602 vs 603 EGR and boost control - PeachParts Mercedes-Benz Forum

JHZR2 · #1 10-10-2022, 11:18 PM

If you look at my signature, you know I have a lot of diesels.

My 91 300D 2.5 has the system where it will not get boost without the EGR working… unless you have a pressure actuated wastegate I guess….

Is the 3.5L 603 the same setup? Either the 3.5L in the w126 or the w140?

I’m trying to get my newest 126 going and will be cleaning out the intake. I’d like to disable the EGR for off-road testing purposes, but am not sure if I’ll be able to load the engine and achieve boost then.

Is the 603 in the w126/140 like the 602, or like the older diesels where egr vacuum is all that needs to be pulled?

dieselbenz1 · #2 10-10-2022, 11:36 PM

602 is vacuum controlled boost same as 603 3.5 in 126 and 140.

JHZR2 · #3 10-11-2022, 12:02 AM

Quote:

Originally Posted by dieselbenz1

602 is vacuum controlled boost same as 603 3.5 in 126 and 140.

So in the 603 you can’t disable the egr because it won’t authorize the wastegate to operate then?

dieselbenz1 · #4 10-11-2022, 07:06 AM

One way is to replace the waste gate operation to pressure control.

Phillytwotank · #5 10-11-2022, 07:50 AM

You could just plug the vacuum supply to the egr. Vacuum makes the egr valve open. As long as there are no leaks everything else should work.

JHZR2 · #6 10-11-2022, 07:50 AM

Quote:

Originally Posted by dieselbenz1

One way is to replace the waste gate operation to pressure control.

Right. I’ve read the very long thread on that for 602 engines. I must have missed that there was a recommended presure actuated model to fit into the 603.

JHZR2 · #7 10-11-2022, 07:52 AM

Quote:

Originally Posted by Phillytwotank

You could just plug the vacuum supply to the egr. Vacuum makes the egr valve open. As long as there are no leaks everything else should work.

Well that’s where I’m trying to get a straight answer. That won’t work for the 602 2.5 turbo. The computer will restrict boost if it doesn’t sense the egr working correctly.

I’m trying to determine if the later 603 (91-93) work that way too. Or if they can just have vacuum restricted to the EGR and call it a day.

Phillytwotank · #8 10-11-2022, 08:07 AM

No I don’t think so… there’s no feedback from the EGR to the computer. if it sends vacuum to open the EGR and its pulling vacuum against the golf tee stuffed in the line it’s gonna think that it’s doing what it supposed to be doing

dieselbenz1 · #9 10-11-2022, 12:08 PM

The only feed back the ECU receives is from the MAF. When called for the EGR opens, intake air is restricted when ECU detects reduced MAF signal boost will not be restricted. A bb in the vacuum line to the EGR valve will effectively disable the EGR if that's what you are looking to do?

JHZR2 · #10 10-11-2022, 10:16 PM

Well the 602 2.5 turbo restricts boost if the MAF/other sensors aren’t satisfied.

If the 693 can be satisfied with a bb, that sounds good. Less complex somehow than the 2.5 turbo.

dieselbenz1 · #11 10-12-2022, 10:26 AM

Quote:

Originally Posted by JHZR2

Well the 602 2.5 turbo restricts boost if the MAF/other sensors aren’t satisfied.

If the 693 can be satisfied with a bb, that sounds good. Less complex somehow than the 2.5 turbo.

Only MAF provides feedback. There is an 85 page document describing in detail how it works and test procedures but I passed that to the new owner of my 602.

603 and 602 of the same Era operate the same. My old 602 had the EGR pipe full of hardened gunk and never worked since I had owned the car and that never affected boost.

JHZR2 · #12 10-13-2022, 01:56 PM

Quote:

Originally Posted by dieselbenz1

Only MAF provides feedback. There is an 85 page document describing in detail how it works and test procedures but I passed that to the new owner of my 602.

603 and 602 of the same Era operate the same. My old 602 had the EGR pipe full of hardened gunk and never worked since I had owned the car and that never affected boost.

So the 603 will restrict boost if the egr is restricted/blocked/bb put in the vac line then.

That’s the point of the 602 2.5 vacuum wastegate control system. And why to overcome it and block/disable EGR you need a pressure actualted wastegate swap.

I don’t recall reading about such a swap being needed on the 603. As in it is a pressure actuated wastegate and will create boost even without the EGR.

Different methods of allowing boost.

But that’s why I’m asking. I’m confused.

602 2.5 Turbo - vacuum activated, computer controlled wastegate
603 3.0/3.5 - pressure activated wastegate (????)

dieselbenz1 · #13 10-13-2022, 04:52 PM

I see your confusion 1987 603 was the last of the pressure controlled waste gate. All 602's & 603 3.5's had the vacuum controlled boost and EGR controls.

JHZR2 · #14 10-13-2022, 08:29 PM

Quote:

Originally Posted by dieselbenz1

I see your confusion 1987 603 was the last of the pressure controlled waste gate. All 602's & 603 3.5's had the vacuum controlled boost and EGR controls.

Ok. So a bb in the 603.97 egr valve will cause a boost restriction.

And thus I need to seek out a pressure activated wastegate similar to what is used as the retrofit on the 602.

Though that said, I was pleasantly surprised at how clean my new 91 350SD intake was.

My 1993 300SD was absolutely caked in soot… I was surprised that this one was so clean.