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.

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.

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?

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

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.

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.

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

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.

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

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.

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.

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?

Ouch.

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

http://www.peachparts.com/shopforum/showthread.php?threadid=54239&perpage=15&highlight=102%20AND%20589&pagenumber=1

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.

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.

I think if you connect your leads to blue/white and brown, you are good to go.

#2 is a ground, you can use any convenient ground (as in the engine block or manifold).

I guess not having the duty cycle meter connected due to having the wire pulled out would work very well.

I don't really want to know why anyone would pull the wires off the diagnostic plug.....

Peter

We did it
 

Chuck, the blue wire was the hot one. I cut off about 1/4-inch of the insulation to get a good, clean contact, I confirmed the O2 sensor with a 69.3% reading & was able to adjust the warm engine readings of apprx 65% to appx 50% with a very small turn of the screw. The car purred, with no shakes or missing feeling. And it was quick and smooth from a dead stop, I couldn't believe it was a 1988 300CE!! When done I separated all the wires from the blue one by putting them into a short piece of plastic tubing & then wrapped them all, including the blue, in electrical tape to keep them clean & away from everything else.

Thanks to both Chuck & Peter for your time & sharing so generously of your knowledge. The people like you who reply on this board make it such an unbelievable resource.

Now, on to the next problem...the neutral safety switch on the 87 300e ( to be posted soon)

swapping parts from a totaled 1991 300e
 

We had an accident with our 91 300E & the car has been declared a total loss. I also have a 87 300e & a 88 300ce. What parts from the 91 should I swap into the older cars, assuming the part numbers are the same, to try to prolong their lives & avoid future repairs? Thanks for your thoughts.

I would definitely keep the Fuel Distributor, it's easy to remove and costs a bomb new or used.

My 2 cents.

Cheers.

Thanks for your reply; this was supposed to be a new thread but I guess I messed up.
Could you explain how to remove the fuel distrib; I've never done that . What about the starter, which I can't seem to find. Is that an easy DIY? Thanks

Here you go...
 

Remove the air filter housing to gain access to the FD.

Fuel system has to be de-pressurised if it hasn't (if the car hasn't been run for awhile there will probably be no retained fuel pressure).Remove gas tank cap to be sure.

To remove the FD firstly involves removing the fuel line unions at the distributor itself - going to the injectors, fuel pressure regulator, cold start valve and fuel supply line.

You need to use open end spanners for each fuel line.

Expect a little fuel to spill out from these lines when you crack them open.

Unplug the wiring harness connected to the EHA valve (black box attached to the side of the FD).

Then you have to slacken and remove 3 Torx bolts which hold the FD down to the Air Flow Sensor.

The FD can be removed once the Torx bolts are out.

There is an O-ring seal between the FD and the Air Flow Sensor.

If you re-fit the FD, fit in a new O-ring seal.

I think it costs less than a dollar on the Fastlane.:D

You will save a bomb if you ever need to replace your FD.

One question - if the car is written off, can you salvage bits from it or do you have swap them part-for-part from your other cars?

Cheers.

Mostly, I'm swapping minor things, like steering wheel (on the 87 the srs light sometimes comes on, even thou I've cleaned the contact rings), with the older 87 & 88, but it so happens I have a suspect fuel distributor from a previously owned 300e, so I thought I would take out the good one & reinstall the suspect one, that way I way have a good spare. I'm really glad you confirmed my idea by recommending swapping the fd. Thanks again for the easy to understand removal directions.

BTW, do you know how to drain the gas tank, it has almost a full tank.

Rich

duty cycle reading on 88 300ce
 

Chuck & Peter, I need your help again. Just had neutral safety switch replaced because car, 87 300e, had died. Tested for CO adjustments- got 90.5 fixed with key on, engine off. Disconnected O2 sensor & attached to a new one in the box. Same reading. With engine on, fluctuations on meter only between 90.1 & 90.8 & no meter changes as I adjusted the screw & the engine got lower in sound & smoother. Wires appeared connected in tester. Now what?
Thanks
Rich

Draining gas tank
 

Rich

The only way I know of doing it (with reference to my trusty Haynes manual) is by siphoning off (or handpump) the fuel via the filler neck.

Cheers.

You are having your share of troubles.

The manual says "Current to EHA implausible." That is not one that I have seen. It sounds like the ECU is getting a set of inputs and is being asked to send a current level to the EHA that is out-of-bounds of it's program.

The only thing that I can think of is that either the decel micro switch or throttle position sensor are bad and they are sending signals that the ECU recognizes as inconsistent. Not being able to figure it out, it shuts down and sends out a constant 90%.

Wish I could help more, but the manual does not give a remedy for this one.

Maybe the techs have seen this one before and can help.

Bad O2 sensor will give you a fixed 50% (open loop mode) signal on the #3 connector.

90.8 with key on, engine off, is a diganostic, indicating electronic problems, I suspect. Steve Brotherton will probably know, but it may be computer time (OUCH). If the computer is buggered, no way you are going to get the mixture set correctly without a CO meter, and you must get to the exhaust in front of the cat....

Can you check the EHA current? This will tell you if the system is working at all -- 0mA means there is no control current being produced.

Check the OVP relay if you haven't -- is you ABS or SRS light coming on and off while you dirve?

Also, check for a good ground for the fuel computer -- if it isn't grounded correctly, it isn't going to work worth diddly.

Peter

Peter

Curious, if there is 0mA EHA current when it's connected to the FD, should the OVP be checked first?

For what its worth, I disconnected the O2 sensor & tested the vehicle connector. At the pin in the square plastic side, it measured -.04mA with key off, and resistance of 11.2 ohms--I did the same resistance test on the 91 300e with the good sensor ( 70% duty cycle with key on, engine off), & got .74k ohms, obviously a different reading. Does this help identify the problem?

I have never tested at the EHA, so if you would be kind enough to explain where to place the probes & what setting I use on the DMM, I can do it. Also, which black box behind the battery is the computer? Is the ground near the negative on the battery? If the computer is bad, I could swap it for a good one from a 91 300e recently totaled (same for EHA, if that is advisable). Thanks for your continued help-the good news is that the 300ce I adjusted with your help runs just super.

BTW, on this same 87 300e I unplugged the instru cluster to swap the outside temp LCD & while pulling it out I seem to have disconnected a vacuum hose ( I hear the telltale hiss, which wasn't there before) , & I can't see or figure out where it goes. Do you know? Thanks

The vacuum line goes to the "economy" guage in the cluster. Connects under the hood right next to the brake booster.

Peter

There are two connections on the EHA - power and ground. You can measure the current by pulling the connector off just a bit and using the mA setting on your Sears DMM. If you search on my recent posts, you will see the readings that I got and their interpretation by the experts.

Thanks Peter. At least that will be an easy fix.