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  #16  
Old 02-22-2003, 12:36 PM
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Join Date: Sep 2002
Location: So. Calif.
Posts: 323
Quote:
Originally posted by pmckechnie
If the EGR valve has a small piece of carbon in the valve seat, it can cause
Poor idle
Unburned fuel from misfire
Rich mixture (the exhause diluts intake air, so less oxygen + same fuel = rich mixture)
Also it will cause a failure of the EGR valve. It is tested by closing the valve and checking the vacuum and mixture, then it open the valve and checks again. It should see a change. It won't if the valve is already open and stays that way.
SO replace the valve, clean out the EGR passages, and retest.


Paul
But these plug up not stick open
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  #17  
Old 02-22-2003, 03:29 PM
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Location: Southern California, U.S.A.
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Actually, the original EGR valves were defective and do stick.

There is a way to check if your EGR valve is not working due to a plugged up hot inlet pipe, or if the valve itself is sticking (open or closed):

The EGR is located on the exhaust manifold on the passenger side of the engine. There is a small vacum line attached to it which comes from a switch-over valve under the front plastic cover in front of engine.

The ECU sends an electric signal to the switch-over valve which opens the EGR valve to engine vacum. The vacum pulls open the diaphragm on the EGR, allowing some of the exhaust gas to recirculate back to the intake manifold (thus the name, Exhaust Gas Recirculation), reducing emissions.

The ECU will not send this electric signal at idle or wide open throttle, or until the engine has warmed up.
So, if you hand pull about 12" of vacum on the EGR at idle with a warm engine, you are creating a very lean condition (vacum leak) and the engine will attemp to stall and run very rough. This tells you not only that the EGR is opening, but also that the hot inlet pipe is not completely plugged up. If, when you pull vacum and nothing changes, then you know that either the valve is not opening up, or the hot inlet pipe is completely blocked.

Now, release the hand vacum and the EGR should snap shut. Engine should smooth out. If the EGR sticks in the open position, the engine will run rough at idle until the engine warms up.

There is another possibility that the diaphragm in the EGR itself may leak and cause an internal leak. The test for this is to see if the hand vacum will hold the EGR open for a period. It is common on vacum leaks to not be as noticeable with a cold engine as the engine is running rich and that helps off-set the added intake of air caused by the leak.

Since you are not complaining of an idle problem either when cold or hot, the EGR valve might not be functioning when in closed loop. It could be either stuck in the closed position or the pipe might be completely blocked.

By the way, I had this problem when I first bought my car, and Arthur Dalton walked me through this process. I first reamed out the hot inlet pipe, but the EGR code still came up. He informed me of the TSB on sticking EGR valves, so I replaced it with the new one, and problem went away.
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2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".
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  #18  
Old 02-24-2003, 04:54 AM
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Join Date: Jul 2002
Posts: 30
The saga continues...

I spent most of the weekend looking for the source of my problems. Found some interesting things, but not the solution. Need some more advice:

First went looking at the 02 sensor. The ECU is not supplying current to the heater, and doesn't appear to be reading the sensor either. The sensor itself tested good, but when I connected a 1.5V battery to the input and ground terminals going to the ECU, I didn't notice any change in the engine. (I understand the engine is supposed to go lean, to the point of almost killing it.)

So is this a bad ECU? I tested for continuity in the wires leading to the ECU, and they are all fine, so that isn't the problem. Do ECUs even go bad? Its all solid state electroincs...

Second, I went looking for my EGR problem. I removed the EGR tube at the intake manifold, and you wouldn't BELIEVE how gunked up it was. I took more than two inches of gunk out of there. It was completely blocked up, and probably had been for a long time. However, that didn't solve my idle problem, which (probably) means it didn't solve the emissions problem, particularly if the 02 sensor isn't being read.
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  #19  
Old 02-24-2003, 09:52 AM
inspector1
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Chris 17H,

First, they did not "PASS" your car for the $300 tune up, State allowed you to licence it, but it is still a "FAILURE" this is called a waiver. Wont happen this year though, rules have changed.

Second, 87 300e's EXCEPT for the 1.9's and 3.0's have EGR's.
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  #20  
Old 02-24-2003, 11:22 AM
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Location: SoCal
Posts: 1,303
"So you're saying the CO is caused by an excessively rich mixture; possibly caused by a bad 02 sensor. The hydrocarbons are caused by another problem, but probably not the EGR system. The other problem may be a misfire..."

Both high HC and high CO are caused by insufficient oxygen in the combustion, or insufficient oxidation in the cat. An engine running lean to reduce both also produces high peak combustion temperatures - and the result of this is an increase in NOx. The EGR valve leaks some exhaust gas back into the intake, and this reduces the combustion temperatures, and thus the NOx.

So, it is reasonable that the same source of your high CO is causing the high HC also. Find why your ECU is out of loop control, and that will likely sove your problem. Note that the O2 sensor is the primary feedback device, but the ECU will also not function if it can't detect engine speed, throttle opening, airflow or any of a select group of other input devices.

Steve
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  #21  
Old 02-24-2003, 05:16 PM
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Join Date: Jul 2002
Posts: 30
From reading the archives, I understand I can put a new catalytic converter in there to reduce the emissions, since (with 175K) mine is probably dead. However, W/O finding and fixing the source of the problem, the catalytic converter won't last, right? I'll have to put another one in there eventually, yes?

So, this brings up the question: does anyone know HOW LONG it will last? Six months? A year? Two? Five? Once again, my emissions readings are:

2500 RPM Test
HC PPM: 208 (should be < 130)
CO %: 1.15 (should be < 1.00)

Idle Test
HC PPM: 287 (should be < 100)
CO %: 2.65 (should be < 1.00)

I won't hold you to it, but any educated guesses?
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  #22  
Old 02-24-2003, 07:02 PM
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Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,316
I still think that you should investigate this from a misfiring angle.

Make sure that your ignition components are in good shape.

Put a fresh set of plugs in.

Spray some carb cleaner around the intake manifold and injectors and see if you can find a vacuum leak.

See if you can isolate the miss by "cracking" the lines on the fuel distributor one-by-one. If you crack one and the miss does not change, then you have found it. Replace the injectors and seals on the weak cylinder(s).
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Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #23  
Old 02-24-2003, 07:23 PM
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Guess I forgot to mention that earlier. I already went hunting for this. I replaced all the plugs a couple months ago (they have about 8K miles on them now) and sprayed starter fluid around this weekend. No vacuum leaks. I didn't check the injector seals, but it doesn't matter -- I've traced the problem to the 02 sensor not being read properly. Problem is, it looks like the ECU, so I don't want to go off and replace it.

Can I put a new cat in to take care of the problem? How long will it last?
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  #24  
Old 02-24-2003, 08:15 PM
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You may well have a problem with the sensor not being read properly. Your converter may be shot. Your fuel distributor may be hosed. Your ECU may be brain-dead. But more than likely, you have a fairly basic problem causing your rich mixture. In the absence of good information, I suggested some simple and inexpensive tests to try to rule out the most common problems.

But do go back and read Steve B's posts on the limitations of the O2 feedback loop before you buy a new cat.

And good luck, I'm outa here.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #25  
Old 02-25-2003, 09:10 AM
inspector1
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A well tuned engine should output about .5% CO and 50ppm HC, so as you can see, your vehicle has more than a little something wrong with it.

Things not yet mentioned concerning high HC readings: Base timing, advance/retard function,CPS, leaky injectors, vacuum leaks.

High CO:air intake restrictions: ie clogged AF, PCV, fuel delivery,EVAP system

Have you adjusted the CO setting?
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  #26  
Old 02-25-2003, 11:10 AM
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Location: SoCal
Posts: 1,303
Going back through posts I may have missed a reference, but if you have no readings at the O2 sensor, have you checked the OVP? If the fuse on top is blown, or the relay is bad, you will have no power to the ECU. Usually I think the ABS lite is on, but maybe not if you have the 2-fuse model.

Also, it is possible you won't have ECU functions if another input sensor - such as crank position, airflow, etc, were malfunctioning. I wouldn't assume the ECU is bad, under the circumstances you indicate.

Steve
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  #27  
Old 02-25-2003, 11:22 AM
inspector1
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Providing the OVP, etc is OK, I just ran across the following method to set A/F for the CIS using the CO screw.

I have not done this, however, the reference states to connect a dwell meter to the pulsed side of the frequency valve or duty cycle test terminal and select 4 cylinder ( typo? perhaps should be set to 6 cylinder?) adjust CO screw in AFM to arrive at 45* dwell.
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  #28  
Old 02-25-2003, 11:29 AM
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Posts: 8,508
His car is HFM, not CIS, and idle, etc. can't be adjusted. HFM fuel injection systems are designed so that idle speed can't be adjusted. Idle speed is completely controlled electronically.
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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".
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  #29  
Old 02-25-2003, 11:55 AM
inspector1
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Who's "he" I thought we were talkin about a 93 300E? Am I trippin? Thats not a CIS?

Thank you for the insight.
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  #30  
Old 02-25-2003, 11:58 AM
inspector1
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I see what I did, I replied to Chris17H, with a 87 300E, before, and got him and the other 93 300E mixed up.
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