I can't get over how many people and how many headaches this little device causes. I hate to beat a dead horse but....

How does all this information apply to a Diesel? 87 300D - I found my fuse blown, replaced the fuse but can't really see a difference. My Tach and CC are still inop.

All those that sent help via this forum! Wow.. I'm impressed and thank you very, very much. This is my first Benz and as a seasoned mechanic but having never worked on a merc I must admit that I'm not only impressed with the so called over-engineering but I'm absolutely in love with these cars from a mechanics point of view. There's few parts that can't be fixed with a little know how and some help from what seems to be a very enthusiastic brotherhood.

Stecebfl,


Thanks for the extremely informative post on the early lambda controls, closed loop operation, etc.. Good stuff, man!


-tp

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.

__________________
Mike Tangas
'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.

Just for references, heres the star of the show;

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Good to see inside the lil devil...

My old ovr MB # 126 5404745 likely 4/82
has only 4 prongs & a plastic

30
31
87
87a/15

There is a rattle intermiitant in it

Replaced w new one made inHungary last night

not sure if its good or not but w 196K on it it might be getting old?

If its just a fuse as has been said why would it cause all those problems?

Anyway got a new one & hope its a good one...

__________________


83 500 SEC Euro 198K

So, on a 300D (w123) where exactly is this lil' bugger located?

and the other side;

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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.

__________________
Jim

Eng
Your E320 has an OVP and one of the original problem ones...

Might want to see if you have the upgraded one..

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.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Thanks Arthur I thought about that after I posted it that is why you see the edit.
Thanks Steve - this is great stuff.

__________________
Jim

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!

Steven you need to try to find a nice 240/300D .

__________________
Jim

Yeah! A diesel will run without any electricity! Put the injector on manual and push it off!!

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!

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician