Bizzarro OVP problem solved! - Page 3 - PeachParts Mercedes-Benz Forum

ctaylor738 · #31 10-21-2003, 09:00 AM

Dunno where I got it, but I always thought it was an early 300E.

And I recently sold my '86 300E, having spent a fair amount of time fighting with the injection. But I kept the CD.

autozen · #32 10-21-2003, 10:29 AM

Half the people on this thread are not reading the thread and adding to the confusion. Some are trying to solve Richard's problem wilth his 85 190E. Richard doesn't have a 190E. In fact he never said what he had until I posed the question. About 9 posts up from this one he states that he has a 49 state 87 300E. Also I believe the thread has switched from the original question posed by 69 and shifted to Richard's question about only getting a constant 90% reading istead of a 50% duty cycle reading. End of Cliff notes.

Peter

Gilly · #33 10-21-2003, 11:07 AM

Yep, I'll admit I was screwed up, I see it now.
I was screwed up from Richard28's first post, I guess since he said he had a "follow up question" I thought I was still dealing with classic69's 1985 190E, then totally blew off the one where he said he had an 87 300E. Oh Boy, sorry guys. I even went through LOOKING for a model listed other than a 190E and missed it. Of course up until 10pm last night, no one had a clue on what the new questions were about. It sure does help to have your year and exact model on your profile, maybe I could have been on track alot sooner.

Gilly

richard28 · #34 10-21-2003, 11:21 AM

Gilly,
I again apologize for not including in my followup questions the model/year, which wasted the time of you & the others. It won't happen again.
Sincerely,
Richard

Gilly · #35 10-21-2003, 12:59 PM

Richard
It would also help to include your vehicle description in your profile. Just simply put "87 300E", that's enough.

Gilly

richard28 · #36 10-21-2003, 02:46 PM

Gilly,
Based on CTaylor's post on 90% duty cycle, it would seem that the first step should be to test /replace the OVP since it powers up the EHA. Is this correct?

autozen · #37 10-21-2003, 04:49 PM

Richard,

You can change a lot of things that provide current, but if you take the time to read the earlier posts again you'll see that you may not even have an EHA current problem. If chuck read the year model right on his CD, 90% deals with EHA current. My Mercedes Benz factory code book published in 93 says 90% isn't used til 90 year model. You could also just have a dead O2 sensor that is reading lean. You could unplug the O2 sensor, go into open loop, and check the output of the sensor with a 10 meg voltmeter. If you read about .2 or .3 volts steady signal, that would send a lean signal causing the mixture to go steady rich at about 90%. We need to find out who has the misprint in their reference material and go from there

richard28 · #38 10-21-2003, 05:33 PM

Thanks Peter. I'm standing by. And sorry again for the earlier confusion.
Richard

AF300E · #39 10-21-2003, 06:25 PM

In my experience, if you get such a reading, you need o richen the mixture almost as far as you can using the lambda adjustment allen screw. They tend to jam at 90% if the mixture gets too lean (unknown why)

autozen · #40 10-22-2003, 09:30 AM

Got this reply in the techs only forum.

RPM55
Member

Registered: Jun 2002
Location: Cumming Ga.
Posts: 86

Tell him to try slightly pushing down on air flow sensor plate to see if readout responds. From what I've seen in the past the reading is 92% and an o2 sensor usually corrects the problem.

__________________
Mercedes Benz Master Tech

Peter

richard28 · #41 10-22-2003, 10:22 AM

Pushing the plated was suggested in an earlier post, and when I did it the duty cycle reading did increase immediately, to about 91.4%, before the engine shut down in what seemed like one second. So, summing up, since there was a change in the duty cycle reading, the problem is the constant false signal from the O2 sensor telling the EHA that the mixture is too lean, and by responding appropriately the EHA actually causes an overrich mixture which can't be effectively overridden by adjusting the mixture control screw. Thanks so much. I'll try to take care of this over the weekend and report back.

autozen · #42 10-22-2003, 10:27 AM

Richard,

Good luck and please be sure to post the results, because that will confirm a viable diagnostic tool for all of us.

Peter

sjsfiji · #43 10-22-2003, 01:46 PM

Hi All,

This was an interesting thread. Since I have an '87 260E, I was wondering where the "Duty Cycle Readings" and/or "90%, 100%,etc...) comes from. Is this from a multi-meter?

sorry...

thanks...

Gilly · #44 10-22-2003, 09:42 PM

From the O2 sensor

Gilly

autozen · #45 10-23-2003, 10:52 AM

Gilly,

That smart ass answer wasn't nice of you.

sjs from Fiji,

To answer your question, the % codes and duty can be read a couple of ways. Supposedly you can use a dwell meter, but I've never tried it. You can use a digital volt meter. If you can find an analog meter with an impedence of 10 meg or more, that would be excellent. You need extremely high o\impedence test equipment here for two reasons. The voltage signal is so low from the sensor that you can load it down and get incorrect readings. If you use a low impedence meter in closed loop, you can load and damage the computer. There are also special pieces of test equipment designed for o2 sensor circuit testing. that is what I use. Maybe others on this thread can let us know what they use.

Peter

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