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Discussion Starter #1 (Edited)
Hi everybody,
I have 1995, E320 (180,000 miles) and it just failed smoke test because of higher Hydrocarbons (68), and the limit is 53 HC. The car is running like a charm, exactly like 15years ago when we bought it.
I did a Tune-up about a month ago, new spark plugs, cables and replaced one coil that was bad in that time. The oxygen sensor is about a year old and the Hydrocarbons are running “68” which doesn’t seem that high anyway, because in 2006 the maximum limit of the HC used to be” 81”, and the car passed with no problem. But since then the state of California lowered the Hydrocarbons limit, and my car doesn’t pass the smog test anymore.
The only thing I did find is that, the vacuum valve that operates EGR valve is not getting ground and therefore EGR valve does not open.
What actually triggers the vacuum valve to open?
Does anybody have wiring diagram of the EGR system?
When does the EGR valve suppose to open?
Any ideas?
Thanks in advance. Jan
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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A couple of things to check first.

1) Check that the EGR itself is functional. With the engine running, attached a vacuum pump w/ dial on the EGR. With you apply vacuum with the handpump the idle should start to stumble slightly. If there is no change, the EGR itself is bad.

2) Another thing these late W124s are prone to doing is clogging of the EGR tube that runs from the EGR valve back to the intake manifold. Seen it many, many times. If you have a code 5 (EGR low flow), 90% it is being caused by a clogged EGR tube vs. a bad EGR valve.

3) Make sure that all your ignition components are good. The coils are a wear 'n tear items and should be replaced with the spark plug wires, coil to plug boots at least every 100K miles.

4) It is critical that you use the proper non-resistor copper core plugs. No platinum, iridium, etc.

5) If you still have the original eco junk engine wiring harnesses, it will mess with your engine ECU and your head until it is replaced.
 

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money pits of various forms
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I was going to say, this sounds like a plus not a minus!
 

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Discussion Starter #5
Thanks for your comments.
EGR tube is clean and the EGR valve is functional, I checked it with vacuum pump.
I am not getting vacuum from the switchover valve to turn on the EGR valve. And the reason being, because the switchover valve doesn’t have a ground. The hot wire is alive but the ground wire is dead. I guess this valve is controlled by the ground from the computer or somewhere else. The wiring harnesses was replaced some time ago but it has been few years.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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Have you verified the switchover valve is functional and all of the engine ground straps are all in place and solid??? The strap between the A/C compressor and driver side frame rail is especially critical.
 

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Discussion Starter #7
Thank you all for your inputs.
Yes, the switchover valve is functional. I ran new ground wire and the valve opens. I just don’t know what controls it. Apparently the valve is controlled by ground from somewhere. Does anybody have wiring diagram of the EGR system?
Jan
 

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1992 300ce, 3.0, 207,00 mi.
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Normally a problem with the EGR system results in high NOX. I believe you may be due for a new cat.
 

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Discussion Starter #9
I am afraid you may be right. That’s what my friend (mechanic) also recommended. I guess I am barking at the wrong tree. According to my friend EGR valve opens somewhere between 1500 -1600 RPM and doesn’t do anything at idle. He also recommended to really warm up the cat before the test and even keep it running about 2000 RPM just before the test. Apparently these cars are notorious for Hydrocarbons right on the edge.
Thanks everybody.
 
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