My '91 124 is giving a code 16, which is EGR. I checked the EGR valve. It holds a vacuum and moves. However, I do not get any RPM change when I operate it with vacuum while the car is idling.

I suppose that means the pipe is stopped up.

We have no inspections in my state. If you can roll it into the street, you can drive it.

Does this thing serve any purpose? Do I care that it is not working? Is it worth cleaning it out?

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2012 E350
2006 Callaway SC560

Reduces NOx by reducing combustion temperatures.

The newest MB engines don't use EGR.

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
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44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

How do they handle the NOx ?

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

NOX is produced under hot combustion (inner-cylinder) temp. Exhaust gas, considered inert, when directed into the intake actually lowers the overall combustion burn temp. Therefore less NOX at the tailpipe.

The EGR valve opens when a control solenoid is energized. The conditions are when the engine is not idling or at wide open throttle. The check engine light will come on after several attempts monitoring the EGR function and it detects errors.

The computer requests EGR and fires the solenoid. Vacuum opens the valve and exhaust flows into the intake. The RPM should drop slightly when this occurs. No RPM drop - flag failure.

You could roll with it plugged or blank the EGR off but increased combustion temp. over an extended period may introduce problems. Mine seems to run as well in or out of circuit. I've have it in because I wanted to retain the Check Engine Light function. You'll either have to reset it constantly or pull the bulb. There's no way to trick the computer into thinking EGR is working.

My guess is they use a variable exhaust cam, like some other engines use.

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95 E320 Cabriolet, 159K

That is correct..double constantly variable cam timing on the M271/272/273 & M156 engines.

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

On my '90 300E I have a leaking EGR diaphragm so I just pulled and plugged the vacuum line. Never have gotten a CEL. Is there a difference in these two cars? I have run almost 2 years and over 40K miles and never had a problem with no EGR. My question is how does the system know the EGR is working or not? The rpm drop doesn't make sense because at speed it wouldn't behave the same as at at idle.

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1983 M-B 240D-Gone too.
1976 M-B 300D-Departed.

"Good" is the worst enemy of "Great".

The 90 may not flag every stupid emission error and may not be looking at EGR function. I had the idea of blanking mine but could never find out if the Euro spec 3.2 had them or how to bypass the detection method.

The only way to poll EGR to see if it is operating would be detection of RPM when pulsed. I read this somewhere but can't find it. I agree it doesn't make sense when driving as the throttle is always changing RPM. They described the method it uses EGR as pulsed not always just on or off. There was something like it checks every X amount of minutes when under run condition. Seemed like after a reset it took 2-3 days of driving to trip the CEL when not operating. It must not be too aggressive of a test.

Think about detection. There could be a switch on the EGR when the valve opens, the switch makes - none. Temp sensor at the EGR inlet on the intake sensing exhaust stream temp - nope. Could this be magic?

Emmissions EGR fault detection is checked by intake manifold pressure sensor [ B5/2] monitoring by the N59 Emmisions Module. If it does not see the required spec. pressure change when EGR Switch-Over-Valve is energized by HFM CU, it triggers the code.
So, on HFM/SFI, an EGR code can be caused by anything from a simple feed line vac leak, SOV, egr, clogged intake tube, .. and on the demand side , a No Electrical Sig from Control Unit.
Always start with the simple test first. [ which is hand vac pump test at idle, right at EGR]

So if an old 110 engine w/flat pistons has a blanked EGR & no cat, would it not have a lower Cylinder-head temp than the Euro version w/domed pistons, no EGR & no cat?
And we are assuming that hot exhaust gases are taking the place of a greater amount of cooler non-EGR mixtures that have a higher potential for combustion. So isn't it a wash w/ or wo/EGR?

This car does not appear to have EGR:youtube 124

Arthur, how do the CIS cars poll the EGR for faults?

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2012 E350
2006 Callaway SC560

The 1990 & later California versions (CIS) used the MAP sensor that built into the EZL to monitor vacuum changes & turn the check engine lamp ON.

There is constant data exchange between CIS & EZL on those cars.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Trouble with these owner sites is bad information. I never liked the RPM detection for EGR functionality. It seemed like a reach.

Mr. Dalton nailed it. Manifold pressure monitoring - cool! I've read considerable (user) info looking into defeating EGR. None of it was correct. The tuner crowd buy programmable modules where they define ranges for EGR to turn on. Like when the engine reaches 300 degrees or when it hits 240 mph. Basically, a simple parameter (in outer space) allows you to blank them off and never trip a code.

Wish we had those. Blasting exhaust into the intake just sounds wrong.