of Tyvek coveralls to clean my Jetta's intake manifold. Balance that agains the maybe 1 qt of oil I would have vented to the atmosphere with the CCV disabled.

gsxr · #12 05-15-2003, 03:56 PM

I think oldsouth has a 3.5L engine (603), not the troublesome 2.5L with the invasive computer. I wish I knew someone who had one that I could play with. There has to be a way to defeat it, we just need to figure out how!

BTW, the easiest way to clean the oily/sooty intake manifolds is to toss them in a box and bring them to your local machine shop. Remove electrical switches/sensors first, of course. Ask them to "hot tank" them. They will come back squeaky clean and you will have zero mess to clean up. Definitely worth the cost, IMO!

Regards,

sixto · #13 05-15-2003, 04:00 PM

Dave,

From my discussions with oldsouth and glancing through the CD manual, the 603 variant in the 140 has a pretty invasive computer system. If you disable the EGR in any way it cuts boost.

Sixto
91 300SE
87 300SDL
83 300SD ... any takers at $1100?

gsxr · #14 05-15-2003, 04:05 PM

sixto,

I'm not 100% sure, but I believe the later 603's did not have a boost control valve - meaning the boost is totally controlled by the turbo wastegate. And I don't think the I had any special electronic controls either. I'll have to take a peek at my 3.5L Intro manual tonight and see if I can find anything in there. The 1990-up 602's definitely have more junk, and the engine manual details the extra parts. I don't recall seeing anything like that for the 603.97x...??