EGR question (on goes the '93 300D 2.5 saga) - PeachParts Mercedes-Benz Forum

cgunderm · #1 03-10-2007, 04:36 PM

Now I have a question about the EGR:
When a local MB indy mechanic suggested the other day that to keep the air intake clear of soot (it had just recently been cleaned before I bought the car) I should disable the EGR, I said, right, put a BB in the vacuum line. He says no, I have a better solution. I'll have my machinist make a metal plate to completely block off the EGR from the intake. I agreed to have him do that. When I pick up the car, it's completely gutless. Essentially like a non-turbo (and this car was fast before), on hills you not only have to floor it but you have to kick down into third gear, and it still won't go really good. When I take it back, he says: oh, we'll have to look into the electronics. It looks like something is wrong there, bad diesel injection controls.... The whole thing seems really fishy to me because the car was running really fast before this, and each time he gets his hands on something he has to "look into" it tends to cost 1 grand +.

So I started wondering if maybe the electronic controls of the intake/injection might be thrown off by this metal plate and not be functioning correctly anymore. Usually if you disable the EGR you get better power and better mileage, right? But I've never heard of anyone putting a metal plate in the intake like that. What are people's thoughts about that...

And btw, I sorted out the supposed valve noise and smoke and skipping idle. It was the injectors. They were completely bad, and the seals bad as well. As someone else wrote here recently, the injector noise can really mimic lifter noise. I could have sworn it was a lifter/lifters...So this is running great now, all the mystery smoke and skipping after about 2 minutes after cold start is gone....

Brian Carlton · #2 03-10-2007, 04:55 PM

Quote:

Originally Posted by cgunderm

So I started wondering if maybe the electronic controls of the intake/injection might be thrown off by this metal plate and not be functioning correctly anymore.

You are correct.

That vehicle has a computer controlled EGR system. If you block the EGR, the airflow will change and the computer will disable all boost.

There are a couple of work arounds in the archives.

Read this thread carefully. It's got everything you need:

Low Turbo Boost

cgunderm · #3 03-10-2007, 10:28 PM

Thank you very much. This was very enlightening! (And reassuring that there isn't some major electronic problem with that car!)
I will eventually figure out whether I go with the ways around the turbo shot-off that are described there. For now I will simply take the plate back out and have a car with turbo boost again.

Anyone with a 601/2/3 on here who runs it on VO or biodiesel? Do you find that the intake gets crudded up less on biofuels?

Quote:

Originally Posted by Brian Carlton

You are correct.

That vehicle has a computer controlled EGR system. If you block the EGR, the airflow will change and the computer will disable all boost.

There are a couple of work arounds in the archives.

Read this thread carefully. It's got everything you need:

Low Turbo Boost

pdrayton · #4 04-30-2007, 04:07 PM

So what I get from this thread and the one Brian Carlton kindly pointed out, is that to disable the EGR on a 602/603 with the EDS you have to either make a circuit (which has the potential to leave the turbo full bore at failure) or get a pressure operated wastegate, which there isn't one for the 1992 300D?

I don't like option 1. Or option 2.

Have I missed the point? Is there an easier way? Please, oh Mercedes deity, let there be an easier way.....!

pdrayton · #5 04-30-2007, 04:26 PM

I have hopefully answered my own question - put an air breather on the EGR intake - see
93 300D 2.5L EGR Experiment

Brian Carlton · #6 04-30-2007, 04:28 PM

Quote:

Originally Posted by pdrayton

I have hopefully answered my own question - put an air breather on the EGR intake - see
93 300D 2.5L EGR Experiment

I was thinking of that.........but..........I'm not sure if it works on the turbo vehicles or just n/a. I seem to recall some issue with a turbo where the lack of exhaust pressure for the EGR valve is a problem........??

2.5Turbo · #7 04-30-2007, 04:36 PM

I would think that's the only way without major modifications. Unless the boost control is taken out of the control of the computer, there really isn't any way of tricking it into thinking the EGR is functioning properly....unless there's a way to trick it into thinking less air is flowing than there really is.

Maybe building a bypass of the airflow meter controlled by the EGR circuit would work. It would think EGR gas is flowing by the reduced amount of airflow through the sensor. And maybe dumping it back in pre-turbo would fool it enough. But then you have to deal with that blasted butterfly valve...

I don't have the time, money, or the will to modify my car to that extent to be the guinea pig for this experiment however

Edit: Geez, we thought of that at the same time...how weird

Edit again: And wouldn't an air breather tube post turbo just leak boost like crazy?

pdrayton · #8 04-30-2007, 04:49 PM

Brian, Yes, you are correct. In my excitement I spoke too soon. The EGR needs pressure from the exhaust manifold to get air into the intake.

Still no easy solution I can see.

Are we sure EGR is not short for EGRegious?

Brian Carlton · #9 04-30-2007, 07:24 PM

Quote:

Originally Posted by pdrayton

Brian, Yes, you are correct. In my excitement I spoke too soon. The EGR needs pressure from the exhaust manifold to get air into the intake.

Still no easy solution I can see.

Are we sure EGR is not short for EGRegious?

I thought so. That solution works fine for the 2.5L n/a vehicles, but, with a turbo, the pressure would just force boost right out of the valve..........the computer would fault that in two seconds.