PeachParts Mercedes-Benz Forum - View Single Post

stevebfl · #21 07-13-2002, 01:47 PM

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.