300E: test sticks on 10% duty cycle - Page 4 - PeachParts Mercedes-Benz Forum

Chris Martens · #46 04-30-2003, 10:09 AM

moin,

some results from the other side of the world...

The part is available in Germany, we are planning a group buy (spelling?) for 51 Euro / USD 51 plus porto and package each. Anyone interested? Send me an email concerning "LMM-Poti Bestellung", that includes you complete name and the delivery address.

I made a post in my favorite W124 board, listing some links to the W126 board, where we discussed this topic.
In case you need translation, try http://babelfish.altavista.com/

best regards,
Christian

1989 300TE

#47 05-05-2003, 06:32 AM

This chapter concludes with the 300E purring at idle like the well-behaved creature Mr. Benz intended.

Adjustment turned out to be a non-event.

I hooked up the duty cycle meter, as well as a multimeter on the EHA. I richened the mixture until EHA swung between roughly -1 and 1 at closed loop, at which point the duty cycle meter swung between around 46-52. Idle on the dashboard tach looks like 750rpm both on start, after idling for 15 mins, and on return to idle after opening the throttle to around 2000.

Although I may revisit this after I deal with some more pressing problems, I saw no immediate need to do any calibration on the pot housing. It just runs too good.

I can now start the car thru the drivers window. Once. No more start, it dies, start again. No need to press the gas pedal.

In 4 or 5 trips to the local town, (total maybe 50-60 miles) the car has yet to drop below around 600 RPM at any stoplight. Has not stalled yet.

There has not been one instance where the idle has spontaneously risen into 4 digits.

I do have one question...after arriving at a destination and putting the shifter in park, idle holds steady at around 1000rpm. Is this by design, or is this something I should adjust out?

I got some marginal results on the compression test, but that is another post...

Chris Martens · #48 05-05-2003, 07:09 AM

>This chapter concludes with the 300E purring at idle like the well-behaved creature Mr. Benz intended.

congratulation!

>Adjustment turned out to be a non-event.

That means, you didn't adjust anything? mhhh...

I did the change of the potentiometer yesterday and didn't have much time for testing yet.

IMHO you have to calibrate the potentiometer. Voltage between pin 1 and pin 2 should be at 0.75V +-0.25V at idle.

Calibration of the lambda (EHA or pin 3 of X11) has to be done afterwards.

>I can now start the car thru the drivers window. Once. No more start, it dies, start again. No need to press the gas pedal.

That is the same I recognized yesterday, immediate start when warm on the very first revs of the starter. great.

>I do have one question...after arriving at a destination and putting the shifter in park, idle holds steady at around 1000rpm. Is this by design, or is this something I should adjust out?

As written before, you should check the adjustment of the poti. Very very small movements will lead to significant changes in the voltage. I had the same high idle before adjustment... and got a constant 10%-fault at pin 3 of X11.

How much did you pay for the potentiometer?

bis denn,
Christian

1989 30TE

#49 05-05-2003, 01:52 PM

Christian,

I paid 65.95us including shipping.
I will check the voltage and adjust.

Did the rubber plug that covers the adjustment screw on the old pot disentegrate when you removed it? What do you intend to use as a replacement?

Chris Martens · #50 05-05-2003, 03:19 PM

hi,

>I will check the voltage and adjust.

I'm awaiting the results!

>Did the rubber plug that covers the adjustment screw on the old pot disentegrate when you removed it?

That "plug" didn't look solid so I didn't try to pry it out.

>What do you intend to use as a replacement?

I think, I'll cover the screw with some silikone sealant.

Did you remove the fuel pressure regulator to get access to the lower right screw? I didn't find another way...

So for adjustment that lower right screw must be a bit loose to have the engine running (with installed pressure regulator) while slightly moving the housing. What do you think?

bis denn,
Christian

1989 300TE

pesuazo · #51 05-05-2003, 04:36 PM

Congratulations on a Job well done!!!

The replacement of the potentiometer should be turned into an article in the DIY section.

Hmmm? idle at 1000 RPM?

Have you ever tried to remove the idle control valve and clean it with carburetor or brake cleaner? It worked great for me.
That's my suggestion to complete the job.

Thanks for keeping us posted.

#52 05-12-2003, 05:50 AM

Chris,

Thank you for prompting me to adjust the pot.

I installed the housing with the air meter out of the car, so did not have the problem with the fuel pressure regluator. I tightened up the housing and am trying to adjust only by turning the tiny brass screw on the side of the housing. I am using a 2mm jewlers screwdriver; wish I had something longer. Even after unbolting the wiring harness tray, it is a pain to get at.

I did have some unexpected results in attempting to adjust. I say attempting because I am not sure if I have adjusted it or not.

I removed the connector, wrapped two pieces of wire around pins 1 and 2, and reinstalled the connector. I clipped my multimeter to the two pieces of wire.

Voltage ranged from about 1v at startup to around .25v at operating temp. I did not attempt to adjust until operating temp. When I did try to adjust, it seemed that turning the screw on the pot had no effect on the voltage. Maybe I did not turn it enough. I was expecting a couple of turns to make a visable change on the multimeter.

I turned off the car and checked the voltage with switch on engine off. (pins 1 & 2)
It sat at .075v. I turned the screw clockwise maybe a turn to .080v, then turned the car back on, and voltage was around .62v. Once again, turning the screw seemed to have no effect with the car running. I turned the car back off and turned the screw clockwise many turns until it was at .2v key on, engine off. Turned the engine on and voltage is still +- .62v.
Clockwise seems to increase the voltage with key on engine off, but I thought I would post and ask about your results before I turned the screw many more turns in an attemt to get running idle to .75 volts.

The .62v is within spec, but my idle is now pretty close to 1000rpm.

I will also check the voltage between pins 1 & 3 next time. The CD says lists 'start' as the operating condition for this test. The other couple of times this requirement is listed it seems to indicate immediately after the car is started. Does this sound right?

stevebfl · #53 05-12-2003, 07:49 AM

I hope you figure this all out.

I have been working on this system for years and nowhere was anyone dealing with this. I mentioned that we were told of the adjustment pot but I doubt that we were told what voltage to set it to. I have learned more in the last 6 months about this than maybe the other 19 years since the KE system came out with the 190.

So, I probably can't be much help here except to remind that the voltage is due to the position of the airflap. As the idle valve changes airflow the plate moves. I attribute the difference between the cold and warm values to this difference in airflow.

An idle of 1000 rpms is too high, so you have a problem. From these discussions we have figured that the idle strategy of closed loop rpm control does not start till the AFP (air flow pot) voltage gets below some value probably .75v. Did it happen? This is where diagnostics and learning have a lot in common. How would we know; no scanner to tell us the control unit recognized closed throttle position (CTP)?

What does control look like? Control is done by pulsing current through the valve. Different current different airflow as the valve moves. This is best viewed with a scope while calculating duty-cycle. So at idle the current if measured with the same harness as EHA should be about 600ma. Turn on the A/C you get another 50ma from where ever you are in control. If you have an airleak and the valve is commanded totally the current could probably reach an amp; I have seen .9a+.

What you will see on the scope or duty cycle is the relative amount of ON time. The maximum duty cycle used is about 70%. So if you find the valve in 70% control it likely is doing all it can to shut down incoming air. If in doubt shut down air until the control duty cycle moves. Think about that one for a while and think about getting the airflow down before you worry too much about adjusting the AFP.

Hurshi · #54 05-12-2003, 11:48 AM

After adjusting the potentiometer my car is now keeping the idle correctly till it warms up to 60 degrees C . After that the idle is surging every 3-4 seconds from 800 rpm to 1200 rpm. It seems like somebody is sitting inside the car and pushing gas every 3-4 seconds.
I have removed my car's idle valve to take a look and clean it but didn't understand how it works. The shops around here don't sell a carb cleaner but they have an injector cleaner that you add to the gasoline.
My question are as follows:
Can I use an injector cleaner for cleaning the idle valve?
When there is no current applied to the idle valve does it stay open or closed?
What should happen when I apply 12volts to the valve and what does an adjustment screw on the side of the valve do for the valve?

stevebfl · #55 05-12-2003, 12:45 PM

With the electric plug off the valve stays at an openning that would run a car about 50rpms greater than would be had if the idle was controlled normally in neutral with the airconditioning off. If this were the case the A/C would then drop the speed (at the fixed volume) to below normal speed and then when put in gear it would be real low.

You need to think of the volume of air needed. If you shove a cork into the valve and drill a 4mm hole in it the engine should run at a little faster than the valve unpowered. (Maybe it was 5mm). That is the size of the openning and a way to verify the proper outside air intake. If you stick this cork in it then it better run at less than 900 or you have air coming in somewhere. Air equals engine speed.

Hurshi · #56 05-12-2003, 03:10 PM

Steve, thanks for the quick answer.
I didn't know that with the electric plug off the idle valve a car would run at about 50rpms greater than usual. This was an important thing to know for correctly adjusting the idle valve.

Below is my understanding of the air valve's operations.
The air control valve stays partially open when disconnected and with a little current it fully closes the air passage. Then, with even more current it partially opens again, and at full 12 volts it open up widely. In the picture below you can see how it happens. The red mark is what blocks the air inside the valve. It move to the left as more voltage is applied. I think the real idle control should be happening at the stage 3 in the picture below.
The screw on the side of it should regulate the amount of air passing through it when it is disconnected.

Can you explain the difference between a carb cleaner and injector cleaner and if the second one can be used for cleaning the valve?

Hurshi · #57 05-12-2003, 03:26 PM

I might be wrong when saying applying 12 volts to the idle control valve should fully open it because in earlier message you wrote at it's max duty cycle the air valve shuts down the incoming air.
However, when I applied 12 volts to my car's idle control valve the engine rpm increased considerably.

Hurshi · #58 05-14-2003, 08:57 AM

After adjusting the idle control valve I was able to fix the problem of irratic idle. The idle valve was set to let through very little air when disconnected and that was resulting in idle of 500-700 rpm. After reading Stevebfl's post that when disconnected the idle valve should run the car at about 50rpms greater than usual I adjusted the screw on the side of the idle control valve so that it would supply more air. Then I restarted the car and the problem was gone!
This is a very good forum! I used to drive with a potentiometer disconnected because it used to give bad reading and the car used to stall. To fix my car I didn't even by a new potentiometer. After reading this thread I unscrewed the potentiometer's 4 screws and moved one of the touching arms(wipers) that touch the potentiometer's resistor surface so that the arm would stay on the right track. One of the arms was bent to the side and was causing drops in readings. Then I adjusted the potentiometer by slowly moving it's right side up and down to supply about 0.75 volts(pin 1-2) at normal idle. After that my car was idling but it was an irratic idle and I solved it by doing the things I described at a very top of this message.
I don't know how much money I saved but I saved a lot!
My car is now idling! Thanks to everyone who helped especially to stevebfl and zhandax.

Hurshi

WANT '71 280SEL · #59 06-12-2003, 12:03 PM

I have all those same problems. I have cleaned the idle valve at least 3 times with carb cleaner. The adjustment screw on the valve that you guys talk about, is it a hex screw? Mine is mostly stripped out. When adjusting the screw should the car be on or off? When I pull the wires off the idle valve the car fluctuates at 500 rpms. That is 100rpms slower than normal.
Thanks
David

WANT '71 280SEL · #60 06-12-2003, 12:18 PM

I am getting ready to buy that housing from olypy parts. Should I just have my mechanic install it since it sounds like you really need to know what you are doing, and need to fully understand the KE injection system? If it was just a drop in and screw thing I could do it but when it comes to electronic diagnostic equipment, etc. I am lost. I had those same symptoms as the starter of the thread had so I believe that this will probably solve the problem.
Thanks
David