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1993 400E, 1999 E55
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35 Posts
Discussion Starter #1
Let me preface this post by saying I have seen other threads (many in fact) on the subject. Many posts seem to get off topic (or some argument ensues, etc.), or just not the solution.

My 400, which has generally run very well over the past couple years, would intermittently rough idle, but it always went away.

I've spared really no expense in upkeep - have replaced the wiring harness, and all the basic ignition components (cap, rotor, wires, etc.) have all been replaced no more than about a year ago and the car is driven less than 5K miles a year.

Car runs smooth and fine before it gets up to operating temperature, then shortly after it reaches that point, it begins to, what feels like randomly miss, then it gets a rougher idle, more misfiring and at that point, it's not drivable.

This use to go away after a couple minutes, or when I pulled away from a stop light, but now it's every time.

The last time I took it to the dealer, (for this issue) they replaced coil T1/2, retested, then said noted that the output of left coil is intermittently lower than normal.

They also noted that the DI module may be in the early stages of failure.

This was about a year ago - and it's been fine up until now for the most part.

My question is, what is the DI module and where is the left ignition coil located?

When I took the car in about 4/5 months ago, I was told I need cam solenoids. Where are those located?

Since this car is less than even a 2nd car us, I'd like to try and do the work myself, so I'm hoping someone here can help me out and get me pointed in the right direction.

In addition to finding out where those components are located, I'm hoping someone can give an opinion on if they think the above parts might be the culprit.

It's been a great car (that I've dumped many $1,000's into) and I'd love to get it back on the road for those occasional drives.

Any help, advice, etc., would be most appreciated.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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17,372 Posts
Which of the engine harnesses got replaced, upper, lower or both??? Has the electronic throttle been replaced, due to it suffering from the same eco junk wiring as the harnesses.

I would replace the other coil and both distributors caps, rotors, spark plug wires and spark plugs.

The whole ignition system is considered consumable and is usually due for replacement about every 100K miles.

Also, what is the voltage at the battery with the engine running @ idle???

The cam solenoid is the the intake cam timer actuator for the variable intake cam timing system.

The diagnostic connector is the round multi-pin connector.

The DI module is one of the 4 modules located inside the brain box located on the passenger side by the firewall. Suggest disconnecting battery and R&R each module to reset and ensure a solid connection.
 

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1993 400E, 1999 E55
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35 Posts
Discussion Starter #3
Which of the engine harnesses got replaced, upper, lower or both??? Has the electronic throttle been replaced, due to it suffering from the same eco junk wiring as the harnesses.

I would replace the other coil and both distributors caps, rotors, spark plug wires and spark plugs.

The whole ignition system is considered consumable and is usually due for replacement about every 100K miles.

Also, what is the voltage at the battery with the engine running @ idle???

The cam solenoid is the the intake cam timer actuator for the variable intake cam timing system.

The diagnostic connector is the round multi-pin connector.

The DI module is one of the 4 modules located inside the brain box located on the passenger side by the firewall. Suggest disconnecting battery and R&R each module to reset and ensure a solid connection.
I'm not sure if it was just the upper harness or both. The cost was roughly $800 so I don't know it one costs more than the other. They never mentioned any other harness (and I didn't know there was more than one until just recently).

The electronic throttle has not been replaced.

Exactly where is the left ignition coil located?

Haven't checked the battery voltage (will do that).

I know where the diagnostic connector is located (brain box near firewall), but which of the 4 modules is the DI?

I will R&R each module in the next day or two.

Thanks for you input!
 

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2005 E55
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785 Posts
Could be the other harness. Has the OVP relay been replaced? Could be a cheap try.

Good luck and wait for other members with the mighty V8 to chime in!
 

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1992 400E Nautical Blue/Andoor Blue/Creme Beige 267,000 miles
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56 Posts
Mine did that too. I replaced both coils with good used ones, and then replaced the caps and rotors. Runs smooth now.
 

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1993 400E, 1999 E55
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35 Posts
Discussion Starter #7
Could be the other harness. Has the OVP relay been replaced? Could be a cheap try.

Good luck and wait for other members with the mighty V8 to chime in!
Thanks for the input... I'm not sure what the OVP relay is. What is the full name and where is it located.

On another note, looks like just before the dealer replaced both coils a year ago, one coil was replaced before that, (probably within a year of this last time).

Do these cars really eat coils and general ignition components this bad? I though these were suppose to be one of the best built! lol

But seriously, what would cause it to go through coils so frequently?

Where are those coils located, anyone know?
 

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86 300e Anke
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1,252 Posts
Im gonna ask you to try something else instead...

Under the floorboard of your right frontside is the connector(s) for the oxygen sensor.
one is a barrell-type (likely black) and the other has 2 wires on it (white).

Disconnect the black one for a day or two... yes the light will come on but will go out once you plug it back in...

If youre experiencing the came thing I am but worse, the engine will default to 'cold' mode and it will tend to run fine all the time.

My oxygen sensor has been bad for awhile now, and I have confirmed it this way AS WELL AS using a digital VOM to check its output, which should be somewhere between 0.2 and 0.8 volts....
Mine CONSTANTLY reads > 0.8 and has almost reached 0.9v... forcing the engine to run leaner & leaner... tho it has NOT died yet. :rolleyes:

(you can check yours this way too... unplug the barrell connector and find a good ground like the seat mounting..)

Once the new one shows up I will replace and report back. :D
 

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1995 E320 Cabriolet, 2007 E350 Sport P2, 1995 E420
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406 Posts
Could be the other harness. Has the OVP relay been replaced? Could be a cheap try.

Good luck and wait for other members with the mighty V8 to chime in!
No OVP on the V-8s. But check the four blade fuses on the base module in he black box referenced above. Do you have the blink code reader. If so check for codes. Most people start with inspecting the caps and rotors. There is a cover piece behind the rotors, once you remove the rotor you'll see he rotor bracket it's held on by 1 5mm hex. Remove it and inspect the cover piece. If you have done your reading you'll see there is no one size fits all fix but you can eliminate the usual suspects.
 

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Premium Member
2005 CLK500 w/30K
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842 Posts
I have a '93 400e.

I replaced my main wiring harness a few months back and was amazed at the improvement, but when I posted that someone quickly reminded me that I needed to also do the ETA/TPS replacement.

I thought that I could skip this, and shortly thereafter my 400e started skipping, at idle.

Typically the issue means it runs poorly when cold then works better as it gets warmer.

I had let the car sit for nearly 2 weeks and today went to pick it up.

It ran really poorly at first, dying 4 times before I could get it out of a parking space at Burbank airport. Finally it got going and seemed fine. A little while later it ran worse than it has ran in years. It chugged at speed and the engine was shaking the entire car t idle. My friend next to me at a light could see the car shaking.

I became worried that it might not make it home but it got back.

I let it sit a few hours and it fired up just fine again, smooth solid idle, purring like a kitten.

I am 99% certain that this is due to never replacing the ETA/TPS unit. The stinky part is you have to replace the whole thing, when only $5 worth of wire is actually bad. If it had a plug at both ends as many other years do, it would just be the wire that needed to be replaced.

I was able to "fix" this for a few weeks by jiggling the wire, but it has come back with gusto.

That being said, if you look through my past posts, it ran in a similar way once and it turned out to be cap & rotor issue.
 

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My car is a 1993 400E with about 206K miles.

I paid to have one harness replaced and it ran fine. It still runs fine at idle; the problem is when the car accelerates to
about 40 mph, (It has been sitting for several months and may be lower now.) The mechanic finally threw up his hands and refused to spend any more time. He did replace the rotors on each side and tried a new air inlet damper but nothing helped. This car has OBD-1 and the mechanic said all codes have been cleared.

Do you think any of this could be caused by problems in the fuel lines such as a filter or debris in the line. I assume my mechanic checked this and I asked but never got an answer.

I am desperate but the engine runs fine at idle and I am reluctant to throw the car away.

Any suggestions would be more than appreciated

Leland Johnson
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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17,372 Posts
Was the throttle body replaced also? It suffers the same wiring degradation as the engine harnesses.

Sounds like you really need to look for a better mechanic.
 

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W124
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5,164 Posts
Agree ^

Your mechanic is in worse shape than your 400e. Codes can be cleared but they come back if unresolved. For him to say "codes are cleared" it sounds like he's not used to diagnosing by any means other than to throw your money at the problem until he can't think of anything else.

Lots of people on this forum are mechanics looking for help. The fact that your mechanic isn't one of them is troubling.

If you get a code indicating the ETA is suspect, then best to have yours replaced. If you are not getting any codes or check engine light, have another mechanic go through the ignition on the car and look closely at the insulators behind the ignition rotors.
 

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Premium Member
2005 CLK500 w/30K
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842 Posts
Get dates from ETA and upper harness.

Either one will gladly confound you with symptoms until you pull all your hair, or get ones made after '97.

Also, somehow my rotors always ended up with moisture inside despite living in a desert.
 
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