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  #16  
Old 07-13-2002, 02:05 PM
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Memory???

Bad OVP, going bad over time and the fuel computer continually adjusts to keep the car running. Until the old OVP is completely shot (although I do understand electronics tend to go out at once).

Now pop in a new OVP, the fuel computer has memory, trying to feed input according to the memory of the bad OVP resulting in running worse with the new OVP installed. Needs time to reset the memory.

Best guess.

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'73 280SEL 4.5 (9/72)- RIP
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  #17  
Old 07-13-2002, 02:30 PM
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Just for references, heres the star of the show;
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Help!! Need OVP plug schematic!-.jpg  
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  #18  
Old 07-13-2002, 02:31 PM
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and the other side;
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Help!! Need OVP plug schematic!-b.jpg  
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  #19  
Old 07-13-2002, 02:43 PM
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Steve - I have just read your "challenge" - been outside installing a replacement window in the right rear door of a 300SD for a friend (made $50 - took 2 hours ).

Anyway, I know a little something (very little) about industrial controls and instrumentation (I know ALOT about pumps and pumping systems) my GUESS would be that a new - "good" working OVP relay could possibly put the correct voltage to a bad idle speed control valve which could possibly prevent the car from running the way it should. Just my GUESS

I'll bet the majority of diyer's on here thoroughly enjoy this type of "challange", I know I do. First prize should be a free tour of Continental Imports in Gainesville, Fla whenever the winner is in Gainesville.
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Last edited by engatwork; 07-13-2002 at 02:48 PM.
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  #20  
Old 07-13-2002, 02:47 PM
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Eng
Your E320 has an OVP and one of the original problem ones...

Might want to see if you have the upgraded one..
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  #21  
Old 07-13-2002, 02:47 PM
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Real close Mike, actual you have the right answer for some of the wrong reasons.

This system is too stupid to make its own adaptations. It only works from real time.

Since you really have it, I am going to paste the reply I have already written. It can then be discussed. The good topic will be how I explain what you have explained and whether it is understood and of course whether it has merit. Here it is:

OK, here is how I see it. I can only get so much from a single statement so for it to give me a clue I must assume a couple things. Obviously that makes for errors and who can be right all the time. without investigation based on small hints I can't say much but occasionally these sets of circumstances clues me to things that allow me to get right answers to very little data.

The statement is that after replacing the OVP the car runs worse. Originally two conditions could have existed; one there is a good OVP and everything is OK or mostly OK (it did get worse). Two is a bad OVP and the car is purely running on the mechanical mixture setting with idle valve hung at a constant position. There are bushel baskets of other parts that we must assume are doing OK. If the second condition is the case two posibilities exist. One that the mechanical setting was done properly and when the OVP died it wasn't needed at idle and other warm running constant state conditions (very good "limp home" characteristics). The second condition here is the key. It would be that somewhere after the OVP died mixture was adjusted to achieve a balance of enough fuel to idle good and get by cold but not so much that it ran poorly warm (this would be the mechanical adjustment of course).

Now with this mechanically adjusted over ridden fuel system in limp home, the OVP is replaced with a good one and the management system sees the rich mixture and fixes it making a condition that doesn't work either beacuse of the other problems that were mechanically compensated for OR by making the electronics work again and their own malfuntion screws the mixture.

Try it from the other end. The original OVP is good. The engine is running with electronic compensation (closed loop). Removal of the OVP removes all electronic compensation. Similar to a bad OVP. Removing electronic comp from a properly set up car is un noticable while warm. So how can a new OVP change the way it runs, only if the OVP was bad in the first place and now electronic compensation is taking it somewhere it wasn't.

I see two ways to explain how a good OVP replacing a bad OVP can make things worse, but I see no ways a bad OVP replacing a good one could make it run worse (with everything else right). I had to throw that last bit in because I just thought of a way that it could happen it requires two faults.

Here it goes. Car has bad O2 sensor telling it that engine is lean. As a result the engine continues to go rich untill there is no more ability. Now someone comes along and mechanically adjusts the car back to useable mixtures (system is still eletrically pegged rich but over ridden mechanically to reasonable mixture).

Now a bad OVP is placed in the circuit and the electronic compensation goes away only leaving the mechanical which was brough lean to compensate. this will make the car run poorer with a bad OVP. Quite a stretch. I still go with some variation of the hypothesis that a bad OVP was replaced with a good and then taken back out leaving a broke car.
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  #22  
Old 07-13-2002, 02:57 PM
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Thanks Arthur I thought about that after I posted it that is why you see the edit.
Thanks Steve - this is great stuff.
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  #23  
Old 07-13-2002, 03:00 PM
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Now; If you feel the urge to point, feel free to do so.
Here's my story, sad but true.
Bought the car it was running fine, Used a good bit of oil though. Within 2000 miles the check engine light would flicker, still ran good. Then the ABS light would come on and go off. About three seconds on. Time on was within what the OM said was normal.
Within a couple of weeks engine began to miss while CE light was on. Problem was intermittant and might happen and then go a week without it. Tech at the local MB ******** told me to replace the OVP. I did. The frequency increased. Tech says "fuel pump relay". Did that. Again, increasingly worse. Next, he installs a resitor in the temp sensor. No change. I replace plugs with Bosch Platinums. Thing runs VERY bad. Go back to copper core and I'm back where I started. Replace O2 sensor. Frequency continues to increase. Finally got to the point where I would have to stop and unplug the CIS-E unit just to "limp home". Actually it ran pretty well like that. Hard to start cold though. Replaced the CISE. No change. Fuel pumps, no change. Car spends all day in the shop. Tech thinks its the contacts in the CIS-E connector. He spreads them and sends me on my way, after I paid him well! No check engine light! Hooray! But, engine ain't runnig smoothly! 50 miles later, yup, check eng liht! I'm about ready to scream now. So oil consuption is at a quart per 400 miles. I figure slowing that down might help. Had head reworked with all new valve guides, new chains, new flywheel position sensor and transmission(it needed one). Now car is very hard to start and gremlin is still there. Also starts in third gear, but that's another issue. OVP, power window relay top of CIS-e all get hot quickly. Voltage is at 13.65 / 13.66. And as you've already heard, idle valve "clicks" after it dies. Tech says, you guessed it... needs new OVP!!
That's why I would like to bypass it just to test for that!
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  #24  
Old 07-13-2002, 03:14 PM
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Steven you need to try to find a nice 240/300D .
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  #25  
Old 07-13-2002, 03:17 PM
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Yeah! A diesel will run without any electricity! Put the injector on manual and push it off!!
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  #26  
Old 07-13-2002, 03:24 PM
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Looks like I picked a lot out of that innocent sentence.

I'm real sorry to hear such stories. I'm the first to defend other techs but I fear he is not working with proper diagnostic technique.

Which is a lot of what you are trying to find. The by-pass techniques here are acceptable but based upon this new info I would guess the OVP isn't the problem. The fact that you ran with the Lambda controller out to get home indicates the senario I posed and also indicated that the controller must be getting power.

You need to read my DIY article and bring what you don't understand to the table. Next stop EHA!
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  #27  
Old 07-13-2002, 04:26 PM
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I think the next stop is Sears. To pick up a DMM with a duty cycle!! To be factual there are two techs in this story. One at the ******** was the one telling me to throw parts at it. The shop that I took it to was reputable European repair shop that specializes in Mercedes. Both use only OEM parts and have good reputations. Most of this happened before I found this forum. I had a very limited brain trust to pull from then! But there's always a challenge out there isn't there? I just wish it hadn't happened to me. A good friend of mine tells me that I know just enough to get into trouble, that often I attempt things that I would be better off leaving alone. I guess that's an accident of birth because it's my nature. And with the help of God and a few friends, I'll work this out. Hmmmmn... Gainesville is only three and a half hours from here!!!!
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  #28  
Old 07-13-2002, 04:38 PM
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Just like school, right answer but showed the wrong work .

Actually, just after posting I took our sitter home, had a while to think on the drive back. I realized that I addressed only the computer side of the equation, and had intended to edit in the possibility of mechanical adjustments to try and overcome the poor run problem. But Steve had already covered that before my return.

Plus, I guess I'm getting adaptive and nonadaptive controls confused, there's just too many different species and the Rainman in me is starting to get confused .

Still, not a bad hip shot.
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'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.
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  #29  
Old 07-13-2002, 04:45 PM
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A little logic based in knowledge and a couple simple instruments covers a lot of territory with this sysetm. Parts used with logic can be efficient testing as long as the customer isn't keeping the parts.

I usually only go to the point of logic testing and basic test confirmation before I hang a part. I own many parts this way but there is a point of deminishing returns to total complete testing with labor as costly as it is. By working only on a couple types of automobile parts replacement testing can be used to great benefit. Once I own a control unit testing of such just became a piece of cake. I usually, when faced with a large diagnostic labor charge to prove a guess (some peoples guesses are better than others - and maybe not a true guess), try to find the unit used. This is particularly in the case of expensive control units. If I am right the customer is miles ahead; less diagnostics and a cheap part. If I am wrong I add to the list of easy to diagnose control units.
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  #30  
Old 07-13-2002, 05:25 PM
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Good hip shop and right on the trail.

Let me tell you a bit about adaptation versus control. Closed loop control started in engines with lambda systems in 1980. The last year of 450s got such control. Very simple idea. Make a mechanical system to get close to a precise amount of fuel and then use an after the fact sensor (the O2 sensor) to evaluate how good the job was done. Then use electronics to correct, then sense the result and correct, and then sense the result and correct. The concept used with a system that could react in about 250 milli seconds was able to achieve an exact mixture by moving rich, lean, rich, lean, etc turning as soon as the midpoint is passed. the quicker the readings the narrower the swing rich, lean, rich. Placed in terms of percent CO (Carbon Monoxide the mixture gas in 5gas testing), the ideal is .5% CO. The O2 sensor reads from 0.0% to 1.0% CO correct running closed loop will have voltage swings from .2 to .8v on the O2 sensor. The faster the reaction the smaller the swing. From zero to one the percent O2 sensor voltage can be directly extrapolated to CO% .5v = .5% CO.

On these systems the base mixture had to be set as the systems ability to correct was limited. Proper mixture was to be set to .5% CO using an analyzer without the O2 sensor connected.

All of this sounds a lot like adaptation because mixtures are being adapted to a value. But it is really just feedback control. Adaptation started with the electronic systems which were no longer adjustable. The non adjustment was required to keep cars in closed loop without constant maintenance AND to prevent people from being able to over ride the system with mechanical adjustments.

So now adaptation is where the car changes its center of correction as the requirements change. If for example the car decides that 10% more fuel on average is needed to maintain mixture in the center of the correction capability it now moves that center ten percent. Current adaptations give the modern controller slightly less ability to go rich than to go lean but the original fuel calculation from algorithm can be moved from .68 of one to 1.25 of one, with one being the original calculation.

During warm closed loop considerations it really doesn't matter so much about adaptation. Where it matters is cold or during all fast activities. Because the car decides that due to wear and infirmity of components the current fuel needs are to be increased by 20% ( say due to restricted injectors) . The system now is running at 1.2 adapted. Now when you go start the car up cold its fuel calculation which was richer (for cold running calculation) anyway is now preset 20 percent richer. This is before the O2 sensor is warm enough to help out. The old car would have corrected rich when hot but when cold it would have went to its middle of the road setting made hot. If there were restricted injectors the car would suffer during cold running and also everywhere there was things hapeening faster than 250milliseconds. (snap acceleration comes to mind)

So I have about got myself confussed, I better stop.

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