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  #1  
Old 08-13-2003, 07:07 PM
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duty cycle readings on 87 300e

I have recently read on these posts that on the old 300e, esp 87/88, the cars have limited diagnostics on board, so I won't get the 70% reading with engine off, key in position. However, on my 87 300e & 88 300ce can I use the favored Sears multimeter I bought to adjust the CO to the 50% range, or is this done some other way? On my first try on the 88 300e, I seemed to have leaned the mixture based on the sound but the readings stayed at between 29-38% regardless of the direction I turned the screw (I'm assuming I actually engaged it, but this is the first time I did this, so I'm not positive). Thanks for your help.
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  #2  
Old 08-13-2003, 07:18 PM
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I use my 70's vintage analog dwell-RPM-voltage meter to check mine, using Pin 3 on the diagnostic socket, so your advanced technology should work.

If the older cars detect a fault, you get a constant percentage reading, and there is a table to decode it in the manual. If the reading is fluctuating, then you should see a change as you diddle the mixture. You should not have to turn it very far to see a change.
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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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  #3  
Old 08-13-2003, 09:54 PM
J.HIDALGO's Avatar
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You actually have to push down...

you will feel the screw engaging and the change in the engine speed will be inmediate. Which screw are you turning?
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J.H.
'86 300E
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  #4  
Old 08-13-2003, 10:27 PM
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The correct screw is under an antitamper plug in the little "stalk" that sticks up between the air flow flap and the fuel distributor. You will need to remove this plug if no one else has, and I don't remember how.

It is spring loaded up, you have to push down with a 3 mm allen (or is it 4? ) to engage it in the actuall screw on the fuel distributor.

With a long allen, you can make this adjustment through the hole in the top of the air filter housing -- this should give you a clue as to where it is.

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #5  
Old 08-14-2003, 11:30 AM
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Thanks, guys. I didn't know the screw engaged another screw in the fuel distributor, so I probably was just turning air. I'll try to adjust it again & will report back. I keep learning from you all, and not only have I saved a fair amount of $$ but the fact that I have learned how to do these things is priceless.
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  #6  
Old 08-14-2003, 01:37 PM
inspector1
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I applaud your efforts, if it is of value here is the procedure for setting co:

1. Disconnect O2 sensor at plug under vehicle. Observe voltmeter reading ( reference does not say where the VM is connected to ) needle should be steady. mark with tape on face of dial, this is the 50% duty cycle reading.

2. Reconnect O2 sensor. The needle should vibrate and should be centered around tape mark on VM ( 50% =/- 10%) if not THEN adjustmetn is nessary

3. Remove plug from mixture control unit. Insert 3mm. allen had wrench and adjust A/F mixture screw by pushing down until the srping loaded adjuster engages with the adjustment screw in theair flow sensor arm. Pushing down on the adjuster will alter the A/F reading somewhat so after each adjustment , disengage adjuster and rev the engine slightly to allow the sensor plate to normalize before checking meter reading)

4.Adjust until the needle is centered around the tape mark on thhe VM dial. ( 50%)

5.remove test equipment and replace the plug.

I hope this helps.
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  #7  
Old 08-14-2003, 01:45 PM
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Thanks, Inspector. I am planning on using the duty cylcle of the multimeter & adjusting based on information steveb has posted before, esp in the DIY on engine management controls. Therefore, novice that I am, I don't understand your references to disconnecting the O2 sensor & voltmeter readings. Thanks
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  #8  
Old 08-16-2003, 12:18 AM
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Help; What does this mean?

OK, courtesy of the Blackout I had some time today, so I hooked the multimeter to the 88 300ce. Key on , engine off, it duty cycle read 100.0%. With the engine running at operating temp, it read the same-100.0% Since there was no fluctuation, I believe that is a fault code. Does anyone know what it means & what I should do next? Thanks for your help.
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  #9  
Old 08-16-2003, 12:00 PM
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Unless you have the probe in the wrong place, it means you have no cycle, just 12V on the signal line, probably indicating an electronic failure.

Steve Brotherton will know far more than I.

Check you connections, but if you indeed have 100% all the time, the electronics aren't working.

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #10  
Old 08-16-2003, 01:39 PM
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From the CD:

No voltage or ground at KE control unit or KE control unit faulty
Lambda setting too lean
O2 sensor faulty (short to ground)
OVP relay or fuse faulty
Lambda control tester faulty

IMHE, what is mostly likely happening is that your sensor is not sending out any voltage which the system interprets as lean and has gone to full "on" trying to richen it up.

You can unhook the sensor - it connects under the carpet in the right front pass compartment near the trans tunnel - and meaure the voltage from the sensor to ground, with your new Sears DMM.
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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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  #11  
Old 08-17-2003, 02:37 AM
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Thanks. Chuck, the OVP is good because I swapped it. The O2 could be the culprit. Could you explain where I place the DMM probes to read the voltage sensor to ground after I disconnect it at the pass.compartment.
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  #12  
Old 08-17-2003, 07:19 PM
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Worse than expected

Today I found the O2 sensor under the pass seat was not connected, so I did that. Reading unchanged & fixed. What to do? I started examining the part on the driver's fender into which the probes get inserted. Looking carefully, I only saw a metal connector in hole #1. There was no metal receptor in the other holes; & when I examined the black feeder, with the four wires inside, I found the wires were completely unattached-their ends had been cut off & when I popped the top plug there was only the connector for #1 - everything else was empty of connectors & wires. (The connectors & plug for the three holes in the semicircle was OK). That explains why I had no readings. This now seems to be way beyond me, but I could be wrong. Can this be fixed/rewired & connected, do I go to a good indie or dealer, or should I let it go? How can mixture be set now?
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  #13  
Old 08-17-2003, 10:12 PM
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Ouch.

You can check the current to the EHA with the test harness. See this thread for details:

Power ONLY at Full Throttle

You can also try finding a place to connect directly to the wire that runs to the test socket. The ETM shows it as .75 blue/white.
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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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  #14  
Old 08-18-2003, 02:04 AM
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What runs to the test socket are four separate wires wrapped in a black plastic sheathing. Late nite idea-I also have a 91 300e (recently totaled) & I've popped the cap on the test socket & I can clearly identify the wires & their respective positions & insulation colors. I'm going to see if they match up with those on the 88 300ce pins 2 & 3, & if they do I'm going to use the probes directly on the ends of the appropriate wires. If they are different, Chuck is there any reason not to just see what happens trial & error since I know that if I find two wires that give the 70% duty cycle reading indicating that the O2 sensor is OK, then I've found the wires for pins #2 &3.

Last edited by richard28; 08-18-2003 at 02:20 AM.
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  #15  
Old 08-18-2003, 09:44 AM
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I think if you connect your leads to blue/white and brown, you are good to go.
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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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