E320 Rough Idle / Egr Problem

[earossi]

I have posted here before with unique problems with my 95 E320, but am now totally stumped..........as is my mechanic.

I have been having an intermittent rough idle problem for several months now. Then, about three weeks ago, the CHECK ENGINE lite came on. I took the car in to my mechanic who is usually very competent.............to unrabel both problems. The computer codes indicated an EGR problem, which may or may not be related to the rough idle. We cleared the codes and they came on once again in about 5 days. Same indication.....EGR valve. I tentatively scheduled to bring the car in the following week to have them check out the EGR and the tube that is known to plug.

Over the weekend, I decided to do some work to sort out the rough idle problem. In researching the archieves, I found a number of threads where Arthur Dalton provided insight to the things that can cause a rough idle. One of them was the connector that connects the plug coil with the spark plug that lies just below the coil. Since I know that none of these had everr been changed in 140,000 miles, I felt it a cheap change to make.

So, I replaced the three connectors below each of the coils, and the car fired up fine. I went to test drive it, and about a block into the drive, the car suddenly started missing very badly. limped home and had the car towed into my mechanic.

"When he pulled the plugs, he found them all completely wetted with fuel. Since I had replaced the plugs within the last month, I find it hard to believe that the plugs are at fault.

However, my mechanic replaced all the plugs and cleared the codes and the car fired up fine. He drove it for a day and pronouched it cured; however, when I pecked the car up, the CHECK ENGINE light came on once again. Though the engine is not misslng nearly as badly as it was when I had it towed in, both my mechanic and I are at a loss. He kind of threw up his hands and suggested that I take it into the dealer who had better diagnistic facilities.. To me, that sounds like an open checkbook.

I would appreciate any insight anyone could provide..........especially, if A. Dalton reads this note!

TIA

[ILUVMILS]

It sounds as though you may be a candidate for an OVP/wiring harness inspection. Have these items been checked?

[Arthur Dalton]

I agree.
The wire harness rears it's ugly head when the wires are disturbed [ changing plug boots]
Do a search on it ..
The egr can easily be checked by using a hand vac pump to open/close it manually and chech for rough idle when open..This indicates a sticking egr , no roughtness indicates tube blockage..
EGR has ben up-graded on this model for sticking part..
The second most common egr code fault is caused by a break in the vac line under the front engine cover going to the egr Switch over valve -- this line is plastic and dries up and cracks/breaks on 104s.... without this line , the egr can not get energized...
The real code you want to verify ignition faults [ which are suspect w/plug condition] is to build a led/sw tool[archives] and go to pin #8 [HFM/SFI module ] or have it scanned...
And lastly , the infamous OVP.. this feeds power to the ECU and a bad one will raise hell with both ignition and fuel..
Check and see if it has the new part # , and if it does not , just change it for insurance sake and future problem possible elimination

[earossi]

Thanks Arthur. Your mention of the EGR vacuum line reminded me that I had just changed out the air pump on this car (bad bearings), which requires that the front cover be removed from the engine to unplug the clutch wiring connector for the pump. I did that and found the original connector missing (had apparently been worked on before by someone else). But, I did take a casual look at the white vacuum line, and it was not visibly broken anywhere that I could see. Is it possible that the line could be cracked? For safety sake, I'll just replace the line to make sure.

The EGR valve is fairly pricey.........Fastlane has it priced at over $200. Can the existing valve be cleaned? Or, is that just a waste of time? Also, the line that plugs; I assume that to be the thin stainless steel line that travels along the right side of the head, correct? Should I replace that line, or attempt to unplug it. I have seen archieve messages in the past indicating that cleaning it is not that easy to do.

I can also change out the OVP relay. Have done that on other cars. But, what sticks in mind is that the fuel flooding problem occured within minutes after I changed out the plug connectors.

If the wiring harness is bad (lots of threads indicating that to be a major problem with the 104 engine), is that a DIY project, or best left to a mechanic? Notes on this board refer to it as a thousand dollar repair (hard to believe). The only part of the harness that I disturbed was the wiring connectors on the plug coils. I had to kind of manhandle the coils to get the old plug connectors to break loose from the respective coils. This may have caused some unusual bending of the wiring harness that plugs into each of the three coils.

Arthur, I usually do most of the PM work on my cars........forces me to look under the hood and sometimes spot things going bad before they become an issue. But, it really bothers me when I can't solve an issue without just replacing parts! Very frustrating.

Once again, thanks for your assistance.

[Arthur Dalton]

I hear ya..
You are running into the few Bads of the E320..
Wire Harness
EGR
OVP
Might as well throw in Head Gasket/lip seal, while we are at it..
But , that is the Nature of the Beast....
Aside from these , these are pretty good cars..
The OVP and plug connectors are no big deal, but the others sure are..

The line that plugs on the EGR is the exhaust gas return line that goes from the egr , back behind the engine , over to the intake side ..
Look up SB article in the DIYer section. There is a pic there..
Some are actually having LUCK with Benz picking up the tab , as there was a Recall on the egr..[ email me off line and I can send it to you --you can then see if yours is in the "Campaign" [ love their use of that over recall ] number series....

It seems that once any of these are taken care off , re-ocurrence does not seem to be a problem.

On the harness , it's a skill level thing , but not really hard --plug in , routing kind of stuff..

[Kestas]

If I remember correctly, the original egr valve was a poor design and was replaced at the dealer whenever these cars appeared for service. The updated valve looked the same as the old, so a red dot was painted on the new egr valve to let other mechanics know this work was done.

There are a few easy things you can do before throwing expensive parts at the problem. The problem egr line is not the thin line you saw, but the 1/2" diameter line that snakes behind the head to the intake manifold. The problem area is typically confined to the first few inches of pipe at the intake manifold where deposits accumulate and needs to be cleaned out. This can set a Code 5.

The other easy thing is the egr valve itself. Apply vacuum to the fitting and see if the valve responds. If there's no movement or if vacuum doesn't hold, the valve needs to be replaced. With the valve removed from the engine, try to blow air across the port. If you can blow air, the valve doesn't seat properly and the valve needs to be replaced. After doing these tests, you'll want to wash your lips before eating .

I can't think of anything in the egr system that would cause plug to become wet with fuel. You're probably looking at more than one issue.

Depending on you level of confidence, changing the engine wiring harness is not that difficult. The part itself is expensive.

[Arthur Dalton]

< >>
Actually, your car was kind of in a transitional time period
of OBD1 to OBD2 systems...
What is cool about this is that anyone owning one of these can still access the fault codes of the different modules using a $5 home-made led/sw tool . [ flash code format]. The one under the hood connects to Emmisions related codes [CE lamp activator], but one can get into the other pins on the diagnostic box w/tool for further , more specific info]
So, for a DIYer , this can be a very valuable feature.
There is plenty of info on it in Archieves...after 95, the E320 went to OBD2 and requires a scanner [ digital format], leaving the flash system

An added thought on your EGR.. Because you mentioned some wiring plug connectors missing/unplugged on your AIR pump, you may want to check the connector at the Switch Over Valves .. these must be funtioning to get the vac TO the egr...if someone unplugged the AIR , they may also have unplugged the SOV connector , knowing that that controls the AIR valve in the pump circuit... just a possible..

[earossi]

Arthur,

Can you explain the function of the SOV you mentioned above?

TIA

[Arthur Dalton]

Originally posted by earossi
Arthur,

Can you explain the function of the SOV you mentioned above?

TIA

Sure..
The egr needs some vac applied to it in order to open..
So, that plastic line up front that I mentioned earlier supplies some engine vac to the egr SOV . The SOV is simply an air flow valve [ in this case -vac flow] that opens when an electrical sig is sent to it from the ECU [ telling the valve to get some vac over to the egr.]
So, the system works like this :
ECU decides it is egr time , sends 12 volts over to the SOV. That opens SOV [ solinoid/coil/plunger arrangement all contained in SOV] and allows engine vac to pass through the SOV to the egr
[ through the small line you referred to before]...
So, this is how the ECU "CONTROLS" the working application of the egr ..
When the vac gets to egr , it pulls a diaphragm up and that opens the egr , allowing exhaust gases to recirculate back to the intake side of the engine.
That's about it....
The reason we apply eng vac to the egr valve with a hand pump to test it is b/c this ELIMINATES the CONTROL system of the egr circuit and narrows down the diagnosis from controls to EGR and plumbing..
It takes both to make the entire system work, and any one defect will throw the CE/EGR fault code...
A little more info for all interested.....
How does the ECU know it is time to CE/fault the system..????
Well. there is a little engine vac reader in the diagnostics system that , when ecu is sending its electric sig to egr , it also looks for a vac differential spec. If it see no change/little change, it knows something is not working..
So, is it just plugged at the tube ,not allowing flow, or egr sticking, or maybe the SOV ain't [ boy, I hate that word] got no vac to it from the broken line , or mabe the connector is unplugged ..ETC.
That is where you and common sense come to the rescue...
Again, the more you know of how things work, the easier they are to figure out and fix...

[earossi]

Thanks to all who helped solve my problem. The culprit turned out to be the dreaded wiring harness. I Zeroxed a hand full of the threads from the archives and went into my dealer. Even though the car now has 150k miles on it, the dealership picked up the cost of the harness and half of the labor. So, I ended up paying for about 3 hours of labor. In the end, it was a great decision to let the dealer change out the harness. In ordering the new harness, they ran into a batch of harnesses that were in the correctly marked package, but which were not the harness for my car. Only on the fifth try did they get the correct harness!

Once installed, the car ran much better, and has picked up almost 5 mpg in fuel economy! I am still getting the code 5, indicating an issue with the EGR, so, I'll find time to perform the vacuum test on the valve and then "attempt" to clean out the EGR pipe.

Again, thanks to all.

[stevebfl]

it just so happens I was playing with that picture trying some paintshop image layering, this weekend.

The EGR blockage is in the intake manifold, not the EGR pipe. (see image). One of the most common problems is getting the vacuum lines to secondary air crossed with the EGR at the switch-over-valves.

[earossi]

Thanks Steve. What a great picture! A couple of questions. Is there enough flex in the EGR pipe to spring it away from the intake flange, as your picture shows? Second, is there a gasket between the two flanges? If not, should I use some RTV or Permatex?

Your last comment about getting the hoses crossed at the SOV between the fresh air and the EGR was interesting. Which line is which? As I recall the SOV, there is one vacuum line on the upstream side along with an electrical connector and two lines on the downstream side, right? If that is correct, why is that an issue. That may seem like a stupid question, but I am curious, and could have mistakenly crossed the two lines on the downstream side of the SOV.

[stevebfl]

There are two solenoids provided with one source. The two outputs go to the EGR and the secondary air cut-off valve.

The vacuum is switched at the times that each system functions which is totally different for each system. The sec air comes on cold and stays on for some period of time...no other control. The EGR does not come on cold, or at idle, or at full throttle. It is open all the warm running time in the lower partial load area and some into upper partial. So switching the output lines causes the systems to work i a way that the EGR is first to be faulted on as it is a continuos monitor. Secondary air is only monitored one time per drive cycle and then only if certain conditions exist.

If you look closely in the photo one can see a big black handled screw driver levering the pipe away from the hole. That is all that is necessary to get at the plug.

[earossi]

Thanks for the reply Steve. Can you respond to my other questions as well......specifically if a gasket is required at the flange where the EGR pipe meets the intake manifold. And, how to determine if I have the vacuum lines correctly placed on the SOV.

Thanks.