Troubleshooting M104 EGR - PeachParts Mercedes-Benz Forum

73Elsinore · #1 11-13-2006, 01:30 AM

Good evening guys. I am chasing a code 5 (EGR failure) in a '93 300E 2.8L, California car. The car passes emissions but won't pass the test since the CEL is on.

I read and followed all the posts I found on this topic (thanks Arthur and others!) but I still have the problem. I reset the CEL to clear the code but it comes right back. Code 5 is the only code I get. Here is what I've done thus far:

- Check manifold vacuum: Manifold vacuum is 24" Hg at idle, at normal operating temperature, measured at the hose that feeds the SOV going to the EGR.

- I stroked the EGR valve using a hand pump. It opens and closes normally. It closes with a nice audible SNAP when I dump the vacuum suddenly.

- I checked operation of the SOV that sends vacuum to the EGR. There is no vacuum at the SOV outlet port until the revs get to about 4000, then I get 22" Hg. Below 4000 rpm, there is no vacuum so the SOV is not opening. I do not know if this is normal.

- Ran engine at idle at normal temperature and stroked the EGR valve using the hand pump to see if the engine would stumble. Nope. No change in engine idle. Still ran just fine, no loping or rough running. Based on that I assumed the tube was blocked.

- Removed EGR valve body and cleaned it. On the bench, I tested it, blew air through it, soaked the valve internals in B-12. On the bench, the valve begins to open when vacuum gets to 4" Hg and is open fully at 8" Hg. It works fine on the bench, holds vacuum, and isn't sticky. It does bleed off vacuum r-e-a-l s-l-o-w, like it will drop 1" Hg in a minute or so. This might have been my connections though.

- Sprayed a bunch of B-12 into the EGR tube and let it soak for an hour or so while I cleaned and tested the EGR valve on the bench. Then I used two bicycle brake cables hooked to a drill motor and roto-rootered the EGR tube real good for about 5 min. A bunch of black crap came out. The cables went into the tube about two feet and wouldn't go any further.

- Reassembled the system with a new EGR base gasket and torqued the two nuts to 10 N-m ( I couldn't find any torque values for these nuts in the Technical Data Book so I just used a typical torque value for an M6 fastener since that's what these are).

- Ran engine and again stroked the EGR valve using the hand pump. No change in idle, no stumbling due to lean mixture.

So I must have done something wrong. There is no way the tube could still be blocked.

Does the throttle butterfly have to be open when roto-rootering the EGR tube? I did not open it.

Thanks guys ! ! ! !
Pete

mbdoc · #2 11-13-2006, 08:14 AM

The tube must be blocked...we install about 10 a month on those cars..VERY common problem..takes a MB tech 2-3 hrs & the parts list for $160+-.

Arthur Dalton · #3 11-13-2006, 08:48 AM

< >>

That is the test and it fails, ... tube blockage verification.
As Doc states, best to take it off and replace it with the new sytle tube, ..otherwise, even if you do get it unblocked, it will be a temp-fix...........

73Elsinore · #4 11-13-2006, 11:11 AM

>The tube must be blocked...we install about 10 a month on those >cars..VERY common problem..takes a MB tech 2-3 hrs & the parts list for >$160+-.

Thanks guys. I was afraid of that. 2-3 hours for you guys equals all day for me... I can't even find the other end of the tube (the manifold end).

Thanks again ! ! !
Pete

mbdoc · #5 11-13-2006, 12:17 PM

The plastic part of the intake must be removed to remove the EGR tube..Takes about half of the noted time to remove & re-install that section of the intake.

73Elsinore · #6 11-13-2006, 12:20 PM

Thanks Doc. I will proceed accordingly. I'll post back here when I get it done.

Thanks!
Pete

J. M. van Swaay · #7 11-13-2006, 03:41 PM

Here's what it looks like under there. (104 992 engine)

73Elsinore · #8 11-13-2006, 07:26 PM

JM - Thanks for the photo; very illustrative. Except your head is a lot cleaner than mine! I have the dreaded head gasket problem on mine so my motor is covered in black goo. I will be dealing with that next summer...

Thanks!
Pete

J. M. van Swaay · #9 11-13-2006, 07:41 PM

If there's a headgasket in your future, you might consider the roto router till then. It takes more than 2 feet, (As I recall it takes about 4 or 5 feet. You should be able to guesstimate by looking at the picture.) Only an old speedo cable is stiff enough. Definitely a band aid fix though.

Kestas · #10 11-13-2006, 07:50 PM

I also cleaned my egr tube with the head off (104.992). I can't imagine doing it with the head on, except by using a flexible cable. I also remember measuring the tube for the next time I had to use a cable to clean it. It was almost exactly 3 feet long. So you'll need a 3'+ cable to clean the egr tube.

Just about all the deposits were within the first few inches of the tube where it connects to the intake manifold.

73Elsinore · #11 11-15-2006, 08:20 PM

Thanks Kestas.

Hirnbeiss · #12 11-15-2006, 09:30 PM

I don't think there is any more useless task than fighting with that stupid tube. If you pass the emissions test, why do you want to go to all that trouble to just dump more crap (exhaust) into your intake?

Kestas · #13 11-15-2006, 10:10 PM

Does pulling the bulb really work (we have no emissions testing here in Michigan)? I would think that part of the test would be to check if the bulb works, since it's such an obvious way to beat that part of the test.

One argument I use for fixing an emissions fault is that you need the check engine light available to prompt you in case any new problems develop.

skiier3_9 · #14 11-15-2006, 11:10 PM

This thread may help as well.

http://www.peachparts.com/shopforum/showthread.php?t=109372&highlight=EGR+tube

Theres a good pic on the first page.

I never fully removed mine - just cleaned out the intake manifold end really good. I haven't had any problems for about 15K miles - but like Arthur said, it will only be a temporary fix. I'm sure I'll have a CEL in the future with this problem again.