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Old 05-11-2012, 02:56 PM
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Join Date: Apr 2006
Posts: 669
What did I do????

I have been working thru my 1990 190e for a while, and was about ready to smog it this week.
Yesterday, I checked, but did not touch the Duty cycle, and it was cycling around 40 to 50%, and the car was running really sweet, and smooth.
I decided to check the voltages at the O2 sensor, and back probed them with my DMM... I was not sure what reading I should be getting, so came in to read up, leaving the car running to warm up.

When I came out, I noticed that the engine sounded a little lumpy.
I goosed the throttle to see if it cleared it, and the engine spluttered and refused to rev.... soon after that it stalled.

Every time I tried to start it after that, it would start and run for a few seconds and then stall.

I left it overnight.
Today, it wont start.
I put a gallon of fuel in, as the tank was getting near empty,still no start.
I checked the fuse in the OVP, and it was good... The OVP looks old and rattles when shaken.
There is a visible spark at the sparkplugs.
There is fuel pressure at the upper chamber of the FD...


1984 Mercedes 190D 2.2 209k miles
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Old 05-11-2012, 06:27 PM
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Join Date: Apr 2006
Posts: 669
Ran some tests....
Pulled out the MAS, and jumpered the fuel pumps.

Fuel output is good. I tested it at 1.2L in 40 sec, however doing the same test I did last week I can get no output from the fuel lines after pushing down the air flap.

What is also interesting is that measuring the duty cycle with ignition on, I get 69.9% which is correct, but when I pushed down the air flap before it changed, and now it does not...
Could this be the OVP?
1984 Mercedes 190D 2.2 209k miles

Last edited by Merkey; 05-12-2012 at 02:25 PM.
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Old 05-14-2012, 02:06 AM
JamesDean's Avatar
Electrical Engineer
Join Date: Apr 2005
Location: NE Ohio
Posts: 5,034
It very well might be the OVP, the OVP supplies power to multiple key electronics including the ECU and MAS units.

Carefully open up the OVP and see whats rattling in it. You can attempt to repair any broken solder joints and clean up any corrosion.

My 190E's OVP was bad and very corroded. I ended up tearing it apart and it fixed up fine, that was 4-5 years ago.
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Old 05-14-2012, 01:52 PM
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Ok, Thanks for the input James...
I pulled it back out.. guess what...
Its date stamped... A3690... so 36th week of 19990... the original OVP!

Upon pulling it apart, I found 2 very clearly cracked solder joints!

These 2... in the middle..

Closest to camera is real easy to see!

I retouched them just enough to reflow the solder.

Put the OVP back in, and....
It started FIRST TIME!
1984 Mercedes 190D 2.2 209k miles
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Old 05-16-2012, 03:14 PM
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what a good repair
plant, and animal life matter. human's had their chance.
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Old 05-16-2012, 04:41 PM
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yeah, it worked as a stop gap until I can get a new one.

What I find interesting, is that clearly, on these MAS later models a bad OVP will kill the car stone dead.
The earlier ones, it goes into a kinda fail mode but still runs.

Good to know!
1984 Mercedes 190D 2.2 209k miles
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Old 05-16-2012, 05:00 PM
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Join Date: Feb 2007
Location: VA
Posts: 621
'84-'89 Porsche 911 has a DME relay that looks nearly identical. It controls power to the engine computer and also fuel pump. It also suffers from cracked solder joints, and car stops stone dead when it fails.

A common problem, and reflowing the solder joints makes for a permanent fix. No need to purchase a new one if you've repaired the broken joints. Although keeping a spare in a glove box is always a good idea.
'98 E300 turbodiesel
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Old 05-16-2012, 06:50 PM
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Join Date: Mar 2007
Location: Hampton Roads, Virginia
Posts: 3,356
Originally Posted by lupin..the..3rd View Post
snip...... Although keeping a spare in a glove box is always a good idea.

I've found that whenever I keep a spare for a component in my car, it acts as a talisman for the installed part, and the installed part rarely fails.....

So, keep the spares, they are good luck!


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